From 76a7d7bfe2572de83a8bc38653573fae210eef57 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Tue, 28 Nov 2023 14:45:35 -0700
Subject: [PATCH 01/26] Make Interpreter() idempotent.

---
 Lib/test/support/interpreters.py |  27 ++++--
 Lib/test/test_interpreters.py    | 161 ++++++++++++++++++++++---------
 2 files changed, 130 insertions(+), 58 deletions(-)

diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index 089fe7ef56df78..f82581146d5c26 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -1,6 +1,7 @@
 """Subinterpreters High Level Module."""
 
 import time
+import weakref
 import _xxsubinterpreters as _interpreters
 import _xxinterpchannels as _channels
 
@@ -58,14 +59,26 @@ def get_main():
     return Interpreter(id)
 
 
+_known = weakref.WeakValueDictionary()
+
 class Interpreter:
     """A single Python interpreter."""
 
-    def __init__(self, id, *, isolated=None):
-        if not isinstance(id, (int, _interpreters.InterpreterID)):
+    def __new__(cls, id, /, *, isolated=None):
+        # There is only one instance for any given ID.
+        if isinstance(id, int):
+            id = _interpreters.InterpreterID(id, force=False)
+        elif not isinstance(id, _interpreters.InterpreterID):
             raise TypeError(f'id must be an int, got {id!r}')
-        self._id = id
-        self._isolated = isolated
+        key = int(id)
+        try:
+            self = _known[key]
+        except KeyError:
+            self = super().__new__(cls)
+            self._id = id
+            self._isolated = bool(isolated)
+            _known[key] = self
+        return self
 
     def __repr__(self):
         data = dict(id=int(self._id), isolated=self._isolated)
@@ -75,12 +88,6 @@ def __repr__(self):
     def __hash__(self):
         return hash(self._id)
 
-    def __eq__(self, other):
-        if not isinstance(other, Interpreter):
-            return NotImplemented
-        else:
-            return other._id == self._id
-
     @property
     def id(self):
         return self._id
diff --git a/Lib/test/test_interpreters.py b/Lib/test/test_interpreters.py
index 5663706c0ccfb7..e3158b690de868 100644
--- a/Lib/test/test_interpreters.py
+++ b/Lib/test/test_interpreters.py
@@ -143,6 +143,23 @@ def test_after_destroy_some(self):
         self.assertEqual(set(interpreters.list_all()), before | {interp3, interp})
 
 
+class GetMainTests(TestBase):
+
+    def test_id(self):
+        main = interpreters.get_main()
+        self.assertEqual(main.id, 0)
+
+    def test_current(self):
+        main = interpreters.get_main()
+        current = interpreters.get_current()
+        self.assertIs(main, current)
+
+    def test_idempotent(self):
+        main1 = interpreters.get_main()
+        main2 = interpreters.get_main()
+        self.assertIs(main1, main2)
+
+
 class GetCurrentTests(TestBase):
 
     def test_main(self):
@@ -151,7 +168,7 @@ def test_main(self):
         self.assertEqual(current, main)
 
     def test_subinterpreter(self):
-        main = _interpreters.get_main()
+        main = interpreters.get_main()
         interp = interpreters.create()
         out = _run_output(interp, dedent("""
             from test.support import interpreters
@@ -159,8 +176,38 @@ def test_subinterpreter(self):
             print(cur.id)
             """))
         current = interpreters.Interpreter(int(out))
+        self.assertEqual(current, interp)
         self.assertNotEqual(current, main)
 
+    def test_idempotent(self):
+        with self.subTest('main'):
+            cur1 = interpreters.get_current()
+            cur2 = interpreters.get_current()
+            self.assertIs(cur1, cur2)
+
+        with self.subTest('subinterpreter'):
+            interp = interpreters.create()
+            out = _run_output(interp, dedent("""
+                from test.support import interpreters
+                cur = interpreters.get_current()
+                print(id(cur))
+                cur = interpreters.get_current()
+                print(id(cur))
+                """))
+            objid1, objid2 = (int(v) for v in out.splitlines())
+            self.assertEqual(objid1, objid2)
+
+        with self.subTest('per-interpreter'):
+            interp = interpreters.create()
+            out = _run_output(interp, dedent("""
+                from test.support import interpreters
+                cur = interpreters.get_current()
+                print(id(cur))
+                """))
+            id1 = int(out)
+            id2 = int(id(interp))
+            self.assertNotEqual(id1, id2)
+
 
 class ListAllTests(TestBase):
 
@@ -191,6 +238,57 @@ def test_after_destroying(self):
 
         self.assertEqual(ids, [main.id, second.id])
 
+    def test_idempotent(self):
+        main = interpreters.get_current()
+        first = interpreters.create()
+        second = interpreters.create()
+        expected = [main, first, second]
+
+        actual = interpreters.list_all()
+
+        self.assertEqual(actual, expected)
+        for interp1, interp2 in zip(actual, expected):
+            self.assertIs(interp1, interp2)
+
+
+class InterpreterInitTests(TestBase):
+
+    def test_int(self):
+        interpid = int(interpreters.get_current().id)
+        interp = interpreters.Interpreter(interpid)
+        self.assertEqual(int(interp.id), interpid)
+
+    def test_interpreter_id(self):
+        interpid = interpreters.get_current().id
+        interp = interpreters.Interpreter(interpid)
+        self.assertEqual(interp.id, interpid)
+
+    def test_unsupported(self):
+        actualid = int(interpreters.get_current().id)
+        for interpid in [
+            str(actualid),
+            float(actualid),
+            object(),
+            None,
+            '',
+        ]:
+            with self.subTest(repr(interpid)):
+                with self.assertRaises(TypeError):
+                    interpreters.Interpreter(interpid)
+
+    def test_idempotent(self):
+        main = interpreters.get_main()
+        interp = interpreters.Interpreter(int(main.id))
+        self.assertIs(interp, main)
+
+    def test_does_not_exist(self):
+        with self.assertRaises(RuntimeError):
+            interpreters.Interpreter(1_000_000)
+
+    def test_bad_id(self):
+        with self.assertRaises(ValueError):
+            interpreters.Interpreter(-1)
+
 
 class TestInterpreterAttrs(TestBase):
 
@@ -202,19 +300,10 @@ def test_id_type(self):
         self.assertIsInstance(current.id, _interpreters.InterpreterID)
         self.assertIsInstance(interp.id, _interpreters.InterpreterID)
 
-    def test_main_id(self):
-        main = interpreters.get_main()
-        self.assertEqual(main.id, 0)
-
-    def test_custom_id(self):
-        interp = interpreters.Interpreter(1)
-        self.assertEqual(interp.id, 1)
-
-        with self.assertRaises(TypeError):
-            interpreters.Interpreter('1')
-
     def test_id_readonly(self):
-        interp = interpreters.Interpreter(1)
+        actual = interpreters.create()
+        interpid = int(actual.id)
+        interp = interpreters.Interpreter(interpid)
         with self.assertRaises(AttributeError):
             interp.id = 2
 
@@ -236,17 +325,23 @@ def test_subinterpreter_isolated_explicit(self):
 
     @unittest.skip('not ready yet (see bpo-32604)')
     def test_custom_isolated_default(self):
-        interp = interpreters.Interpreter(1)
+        actual = interpreters.create()
+        interpid = int(actual.id)
+        interp = interpreters.Interpreter(interpid)
         self.assertFalse(interp.isolated)
 
     def test_custom_isolated_explicit(self):
-        interp1 = interpreters.Interpreter(1, isolated=True)
-        interp2 = interpreters.Interpreter(1, isolated=False)
+        actual = interpreters.create()
+        interpid = int(actual.id)
+        interp1 = interpreters.Interpreter(interpid, isolated=True)
+        interp2 = interpreters.Interpreter(interpid, isolated=False)
         self.assertTrue(interp1.isolated)
-        self.assertFalse(interp2.isolated)
+        self.assertTrue(interp2.isolated)
 
     def test_isolated_readonly(self):
-        interp = interpreters.Interpreter(1)
+        actual = interpreters.create()
+        interpid = int(actual.id)
+        interp = interpreters.Interpreter(interpid)
         with self.assertRaises(AttributeError):
             interp.isolated = True
 
@@ -299,16 +394,6 @@ def test_already_destroyed(self):
         with self.assertRaises(RuntimeError):
             interp.is_running()
 
-    def test_does_not_exist(self):
-        interp = interpreters.Interpreter(1_000_000)
-        with self.assertRaises(RuntimeError):
-            interp.is_running()
-
-    def test_bad_id(self):
-        interp = interpreters.Interpreter(-1)
-        with self.assertRaises(ValueError):
-            interp.is_running()
-
     def test_with_only_background_threads(self):
         r_interp, w_interp = self.pipe()
         r_thread, w_thread = self.pipe()
@@ -378,16 +463,6 @@ def test_already_destroyed(self):
         with self.assertRaises(RuntimeError):
             interp.close()
 
-    def test_does_not_exist(self):
-        interp = interpreters.Interpreter(1_000_000)
-        with self.assertRaises(RuntimeError):
-            interp.close()
-
-    def test_bad_id(self):
-        interp = interpreters.Interpreter(-1)
-        with self.assertRaises(ValueError):
-            interp.close()
-
     def test_from_current(self):
         main, = interpreters.list_all()
         interp = interpreters.create()
@@ -527,16 +602,6 @@ def test_already_running(self):
             with self.assertRaises(RuntimeError):
                 interp.run('print("spam")')
 
-    def test_does_not_exist(self):
-        interp = interpreters.Interpreter(1_000_000)
-        with self.assertRaises(RuntimeError):
-            interp.run('print("spam")')
-
-    def test_bad_id(self):
-        interp = interpreters.Interpreter(-1)
-        with self.assertRaises(ValueError):
-            interp.run('print("spam")')
-
     def test_bad_script(self):
         interp = interpreters.create()
         with self.assertRaises(TypeError):

From 57a3c194bd3688548c53cc6281909e1d4326d75d Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Tue, 28 Nov 2023 14:49:32 -0700
Subject: [PATCH 02/26] Interpreters are always isolated.

---
 Lib/test/support/interpreters.py | 19 +++---------
 Lib/test/test_interpreters.py    | 53 ++++----------------------------
 2 files changed, 11 insertions(+), 61 deletions(-)

diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index f82581146d5c26..48c80f6d1eee4f 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -36,10 +36,10 @@ def __init__(self, excinfo):
         self.snapshot = excinfo
 
 
-def create(*, isolated=True):
+def create():
     """Return a new (idle) Python interpreter."""
-    id = _interpreters.create(isolated=isolated)
-    return Interpreter(id, isolated=isolated)
+    id = _interpreters.create(isolated=True)
+    return Interpreter(id)
 
 
 def list_all():
@@ -64,7 +64,7 @@ def get_main():
 class Interpreter:
     """A single Python interpreter."""
 
-    def __new__(cls, id, /, *, isolated=None):
+    def __new__(cls, id, /):
         # There is only one instance for any given ID.
         if isinstance(id, int):
             id = _interpreters.InterpreterID(id, force=False)
@@ -76,12 +76,11 @@ def __new__(cls, id, /, *, isolated=None):
         except KeyError:
             self = super().__new__(cls)
             self._id = id
-            self._isolated = bool(isolated)
             _known[key] = self
         return self
 
     def __repr__(self):
-        data = dict(id=int(self._id), isolated=self._isolated)
+        data = dict(id=int(self._id))
         kwargs = (f'{k}={v!r}' for k, v in data.items())
         return f'{type(self).__name__}({", ".join(kwargs)})'
 
@@ -92,14 +91,6 @@ def __hash__(self):
     def id(self):
         return self._id
 
-    @property
-    def isolated(self):
-        if self._isolated is None:
-            # XXX The low-level function has not been added yet.
-            # See bpo-....
-            self._isolated = _interpreters.is_isolated(self._id)
-        return self._isolated
-
     def is_running(self):
         """Return whether or not the identified interpreter is running."""
         return _interpreters.is_running(self._id)
diff --git a/Lib/test/test_interpreters.py b/Lib/test/test_interpreters.py
index e3158b690de868..fb0fde362bc70c 100644
--- a/Lib/test/test_interpreters.py
+++ b/Lib/test/test_interpreters.py
@@ -251,19 +251,19 @@ def test_idempotent(self):
             self.assertIs(interp1, interp2)
 
 
-class InterpreterInitTests(TestBase):
+class InterpreterObjectTests(TestBase):
 
-    def test_int(self):
+    def test_init_int(self):
         interpid = int(interpreters.get_current().id)
         interp = interpreters.Interpreter(interpid)
         self.assertEqual(int(interp.id), interpid)
 
-    def test_interpreter_id(self):
+    def test_init_interpreter_id(self):
         interpid = interpreters.get_current().id
         interp = interpreters.Interpreter(interpid)
         self.assertEqual(interp.id, interpid)
 
-    def test_unsupported(self):
+    def test_init_unsupported(self):
         actualid = int(interpreters.get_current().id)
         for interpid in [
             str(actualid),
@@ -281,17 +281,14 @@ def test_idempotent(self):
         interp = interpreters.Interpreter(int(main.id))
         self.assertIs(interp, main)
 
-    def test_does_not_exist(self):
+    def test_init_does_not_exist(self):
         with self.assertRaises(RuntimeError):
             interpreters.Interpreter(1_000_000)
 
-    def test_bad_id(self):
+    def test_init_bad_id(self):
         with self.assertRaises(ValueError):
             interpreters.Interpreter(-1)
 
-
-class TestInterpreterAttrs(TestBase):
-
     def test_id_type(self):
         main = interpreters.get_main()
         current = interpreters.get_current()
@@ -307,44 +304,6 @@ def test_id_readonly(self):
         with self.assertRaises(AttributeError):
             interp.id = 2
 
-    @unittest.skip('not ready yet (see bpo-32604)')
-    def test_main_isolated(self):
-        main = interpreters.get_main()
-        self.assertFalse(main.isolated)
-
-    @unittest.skip('not ready yet (see bpo-32604)')
-    def test_subinterpreter_isolated_default(self):
-        interp = interpreters.create()
-        self.assertFalse(interp.isolated)
-
-    def test_subinterpreter_isolated_explicit(self):
-        interp1 = interpreters.create(isolated=True)
-        interp2 = interpreters.create(isolated=False)
-        self.assertTrue(interp1.isolated)
-        self.assertFalse(interp2.isolated)
-
-    @unittest.skip('not ready yet (see bpo-32604)')
-    def test_custom_isolated_default(self):
-        actual = interpreters.create()
-        interpid = int(actual.id)
-        interp = interpreters.Interpreter(interpid)
-        self.assertFalse(interp.isolated)
-
-    def test_custom_isolated_explicit(self):
-        actual = interpreters.create()
-        interpid = int(actual.id)
-        interp1 = interpreters.Interpreter(interpid, isolated=True)
-        interp2 = interpreters.Interpreter(interpid, isolated=False)
-        self.assertTrue(interp1.isolated)
-        self.assertTrue(interp2.isolated)
-
-    def test_isolated_readonly(self):
-        actual = interpreters.create()
-        interpid = int(actual.id)
-        interp = interpreters.Interpreter(interpid)
-        with self.assertRaises(AttributeError):
-            interp.isolated = True
-
     def test_equality(self):
         interp1 = interpreters.create()
         interp2 = interpreters.create()

From 747e5425a8f85e9a4fea8ace7b7bdb125f9ab461 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Tue, 28 Nov 2023 14:55:34 -0700
Subject: [PATCH 03/26] interp.id is always int.

---
 Lib/test/support/interpreters.py |  2 +-
 Lib/test/test_interpreters.py    | 30 ++++++++++++++----------------
 2 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index 48c80f6d1eee4f..16597967d66cf0 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -89,7 +89,7 @@ def __hash__(self):
 
     @property
     def id(self):
-        return self._id
+        return int(self._id)
 
     def is_running(self):
         """Return whether or not the identified interpreter is running."""
diff --git a/Lib/test/test_interpreters.py b/Lib/test/test_interpreters.py
index fb0fde362bc70c..df0c30fa199b6e 100644
--- a/Lib/test/test_interpreters.py
+++ b/Lib/test/test_interpreters.py
@@ -205,7 +205,7 @@ def test_idempotent(self):
                 print(id(cur))
                 """))
             id1 = int(out)
-            id2 = int(id(interp))
+            id2 = id(interp)
             self.assertNotEqual(id1, id2)
 
 
@@ -254,17 +254,17 @@ def test_idempotent(self):
 class InterpreterObjectTests(TestBase):
 
     def test_init_int(self):
-        interpid = int(interpreters.get_current().id)
+        interpid = interpreters.get_current().id
         interp = interpreters.Interpreter(interpid)
-        self.assertEqual(int(interp.id), interpid)
+        self.assertEqual(interp.id, interpid)
 
     def test_init_interpreter_id(self):
-        interpid = interpreters.get_current().id
+        interpid = interpreters.get_current()._id
         interp = interpreters.Interpreter(interpid)
-        self.assertEqual(interp.id, interpid)
+        self.assertEqual(interp._id, interpid)
 
     def test_init_unsupported(self):
-        actualid = int(interpreters.get_current().id)
+        actualid = interpreters.get_current().id
         for interpid in [
             str(actualid),
             float(actualid),
@@ -278,7 +278,7 @@ def test_init_unsupported(self):
 
     def test_idempotent(self):
         main = interpreters.get_main()
-        interp = interpreters.Interpreter(int(main.id))
+        interp = interpreters.Interpreter(main.id)
         self.assertIs(interp, main)
 
     def test_init_does_not_exist(self):
@@ -293,16 +293,14 @@ def test_id_type(self):
         main = interpreters.get_main()
         current = interpreters.get_current()
         interp = interpreters.create()
-        self.assertIsInstance(main.id, _interpreters.InterpreterID)
-        self.assertIsInstance(current.id, _interpreters.InterpreterID)
-        self.assertIsInstance(interp.id, _interpreters.InterpreterID)
+        self.assertIsInstance(main.id, int)
+        self.assertIsInstance(current.id, int)
+        self.assertIsInstance(interp.id, int)
 
     def test_id_readonly(self):
-        actual = interpreters.create()
-        interpid = int(actual.id)
-        interp = interpreters.Interpreter(interpid)
+        interp = interpreters.create()
         with self.assertRaises(AttributeError):
-            interp.id = 2
+            interp.id = 1_000_000
 
     def test_equality(self):
         interp1 = interpreters.create()
@@ -427,7 +425,7 @@ def test_from_current(self):
         interp = interpreters.create()
         out = _run_output(interp, dedent(f"""
             from test.support import interpreters
-            interp = interpreters.Interpreter({int(interp.id)})
+            interp = interpreters.Interpreter({interp.id})
             try:
                 interp.close()
             except RuntimeError:
@@ -444,7 +442,7 @@ def test_from_sibling(self):
                          {main, interp1, interp2})
         interp1.run(dedent(f"""
             from test.support import interpreters
-            interp2 = interpreters.Interpreter(int({interp2.id}))
+            interp2 = interpreters.Interpreter({interp2.id})
             interp2.close()
             interp3 = interpreters.create()
             interp3.close()

From 0ed9fb0684cc39465aa871b9c391ba0d550fd2a9 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Fri, 1 Dec 2023 14:05:05 -0700
Subject: [PATCH 04/26] Add InterpreterNotFoundError.

---
 Include/internal/pycore_crossinterp.h | 10 +++++
 Lib/test/support/interpreters.py      |  7 ++-
 Lib/test/test_interpreters.py         |  7 +--
 Modules/_xxsubinterpretersmodule.c    |  8 ++++
 Python/crossinterp.c                  | 62 +++++++++++++++++++++++++++
 Python/pylifecycle.c                  |  6 +++
 Python/pystate.c                      |  2 +-
 7 files changed, 96 insertions(+), 6 deletions(-)

diff --git a/Include/internal/pycore_crossinterp.h b/Include/internal/pycore_crossinterp.h
index ec9dac96292f35..cb006bb5a51770 100644
--- a/Include/internal/pycore_crossinterp.h
+++ b/Include/internal/pycore_crossinterp.h
@@ -10,6 +10,13 @@ extern "C" {
 
 #include "pycore_pyerrors.h"
 
+/**************/
+/* exceptions */
+/**************/
+
+PyAPI_DATA(PyObject *) PyExc_InterpreterError;
+PyAPI_DATA(PyObject *) PyExc_InterpreterNotFoundError;
+
 
 /***************************/
 /* cross-interpreter calls */
@@ -159,6 +166,9 @@ struct _xi_state {
 extern PyStatus _PyXI_Init(PyInterpreterState *interp);
 extern void _PyXI_Fini(PyInterpreterState *interp);
 
+extern PyStatus _PyXI_InitTypes(PyInterpreterState *interp);
+extern void _PyXI_FiniTypes(PyInterpreterState *interp);
+
 
 /***************************/
 /* short-term data sharing */
diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index 16597967d66cf0..d956954718c06d 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -6,7 +6,10 @@
 import _xxinterpchannels as _channels
 
 # aliases:
-from _xxsubinterpreters import is_shareable
+from _xxsubinterpreters import (
+    InterpreterError, InterpreterNotFoundError,
+    is_shareable,
+)
 from _xxinterpchannels import (
     ChannelError, ChannelNotFoundError, ChannelClosedError,
     ChannelEmptyError, ChannelNotEmptyError,
@@ -15,7 +18,7 @@
 
 __all__ = [
     'Interpreter', 'get_current', 'get_main', 'create', 'list_all',
-    'RunFailedError',
+    'InterpreterError', 'InterpreterNotFoundError', 'RunFailedError',
     'SendChannel', 'RecvChannel',
     'create_channel', 'list_all_channels', 'is_shareable',
     'ChannelError', 'ChannelNotFoundError',
diff --git a/Lib/test/test_interpreters.py b/Lib/test/test_interpreters.py
index df0c30fa199b6e..02c4722ab9bdcb 100644
--- a/Lib/test/test_interpreters.py
+++ b/Lib/test/test_interpreters.py
@@ -15,6 +15,7 @@
 _interpreters = import_helper.import_module('_xxsubinterpreters')
 _channels = import_helper.import_module('_xxinterpchannels')
 from test.support import interpreters
+from test.support.interpreters import InterpreterNotFoundError
 
 
 def _captured_script(script):
@@ -282,7 +283,7 @@ def test_idempotent(self):
         self.assertIs(interp, main)
 
     def test_init_does_not_exist(self):
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interpreters.Interpreter(1_000_000)
 
     def test_init_bad_id(self):
@@ -348,7 +349,7 @@ def test_from_subinterpreter(self):
     def test_already_destroyed(self):
         interp = interpreters.create()
         interp.close()
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interp.is_running()
 
     def test_with_only_background_threads(self):
@@ -417,7 +418,7 @@ def f():
     def test_already_destroyed(self):
         interp = interpreters.create()
         interp.close()
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interp.close()
 
     def test_from_current(self):
diff --git a/Modules/_xxsubinterpretersmodule.c b/Modules/_xxsubinterpretersmodule.c
index 02c2abed27ddfa..f803f77bc81fc6 100644
--- a/Modules/_xxsubinterpretersmodule.c
+++ b/Modules/_xxsubinterpretersmodule.c
@@ -725,6 +725,14 @@ module_exec(PyObject *mod)
         goto error;
     }
 
+    // exceptions
+    if (PyModule_AddType(mod, (PyTypeObject *)PyExc_InterpreterError) < 0) {
+        goto error;
+    }
+    if (PyModule_AddType(mod, (PyTypeObject *)PyExc_InterpreterNotFoundError) < 0) {
+        goto error;
+    }
+
     return 0;
 
 error:
diff --git a/Python/crossinterp.c b/Python/crossinterp.c
index 21b96ef05ed799..f27c7a9e8e32da 100644
--- a/Python/crossinterp.c
+++ b/Python/crossinterp.c
@@ -12,6 +12,53 @@
 #include "pycore_weakref.h"       // _PyWeakref_GET_REF()
 
 
+/**************/
+/* exceptions */
+/**************/
+
+/* InterpreterError extends Exception */
+
+static PyTypeObject _PyExc_InterpreterError = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    .tp_name = "InterpreterError",
+    .tp_doc = PyDoc_STR("An interpreter was not found."),
+    //.tp_base = (PyTypeObject *)PyExc_BaseException,
+};
+PyObject *PyExc_InterpreterError = (PyObject *)&_PyExc_InterpreterError;
+
+/* InterpreterNotFoundError extends InterpreterError */
+
+static PyTypeObject _PyExc_InterpreterNotFoundError = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    .tp_name = "InterpreterNotFoundError",
+    .tp_doc = PyDoc_STR("An interpreter was not found."),
+    .tp_base = &_PyExc_InterpreterError,
+};
+PyObject *PyExc_InterpreterNotFoundError = (PyObject *)&_PyExc_InterpreterNotFoundError;
+
+/* lifecycle */
+
+static int
+init_exceptions(PyInterpreterState *interp)
+{
+    _PyExc_InterpreterError.tp_base = (PyTypeObject *)PyExc_BaseException;
+    if (_PyStaticType_InitBuiltin(interp, &_PyExc_InterpreterError) < 0) {
+        return -1;
+    }
+    if (_PyStaticType_InitBuiltin(interp, &_PyExc_InterpreterNotFoundError) < 0) {
+        return -1;
+    }
+    return 0;
+}
+
+static void
+fini_exceptions(PyInterpreterState *interp)
+{
+    _PyStaticType_Dealloc(interp, &_PyExc_InterpreterNotFoundError);
+    _PyStaticType_Dealloc(interp, &_PyExc_InterpreterError);
+}
+
+
 /***************************/
 /* cross-interpreter calls */
 /***************************/
@@ -2118,3 +2165,18 @@ _PyXI_Fini(PyInterpreterState *interp)
         _xidregistry_fini(_get_global_xidregistry(interp->runtime));
     }
 }
+
+PyStatus
+_PyXI_InitTypes(PyInterpreterState *interp)
+{
+    if (init_exceptions(interp) < 0) {
+        return _PyStatus_ERR("failed to initialize an exception type");
+    }
+    return _PyStatus_OK();
+}
+
+void
+_PyXI_FiniTypes(PyInterpreterState *interp)
+{
+    fini_exceptions(interp);
+}
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index ac8d5208322882..acb69f6d8982d0 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -739,6 +739,11 @@ pycore_init_types(PyInterpreterState *interp)
         return status;
     }
 
+    status = _PyXI_InitTypes(interp);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
+
     return _PyStatus_OK();
 }
 
@@ -1742,6 +1747,7 @@ finalize_interp_types(PyInterpreterState *interp)
 {
     _PyUnicode_FiniTypes(interp);
     _PySys_FiniTypes(interp);
+    _PyXI_FiniTypes(interp);
     _PyExc_Fini(interp);
     _PyAsyncGen_Fini(interp);
     _PyContext_Fini(interp);
diff --git a/Python/pystate.c b/Python/pystate.c
index 6196b15da0117a..9f37d7b2cd97d2 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -1309,7 +1309,7 @@ _PyInterpreterState_LookUpID(int64_t requested_id)
         HEAD_UNLOCK(runtime);
     }
     if (interp == NULL && !PyErr_Occurred()) {
-        PyErr_Format(PyExc_RuntimeError,
+        PyErr_Format(PyExc_InterpreterNotFoundError,
                      "unrecognized interpreter ID %lld", requested_id);
     }
     return interp;

From 98f9cf388640856fcf97af3d5238b893d931a49b Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Fri, 1 Dec 2023 14:47:17 -0700
Subject: [PATCH 05/26] Stop using InterpreterID in _interpreters.

---
 Include/internal/pycore_interp.h    |   6 +-
 Lib/test/support/interpreters.py    |  38 +++++--
 Lib/test/test__xxinterpchannels.py  |   3 +-
 Lib/test/test__xxsubinterpreters.py |  82 ++------------
 Lib/test/test_capi/test_misc.py     | 131 ++++++++++++++++++++++
 Lib/test/test_interpreters.py       |   6 +-
 Modules/_testcapimodule.c           |  34 ++++++
 Modules/_testinternalcapi.c         |  12 ++
 Modules/_xxsubinterpretersmodule.c  | 168 +++++++++++++++++++++++++---
 9 files changed, 378 insertions(+), 102 deletions(-)

diff --git a/Include/internal/pycore_interp.h b/Include/internal/pycore_interp.h
index 498db8becf114c..b27ee0a8b882e1 100644
--- a/Include/internal/pycore_interp.h
+++ b/Include/internal/pycore_interp.h
@@ -249,9 +249,9 @@ _PyInterpreterState_SetFinalizing(PyInterpreterState *interp, PyThreadState *tst
 // Export for the _xxinterpchannels module.
 PyAPI_FUNC(PyInterpreterState *) _PyInterpreterState_LookUpID(int64_t);
 
-extern int _PyInterpreterState_IDInitref(PyInterpreterState *);
-extern int _PyInterpreterState_IDIncref(PyInterpreterState *);
-extern void _PyInterpreterState_IDDecref(PyInterpreterState *);
+PyAPI_FUNC(int) _PyInterpreterState_IDInitref(PyInterpreterState *);
+PyAPI_FUNC(int) _PyInterpreterState_IDIncref(PyInterpreterState *);
+PyAPI_FUNC(void) _PyInterpreterState_IDDecref(PyInterpreterState *);
 
 extern const PyConfig* _PyInterpreterState_GetConfig(PyInterpreterState *interp);
 
diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index d956954718c06d..cf72aa5f44a4a1 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -69,30 +69,48 @@ class Interpreter:
 
     def __new__(cls, id, /):
         # There is only one instance for any given ID.
-        if isinstance(id, int):
-            id = _interpreters.InterpreterID(id, force=False)
-        elif not isinstance(id, _interpreters.InterpreterID):
+        if not isinstance(id, int):
             raise TypeError(f'id must be an int, got {id!r}')
-        key = int(id)
+        id = int(id)
         try:
-            self = _known[key]
+            self = _known[id]
+            assert hasattr(self, '_ownsref')
         except KeyError:
-            self = super().__new__(cls)
-            self._id = id
-            _known[key] = self
+            # This may raise InterpreterNotFoundError:
+            _interpreters._incref(id)
+            try:
+                self = super().__new__(cls)
+                self._id = id
+                self._ownsref = True
+            except BaseException:
+                _interpreters._deccref(id)
+                raise
+            _known[id] = self
         return self
 
     def __repr__(self):
-        data = dict(id=int(self._id))
+        data = dict(id=self._id)
         kwargs = (f'{k}={v!r}' for k, v in data.items())
         return f'{type(self).__name__}({", ".join(kwargs)})'
 
     def __hash__(self):
         return hash(self._id)
 
+    def __del__(self):
+        self._decref()
+
+    def _decref(self):
+        if not self._ownsref:
+            return
+        self._ownsref = False
+        try:
+            _interpreters._decref(self.id)
+        except InterpreterNotFoundError:
+            pass
+
     @property
     def id(self):
-        return int(self._id)
+        return self._id
 
     def is_running(self):
         """Return whether or not the identified interpreter is running."""
diff --git a/Lib/test/test__xxinterpchannels.py b/Lib/test/test__xxinterpchannels.py
index 2b75e2f1916c82..13c8a10296e502 100644
--- a/Lib/test/test__xxinterpchannels.py
+++ b/Lib/test/test__xxinterpchannels.py
@@ -79,8 +79,7 @@ def __new__(cls, name=None, id=None):
                 name = 'interp'
             elif name == 'main':
                 raise ValueError('name mismatch (unexpected "main")')
-            if not isinstance(id, interpreters.InterpreterID):
-                id = interpreters.InterpreterID(id)
+            assert isinstance(id, int), repr(id)
         elif not name or name == 'main':
             name = 'main'
             id = main
diff --git a/Lib/test/test__xxsubinterpreters.py b/Lib/test/test__xxsubinterpreters.py
index 64a9db95e5eaf5..260ab64b07cb2d 100644
--- a/Lib/test/test__xxsubinterpreters.py
+++ b/Lib/test/test__xxsubinterpreters.py
@@ -15,6 +15,7 @@
 
 
 interpreters = import_helper.import_module('_xxsubinterpreters')
+from _xxsubinterpreters import InterpreterNotFoundError
 
 
 ##################################
@@ -266,7 +267,7 @@ def test_main(self):
         main = interpreters.get_main()
         cur = interpreters.get_current()
         self.assertEqual(cur, main)
-        self.assertIsInstance(cur, interpreters.InterpreterID)
+        self.assertIsInstance(cur, int)
 
     def test_subinterpreter(self):
         main = interpreters.get_main()
@@ -275,7 +276,7 @@ def test_subinterpreter(self):
             import _xxsubinterpreters as _interpreters
             cur = _interpreters.get_current()
             print(cur)
-            assert isinstance(cur, _interpreters.InterpreterID)
+            assert isinstance(cur, int)
             """))
         cur = int(out.strip())
         _, expected = interpreters.list_all()
@@ -289,7 +290,7 @@ def test_from_main(self):
         [expected] = interpreters.list_all()
         main = interpreters.get_main()
         self.assertEqual(main, expected)
-        self.assertIsInstance(main, interpreters.InterpreterID)
+        self.assertIsInstance(main, int)
 
     def test_from_subinterpreter(self):
         [expected] = interpreters.list_all()
@@ -298,7 +299,7 @@ def test_from_subinterpreter(self):
             import _xxsubinterpreters as _interpreters
             main = _interpreters.get_main()
             print(main)
-            assert isinstance(main, _interpreters.InterpreterID)
+            assert isinstance(main, int)
             """))
         main = int(out.strip())
         self.assertEqual(main, expected)
@@ -333,11 +334,11 @@ def test_from_subinterpreter(self):
     def test_already_destroyed(self):
         interp = interpreters.create()
         interpreters.destroy(interp)
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interpreters.is_running(interp)
 
     def test_does_not_exist(self):
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interpreters.is_running(1_000_000)
 
     def test_bad_id(self):
@@ -345,70 +346,11 @@ def test_bad_id(self):
             interpreters.is_running(-1)
 
 
-class InterpreterIDTests(TestBase):
-
-    def test_with_int(self):
-        id = interpreters.InterpreterID(10, force=True)
-
-        self.assertEqual(int(id), 10)
-
-    def test_coerce_id(self):
-        class Int(str):
-            def __index__(self):
-                return 10
-
-        id = interpreters.InterpreterID(Int(), force=True)
-        self.assertEqual(int(id), 10)
-
-    def test_bad_id(self):
-        self.assertRaises(TypeError, interpreters.InterpreterID, object())
-        self.assertRaises(TypeError, interpreters.InterpreterID, 10.0)
-        self.assertRaises(TypeError, interpreters.InterpreterID, '10')
-        self.assertRaises(TypeError, interpreters.InterpreterID, b'10')
-        self.assertRaises(ValueError, interpreters.InterpreterID, -1)
-        self.assertRaises(OverflowError, interpreters.InterpreterID, 2**64)
-
-    def test_does_not_exist(self):
-        id = interpreters.create()
-        with self.assertRaises(RuntimeError):
-            interpreters.InterpreterID(int(id) + 1)  # unforced
-
-    def test_str(self):
-        id = interpreters.InterpreterID(10, force=True)
-        self.assertEqual(str(id), '10')
-
-    def test_repr(self):
-        id = interpreters.InterpreterID(10, force=True)
-        self.assertEqual(repr(id), 'InterpreterID(10)')
-
-    def test_equality(self):
-        id1 = interpreters.create()
-        id2 = interpreters.InterpreterID(int(id1))
-        id3 = interpreters.create()
-
-        self.assertTrue(id1 == id1)
-        self.assertTrue(id1 == id2)
-        self.assertTrue(id1 == int(id1))
-        self.assertTrue(int(id1) == id1)
-        self.assertTrue(id1 == float(int(id1)))
-        self.assertTrue(float(int(id1)) == id1)
-        self.assertFalse(id1 == float(int(id1)) + 0.1)
-        self.assertFalse(id1 == str(int(id1)))
-        self.assertFalse(id1 == 2**1000)
-        self.assertFalse(id1 == float('inf'))
-        self.assertFalse(id1 == 'spam')
-        self.assertFalse(id1 == id3)
-
-        self.assertFalse(id1 != id1)
-        self.assertFalse(id1 != id2)
-        self.assertTrue(id1 != id3)
-
-
 class CreateTests(TestBase):
 
     def test_in_main(self):
         id = interpreters.create()
-        self.assertIsInstance(id, interpreters.InterpreterID)
+        self.assertIsInstance(id, int)
 
         self.assertIn(id, interpreters.list_all())
 
@@ -444,7 +386,7 @@ def test_in_subinterpreter(self):
             import _xxsubinterpreters as _interpreters
             id = _interpreters.create()
             print(id)
-            assert isinstance(id, _interpreters.InterpreterID)
+            assert isinstance(id, int)
             """))
         id2 = int(out.strip())
 
@@ -536,11 +478,11 @@ def f():
     def test_already_destroyed(self):
         id = interpreters.create()
         interpreters.destroy(id)
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interpreters.destroy(id)
 
     def test_does_not_exist(self):
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interpreters.destroy(1_000_000)
 
     def test_bad_id(self):
@@ -741,7 +683,7 @@ def test_does_not_exist(self):
         id = 0
         while id in interpreters.list_all():
             id += 1
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interpreters.run_string(id, 'print("spam")')
 
     def test_error_id(self):
diff --git a/Lib/test/test_capi/test_misc.py b/Lib/test/test_capi/test_misc.py
index 6cbf5d22203804..dec68977a6ba45 100644
--- a/Lib/test/test_capi/test_misc.py
+++ b/Lib/test/test_capi/test_misc.py
@@ -2020,6 +2020,137 @@ def test_module_state_shared_in_global(self):
         self.assertEqual(main_attr_id, subinterp_attr_id)
 
 
+@requires_subinterpreters
+class InterpreterIDTests(unittest.TestCase):
+
+    InterpreterID = _testcapi.get_interpreterid_type()
+
+    def new_interpreter(self):
+        def ensure_destroyed(interpid):
+            try:
+                _interpreters.destroy(interpid)
+            except _interpreters.InterpreterNotFoundError:
+                pass
+        id = _interpreters.create()
+        self.addCleanup(lambda: ensure_destroyed(id))
+        return id
+
+    def test_with_int(self):
+        id = self.InterpreterID(10, force=True)
+
+        self.assertEqual(int(id), 10)
+
+    def test_coerce_id(self):
+        class Int(str):
+            def __index__(self):
+                return 10
+
+        id = self.InterpreterID(Int(), force=True)
+        self.assertEqual(int(id), 10)
+
+    def test_bad_id(self):
+        for badid in [
+            object(),
+            10.0,
+            '10',
+            b'10',
+        ]:
+            with self.subTest(badid):
+                with self.assertRaises(TypeError):
+                    self.InterpreterID(badid)
+
+        badid = -1
+        with self.subTest(badid):
+            with self.assertRaises(ValueError):
+                self.InterpreterID(badid)
+
+        badid = 2**64
+        with self.subTest(badid):
+            with self.assertRaises(OverflowError):
+                self.InterpreterID(badid)
+
+    def test_exists(self):
+        id = self.new_interpreter()
+        with self.assertRaises(_interpreters.InterpreterNotFoundError):
+            self.InterpreterID(int(id) + 1)  # unforced
+
+    def test_does_not_exist(self):
+        id = self.new_interpreter()
+        with self.assertRaises(_interpreters.InterpreterNotFoundError):
+            self.InterpreterID(int(id) + 1)  # unforced
+
+    def test_does_not_exist(self):
+        id = _interpreters.create()
+        _interpreters.destroy(id)
+        with self.assertRaises(_interpreters.InterpreterNotFoundError):
+            self.InterpreterID(id)  # unforced
+
+    def test_str(self):
+        id = self.InterpreterID(10, force=True)
+        self.assertEqual(str(id), '10')
+
+    def test_repr(self):
+        id = self.InterpreterID(10, force=True)
+        self.assertEqual(repr(id), 'InterpreterID(10)')
+
+    def test_equality(self):
+        id1 = self.new_interpreter()
+        id2 = self.InterpreterID(id1)
+        id3 = self.InterpreterID(
+                self.new_interpreter())
+
+        self.assertTrue(id2 == id2)  # identity
+        self.assertTrue(id2 == id1)  # int-equivalent
+        self.assertTrue(id1 == id2)  # reversed
+        self.assertTrue(id2 == int(id2))
+        self.assertTrue(id2 == float(int(id2)))
+        self.assertTrue(float(int(id2)) == id2)
+        self.assertFalse(id2 == float(int(id2)) + 0.1)
+        self.assertFalse(id2 == str(int(id2)))
+        self.assertFalse(id2 == 2**1000)
+        self.assertFalse(id2 == float('inf'))
+        self.assertFalse(id2 == 'spam')
+        self.assertFalse(id2 == id3)
+
+        self.assertFalse(id2 != id2)
+        self.assertFalse(id2 != id1)
+        self.assertFalse(id1 != id2)
+        self.assertTrue(id2 != id3)
+
+    def test_linked_lifecycle(self):
+        id1 = _interpreters.create()
+        _testcapi.unlink_interpreter_refcount(id1)
+        self.assertEqual(
+            _testinternalcapi.get_interpreter_refcount(id1),
+            0)
+
+        id2 = self.InterpreterID(id1)
+        self.assertEqual(
+            _testinternalcapi.get_interpreter_refcount(id1),
+            1)
+
+        # The interpreter isn't linked to ID objects, so it isn't destroyed.
+        del id2
+        self.assertEqual(
+            _testinternalcapi.get_interpreter_refcount(id1),
+            0)
+
+        _testcapi.link_interpreter_refcount(id1)
+        self.assertEqual(
+            _testinternalcapi.get_interpreter_refcount(id1),
+            0)
+
+        id3 = self.InterpreterID(id1)
+        self.assertEqual(
+            _testinternalcapi.get_interpreter_refcount(id1),
+            1)
+
+        # The interpreter is linked now so is destroyed.
+        del id3
+        with self.assertRaises(_interpreters.InterpreterNotFoundError):
+            _testinternalcapi.get_interpreter_refcount(id1)
+
+
 class BuiltinStaticTypesTests(unittest.TestCase):
 
     TYPES = [
diff --git a/Lib/test/test_interpreters.py b/Lib/test/test_interpreters.py
index 02c4722ab9bdcb..4e37da92b31bca 100644
--- a/Lib/test/test_interpreters.py
+++ b/Lib/test/test_interpreters.py
@@ -778,10 +778,12 @@ def test_sys_path_0(self):
 class FinalizationTests(TestBase):
 
     def test_gh_109793(self):
+        # Make sure finalization finishes and the correct error code
+        # is reported, even when subinterpreters get cleaned up at the end.
         import subprocess
         argv = [sys.executable, '-c', '''if True:
-            import _xxsubinterpreters as _interpreters
-            interpid = _interpreters.create()
+            from test.support import interpreters
+            interp = interpreters.create()
             raise Exception
             ''']
         proc = subprocess.run(argv, capture_output=True, text=True)
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 9fdd67093338e4..b3ddfae58e6fc0 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -13,6 +13,7 @@
 #include "_testcapi/parts.h"
 
 #include "frameobject.h"          // PyFrame_New()
+#include "interpreteridobject.h"  // PyInterpreterID_Type
 #include "marshal.h"              // PyMarshal_WriteLongToFile()
 
 #include <float.h>                // FLT_MAX
@@ -1451,6 +1452,36 @@ run_in_subinterp(PyObject *self, PyObject *args)
     return PyLong_FromLong(r);
 }
 
+static PyObject *
+get_interpreterid_type(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    return Py_NewRef(&PyInterpreterID_Type);
+}
+
+static PyObject *
+link_interpreter_refcount(PyObject *self, PyObject *idobj)
+{
+    PyInterpreterState *interp = PyInterpreterID_LookUp(idobj);
+    if (interp == NULL) {
+        assert(PyErr_Occurred());
+        return NULL;
+    }
+    _PyInterpreterState_RequireIDRef(interp, 1);
+    Py_RETURN_NONE;
+}
+
+static PyObject *
+unlink_interpreter_refcount(PyObject *self, PyObject *idobj)
+{
+    PyInterpreterState *interp = PyInterpreterID_LookUp(idobj);
+    if (interp == NULL) {
+        assert(PyErr_Occurred());
+        return NULL;
+    }
+    _PyInterpreterState_RequireIDRef(interp, 0);
+    Py_RETURN_NONE;
+}
+
 static PyMethodDef ml;
 
 static PyObject *
@@ -3237,6 +3268,9 @@ static PyMethodDef TestMethods[] = {
     {"crash_no_current_thread", crash_no_current_thread,         METH_NOARGS},
     {"test_current_tstate_matches", test_current_tstate_matches, METH_NOARGS},
     {"run_in_subinterp",        run_in_subinterp,                METH_VARARGS},
+    {"get_interpreterid_type",  get_interpreterid_type,          METH_NOARGS},
+    {"link_interpreter_refcount", link_interpreter_refcount,     METH_O},
+    {"unlink_interpreter_refcount", unlink_interpreter_refcount, METH_O},
     {"create_cfunction",        create_cfunction,                METH_NOARGS},
     {"call_in_temporary_c_thread", call_in_temporary_c_thread, METH_VARARGS,
      PyDoc_STR("set_error_class(error_class) -> None")},
diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 4607a3faf17f74..25088af5786806 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -1475,6 +1475,17 @@ run_in_subinterp_with_config(PyObject *self, PyObject *args, PyObject *kwargs)
 }
 
 
+static PyObject *
+get_interpreter_refcount(PyObject *self, PyObject *idobj)
+{
+    PyInterpreterState *interp = PyInterpreterID_LookUp(idobj);
+    if (interp == NULL) {
+        return NULL;
+    }
+    return PyLong_FromLongLong(interp->id_refcount);
+}
+
+
 static void
 _xid_capsule_destructor(PyObject *capsule)
 {
@@ -1682,6 +1693,7 @@ static PyMethodDef module_functions[] = {
     {"run_in_subinterp_with_config",
      _PyCFunction_CAST(run_in_subinterp_with_config),
      METH_VARARGS | METH_KEYWORDS},
+    {"get_interpreter_refcount", get_interpreter_refcount, METH_O},
     {"compile_perf_trampoline_entry", compile_perf_trampoline_entry, METH_VARARGS},
     {"perf_trampoline_set_persist_after_fork", perf_trampoline_set_persist_after_fork, METH_VARARGS},
     {"get_crossinterp_data",    get_crossinterp_data,            METH_VARARGS},
diff --git a/Modules/_xxsubinterpretersmodule.c b/Modules/_xxsubinterpretersmodule.c
index f803f77bc81fc6..5954d47e2555ec 100644
--- a/Modules/_xxsubinterpretersmodule.c
+++ b/Modules/_xxsubinterpretersmodule.c
@@ -6,11 +6,13 @@
 #endif
 
 #include "Python.h"
+#include "pycore_abstract.h"      // _PyIndex_Check()
 #include "pycore_crossinterp.h"   // struct _xid
-#include "pycore_pyerrors.h"      // _Py_excinfo
+#include "pycore_interp.h"        // _PyInterpreterState_IDIncref()
 #include "pycore_initconfig.h"    // _PyErr_SetFromPyStatus()
+#include "pycore_long.h"          // _PyLong_IsNegative()
 #include "pycore_modsupport.h"    // _PyArg_BadArgument()
-#include "pycore_pyerrors.h"      // _PyErr_ChainExceptions1()
+#include "pycore_pyerrors.h"      // _Py_excinfo
 #include "pycore_pystate.h"       // _PyInterpreterState_SetRunningMain()
 
 #include "interpreteridobject.h"
@@ -28,6 +30,97 @@ _get_current_interp(void)
     return PyInterpreterState_Get();
 }
 
+static int64_t
+pylong_to_interpid(PyObject *idobj)
+{
+    assert(PyLong_CheckExact(idobj));
+
+    if (_PyLong_IsNegative((PyLongObject *)idobj)) {
+        PyErr_Format(PyExc_ValueError,
+                     "interpreter ID must be a non-negative int, got %R",
+                     idobj);
+        return -1;
+    }
+
+    int overflow;
+    long long id = PyLong_AsLongLongAndOverflow(idobj, &overflow);
+    if (id == -1) {
+        if (!overflow) {
+            assert(PyErr_Occurred());
+            return -1;
+        }
+        assert(!PyErr_Occurred());
+        // For now, we don't worry about if LLONG_MAX < INT64_MAX.
+        goto bad_id;
+    }
+#if LONG_LONG_MAX > INT64_MAX
+    if (id > INT64_MAX) {
+        goto bad_id;
+    }
+#endif
+    return (int64_t)id;
+
+bad_id:
+    PyErr_Format(PyExc_RuntimeError,
+                 "unrecognized interpreter ID %O", idobj);
+    return -1;
+}
+
+static int64_t
+convert_interpid_obj(PyObject *arg)
+{
+    int64_t id = -1;
+    if (_PyIndex_Check(arg)) {
+        PyObject *idobj = PyNumber_Long(arg);
+        if (idobj == NULL) {
+            return -1;
+        }
+        id = pylong_to_interpid(idobj);
+        Py_DECREF(idobj);
+        if (id < 0) {
+            return -1;
+        }
+    }
+    else {
+        PyErr_Format(PyExc_TypeError,
+                     "interpreter ID must be an int, got %.100s",
+                     Py_TYPE(arg)->tp_name);
+        return -1;
+    }
+    return id;
+}
+
+static PyInterpreterState *
+look_up_interp(PyObject *arg)
+{
+    int64_t id = convert_interpid_obj(arg);
+    if (id < 0) {
+        return NULL;
+    }
+    return _PyInterpreterState_LookUpID(id);
+}
+
+
+static PyObject *
+interpid_to_pylong(int64_t id)
+{
+    assert(id < LONG_LONG_MAX);
+    return PyLong_FromLongLong(id);
+}
+
+static PyObject *
+get_interpid_obj(PyInterpreterState *interp)
+{
+    if (_PyInterpreterState_IDInitref(interp) != 0) {
+        return NULL;
+    };
+    int64_t id = PyInterpreterState_GetID(interp);
+    if (id < 0) {
+        return NULL;
+    }
+    return interpid_to_pylong(id);
+}
+
 
 /* module state *************************************************************/
 
@@ -254,7 +347,7 @@ interp_create(PyObject *self, PyObject *args, PyObject *kwds)
     assert(tstate != NULL);
 
     PyInterpreterState *interp = PyThreadState_GetInterpreter(tstate);
-    PyObject *idobj = PyInterpreterState_GetIDObject(interp);
+    PyObject *idobj = get_interpid_obj(interp);
     if (idobj == NULL) {
         // XXX Possible GILState issues?
         save_tstate = PyThreadState_Swap(tstate);
@@ -273,7 +366,9 @@ interp_create(PyObject *self, PyObject *args, PyObject *kwds)
 PyDoc_STRVAR(create_doc,
 "create() -> ID\n\
 \n\
-Create a new interpreter and return a unique generated ID.");
+Create a new interpreter and return a unique generated ID.\n\
+\n\
+The caller is responsible for destroying the interpreter before exiting.");
 
 
 static PyObject *
@@ -288,7 +383,7 @@ interp_destroy(PyObject *self, PyObject *args, PyObject *kwds)
     }
 
     // Look up the interpreter.
-    PyInterpreterState *interp = PyInterpreterID_LookUp(id);
+    PyInterpreterState *interp = look_up_interp(id);
     if (interp == NULL) {
         return NULL;
     }
@@ -345,7 +440,7 @@ interp_list_all(PyObject *self, PyObject *Py_UNUSED(ignored))
 
     interp = PyInterpreterState_Head();
     while (interp != NULL) {
-        id = PyInterpreterState_GetIDObject(interp);
+        id = get_interpid_obj(interp);
         if (id == NULL) {
             Py_DECREF(ids);
             return NULL;
@@ -377,7 +472,7 @@ interp_get_current(PyObject *self, PyObject *Py_UNUSED(ignored))
     if (interp == NULL) {
         return NULL;
     }
-    return PyInterpreterState_GetIDObject(interp);
+    return get_interpid_obj(interp);
 }
 
 PyDoc_STRVAR(get_current_doc,
@@ -391,7 +486,7 @@ interp_get_main(PyObject *self, PyObject *Py_UNUSED(ignored))
 {
     // Currently, 0 is always the main interpreter.
     int64_t id = 0;
-    return PyInterpreterID_New(id);
+    return PyLong_FromLongLong(id);
 }
 
 PyDoc_STRVAR(get_main_doc,
@@ -481,7 +576,7 @@ _interp_exec(PyObject *self,
              PyObject **p_excinfo)
 {
     // Look up the interpreter.
-    PyInterpreterState *interp = PyInterpreterID_LookUp(id_arg);
+    PyInterpreterState *interp = look_up_interp(id_arg);
     if (interp == NULL) {
         return -1;
     }
@@ -667,7 +762,7 @@ interp_is_running(PyObject *self, PyObject *args, PyObject *kwds)
         return NULL;
     }
 
-    PyInterpreterState *interp = PyInterpreterID_LookUp(id);
+    PyInterpreterState *interp = look_up_interp(id);
     if (interp == NULL) {
         return NULL;
     }
@@ -683,6 +778,49 @@ PyDoc_STRVAR(is_running_doc,
 Return whether or not the identified interpreter is running.");
 
 
+static PyObject *
+interp_incref(PyObject *self, PyObject *args, PyObject *kwds)
+{
+    static char *kwlist[] = {"id", NULL};
+    PyObject *id;
+    if (!PyArg_ParseTupleAndKeywords(args, kwds,
+                                     "O:_incref", kwlist, &id)) {
+        return NULL;
+    }
+
+    PyInterpreterState *interp = look_up_interp(id);
+    if (interp == NULL) {
+        return NULL;
+    }
+    if (_PyInterpreterState_IDInitref(interp) < 0) {
+        return NULL;
+    }
+    _PyInterpreterState_IDIncref(interp);
+
+    Py_RETURN_NONE;
+}
+
+
+static PyObject *
+interp_decref(PyObject *self, PyObject *args, PyObject *kwds)
+{
+    static char *kwlist[] = {"id", NULL};
+    PyObject *id;
+    if (!PyArg_ParseTupleAndKeywords(args, kwds,
+                                     "O:_incref", kwlist, &id)) {
+        return NULL;
+    }
+
+    PyInterpreterState *interp = look_up_interp(id);
+    if (interp == NULL) {
+        return NULL;
+    }
+    _PyInterpreterState_IDDecref(interp);
+
+    Py_RETURN_NONE;
+}
+
+
 static PyMethodDef module_functions[] = {
     {"create",                    _PyCFunction_CAST(interp_create),
      METH_VARARGS | METH_KEYWORDS, create_doc},
@@ -707,6 +845,11 @@ static PyMethodDef module_functions[] = {
     {"is_shareable",              _PyCFunction_CAST(object_is_shareable),
      METH_VARARGS | METH_KEYWORDS, is_shareable_doc},
 
+    {"_incref",                   _PyCFunction_CAST(interp_incref),
+     METH_VARARGS | METH_KEYWORDS, NULL},
+    {"_decref",                   _PyCFunction_CAST(interp_decref),
+     METH_VARARGS | METH_KEYWORDS, NULL},
+
     {NULL,                        NULL}           /* sentinel */
 };
 
@@ -720,11 +863,6 @@ The 'interpreters' module provides a more convenient interface.");
 static int
 module_exec(PyObject *mod)
 {
-    // PyInterpreterID
-    if (PyModule_AddType(mod, &PyInterpreterID_Type) < 0) {
-        goto error;
-    }
-
     // exceptions
     if (PyModule_AddType(mod, (PyTypeObject *)PyExc_InterpreterError) < 0) {
         goto error;

From 0277878313085738c7f14df1667f4532502b6b56 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Tue, 28 Nov 2023 14:57:14 -0700
Subject: [PATCH 06/26] Fix Interpreter.__repr__().

---
 Lib/test/support/interpreters.py | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index cf72aa5f44a4a1..ba62246d123118 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -89,9 +89,7 @@ def __new__(cls, id, /):
         return self
 
     def __repr__(self):
-        data = dict(id=self._id)
-        kwargs = (f'{k}={v!r}' for k, v in data.items())
-        return f'{type(self).__name__}({", ".join(kwargs)})'
+        return f'{type(self).__name__}({self.id})'
 
     def __hash__(self):
         return hash(self._id)

From 59c8227c72e67dde383280010e05b67b65ccf6b2 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Tue, 28 Nov 2023 15:03:14 -0700
Subject: [PATCH 07/26] .run() -> .exec_sync()

---
 Lib/test/support/interpreters.py |  5 ++--
 Lib/test/test_interpreters.py    | 43 ++++++++++++++++----------------
 2 files changed, 24 insertions(+), 24 deletions(-)

diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index ba62246d123118..9a4680291ea103 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -122,8 +122,7 @@ def close(self):
         """
         return _interpreters.destroy(self._id)
 
-    # XXX Rename "run" to "exec"?
-    def run(self, src_str, /, channels=None):
+    def exec_sync(self, code, /, channels=None):
         """Run the given source code in the interpreter.
 
         This is essentially the same as calling the builtin "exec"
@@ -141,7 +140,7 @@ def run(self, src_str, /, channels=None):
         that time, the previous interpreter is allowed to run
         in other threads.
         """
-        excinfo = _interpreters.exec(self._id, src_str, channels)
+        excinfo = _interpreters.exec(self._id, code, channels)
         if excinfo is not None:
             raise RunFailedError(excinfo)
 
diff --git a/Lib/test/test_interpreters.py b/Lib/test/test_interpreters.py
index 4e37da92b31bca..49f8b9a6f80c29 100644
--- a/Lib/test/test_interpreters.py
+++ b/Lib/test/test_interpreters.py
@@ -43,7 +43,7 @@ def clean_up_interpreters():
 def _run_output(interp, request, channels=None):
     script, rpipe = _captured_script(request)
     with rpipe:
-        interp.run(script, channels=channels)
+        interp.exec_sync(script, channels=channels)
         return rpipe.read()
 
 
@@ -51,7 +51,7 @@ def _run_output(interp, request, channels=None):
 def _running(interp):
     r, w = os.pipe()
     def run():
-        interp.run(dedent(f"""
+        interp.exec_sync(dedent(f"""
             # wait for "signal"
             with open({r}) as rpipe:
                 rpipe.read()
@@ -328,7 +328,7 @@ def test_subinterpreter(self):
     def test_finished(self):
         r, w = self.pipe()
         interp = interpreters.create()
-        interp.run(f"""if True:
+        interp.exec_sync(f"""if True:
             import os
             os.write({w}, b'x')
             """)
@@ -360,7 +360,7 @@ def test_with_only_background_threads(self):
         FINISHED = b'F'
 
         interp = interpreters.create()
-        interp.run(f"""if True:
+        interp.exec_sync(f"""if True:
             import os
             import threading
 
@@ -374,7 +374,7 @@ def task():
         self.assertFalse(interp.is_running())
 
         os.write(w_thread, DONE)
-        interp.run('t.join()')
+        interp.exec_sync('t.join()')
         self.assertEqual(os.read(r_interp, 1), FINISHED)
 
 
@@ -441,7 +441,7 @@ def test_from_sibling(self):
         interp2 = interpreters.create()
         self.assertEqual(set(interpreters.list_all()),
                          {main, interp1, interp2})
-        interp1.run(dedent(f"""
+        interp1.exec_sync(dedent(f"""
             from test.support import interpreters
             interp2 = interpreters.Interpreter({interp2.id})
             interp2.close()
@@ -475,7 +475,7 @@ def test_subthreads_still_running(self):
         FINISHED = b'F'
 
         interp = interpreters.create()
-        interp.run(f"""if True:
+        interp.exec_sync(f"""if True:
             import os
             import threading
             import time
@@ -506,7 +506,7 @@ def test_success(self):
         interp = interpreters.create()
         script, file = _captured_script('print("it worked!", end="")')
         with file:
-            interp.run(script)
+            interp.exec_sync(script)
             out = file.read()
 
         self.assertEqual(out, 'it worked!')
@@ -514,14 +514,14 @@ def test_success(self):
     def test_failure(self):
         interp = interpreters.create()
         with self.assertRaises(interpreters.RunFailedError):
-            interp.run('raise Exception')
+            interp.exec_sync('raise Exception')
 
     def test_in_thread(self):
         interp = interpreters.create()
         script, file = _captured_script('print("it worked!", end="")')
         with file:
             def f():
-                interp.run(script)
+                interp.exec_sync(script)
 
             t = threading.Thread(target=f)
             t.start()
@@ -547,7 +547,7 @@ def test_fork(self):
                     with open('{file.name}', 'w', encoding='utf-8') as out:
                         out.write('{expected}')
                 """)
-            interp.run(script)
+            interp.exec_sync(script)
 
             file.seek(0)
             content = file.read()
@@ -558,17 +558,17 @@ def test_already_running(self):
         interp = interpreters.create()
         with _running(interp):
             with self.assertRaises(RuntimeError):
-                interp.run('print("spam")')
+                interp.exec_sync('print("spam")')
 
     def test_bad_script(self):
         interp = interpreters.create()
         with self.assertRaises(TypeError):
-            interp.run(10)
+            interp.exec_sync(10)
 
     def test_bytes_for_script(self):
         interp = interpreters.create()
         with self.assertRaises(TypeError):
-            interp.run(b'print("spam")')
+            interp.exec_sync(b'print("spam")')
 
     def test_with_background_threads_still_running(self):
         r_interp, w_interp = self.pipe()
@@ -579,7 +579,7 @@ def test_with_background_threads_still_running(self):
         FINISHED = b'F'
 
         interp = interpreters.create()
-        interp.run(f"""if True:
+        interp.exec_sync(f"""if True:
             import os
             import threading
 
@@ -591,17 +591,18 @@ def task():
             t.start()
             os.write({w_interp}, {RAN!r})
             """)
-        interp.run(f"""if True:
+        interp.exec_sync(f"""if True:
             os.write({w_interp}, {RAN!r})
             """)
 
         os.write(w_thread, DONE)
-        interp.run('t.join()')
+        interp.exec_sync('t.join()')
         self.assertEqual(os.read(r_interp, 1), RAN)
         self.assertEqual(os.read(r_interp, 1), RAN)
         self.assertEqual(os.read(r_interp, 1), FINISHED)
 
-    # test_xxsubinterpreters covers the remaining Interpreter.run() behavior.
+    # test_xxsubinterpreters covers the remaining
+    # Interpreter.exec_sync() behavior.
 
 
 class StressTests(TestBase):
@@ -737,7 +738,7 @@ def test_sys_path_0(self):
             orig = sys.path[0]
 
             interp = interpreters.create()
-            interp.run(f"""if True:
+            interp.exec_sync(f"""if True:
                 import json
                 import sys
                 print(json.dumps({{
@@ -958,7 +959,7 @@ def test_send_recv_main(self):
 
     def test_send_recv_same_interpreter(self):
         interp = interpreters.create()
-        interp.run(dedent("""
+        interp.exec_sync(dedent("""
             from test.support import interpreters
             r, s = interpreters.create_channel()
             orig = b'spam'
@@ -1031,7 +1032,7 @@ def test_send_recv_nowait_main_with_default(self):
 
     def test_send_recv_nowait_same_interpreter(self):
         interp = interpreters.create()
-        interp.run(dedent("""
+        interp.exec_sync(dedent("""
             from test.support import interpreters
             r, s = interpreters.create_channel()
             orig = b'spam'

From fa132a290b85fab376f94351d00fcfab0afb619d Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Tue, 28 Nov 2023 16:54:50 -0700
Subject: [PATCH 08/26] RunFailedError -> ExecFailure

---
 Lib/test/support/interpreters.py | 8 ++++----
 Lib/test/test_interpreters.py    | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index 9a4680291ea103..d2a78ccce57b74 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -18,7 +18,7 @@
 
 __all__ = [
     'Interpreter', 'get_current', 'get_main', 'create', 'list_all',
-    'InterpreterError', 'InterpreterNotFoundError', 'RunFailedError',
+    'InterpreterError', 'InterpreterNotFoundError', 'ExecFailure',
     'SendChannel', 'RecvChannel',
     'create_channel', 'list_all_channels', 'is_shareable',
     'ChannelError', 'ChannelNotFoundError',
@@ -26,7 +26,7 @@
     ]
 
 
-class RunFailedError(RuntimeError):
+class ExecFailure(RuntimeError):
 
     def __init__(self, excinfo):
         msg = excinfo.formatted
@@ -131,7 +131,7 @@ def exec_sync(self, code, /, channels=None):
 
         There is no return value.
 
-        If the code raises an unhandled exception then a RunFailedError
+        If the code raises an unhandled exception then an ExecFailure
         is raised, which summarizes the unhandled exception.  The actual
         exception is discarded because objects cannot be shared between
         interpreters.
@@ -142,7 +142,7 @@ def exec_sync(self, code, /, channels=None):
         """
         excinfo = _interpreters.exec(self._id, code, channels)
         if excinfo is not None:
-            raise RunFailedError(excinfo)
+            raise ExecFailure(excinfo)
 
 
 def create_channel():
diff --git a/Lib/test/test_interpreters.py b/Lib/test/test_interpreters.py
index 49f8b9a6f80c29..60db7373db6dcf 100644
--- a/Lib/test/test_interpreters.py
+++ b/Lib/test/test_interpreters.py
@@ -500,7 +500,7 @@ def task():
         self.assertEqual(os.read(r_interp, 1), FINISHED)
 
 
-class TestInterpreterRun(TestBase):
+class TestInterpreterExecSync(TestBase):
 
     def test_success(self):
         interp = interpreters.create()
@@ -513,7 +513,7 @@ def test_success(self):
 
     def test_failure(self):
         interp = interpreters.create()
-        with self.assertRaises(interpreters.RunFailedError):
+        with self.assertRaises(interpreters.ExecFailure):
             interp.exec_sync('raise Exception')
 
     def test_in_thread(self):

From 644efa59ae80df07339a006d849aa36c77a4a94b Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Tue, 28 Nov 2023 16:58:14 -0700
Subject: [PATCH 09/26] Add Interpreter.run().

---
 Lib/test/support/interpreters.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index d2a78ccce57b74..1d642b3ed18de7 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -144,6 +144,13 @@ def exec_sync(self, code, /, channels=None):
         if excinfo is not None:
             raise ExecFailure(excinfo)
 
+    def run(self, code, /, channels=None):
+        def task():
+            self.exec_sync(code, channels=channels)
+        t = threading.Thread(target=task)
+        t.start()
+        return t
+
 
 def create_channel():
     """Return (recv, send) for a new cross-interpreter channel.

From abf2aa8ce2d9aeb5131803febb2f8ffe1af99041 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Fri, 1 Dec 2023 15:39:25 -0700
Subject: [PATCH 10/26] Make the interpreters module a package.

---
 Lib/test/support/interpreters/__init__.py     |  145 ++
 .../channel.py}                               |  145 +-
 Lib/test/test_interpreters.py                 | 1162 -----------------
 Lib/test/test_interpreters/__init__.py        |    5 +
 Lib/test/test_interpreters/__main__.py        |    4 +
 Lib/test/test_interpreters/test_api.py        |  596 +++++++++
 Lib/test/test_interpreters/test_channel.py    |  328 +++++
 Lib/test/test_interpreters/test_lifecycle.py  |  189 +++
 Lib/test/test_interpreters/test_stress.py     |   38 +
 Lib/test/test_interpreters/utils.py           |   73 ++
 10 files changed, 1383 insertions(+), 1302 deletions(-)
 create mode 100644 Lib/test/support/interpreters/__init__.py
 rename Lib/test/support/{interpreters.py => interpreters/channel.py} (54%)
 delete mode 100644 Lib/test/test_interpreters.py
 create mode 100644 Lib/test/test_interpreters/__init__.py
 create mode 100644 Lib/test/test_interpreters/__main__.py
 create mode 100644 Lib/test/test_interpreters/test_api.py
 create mode 100644 Lib/test/test_interpreters/test_channel.py
 create mode 100644 Lib/test/test_interpreters/test_lifecycle.py
 create mode 100644 Lib/test/test_interpreters/test_stress.py
 create mode 100644 Lib/test/test_interpreters/utils.py

diff --git a/Lib/test/support/interpreters/__init__.py b/Lib/test/support/interpreters/__init__.py
new file mode 100644
index 00000000000000..86b625640a439f
--- /dev/null
+++ b/Lib/test/support/interpreters/__init__.py
@@ -0,0 +1,145 @@
+"""Subinterpreters High Level Module."""
+
+import weakref
+import _xxsubinterpreters as _interpreters
+
+# aliases:
+from _xxsubinterpreters import (
+    InterpreterError, InterpreterNotFoundError,
+    is_shareable,
+)
+from .channel import create as create_channel
+
+
+__all__ = [
+    'get_current', 'get_main', 'create', 'list_all', 'is_shareable',
+    'Interpreter',
+    'InterpreterError', 'InterpreterNotFoundError', 'ExecFailure',
+    'create_channel',
+]
+
+
+class ExecFailure(RuntimeError):
+
+    def __init__(self, excinfo):
+        msg = excinfo.formatted
+        if not msg:
+            if excinfo.type and snapshot.msg:
+                msg = f'{snapshot.type.__name__}: {snapshot.msg}'
+            else:
+                msg = snapshot.type.__name__ or snapshot.msg
+        super().__init__(msg)
+        self.snapshot = excinfo
+
+
+def create():
+    """Return a new (idle) Python interpreter."""
+    id = _interpreters.create(isolated=True)
+    return Interpreter(id)
+
+
+def list_all():
+    """Return all existing interpreters."""
+    return [Interpreter(id) for id in _interpreters.list_all()]
+
+
+def get_current():
+    """Return the currently running interpreter."""
+    id = _interpreters.get_current()
+    return Interpreter(id)
+
+
+def get_main():
+    """Return the main interpreter."""
+    id = _interpreters.get_main()
+    return Interpreter(id)
+
+
+_known = weakref.WeakValueDictionary()
+
+class Interpreter:
+    """A single Python interpreter."""
+
+    def __new__(cls, id, /):
+        # There is only one instance for any given ID.
+        if not isinstance(id, int):
+            raise TypeError(f'id must be an int, got {id!r}')
+        id = int(id)
+        try:
+            self = _known[id]
+            assert hasattr(self, '_ownsref')
+        except KeyError:
+            # This may raise InterpreterNotFoundError:
+            _interpreters._incref(id)
+            try:
+                self = super().__new__(cls)
+                self._id = id
+                self._ownsref = True
+            except BaseException:
+                _interpreters._deccref(id)
+                raise
+            _known[id] = self
+        return self
+
+    def __repr__(self):
+        return f'{type(self).__name__}({self.id})'
+
+    def __hash__(self):
+        return hash(self._id)
+
+    def __del__(self):
+        self._decref()
+
+    def _decref(self):
+        if not self._ownsref:
+            return
+        self._ownsref = False
+        try:
+            _interpreters._decref(self.id)
+        except InterpreterNotFoundError:
+            pass
+
+    @property
+    def id(self):
+        return self._id
+
+    def is_running(self):
+        """Return whether or not the identified interpreter is running."""
+        return _interpreters.is_running(self._id)
+
+    def close(self):
+        """Finalize and destroy the interpreter.
+
+        Attempting to destroy the current interpreter results
+        in a RuntimeError.
+        """
+        return _interpreters.destroy(self._id)
+
+    def exec_sync(self, code, /, channels=None):
+        """Run the given source code in the interpreter.
+
+        This is essentially the same as calling the builtin "exec"
+        with this interpreter, using the __dict__ of its __main__
+        module as both globals and locals.
+
+        There is no return value.
+
+        If the code raises an unhandled exception then an ExecFailure
+        is raised, which summarizes the unhandled exception.  The actual
+        exception is discarded because objects cannot be shared between
+        interpreters.
+
+        This blocks the current Python thread until done.  During
+        that time, the previous interpreter is allowed to run
+        in other threads.
+        """
+        excinfo = _interpreters.exec(self._id, code, channels)
+        if excinfo is not None:
+            raise ExecFailure(excinfo)
+
+    def run(self, code, /, channels=None):
+        def task():
+            self.exec_sync(code, channels=channels)
+        t = threading.Thread(target=task)
+        t.start()
+        return t
diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters/channel.py
similarity index 54%
rename from Lib/test/support/interpreters.py
rename to Lib/test/support/interpreters/channel.py
index 1d642b3ed18de7..75a5a60f54f926 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters/channel.py
@@ -1,15 +1,9 @@
-"""Subinterpreters High Level Module."""
+"""Cross-interpreter Channels High Level Module."""
 
 import time
-import weakref
-import _xxsubinterpreters as _interpreters
 import _xxinterpchannels as _channels
 
 # aliases:
-from _xxsubinterpreters import (
-    InterpreterError, InterpreterNotFoundError,
-    is_shareable,
-)
 from _xxinterpchannels import (
     ChannelError, ChannelNotFoundError, ChannelClosedError,
     ChannelEmptyError, ChannelNotEmptyError,
@@ -17,142 +11,13 @@
 
 
 __all__ = [
-    'Interpreter', 'get_current', 'get_main', 'create', 'list_all',
-    'InterpreterError', 'InterpreterNotFoundError', 'ExecFailure',
+    'create', 'list_all',
     'SendChannel', 'RecvChannel',
-    'create_channel', 'list_all_channels', 'is_shareable',
-    'ChannelError', 'ChannelNotFoundError',
-    'ChannelEmptyError',
-    ]
-
-
-class ExecFailure(RuntimeError):
-
-    def __init__(self, excinfo):
-        msg = excinfo.formatted
-        if not msg:
-            if excinfo.type and snapshot.msg:
-                msg = f'{snapshot.type.__name__}: {snapshot.msg}'
-            else:
-                msg = snapshot.type.__name__ or snapshot.msg
-        super().__init__(msg)
-        self.snapshot = excinfo
+    'ChannelError', 'ChannelNotFoundError', 'ChannelEmptyError',
+]
 
 
 def create():
-    """Return a new (idle) Python interpreter."""
-    id = _interpreters.create(isolated=True)
-    return Interpreter(id)
-
-
-def list_all():
-    """Return all existing interpreters."""
-    return [Interpreter(id) for id in _interpreters.list_all()]
-
-
-def get_current():
-    """Return the currently running interpreter."""
-    id = _interpreters.get_current()
-    return Interpreter(id)
-
-
-def get_main():
-    """Return the main interpreter."""
-    id = _interpreters.get_main()
-    return Interpreter(id)
-
-
-_known = weakref.WeakValueDictionary()
-
-class Interpreter:
-    """A single Python interpreter."""
-
-    def __new__(cls, id, /):
-        # There is only one instance for any given ID.
-        if not isinstance(id, int):
-            raise TypeError(f'id must be an int, got {id!r}')
-        id = int(id)
-        try:
-            self = _known[id]
-            assert hasattr(self, '_ownsref')
-        except KeyError:
-            # This may raise InterpreterNotFoundError:
-            _interpreters._incref(id)
-            try:
-                self = super().__new__(cls)
-                self._id = id
-                self._ownsref = True
-            except BaseException:
-                _interpreters._deccref(id)
-                raise
-            _known[id] = self
-        return self
-
-    def __repr__(self):
-        return f'{type(self).__name__}({self.id})'
-
-    def __hash__(self):
-        return hash(self._id)
-
-    def __del__(self):
-        self._decref()
-
-    def _decref(self):
-        if not self._ownsref:
-            return
-        self._ownsref = False
-        try:
-            _interpreters._decref(self.id)
-        except InterpreterNotFoundError:
-            pass
-
-    @property
-    def id(self):
-        return self._id
-
-    def is_running(self):
-        """Return whether or not the identified interpreter is running."""
-        return _interpreters.is_running(self._id)
-
-    def close(self):
-        """Finalize and destroy the interpreter.
-
-        Attempting to destroy the current interpreter results
-        in a RuntimeError.
-        """
-        return _interpreters.destroy(self._id)
-
-    def exec_sync(self, code, /, channels=None):
-        """Run the given source code in the interpreter.
-
-        This is essentially the same as calling the builtin "exec"
-        with this interpreter, using the __dict__ of its __main__
-        module as both globals and locals.
-
-        There is no return value.
-
-        If the code raises an unhandled exception then an ExecFailure
-        is raised, which summarizes the unhandled exception.  The actual
-        exception is discarded because objects cannot be shared between
-        interpreters.
-
-        This blocks the current Python thread until done.  During
-        that time, the previous interpreter is allowed to run
-        in other threads.
-        """
-        excinfo = _interpreters.exec(self._id, code, channels)
-        if excinfo is not None:
-            raise ExecFailure(excinfo)
-
-    def run(self, code, /, channels=None):
-        def task():
-            self.exec_sync(code, channels=channels)
-        t = threading.Thread(target=task)
-        t.start()
-        return t
-
-
-def create_channel():
     """Return (recv, send) for a new cross-interpreter channel.
 
     The channel may be used to pass data safely between interpreters.
@@ -162,7 +27,7 @@ def create_channel():
     return recv, send
 
 
-def list_all_channels():
+def list_all():
     """Return a list of (recv, send) for all open channels."""
     return [(RecvChannel(cid), SendChannel(cid))
             for cid in _channels.list_all()]
diff --git a/Lib/test/test_interpreters.py b/Lib/test/test_interpreters.py
deleted file mode 100644
index 60db7373db6dcf..00000000000000
--- a/Lib/test/test_interpreters.py
+++ /dev/null
@@ -1,1162 +0,0 @@
-import contextlib
-import json
-import os
-import os.path
-import sys
-import threading
-from textwrap import dedent
-import unittest
-import time
-
-from test import support
-from test.support import import_helper
-from test.support import threading_helper
-from test.support import os_helper
-_interpreters = import_helper.import_module('_xxsubinterpreters')
-_channels = import_helper.import_module('_xxinterpchannels')
-from test.support import interpreters
-from test.support.interpreters import InterpreterNotFoundError
-
-
-def _captured_script(script):
-    r, w = os.pipe()
-    indented = script.replace('\n', '\n                ')
-    wrapped = dedent(f"""
-        import contextlib
-        with open({w}, 'w', encoding='utf-8') as spipe:
-            with contextlib.redirect_stdout(spipe):
-                {indented}
-        """)
-    return wrapped, open(r, encoding='utf-8')
-
-
-def clean_up_interpreters():
-    for interp in interpreters.list_all():
-        if interp.id == 0:  # main
-            continue
-        try:
-            interp.close()
-        except RuntimeError:
-            pass  # already destroyed
-
-
-def _run_output(interp, request, channels=None):
-    script, rpipe = _captured_script(request)
-    with rpipe:
-        interp.exec_sync(script, channels=channels)
-        return rpipe.read()
-
-
-@contextlib.contextmanager
-def _running(interp):
-    r, w = os.pipe()
-    def run():
-        interp.exec_sync(dedent(f"""
-            # wait for "signal"
-            with open({r}) as rpipe:
-                rpipe.read()
-            """))
-
-    t = threading.Thread(target=run)
-    t.start()
-
-    yield
-
-    with open(w, 'w') as spipe:
-        spipe.write('done')
-    t.join()
-
-
-class TestBase(unittest.TestCase):
-
-    def pipe(self):
-        def ensure_closed(fd):
-            try:
-                os.close(fd)
-            except OSError:
-                pass
-        r, w = os.pipe()
-        self.addCleanup(lambda: ensure_closed(r))
-        self.addCleanup(lambda: ensure_closed(w))
-        return r, w
-
-    def tearDown(self):
-        clean_up_interpreters()
-
-
-class CreateTests(TestBase):
-
-    def test_in_main(self):
-        interp = interpreters.create()
-        self.assertIsInstance(interp, interpreters.Interpreter)
-        self.assertIn(interp, interpreters.list_all())
-
-    def test_in_thread(self):
-        lock = threading.Lock()
-        interp = None
-        def f():
-            nonlocal interp
-            interp = interpreters.create()
-            lock.acquire()
-            lock.release()
-        t = threading.Thread(target=f)
-        with lock:
-            t.start()
-        t.join()
-        self.assertIn(interp, interpreters.list_all())
-
-    def test_in_subinterpreter(self):
-        main, = interpreters.list_all()
-        interp = interpreters.create()
-        out = _run_output(interp, dedent("""
-            from test.support import interpreters
-            interp = interpreters.create()
-            print(interp.id)
-            """))
-        interp2 = interpreters.Interpreter(int(out))
-        self.assertEqual(interpreters.list_all(), [main, interp, interp2])
-
-    def test_after_destroy_all(self):
-        before = set(interpreters.list_all())
-        # Create 3 subinterpreters.
-        interp_lst = []
-        for _ in range(3):
-            interps = interpreters.create()
-            interp_lst.append(interps)
-        # Now destroy them.
-        for interp in interp_lst:
-            interp.close()
-        # Finally, create another.
-        interp = interpreters.create()
-        self.assertEqual(set(interpreters.list_all()), before | {interp})
-
-    def test_after_destroy_some(self):
-        before = set(interpreters.list_all())
-        # Create 3 subinterpreters.
-        interp1 = interpreters.create()
-        interp2 = interpreters.create()
-        interp3 = interpreters.create()
-        # Now destroy 2 of them.
-        interp1.close()
-        interp2.close()
-        # Finally, create another.
-        interp = interpreters.create()
-        self.assertEqual(set(interpreters.list_all()), before | {interp3, interp})
-
-
-class GetMainTests(TestBase):
-
-    def test_id(self):
-        main = interpreters.get_main()
-        self.assertEqual(main.id, 0)
-
-    def test_current(self):
-        main = interpreters.get_main()
-        current = interpreters.get_current()
-        self.assertIs(main, current)
-
-    def test_idempotent(self):
-        main1 = interpreters.get_main()
-        main2 = interpreters.get_main()
-        self.assertIs(main1, main2)
-
-
-class GetCurrentTests(TestBase):
-
-    def test_main(self):
-        main = interpreters.get_main()
-        current = interpreters.get_current()
-        self.assertEqual(current, main)
-
-    def test_subinterpreter(self):
-        main = interpreters.get_main()
-        interp = interpreters.create()
-        out = _run_output(interp, dedent("""
-            from test.support import interpreters
-            cur = interpreters.get_current()
-            print(cur.id)
-            """))
-        current = interpreters.Interpreter(int(out))
-        self.assertEqual(current, interp)
-        self.assertNotEqual(current, main)
-
-    def test_idempotent(self):
-        with self.subTest('main'):
-            cur1 = interpreters.get_current()
-            cur2 = interpreters.get_current()
-            self.assertIs(cur1, cur2)
-
-        with self.subTest('subinterpreter'):
-            interp = interpreters.create()
-            out = _run_output(interp, dedent("""
-                from test.support import interpreters
-                cur = interpreters.get_current()
-                print(id(cur))
-                cur = interpreters.get_current()
-                print(id(cur))
-                """))
-            objid1, objid2 = (int(v) for v in out.splitlines())
-            self.assertEqual(objid1, objid2)
-
-        with self.subTest('per-interpreter'):
-            interp = interpreters.create()
-            out = _run_output(interp, dedent("""
-                from test.support import interpreters
-                cur = interpreters.get_current()
-                print(id(cur))
-                """))
-            id1 = int(out)
-            id2 = id(interp)
-            self.assertNotEqual(id1, id2)
-
-
-class ListAllTests(TestBase):
-
-    def test_initial(self):
-        interps = interpreters.list_all()
-        self.assertEqual(1, len(interps))
-
-    def test_after_creating(self):
-        main = interpreters.get_current()
-        first = interpreters.create()
-        second = interpreters.create()
-
-        ids = []
-        for interp in interpreters.list_all():
-            ids.append(interp.id)
-
-        self.assertEqual(ids, [main.id, first.id, second.id])
-
-    def test_after_destroying(self):
-        main = interpreters.get_current()
-        first = interpreters.create()
-        second = interpreters.create()
-        first.close()
-
-        ids = []
-        for interp in interpreters.list_all():
-            ids.append(interp.id)
-
-        self.assertEqual(ids, [main.id, second.id])
-
-    def test_idempotent(self):
-        main = interpreters.get_current()
-        first = interpreters.create()
-        second = interpreters.create()
-        expected = [main, first, second]
-
-        actual = interpreters.list_all()
-
-        self.assertEqual(actual, expected)
-        for interp1, interp2 in zip(actual, expected):
-            self.assertIs(interp1, interp2)
-
-
-class InterpreterObjectTests(TestBase):
-
-    def test_init_int(self):
-        interpid = interpreters.get_current().id
-        interp = interpreters.Interpreter(interpid)
-        self.assertEqual(interp.id, interpid)
-
-    def test_init_interpreter_id(self):
-        interpid = interpreters.get_current()._id
-        interp = interpreters.Interpreter(interpid)
-        self.assertEqual(interp._id, interpid)
-
-    def test_init_unsupported(self):
-        actualid = interpreters.get_current().id
-        for interpid in [
-            str(actualid),
-            float(actualid),
-            object(),
-            None,
-            '',
-        ]:
-            with self.subTest(repr(interpid)):
-                with self.assertRaises(TypeError):
-                    interpreters.Interpreter(interpid)
-
-    def test_idempotent(self):
-        main = interpreters.get_main()
-        interp = interpreters.Interpreter(main.id)
-        self.assertIs(interp, main)
-
-    def test_init_does_not_exist(self):
-        with self.assertRaises(InterpreterNotFoundError):
-            interpreters.Interpreter(1_000_000)
-
-    def test_init_bad_id(self):
-        with self.assertRaises(ValueError):
-            interpreters.Interpreter(-1)
-
-    def test_id_type(self):
-        main = interpreters.get_main()
-        current = interpreters.get_current()
-        interp = interpreters.create()
-        self.assertIsInstance(main.id, int)
-        self.assertIsInstance(current.id, int)
-        self.assertIsInstance(interp.id, int)
-
-    def test_id_readonly(self):
-        interp = interpreters.create()
-        with self.assertRaises(AttributeError):
-            interp.id = 1_000_000
-
-    def test_equality(self):
-        interp1 = interpreters.create()
-        interp2 = interpreters.create()
-        self.assertEqual(interp1, interp1)
-        self.assertNotEqual(interp1, interp2)
-
-
-class TestInterpreterIsRunning(TestBase):
-
-    def test_main(self):
-        main = interpreters.get_main()
-        self.assertTrue(main.is_running())
-
-    @unittest.skip('Fails on FreeBSD')
-    def test_subinterpreter(self):
-        interp = interpreters.create()
-        self.assertFalse(interp.is_running())
-
-        with _running(interp):
-            self.assertTrue(interp.is_running())
-        self.assertFalse(interp.is_running())
-
-    def test_finished(self):
-        r, w = self.pipe()
-        interp = interpreters.create()
-        interp.exec_sync(f"""if True:
-            import os
-            os.write({w}, b'x')
-            """)
-        self.assertFalse(interp.is_running())
-        self.assertEqual(os.read(r, 1), b'x')
-
-    def test_from_subinterpreter(self):
-        interp = interpreters.create()
-        out = _run_output(interp, dedent(f"""
-            import _xxsubinterpreters as _interpreters
-            if _interpreters.is_running({interp.id}):
-                print(True)
-            else:
-                print(False)
-            """))
-        self.assertEqual(out.strip(), 'True')
-
-    def test_already_destroyed(self):
-        interp = interpreters.create()
-        interp.close()
-        with self.assertRaises(InterpreterNotFoundError):
-            interp.is_running()
-
-    def test_with_only_background_threads(self):
-        r_interp, w_interp = self.pipe()
-        r_thread, w_thread = self.pipe()
-
-        DONE = b'D'
-        FINISHED = b'F'
-
-        interp = interpreters.create()
-        interp.exec_sync(f"""if True:
-            import os
-            import threading
-
-            def task():
-                v = os.read({r_thread}, 1)
-                assert v == {DONE!r}
-                os.write({w_interp}, {FINISHED!r})
-            t = threading.Thread(target=task)
-            t.start()
-            """)
-        self.assertFalse(interp.is_running())
-
-        os.write(w_thread, DONE)
-        interp.exec_sync('t.join()')
-        self.assertEqual(os.read(r_interp, 1), FINISHED)
-
-
-class TestInterpreterClose(TestBase):
-
-    def test_basic(self):
-        main = interpreters.get_main()
-        interp1 = interpreters.create()
-        interp2 = interpreters.create()
-        interp3 = interpreters.create()
-        self.assertEqual(set(interpreters.list_all()),
-                         {main, interp1, interp2, interp3})
-        interp2.close()
-        self.assertEqual(set(interpreters.list_all()),
-                         {main, interp1, interp3})
-
-    def test_all(self):
-        before = set(interpreters.list_all())
-        interps = set()
-        for _ in range(3):
-            interp = interpreters.create()
-            interps.add(interp)
-        self.assertEqual(set(interpreters.list_all()), before | interps)
-        for interp in interps:
-            interp.close()
-        self.assertEqual(set(interpreters.list_all()), before)
-
-    def test_main(self):
-        main, = interpreters.list_all()
-        with self.assertRaises(RuntimeError):
-            main.close()
-
-        def f():
-            with self.assertRaises(RuntimeError):
-                main.close()
-
-        t = threading.Thread(target=f)
-        t.start()
-        t.join()
-
-    def test_already_destroyed(self):
-        interp = interpreters.create()
-        interp.close()
-        with self.assertRaises(InterpreterNotFoundError):
-            interp.close()
-
-    def test_from_current(self):
-        main, = interpreters.list_all()
-        interp = interpreters.create()
-        out = _run_output(interp, dedent(f"""
-            from test.support import interpreters
-            interp = interpreters.Interpreter({interp.id})
-            try:
-                interp.close()
-            except RuntimeError:
-                print('failed')
-            """))
-        self.assertEqual(out.strip(), 'failed')
-        self.assertEqual(set(interpreters.list_all()), {main, interp})
-
-    def test_from_sibling(self):
-        main, = interpreters.list_all()
-        interp1 = interpreters.create()
-        interp2 = interpreters.create()
-        self.assertEqual(set(interpreters.list_all()),
-                         {main, interp1, interp2})
-        interp1.exec_sync(dedent(f"""
-            from test.support import interpreters
-            interp2 = interpreters.Interpreter({interp2.id})
-            interp2.close()
-            interp3 = interpreters.create()
-            interp3.close()
-            """))
-        self.assertEqual(set(interpreters.list_all()), {main, interp1})
-
-    def test_from_other_thread(self):
-        interp = interpreters.create()
-        def f():
-            interp.close()
-
-        t = threading.Thread(target=f)
-        t.start()
-        t.join()
-
-    @unittest.skip('Fails on FreeBSD')
-    def test_still_running(self):
-        main, = interpreters.list_all()
-        interp = interpreters.create()
-        with _running(interp):
-            with self.assertRaises(RuntimeError):
-                interp.close()
-            self.assertTrue(interp.is_running())
-
-    def test_subthreads_still_running(self):
-        r_interp, w_interp = self.pipe()
-        r_thread, w_thread = self.pipe()
-
-        FINISHED = b'F'
-
-        interp = interpreters.create()
-        interp.exec_sync(f"""if True:
-            import os
-            import threading
-            import time
-
-            done = False
-
-            def notify_fini():
-                global done
-                done = True
-                t.join()
-            threading._register_atexit(notify_fini)
-
-            def task():
-                while not done:
-                    time.sleep(0.1)
-                os.write({w_interp}, {FINISHED!r})
-            t = threading.Thread(target=task)
-            t.start()
-            """)
-        interp.close()
-
-        self.assertEqual(os.read(r_interp, 1), FINISHED)
-
-
-class TestInterpreterExecSync(TestBase):
-
-    def test_success(self):
-        interp = interpreters.create()
-        script, file = _captured_script('print("it worked!", end="")')
-        with file:
-            interp.exec_sync(script)
-            out = file.read()
-
-        self.assertEqual(out, 'it worked!')
-
-    def test_failure(self):
-        interp = interpreters.create()
-        with self.assertRaises(interpreters.ExecFailure):
-            interp.exec_sync('raise Exception')
-
-    def test_in_thread(self):
-        interp = interpreters.create()
-        script, file = _captured_script('print("it worked!", end="")')
-        with file:
-            def f():
-                interp.exec_sync(script)
-
-            t = threading.Thread(target=f)
-            t.start()
-            t.join()
-            out = file.read()
-
-        self.assertEqual(out, 'it worked!')
-
-    @support.requires_fork()
-    def test_fork(self):
-        interp = interpreters.create()
-        import tempfile
-        with tempfile.NamedTemporaryFile('w+', encoding='utf-8') as file:
-            file.write('')
-            file.flush()
-
-            expected = 'spam spam spam spam spam'
-            script = dedent(f"""
-                import os
-                try:
-                    os.fork()
-                except RuntimeError:
-                    with open('{file.name}', 'w', encoding='utf-8') as out:
-                        out.write('{expected}')
-                """)
-            interp.exec_sync(script)
-
-            file.seek(0)
-            content = file.read()
-            self.assertEqual(content, expected)
-
-    @unittest.skip('Fails on FreeBSD')
-    def test_already_running(self):
-        interp = interpreters.create()
-        with _running(interp):
-            with self.assertRaises(RuntimeError):
-                interp.exec_sync('print("spam")')
-
-    def test_bad_script(self):
-        interp = interpreters.create()
-        with self.assertRaises(TypeError):
-            interp.exec_sync(10)
-
-    def test_bytes_for_script(self):
-        interp = interpreters.create()
-        with self.assertRaises(TypeError):
-            interp.exec_sync(b'print("spam")')
-
-    def test_with_background_threads_still_running(self):
-        r_interp, w_interp = self.pipe()
-        r_thread, w_thread = self.pipe()
-
-        RAN = b'R'
-        DONE = b'D'
-        FINISHED = b'F'
-
-        interp = interpreters.create()
-        interp.exec_sync(f"""if True:
-            import os
-            import threading
-
-            def task():
-                v = os.read({r_thread}, 1)
-                assert v == {DONE!r}
-                os.write({w_interp}, {FINISHED!r})
-            t = threading.Thread(target=task)
-            t.start()
-            os.write({w_interp}, {RAN!r})
-            """)
-        interp.exec_sync(f"""if True:
-            os.write({w_interp}, {RAN!r})
-            """)
-
-        os.write(w_thread, DONE)
-        interp.exec_sync('t.join()')
-        self.assertEqual(os.read(r_interp, 1), RAN)
-        self.assertEqual(os.read(r_interp, 1), RAN)
-        self.assertEqual(os.read(r_interp, 1), FINISHED)
-
-    # test_xxsubinterpreters covers the remaining
-    # Interpreter.exec_sync() behavior.
-
-
-class StressTests(TestBase):
-
-    # In these tests we generally want a lot of interpreters,
-    # but not so many that any test takes too long.
-
-    @support.requires_resource('cpu')
-    def test_create_many_sequential(self):
-        alive = []
-        for _ in range(100):
-            interp = interpreters.create()
-            alive.append(interp)
-
-    @support.requires_resource('cpu')
-    def test_create_many_threaded(self):
-        alive = []
-        def task():
-            interp = interpreters.create()
-            alive.append(interp)
-        threads = (threading.Thread(target=task) for _ in range(200))
-        with threading_helper.start_threads(threads):
-            pass
-
-
-class StartupTests(TestBase):
-
-    # We want to ensure the initial state of subinterpreters
-    # matches expectations.
-
-    _subtest_count = 0
-
-    @contextlib.contextmanager
-    def subTest(self, *args):
-        with super().subTest(*args) as ctx:
-            self._subtest_count += 1
-            try:
-                yield ctx
-            finally:
-                if self._debugged_in_subtest:
-                    if self._subtest_count == 1:
-                        # The first subtest adds a leading newline, so we
-                        # compensate here by not printing a trailing newline.
-                        print('### end subtest debug ###', end='')
-                    else:
-                        print('### end subtest debug ###')
-                self._debugged_in_subtest = False
-
-    def debug(self, msg, *, header=None):
-        if header:
-            self._debug(f'--- {header} ---')
-            if msg:
-                if msg.endswith(os.linesep):
-                    self._debug(msg[:-len(os.linesep)])
-                else:
-                    self._debug(msg)
-                    self._debug('<no newline>')
-            self._debug('------')
-        else:
-            self._debug(msg)
-
-    _debugged = False
-    _debugged_in_subtest = False
-    def _debug(self, msg):
-        if not self._debugged:
-            print()
-            self._debugged = True
-        if self._subtest is not None:
-            if True:
-                if not self._debugged_in_subtest:
-                    self._debugged_in_subtest = True
-                    print('### start subtest debug ###')
-                print(msg)
-        else:
-            print(msg)
-
-    def create_temp_dir(self):
-        import tempfile
-        tmp = tempfile.mkdtemp(prefix='test_interpreters_')
-        tmp = os.path.realpath(tmp)
-        self.addCleanup(os_helper.rmtree, tmp)
-        return tmp
-
-    def write_script(self, *path, text):
-        filename = os.path.join(*path)
-        dirname = os.path.dirname(filename)
-        if dirname:
-            os.makedirs(dirname, exist_ok=True)
-        with open(filename, 'w', encoding='utf-8') as outfile:
-            outfile.write(dedent(text))
-        return filename
-
-    @support.requires_subprocess()
-    def run_python(self, argv, *, cwd=None):
-        # This method is inspired by
-        # EmbeddingTestsMixin.run_embedded_interpreter() in test_embed.py.
-        import shlex
-        import subprocess
-        if isinstance(argv, str):
-            argv = shlex.split(argv)
-        argv = [sys.executable, *argv]
-        try:
-            proc = subprocess.run(
-                argv,
-                cwd=cwd,
-                capture_output=True,
-                text=True,
-            )
-        except Exception as exc:
-            self.debug(f'# cmd: {shlex.join(argv)}')
-            if isinstance(exc, FileNotFoundError) and not exc.filename:
-                if os.path.exists(argv[0]):
-                    exists = 'exists'
-                else:
-                    exists = 'does not exist'
-                self.debug(f'{argv[0]} {exists}')
-            raise  # re-raise
-        assert proc.stderr == '' or proc.returncode != 0, proc.stderr
-        if proc.returncode != 0 and support.verbose:
-            self.debug(f'# python3 {shlex.join(argv[1:])} failed:')
-            self.debug(proc.stdout, header='stdout')
-            self.debug(proc.stderr, header='stderr')
-        self.assertEqual(proc.returncode, 0)
-        self.assertEqual(proc.stderr, '')
-        return proc.stdout
-
-    def test_sys_path_0(self):
-        # The main interpreter's sys.path[0] should be used by subinterpreters.
-        script = '''
-            import sys
-            from test.support import interpreters
-
-            orig = sys.path[0]
-
-            interp = interpreters.create()
-            interp.exec_sync(f"""if True:
-                import json
-                import sys
-                print(json.dumps({{
-                    'main': {orig!r},
-                    'sub': sys.path[0],
-                }}, indent=4), flush=True)
-                """)
-            '''
-        # <tmp>/
-        #   pkg/
-        #     __init__.py
-        #     __main__.py
-        #     script.py
-        #   script.py
-        cwd = self.create_temp_dir()
-        self.write_script(cwd, 'pkg', '__init__.py', text='')
-        self.write_script(cwd, 'pkg', '__main__.py', text=script)
-        self.write_script(cwd, 'pkg', 'script.py', text=script)
-        self.write_script(cwd, 'script.py', text=script)
-
-        cases = [
-            ('script.py', cwd),
-            ('-m script', cwd),
-            ('-m pkg', cwd),
-            ('-m pkg.script', cwd),
-            ('-c "import script"', ''),
-        ]
-        for argv, expected in cases:
-            with self.subTest(f'python3 {argv}'):
-                out = self.run_python(argv, cwd=cwd)
-                data = json.loads(out)
-                sp0_main, sp0_sub = data['main'], data['sub']
-                self.assertEqual(sp0_sub, sp0_main)
-                self.assertEqual(sp0_sub, expected)
-        # XXX Also check them all with the -P cmdline flag?
-
-
-class FinalizationTests(TestBase):
-
-    def test_gh_109793(self):
-        # Make sure finalization finishes and the correct error code
-        # is reported, even when subinterpreters get cleaned up at the end.
-        import subprocess
-        argv = [sys.executable, '-c', '''if True:
-            from test.support import interpreters
-            interp = interpreters.create()
-            raise Exception
-            ''']
-        proc = subprocess.run(argv, capture_output=True, text=True)
-        self.assertIn('Traceback', proc.stderr)
-        if proc.returncode == 0 and support.verbose:
-            print()
-            print("--- cmd unexpected succeeded ---")
-            print(f"stdout:\n{proc.stdout}")
-            print(f"stderr:\n{proc.stderr}")
-            print("------")
-        self.assertEqual(proc.returncode, 1)
-
-
-class TestIsShareable(TestBase):
-
-    def test_default_shareables(self):
-        shareables = [
-                # singletons
-                None,
-                # builtin objects
-                b'spam',
-                'spam',
-                10,
-                -10,
-                True,
-                False,
-                100.0,
-                (),
-                (1, ('spam', 'eggs'), True),
-                ]
-        for obj in shareables:
-            with self.subTest(obj):
-                shareable = interpreters.is_shareable(obj)
-                self.assertTrue(shareable)
-
-    def test_not_shareable(self):
-        class Cheese:
-            def __init__(self, name):
-                self.name = name
-            def __str__(self):
-                return self.name
-
-        class SubBytes(bytes):
-            """A subclass of a shareable type."""
-
-        not_shareables = [
-                # singletons
-                NotImplemented,
-                ...,
-                # builtin types and objects
-                type,
-                object,
-                object(),
-                Exception(),
-                # user-defined types and objects
-                Cheese,
-                Cheese('Wensleydale'),
-                SubBytes(b'spam'),
-                ]
-        for obj in not_shareables:
-            with self.subTest(repr(obj)):
-                self.assertFalse(
-                    interpreters.is_shareable(obj))
-
-
-class TestChannels(TestBase):
-
-    def test_create(self):
-        r, s = interpreters.create_channel()
-        self.assertIsInstance(r, interpreters.RecvChannel)
-        self.assertIsInstance(s, interpreters.SendChannel)
-
-    def test_list_all(self):
-        self.assertEqual(interpreters.list_all_channels(), [])
-        created = set()
-        for _ in range(3):
-            ch = interpreters.create_channel()
-            created.add(ch)
-        after = set(interpreters.list_all_channels())
-        self.assertEqual(after, created)
-
-    def test_shareable(self):
-        rch, sch = interpreters.create_channel()
-
-        self.assertTrue(
-            interpreters.is_shareable(rch))
-        self.assertTrue(
-            interpreters.is_shareable(sch))
-
-        sch.send_nowait(rch)
-        sch.send_nowait(sch)
-        rch2 = rch.recv()
-        sch2 = rch.recv()
-
-        self.assertEqual(rch2, rch)
-        self.assertEqual(sch2, sch)
-
-    def test_is_closed(self):
-        rch, sch = interpreters.create_channel()
-        rbefore = rch.is_closed
-        sbefore = sch.is_closed
-        rch.close()
-        rafter = rch.is_closed
-        safter = sch.is_closed
-
-        self.assertFalse(rbefore)
-        self.assertFalse(sbefore)
-        self.assertTrue(rafter)
-        self.assertTrue(safter)
-
-
-class TestRecvChannelAttrs(TestBase):
-
-    def test_id_type(self):
-        rch, _ = interpreters.create_channel()
-        self.assertIsInstance(rch.id, _channels.ChannelID)
-
-    def test_custom_id(self):
-        rch = interpreters.RecvChannel(1)
-        self.assertEqual(rch.id, 1)
-
-        with self.assertRaises(TypeError):
-            interpreters.RecvChannel('1')
-
-    def test_id_readonly(self):
-        rch = interpreters.RecvChannel(1)
-        with self.assertRaises(AttributeError):
-            rch.id = 2
-
-    def test_equality(self):
-        ch1, _ = interpreters.create_channel()
-        ch2, _ = interpreters.create_channel()
-        self.assertEqual(ch1, ch1)
-        self.assertNotEqual(ch1, ch2)
-
-
-class TestSendChannelAttrs(TestBase):
-
-    def test_id_type(self):
-        _, sch = interpreters.create_channel()
-        self.assertIsInstance(sch.id, _channels.ChannelID)
-
-    def test_custom_id(self):
-        sch = interpreters.SendChannel(1)
-        self.assertEqual(sch.id, 1)
-
-        with self.assertRaises(TypeError):
-            interpreters.SendChannel('1')
-
-    def test_id_readonly(self):
-        sch = interpreters.SendChannel(1)
-        with self.assertRaises(AttributeError):
-            sch.id = 2
-
-    def test_equality(self):
-        _, ch1 = interpreters.create_channel()
-        _, ch2 = interpreters.create_channel()
-        self.assertEqual(ch1, ch1)
-        self.assertNotEqual(ch1, ch2)
-
-
-class TestSendRecv(TestBase):
-
-    def test_send_recv_main(self):
-        r, s = interpreters.create_channel()
-        orig = b'spam'
-        s.send_nowait(orig)
-        obj = r.recv()
-
-        self.assertEqual(obj, orig)
-        self.assertIsNot(obj, orig)
-
-    def test_send_recv_same_interpreter(self):
-        interp = interpreters.create()
-        interp.exec_sync(dedent("""
-            from test.support import interpreters
-            r, s = interpreters.create_channel()
-            orig = b'spam'
-            s.send_nowait(orig)
-            obj = r.recv()
-            assert obj == orig, 'expected: obj == orig'
-            assert obj is not orig, 'expected: obj is not orig'
-            """))
-
-    @unittest.skip('broken (see BPO-...)')
-    def test_send_recv_different_interpreters(self):
-        r1, s1 = interpreters.create_channel()
-        r2, s2 = interpreters.create_channel()
-        orig1 = b'spam'
-        s1.send_nowait(orig1)
-        out = _run_output(
-            interpreters.create(),
-            dedent(f"""
-                obj1 = r.recv()
-                assert obj1 == b'spam', 'expected: obj1 == orig1'
-                # When going to another interpreter we get a copy.
-                assert id(obj1) != {id(orig1)}, 'expected: obj1 is not orig1'
-                orig2 = b'eggs'
-                print(id(orig2))
-                s.send_nowait(orig2)
-                """),
-            channels=dict(r=r1, s=s2),
-            )
-        obj2 = r2.recv()
-
-        self.assertEqual(obj2, b'eggs')
-        self.assertNotEqual(id(obj2), int(out))
-
-    def test_send_recv_different_threads(self):
-        r, s = interpreters.create_channel()
-
-        def f():
-            while True:
-                try:
-                    obj = r.recv()
-                    break
-                except interpreters.ChannelEmptyError:
-                    time.sleep(0.1)
-            s.send(obj)
-        t = threading.Thread(target=f)
-        t.start()
-
-        orig = b'spam'
-        s.send(orig)
-        obj = r.recv()
-        t.join()
-
-        self.assertEqual(obj, orig)
-        self.assertIsNot(obj, orig)
-
-    def test_send_recv_nowait_main(self):
-        r, s = interpreters.create_channel()
-        orig = b'spam'
-        s.send_nowait(orig)
-        obj = r.recv_nowait()
-
-        self.assertEqual(obj, orig)
-        self.assertIsNot(obj, orig)
-
-    def test_send_recv_nowait_main_with_default(self):
-        r, _ = interpreters.create_channel()
-        obj = r.recv_nowait(None)
-
-        self.assertIsNone(obj)
-
-    def test_send_recv_nowait_same_interpreter(self):
-        interp = interpreters.create()
-        interp.exec_sync(dedent("""
-            from test.support import interpreters
-            r, s = interpreters.create_channel()
-            orig = b'spam'
-            s.send_nowait(orig)
-            obj = r.recv_nowait()
-            assert obj == orig, 'expected: obj == orig'
-            # When going back to the same interpreter we get the same object.
-            assert obj is not orig, 'expected: obj is not orig'
-            """))
-
-    @unittest.skip('broken (see BPO-...)')
-    def test_send_recv_nowait_different_interpreters(self):
-        r1, s1 = interpreters.create_channel()
-        r2, s2 = interpreters.create_channel()
-        orig1 = b'spam'
-        s1.send_nowait(orig1)
-        out = _run_output(
-            interpreters.create(),
-            dedent(f"""
-                obj1 = r.recv_nowait()
-                assert obj1 == b'spam', 'expected: obj1 == orig1'
-                # When going to another interpreter we get a copy.
-                assert id(obj1) != {id(orig1)}, 'expected: obj1 is not orig1'
-                orig2 = b'eggs'
-                print(id(orig2))
-                s.send_nowait(orig2)
-                """),
-            channels=dict(r=r1, s=s2),
-            )
-        obj2 = r2.recv_nowait()
-
-        self.assertEqual(obj2, b'eggs')
-        self.assertNotEqual(id(obj2), int(out))
-
-    def test_recv_timeout(self):
-        r, _ = interpreters.create_channel()
-        with self.assertRaises(TimeoutError):
-            r.recv(timeout=1)
-
-    def test_recv_channel_does_not_exist(self):
-        ch = interpreters.RecvChannel(1_000_000)
-        with self.assertRaises(interpreters.ChannelNotFoundError):
-            ch.recv()
-
-    def test_send_channel_does_not_exist(self):
-        ch = interpreters.SendChannel(1_000_000)
-        with self.assertRaises(interpreters.ChannelNotFoundError):
-            ch.send(b'spam')
-
-    def test_recv_nowait_channel_does_not_exist(self):
-        ch = interpreters.RecvChannel(1_000_000)
-        with self.assertRaises(interpreters.ChannelNotFoundError):
-            ch.recv_nowait()
-
-    def test_send_nowait_channel_does_not_exist(self):
-        ch = interpreters.SendChannel(1_000_000)
-        with self.assertRaises(interpreters.ChannelNotFoundError):
-            ch.send_nowait(b'spam')
-
-    def test_recv_nowait_empty(self):
-        ch, _ = interpreters.create_channel()
-        with self.assertRaises(interpreters.ChannelEmptyError):
-            ch.recv_nowait()
-
-    def test_recv_nowait_default(self):
-        default = object()
-        rch, sch = interpreters.create_channel()
-        obj1 = rch.recv_nowait(default)
-        sch.send_nowait(None)
-        sch.send_nowait(1)
-        sch.send_nowait(b'spam')
-        sch.send_nowait(b'eggs')
-        obj2 = rch.recv_nowait(default)
-        obj3 = rch.recv_nowait(default)
-        obj4 = rch.recv_nowait()
-        obj5 = rch.recv_nowait(default)
-        obj6 = rch.recv_nowait(default)
-
-        self.assertIs(obj1, default)
-        self.assertIs(obj2, None)
-        self.assertEqual(obj3, 1)
-        self.assertEqual(obj4, b'spam')
-        self.assertEqual(obj5, b'eggs')
-        self.assertIs(obj6, default)
-
-    def test_send_buffer(self):
-        buf = bytearray(b'spamspamspam')
-        obj = None
-        rch, sch = interpreters.create_channel()
-
-        def f():
-            nonlocal obj
-            while True:
-                try:
-                    obj = rch.recv()
-                    break
-                except interpreters.ChannelEmptyError:
-                    time.sleep(0.1)
-        t = threading.Thread(target=f)
-        t.start()
-
-        sch.send_buffer(buf)
-        t.join()
-
-        self.assertIsNot(obj, buf)
-        self.assertIsInstance(obj, memoryview)
-        self.assertEqual(obj, buf)
-
-        buf[4:8] = b'eggs'
-        self.assertEqual(obj, buf)
-        obj[4:8] = b'ham.'
-        self.assertEqual(obj, buf)
-
-    def test_send_buffer_nowait(self):
-        buf = bytearray(b'spamspamspam')
-        rch, sch = interpreters.create_channel()
-        sch.send_buffer_nowait(buf)
-        obj = rch.recv()
-
-        self.assertIsNot(obj, buf)
-        self.assertIsInstance(obj, memoryview)
-        self.assertEqual(obj, buf)
-
-        buf[4:8] = b'eggs'
-        self.assertEqual(obj, buf)
-        obj[4:8] = b'ham.'
-        self.assertEqual(obj, buf)
diff --git a/Lib/test/test_interpreters/__init__.py b/Lib/test/test_interpreters/__init__.py
new file mode 100644
index 00000000000000..4b16ecc31156a5
--- /dev/null
+++ b/Lib/test/test_interpreters/__init__.py
@@ -0,0 +1,5 @@
+import os
+from test.support import load_package_tests
+
+def load_tests(*args):
+    return load_package_tests(os.path.dirname(__file__), *args)
diff --git a/Lib/test/test_interpreters/__main__.py b/Lib/test/test_interpreters/__main__.py
new file mode 100644
index 00000000000000..8641229877b2be
--- /dev/null
+++ b/Lib/test/test_interpreters/__main__.py
@@ -0,0 +1,4 @@
+from . import load_tests
+import unittest
+
+nittest.main()
diff --git a/Lib/test/test_interpreters/test_api.py b/Lib/test/test_interpreters/test_api.py
new file mode 100644
index 00000000000000..d94a03bccf2e97
--- /dev/null
+++ b/Lib/test/test_interpreters/test_api.py
@@ -0,0 +1,596 @@
+import os
+import threading
+from textwrap import dedent
+import unittest
+
+from test import support
+from test.support import import_helper
+# Raise SkipTest if subinterpreters not supported.
+import_helper.import_module('_xxsubinterpreters')
+from test.support import interpreters
+from test.support.interpreters import InterpreterNotFoundError
+from .utils import _captured_script, _run_output, _running, TestBase
+
+
+class CreateTests(TestBase):
+
+    def test_in_main(self):
+        interp = interpreters.create()
+        self.assertIsInstance(interp, interpreters.Interpreter)
+        self.assertIn(interp, interpreters.list_all())
+
+    def test_in_thread(self):
+        lock = threading.Lock()
+        interp = None
+        def f():
+            nonlocal interp
+            interp = interpreters.create()
+            lock.acquire()
+            lock.release()
+        t = threading.Thread(target=f)
+        with lock:
+            t.start()
+        t.join()
+        self.assertIn(interp, interpreters.list_all())
+
+    def test_in_subinterpreter(self):
+        main, = interpreters.list_all()
+        interp = interpreters.create()
+        out = _run_output(interp, dedent("""
+            from test.support import interpreters
+            interp = interpreters.create()
+            print(interp.id)
+            """))
+        interp2 = interpreters.Interpreter(int(out))
+        self.assertEqual(interpreters.list_all(), [main, interp, interp2])
+
+    def test_after_destroy_all(self):
+        before = set(interpreters.list_all())
+        # Create 3 subinterpreters.
+        interp_lst = []
+        for _ in range(3):
+            interps = interpreters.create()
+            interp_lst.append(interps)
+        # Now destroy them.
+        for interp in interp_lst:
+            interp.close()
+        # Finally, create another.
+        interp = interpreters.create()
+        self.assertEqual(set(interpreters.list_all()), before | {interp})
+
+    def test_after_destroy_some(self):
+        before = set(interpreters.list_all())
+        # Create 3 subinterpreters.
+        interp1 = interpreters.create()
+        interp2 = interpreters.create()
+        interp3 = interpreters.create()
+        # Now destroy 2 of them.
+        interp1.close()
+        interp2.close()
+        # Finally, create another.
+        interp = interpreters.create()
+        self.assertEqual(set(interpreters.list_all()), before | {interp3, interp})
+
+
+class GetMainTests(TestBase):
+
+    def test_id(self):
+        main = interpreters.get_main()
+        self.assertEqual(main.id, 0)
+
+    def test_current(self):
+        main = interpreters.get_main()
+        current = interpreters.get_current()
+        self.assertIs(main, current)
+
+    def test_idempotent(self):
+        main1 = interpreters.get_main()
+        main2 = interpreters.get_main()
+        self.assertIs(main1, main2)
+
+
+class GetCurrentTests(TestBase):
+
+    def test_main(self):
+        main = interpreters.get_main()
+        current = interpreters.get_current()
+        self.assertEqual(current, main)
+
+    def test_subinterpreter(self):
+        main = interpreters.get_main()
+        interp = interpreters.create()
+        out = _run_output(interp, dedent("""
+            from test.support import interpreters
+            cur = interpreters.get_current()
+            print(cur.id)
+            """))
+        current = interpreters.Interpreter(int(out))
+        self.assertEqual(current, interp)
+        self.assertNotEqual(current, main)
+
+    def test_idempotent(self):
+        with self.subTest('main'):
+            cur1 = interpreters.get_current()
+            cur2 = interpreters.get_current()
+            self.assertIs(cur1, cur2)
+
+        with self.subTest('subinterpreter'):
+            interp = interpreters.create()
+            out = _run_output(interp, dedent("""
+                from test.support import interpreters
+                cur = interpreters.get_current()
+                print(id(cur))
+                cur = interpreters.get_current()
+                print(id(cur))
+                """))
+            objid1, objid2 = (int(v) for v in out.splitlines())
+            self.assertEqual(objid1, objid2)
+
+        with self.subTest('per-interpreter'):
+            interp = interpreters.create()
+            out = _run_output(interp, dedent("""
+                from test.support import interpreters
+                cur = interpreters.get_current()
+                print(id(cur))
+                """))
+            id1 = int(out)
+            id2 = id(interp)
+            self.assertNotEqual(id1, id2)
+
+
+class ListAllTests(TestBase):
+
+    def test_initial(self):
+        interps = interpreters.list_all()
+        self.assertEqual(1, len(interps))
+
+    def test_after_creating(self):
+        main = interpreters.get_current()
+        first = interpreters.create()
+        second = interpreters.create()
+
+        ids = []
+        for interp in interpreters.list_all():
+            ids.append(interp.id)
+
+        self.assertEqual(ids, [main.id, first.id, second.id])
+
+    def test_after_destroying(self):
+        main = interpreters.get_current()
+        first = interpreters.create()
+        second = interpreters.create()
+        first.close()
+
+        ids = []
+        for interp in interpreters.list_all():
+            ids.append(interp.id)
+
+        self.assertEqual(ids, [main.id, second.id])
+
+    def test_idempotent(self):
+        main = interpreters.get_current()
+        first = interpreters.create()
+        second = interpreters.create()
+        expected = [main, first, second]
+
+        actual = interpreters.list_all()
+
+        self.assertEqual(actual, expected)
+        for interp1, interp2 in zip(actual, expected):
+            self.assertIs(interp1, interp2)
+
+
+class InterpreterObjectTests(TestBase):
+
+    def test_init_int(self):
+        interpid = interpreters.get_current().id
+        interp = interpreters.Interpreter(interpid)
+        self.assertEqual(interp.id, interpid)
+
+    def test_init_interpreter_id(self):
+        interpid = interpreters.get_current()._id
+        interp = interpreters.Interpreter(interpid)
+        self.assertEqual(interp._id, interpid)
+
+    def test_init_unsupported(self):
+        actualid = interpreters.get_current().id
+        for interpid in [
+            str(actualid),
+            float(actualid),
+            object(),
+            None,
+            '',
+        ]:
+            with self.subTest(repr(interpid)):
+                with self.assertRaises(TypeError):
+                    interpreters.Interpreter(interpid)
+
+    def test_idempotent(self):
+        main = interpreters.get_main()
+        interp = interpreters.Interpreter(main.id)
+        self.assertIs(interp, main)
+
+    def test_init_does_not_exist(self):
+        with self.assertRaises(InterpreterNotFoundError):
+            interpreters.Interpreter(1_000_000)
+
+    def test_init_bad_id(self):
+        with self.assertRaises(ValueError):
+            interpreters.Interpreter(-1)
+
+    def test_id_type(self):
+        main = interpreters.get_main()
+        current = interpreters.get_current()
+        interp = interpreters.create()
+        self.assertIsInstance(main.id, int)
+        self.assertIsInstance(current.id, int)
+        self.assertIsInstance(interp.id, int)
+
+    def test_id_readonly(self):
+        interp = interpreters.create()
+        with self.assertRaises(AttributeError):
+            interp.id = 1_000_000
+
+    def test_hashable(self):
+        interp = interpreters.create()
+        expected = hash(interp.id)
+        actual = hash(interp)
+        self.assertEqual(actual, expected)
+
+    def test_equality(self):
+        interp1 = interpreters.create()
+        interp2 = interpreters.create()
+        self.assertEqual(interp1, interp1)
+        self.assertNotEqual(interp1, interp2)
+
+
+class TestInterpreterIsRunning(TestBase):
+
+    def test_main(self):
+        main = interpreters.get_main()
+        self.assertTrue(main.is_running())
+
+    @unittest.skip('Fails on FreeBSD')
+    def test_subinterpreter(self):
+        interp = interpreters.create()
+        self.assertFalse(interp.is_running())
+
+        with _running(interp):
+            self.assertTrue(interp.is_running())
+        self.assertFalse(interp.is_running())
+
+    def test_finished(self):
+        r, w = self.pipe()
+        interp = interpreters.create()
+        interp.exec_sync(f"""if True:
+            import os
+            os.write({w}, b'x')
+            """)
+        self.assertFalse(interp.is_running())
+        self.assertEqual(os.read(r, 1), b'x')
+
+    def test_from_subinterpreter(self):
+        interp = interpreters.create()
+        out = _run_output(interp, dedent(f"""
+            import _xxsubinterpreters as _interpreters
+            if _interpreters.is_running({interp.id}):
+                print(True)
+            else:
+                print(False)
+            """))
+        self.assertEqual(out.strip(), 'True')
+
+    def test_already_destroyed(self):
+        interp = interpreters.create()
+        interp.close()
+        with self.assertRaises(InterpreterNotFoundError):
+            interp.is_running()
+
+    def test_with_only_background_threads(self):
+        r_interp, w_interp = self.pipe()
+        r_thread, w_thread = self.pipe()
+
+        DONE = b'D'
+        FINISHED = b'F'
+
+        interp = interpreters.create()
+        interp.exec_sync(f"""if True:
+            import os
+            import threading
+
+            def task():
+                v = os.read({r_thread}, 1)
+                assert v == {DONE!r}
+                os.write({w_interp}, {FINISHED!r})
+            t = threading.Thread(target=task)
+            t.start()
+            """)
+        self.assertFalse(interp.is_running())
+
+        os.write(w_thread, DONE)
+        interp.exec_sync('t.join()')
+        self.assertEqual(os.read(r_interp, 1), FINISHED)
+
+
+class TestInterpreterClose(TestBase):
+
+    def test_basic(self):
+        main = interpreters.get_main()
+        interp1 = interpreters.create()
+        interp2 = interpreters.create()
+        interp3 = interpreters.create()
+        self.assertEqual(set(interpreters.list_all()),
+                         {main, interp1, interp2, interp3})
+        interp2.close()
+        self.assertEqual(set(interpreters.list_all()),
+                         {main, interp1, interp3})
+
+    def test_all(self):
+        before = set(interpreters.list_all())
+        interps = set()
+        for _ in range(3):
+            interp = interpreters.create()
+            interps.add(interp)
+        self.assertEqual(set(interpreters.list_all()), before | interps)
+        for interp in interps:
+            interp.close()
+        self.assertEqual(set(interpreters.list_all()), before)
+
+    def test_main(self):
+        main, = interpreters.list_all()
+        with self.assertRaises(RuntimeError):
+            main.close()
+
+        def f():
+            with self.assertRaises(RuntimeError):
+                main.close()
+
+        t = threading.Thread(target=f)
+        t.start()
+        t.join()
+
+    def test_already_destroyed(self):
+        interp = interpreters.create()
+        interp.close()
+        with self.assertRaises(InterpreterNotFoundError):
+            interp.close()
+
+    def test_from_current(self):
+        main, = interpreters.list_all()
+        interp = interpreters.create()
+        out = _run_output(interp, dedent(f"""
+            from test.support import interpreters
+            interp = interpreters.Interpreter({interp.id})
+            try:
+                interp.close()
+            except RuntimeError:
+                print('failed')
+            """))
+        self.assertEqual(out.strip(), 'failed')
+        self.assertEqual(set(interpreters.list_all()), {main, interp})
+
+    def test_from_sibling(self):
+        main, = interpreters.list_all()
+        interp1 = interpreters.create()
+        interp2 = interpreters.create()
+        self.assertEqual(set(interpreters.list_all()),
+                         {main, interp1, interp2})
+        interp1.exec_sync(dedent(f"""
+            from test.support import interpreters
+            interp2 = interpreters.Interpreter({interp2.id})
+            interp2.close()
+            interp3 = interpreters.create()
+            interp3.close()
+            """))
+        self.assertEqual(set(interpreters.list_all()), {main, interp1})
+
+    def test_from_other_thread(self):
+        interp = interpreters.create()
+        def f():
+            interp.close()
+
+        t = threading.Thread(target=f)
+        t.start()
+        t.join()
+
+    @unittest.skip('Fails on FreeBSD')
+    def test_still_running(self):
+        main, = interpreters.list_all()
+        interp = interpreters.create()
+        with _running(interp):
+            with self.assertRaises(RuntimeError):
+                interp.close()
+            self.assertTrue(interp.is_running())
+
+    def test_subthreads_still_running(self):
+        r_interp, w_interp = self.pipe()
+        r_thread, w_thread = self.pipe()
+
+        FINISHED = b'F'
+
+        interp = interpreters.create()
+        interp.exec_sync(f"""if True:
+            import os
+            import threading
+            import time
+
+            done = False
+
+            def notify_fini():
+                global done
+                done = True
+                t.join()
+            threading._register_atexit(notify_fini)
+
+            def task():
+                while not done:
+                    time.sleep(0.1)
+                os.write({w_interp}, {FINISHED!r})
+            t = threading.Thread(target=task)
+            t.start()
+            """)
+        interp.close()
+
+        self.assertEqual(os.read(r_interp, 1), FINISHED)
+
+
+class TestInterpreterExecSync(TestBase):
+
+    def test_success(self):
+        interp = interpreters.create()
+        script, file = _captured_script('print("it worked!", end="")')
+        with file:
+            interp.exec_sync(script)
+            out = file.read()
+
+        self.assertEqual(out, 'it worked!')
+
+    def test_failure(self):
+        interp = interpreters.create()
+        with self.assertRaises(interpreters.ExecFailure):
+            interp.exec_sync('raise Exception')
+
+    def test_in_thread(self):
+        interp = interpreters.create()
+        script, file = _captured_script('print("it worked!", end="")')
+        with file:
+            def f():
+                interp.exec_sync(script)
+
+            t = threading.Thread(target=f)
+            t.start()
+            t.join()
+            out = file.read()
+
+        self.assertEqual(out, 'it worked!')
+
+    @support.requires_fork()
+    def test_fork(self):
+        interp = interpreters.create()
+        import tempfile
+        with tempfile.NamedTemporaryFile('w+', encoding='utf-8') as file:
+            file.write('')
+            file.flush()
+
+            expected = 'spam spam spam spam spam'
+            script = dedent(f"""
+                import os
+                try:
+                    os.fork()
+                except RuntimeError:
+                    with open('{file.name}', 'w', encoding='utf-8') as out:
+                        out.write('{expected}')
+                """)
+            interp.exec_sync(script)
+
+            file.seek(0)
+            content = file.read()
+            self.assertEqual(content, expected)
+
+    @unittest.skip('Fails on FreeBSD')
+    def test_already_running(self):
+        interp = interpreters.create()
+        with _running(interp):
+            with self.assertRaises(RuntimeError):
+                interp.exec_sync('print("spam")')
+
+    def test_bad_script(self):
+        interp = interpreters.create()
+        with self.assertRaises(TypeError):
+            interp.exec_sync(10)
+
+    def test_bytes_for_script(self):
+        interp = interpreters.create()
+        with self.assertRaises(TypeError):
+            interp.exec_sync(b'print("spam")')
+
+    def test_with_background_threads_still_running(self):
+        r_interp, w_interp = self.pipe()
+        r_thread, w_thread = self.pipe()
+
+        RAN = b'R'
+        DONE = b'D'
+        FINISHED = b'F'
+
+        interp = interpreters.create()
+        interp.exec_sync(f"""if True:
+            import os
+            import threading
+
+            def task():
+                v = os.read({r_thread}, 1)
+                assert v == {DONE!r}
+                os.write({w_interp}, {FINISHED!r})
+            t = threading.Thread(target=task)
+            t.start()
+            os.write({w_interp}, {RAN!r})
+            """)
+        interp.exec_sync(f"""if True:
+            os.write({w_interp}, {RAN!r})
+            """)
+
+        os.write(w_thread, DONE)
+        interp.exec_sync('t.join()')
+        self.assertEqual(os.read(r_interp, 1), RAN)
+        self.assertEqual(os.read(r_interp, 1), RAN)
+        self.assertEqual(os.read(r_interp, 1), FINISHED)
+
+    # test_xxsubinterpreters covers the remaining
+    # Interpreter.exec_sync() behavior.
+
+
+class TestIsShareable(TestBase):
+
+    def test_default_shareables(self):
+        shareables = [
+                # singletons
+                None,
+                # builtin objects
+                b'spam',
+                'spam',
+                10,
+                -10,
+                True,
+                False,
+                100.0,
+                (),
+                (1, ('spam', 'eggs'), True),
+                ]
+        for obj in shareables:
+            with self.subTest(obj):
+                shareable = interpreters.is_shareable(obj)
+                self.assertTrue(shareable)
+
+    def test_not_shareable(self):
+        class Cheese:
+            def __init__(self, name):
+                self.name = name
+            def __str__(self):
+                return self.name
+
+        class SubBytes(bytes):
+            """A subclass of a shareable type."""
+
+        not_shareables = [
+                # singletons
+                NotImplemented,
+                ...,
+                # builtin types and objects
+                type,
+                object,
+                object(),
+                Exception(),
+                # user-defined types and objects
+                Cheese,
+                Cheese('Wensleydale'),
+                SubBytes(b'spam'),
+                ]
+        for obj in not_shareables:
+            with self.subTest(repr(obj)):
+                self.assertFalse(
+                    interpreters.is_shareable(obj))
+
+
+if __name__ == '__main__':
+    # Test needs to be a package, so we can do relative imports.
+    unittest.main()
diff --git a/Lib/test/test_interpreters/test_channel.py b/Lib/test/test_interpreters/test_channel.py
new file mode 100644
index 00000000000000..f38237e0b153b9
--- /dev/null
+++ b/Lib/test/test_interpreters/test_channel.py
@@ -0,0 +1,328 @@
+import threading
+from textwrap import dedent
+import unittest
+import time
+
+from test.support import import_helper
+# Raise SkipTest if subinterpreters not supported.
+_channels = import_helper.import_module('_xxinterpchannels')
+from test.support import interpreters
+import test.support.interpreters.channel as channels
+from .utils import _run_output, TestBase
+
+
+class TestChannels(TestBase):
+
+    def test_create(self):
+        r, s = channels.create()
+        self.assertIsInstance(r, channels.RecvChannel)
+        self.assertIsInstance(s, channels.SendChannel)
+
+    def test_list_all(self):
+        self.assertEqual(channels.list_all(), [])
+        created = set()
+        for _ in range(3):
+            ch = channels.create()
+            created.add(ch)
+        after = set(channels.list_all())
+        self.assertEqual(after, created)
+
+    def test_shareable(self):
+        rch, sch = channels.create()
+
+        self.assertTrue(
+            interpreters.is_shareable(rch))
+        self.assertTrue(
+            interpreters.is_shareable(sch))
+
+        sch.send_nowait(rch)
+        sch.send_nowait(sch)
+        rch2 = rch.recv()
+        sch2 = rch.recv()
+
+        self.assertEqual(rch2, rch)
+        self.assertEqual(sch2, sch)
+
+    def test_is_closed(self):
+        rch, sch = channels.create()
+        rbefore = rch.is_closed
+        sbefore = sch.is_closed
+        rch.close()
+        rafter = rch.is_closed
+        safter = sch.is_closed
+
+        self.assertFalse(rbefore)
+        self.assertFalse(sbefore)
+        self.assertTrue(rafter)
+        self.assertTrue(safter)
+
+
+class TestRecvChannelAttrs(TestBase):
+
+    def test_id_type(self):
+        rch, _ = channels.create()
+        self.assertIsInstance(rch.id, _channels.ChannelID)
+
+    def test_custom_id(self):
+        rch = channels.RecvChannel(1)
+        self.assertEqual(rch.id, 1)
+
+        with self.assertRaises(TypeError):
+            channels.RecvChannel('1')
+
+    def test_id_readonly(self):
+        rch = channels.RecvChannel(1)
+        with self.assertRaises(AttributeError):
+            rch.id = 2
+
+    def test_equality(self):
+        ch1, _ = channels.create()
+        ch2, _ = channels.create()
+        self.assertEqual(ch1, ch1)
+        self.assertNotEqual(ch1, ch2)
+
+
+class TestSendChannelAttrs(TestBase):
+
+    def test_id_type(self):
+        _, sch = channels.create()
+        self.assertIsInstance(sch.id, _channels.ChannelID)
+
+    def test_custom_id(self):
+        sch = channels.SendChannel(1)
+        self.assertEqual(sch.id, 1)
+
+        with self.assertRaises(TypeError):
+            channels.SendChannel('1')
+
+    def test_id_readonly(self):
+        sch = channels.SendChannel(1)
+        with self.assertRaises(AttributeError):
+            sch.id = 2
+
+    def test_equality(self):
+        _, ch1 = channels.create()
+        _, ch2 = channels.create()
+        self.assertEqual(ch1, ch1)
+        self.assertNotEqual(ch1, ch2)
+
+
+class TestSendRecv(TestBase):
+
+    def test_send_recv_main(self):
+        r, s = channels.create()
+        orig = b'spam'
+        s.send_nowait(orig)
+        obj = r.recv()
+
+        self.assertEqual(obj, orig)
+        self.assertIsNot(obj, orig)
+
+    def test_send_recv_same_interpreter(self):
+        interp = interpreters.create()
+        interp.exec_sync(dedent("""
+            import test.support.interpreters.channel as channels
+            r, s = channels.create()
+            orig = b'spam'
+            s.send_nowait(orig)
+            obj = r.recv()
+            assert obj == orig, 'expected: obj == orig'
+            assert obj is not orig, 'expected: obj is not orig'
+            """))
+
+    @unittest.skip('broken (see BPO-...)')
+    def test_send_recv_different_interpreters(self):
+        r1, s1 = channels.create()
+        r2, s2 = channels.create()
+        orig1 = b'spam'
+        s1.send_nowait(orig1)
+        out = _run_output(
+            interpreters.create(),
+            dedent(f"""
+                obj1 = r.recv()
+                assert obj1 == b'spam', 'expected: obj1 == orig1'
+                # When going to another interpreter we get a copy.
+                assert id(obj1) != {id(orig1)}, 'expected: obj1 is not orig1'
+                orig2 = b'eggs'
+                print(id(orig2))
+                s.send_nowait(orig2)
+                """),
+            channels=dict(r=r1, s=s2),
+            )
+        obj2 = r2.recv()
+
+        self.assertEqual(obj2, b'eggs')
+        self.assertNotEqual(id(obj2), int(out))
+
+    def test_send_recv_different_threads(self):
+        r, s = channels.create()
+
+        def f():
+            while True:
+                try:
+                    obj = r.recv()
+                    break
+                except channels.ChannelEmptyError:
+                    time.sleep(0.1)
+            s.send(obj)
+        t = threading.Thread(target=f)
+        t.start()
+
+        orig = b'spam'
+        s.send(orig)
+        obj = r.recv()
+        t.join()
+
+        self.assertEqual(obj, orig)
+        self.assertIsNot(obj, orig)
+
+    def test_send_recv_nowait_main(self):
+        r, s = channels.create()
+        orig = b'spam'
+        s.send_nowait(orig)
+        obj = r.recv_nowait()
+
+        self.assertEqual(obj, orig)
+        self.assertIsNot(obj, orig)
+
+    def test_send_recv_nowait_main_with_default(self):
+        r, _ = channels.create()
+        obj = r.recv_nowait(None)
+
+        self.assertIsNone(obj)
+
+    def test_send_recv_nowait_same_interpreter(self):
+        interp = interpreters.create()
+        interp.exec_sync(dedent("""
+            import test.support.interpreters.channel as channels
+            r, s = channels.create()
+            orig = b'spam'
+            s.send_nowait(orig)
+            obj = r.recv_nowait()
+            assert obj == orig, 'expected: obj == orig'
+            # When going back to the same interpreter we get the same object.
+            assert obj is not orig, 'expected: obj is not orig'
+            """))
+
+    @unittest.skip('broken (see BPO-...)')
+    def test_send_recv_nowait_different_interpreters(self):
+        r1, s1 = channels.create()
+        r2, s2 = channels.create()
+        orig1 = b'spam'
+        s1.send_nowait(orig1)
+        out = _run_output(
+            interpreters.create(),
+            dedent(f"""
+                obj1 = r.recv_nowait()
+                assert obj1 == b'spam', 'expected: obj1 == orig1'
+                # When going to another interpreter we get a copy.
+                assert id(obj1) != {id(orig1)}, 'expected: obj1 is not orig1'
+                orig2 = b'eggs'
+                print(id(orig2))
+                s.send_nowait(orig2)
+                """),
+            channels=dict(r=r1, s=s2),
+            )
+        obj2 = r2.recv_nowait()
+
+        self.assertEqual(obj2, b'eggs')
+        self.assertNotEqual(id(obj2), int(out))
+
+    def test_recv_timeout(self):
+        r, _ = channels.create()
+        with self.assertRaises(TimeoutError):
+            r.recv(timeout=1)
+
+    def test_recv_channel_does_not_exist(self):
+        ch = channels.RecvChannel(1_000_000)
+        with self.assertRaises(channels.ChannelNotFoundError):
+            ch.recv()
+
+    def test_send_channel_does_not_exist(self):
+        ch = channels.SendChannel(1_000_000)
+        with self.assertRaises(channels.ChannelNotFoundError):
+            ch.send(b'spam')
+
+    def test_recv_nowait_channel_does_not_exist(self):
+        ch = channels.RecvChannel(1_000_000)
+        with self.assertRaises(channels.ChannelNotFoundError):
+            ch.recv_nowait()
+
+    def test_send_nowait_channel_does_not_exist(self):
+        ch = channels.SendChannel(1_000_000)
+        with self.assertRaises(channels.ChannelNotFoundError):
+            ch.send_nowait(b'spam')
+
+    def test_recv_nowait_empty(self):
+        ch, _ = channels.create()
+        with self.assertRaises(channels.ChannelEmptyError):
+            ch.recv_nowait()
+
+    def test_recv_nowait_default(self):
+        default = object()
+        rch, sch = channels.create()
+        obj1 = rch.recv_nowait(default)
+        sch.send_nowait(None)
+        sch.send_nowait(1)
+        sch.send_nowait(b'spam')
+        sch.send_nowait(b'eggs')
+        obj2 = rch.recv_nowait(default)
+        obj3 = rch.recv_nowait(default)
+        obj4 = rch.recv_nowait()
+        obj5 = rch.recv_nowait(default)
+        obj6 = rch.recv_nowait(default)
+
+        self.assertIs(obj1, default)
+        self.assertIs(obj2, None)
+        self.assertEqual(obj3, 1)
+        self.assertEqual(obj4, b'spam')
+        self.assertEqual(obj5, b'eggs')
+        self.assertIs(obj6, default)
+
+    def test_send_buffer(self):
+        buf = bytearray(b'spamspamspam')
+        obj = None
+        rch, sch = channels.create()
+
+        def f():
+            nonlocal obj
+            while True:
+                try:
+                    obj = rch.recv()
+                    break
+                except channels.ChannelEmptyError:
+                    time.sleep(0.1)
+        t = threading.Thread(target=f)
+        t.start()
+
+        sch.send_buffer(buf)
+        t.join()
+
+        self.assertIsNot(obj, buf)
+        self.assertIsInstance(obj, memoryview)
+        self.assertEqual(obj, buf)
+
+        buf[4:8] = b'eggs'
+        self.assertEqual(obj, buf)
+        obj[4:8] = b'ham.'
+        self.assertEqual(obj, buf)
+
+    def test_send_buffer_nowait(self):
+        buf = bytearray(b'spamspamspam')
+        rch, sch = channels.create()
+        sch.send_buffer_nowait(buf)
+        obj = rch.recv()
+
+        self.assertIsNot(obj, buf)
+        self.assertIsInstance(obj, memoryview)
+        self.assertEqual(obj, buf)
+
+        buf[4:8] = b'eggs'
+        self.assertEqual(obj, buf)
+        obj[4:8] = b'ham.'
+        self.assertEqual(obj, buf)
+
+
+if __name__ == '__main__':
+    # Test needs to be a package, so we can do relative imports.
+    unittest.main()
diff --git a/Lib/test/test_interpreters/test_lifecycle.py b/Lib/test/test_interpreters/test_lifecycle.py
new file mode 100644
index 00000000000000..c2917d839904f9
--- /dev/null
+++ b/Lib/test/test_interpreters/test_lifecycle.py
@@ -0,0 +1,189 @@
+import contextlib
+import json
+import os
+import os.path
+import sys
+from textwrap import dedent
+import unittest
+
+from test import support
+from test.support import import_helper
+from test.support import os_helper
+# Raise SkipTest if subinterpreters not supported.
+import_helper.import_module('_xxsubinterpreters')
+from .utils import TestBase
+
+
+class StartupTests(TestBase):
+
+    # We want to ensure the initial state of subinterpreters
+    # matches expectations.
+
+    _subtest_count = 0
+
+    @contextlib.contextmanager
+    def subTest(self, *args):
+        with super().subTest(*args) as ctx:
+            self._subtest_count += 1
+            try:
+                yield ctx
+            finally:
+                if self._debugged_in_subtest:
+                    if self._subtest_count == 1:
+                        # The first subtest adds a leading newline, so we
+                        # compensate here by not printing a trailing newline.
+                        print('### end subtest debug ###', end='')
+                    else:
+                        print('### end subtest debug ###')
+                self._debugged_in_subtest = False
+
+    def debug(self, msg, *, header=None):
+        if header:
+            self._debug(f'--- {header} ---')
+            if msg:
+                if msg.endswith(os.linesep):
+                    self._debug(msg[:-len(os.linesep)])
+                else:
+                    self._debug(msg)
+                    self._debug('<no newline>')
+            self._debug('------')
+        else:
+            self._debug(msg)
+
+    _debugged = False
+    _debugged_in_subtest = False
+    def _debug(self, msg):
+        if not self._debugged:
+            print()
+            self._debugged = True
+        if self._subtest is not None:
+            if True:
+                if not self._debugged_in_subtest:
+                    self._debugged_in_subtest = True
+                    print('### start subtest debug ###')
+                print(msg)
+        else:
+            print(msg)
+
+    def create_temp_dir(self):
+        import tempfile
+        tmp = tempfile.mkdtemp(prefix='test_interpreters_')
+        tmp = os.path.realpath(tmp)
+        self.addCleanup(os_helper.rmtree, tmp)
+        return tmp
+
+    def write_script(self, *path, text):
+        filename = os.path.join(*path)
+        dirname = os.path.dirname(filename)
+        if dirname:
+            os.makedirs(dirname, exist_ok=True)
+        with open(filename, 'w', encoding='utf-8') as outfile:
+            outfile.write(dedent(text))
+        return filename
+
+    @support.requires_subprocess()
+    def run_python(self, argv, *, cwd=None):
+        # This method is inspired by
+        # EmbeddingTestsMixin.run_embedded_interpreter() in test_embed.py.
+        import shlex
+        import subprocess
+        if isinstance(argv, str):
+            argv = shlex.split(argv)
+        argv = [sys.executable, *argv]
+        try:
+            proc = subprocess.run(
+                argv,
+                cwd=cwd,
+                capture_output=True,
+                text=True,
+            )
+        except Exception as exc:
+            self.debug(f'# cmd: {shlex.join(argv)}')
+            if isinstance(exc, FileNotFoundError) and not exc.filename:
+                if os.path.exists(argv[0]):
+                    exists = 'exists'
+                else:
+                    exists = 'does not exist'
+                self.debug(f'{argv[0]} {exists}')
+            raise  # re-raise
+        assert proc.stderr == '' or proc.returncode != 0, proc.stderr
+        if proc.returncode != 0 and support.verbose:
+            self.debug(f'# python3 {shlex.join(argv[1:])} failed:')
+            self.debug(proc.stdout, header='stdout')
+            self.debug(proc.stderr, header='stderr')
+        self.assertEqual(proc.returncode, 0)
+        self.assertEqual(proc.stderr, '')
+        return proc.stdout
+
+    def test_sys_path_0(self):
+        # The main interpreter's sys.path[0] should be used by subinterpreters.
+        script = '''
+            import sys
+            from test.support import interpreters
+
+            orig = sys.path[0]
+
+            interp = interpreters.create()
+            interp.exec_sync(f"""if True:
+                import json
+                import sys
+                print(json.dumps({{
+                    'main': {orig!r},
+                    'sub': sys.path[0],
+                }}, indent=4), flush=True)
+                """)
+            '''
+        # <tmp>/
+        #   pkg/
+        #     __init__.py
+        #     __main__.py
+        #     script.py
+        #   script.py
+        cwd = self.create_temp_dir()
+        self.write_script(cwd, 'pkg', '__init__.py', text='')
+        self.write_script(cwd, 'pkg', '__main__.py', text=script)
+        self.write_script(cwd, 'pkg', 'script.py', text=script)
+        self.write_script(cwd, 'script.py', text=script)
+
+        cases = [
+            ('script.py', cwd),
+            ('-m script', cwd),
+            ('-m pkg', cwd),
+            ('-m pkg.script', cwd),
+            ('-c "import script"', ''),
+        ]
+        for argv, expected in cases:
+            with self.subTest(f'python3 {argv}'):
+                out = self.run_python(argv, cwd=cwd)
+                data = json.loads(out)
+                sp0_main, sp0_sub = data['main'], data['sub']
+                self.assertEqual(sp0_sub, sp0_main)
+                self.assertEqual(sp0_sub, expected)
+        # XXX Also check them all with the -P cmdline flag?
+
+
+class FinalizationTests(TestBase):
+
+    def test_gh_109793(self):
+        # Make sure finalization finishes and the correct error code
+        # is reported, even when subinterpreters get cleaned up at the end.
+        import subprocess
+        argv = [sys.executable, '-c', '''if True:
+            from test.support import interpreters
+            interp = interpreters.create()
+            raise Exception
+            ''']
+        proc = subprocess.run(argv, capture_output=True, text=True)
+        self.assertIn('Traceback', proc.stderr)
+        if proc.returncode == 0 and support.verbose:
+            print()
+            print("--- cmd unexpected succeeded ---")
+            print(f"stdout:\n{proc.stdout}")
+            print(f"stderr:\n{proc.stderr}")
+            print("------")
+        self.assertEqual(proc.returncode, 1)
+
+
+if __name__ == '__main__':
+    # Test needs to be a package, so we can do relative imports.
+    unittest.main()
diff --git a/Lib/test/test_interpreters/test_stress.py b/Lib/test/test_interpreters/test_stress.py
new file mode 100644
index 00000000000000..3cc570b3bf7128
--- /dev/null
+++ b/Lib/test/test_interpreters/test_stress.py
@@ -0,0 +1,38 @@
+import threading
+import unittest
+
+from test import support
+from test.support import import_helper
+from test.support import threading_helper
+# Raise SkipTest if subinterpreters not supported.
+import_helper.import_module('_xxsubinterpreters')
+from test.support import interpreters
+from .utils import TestBase
+
+
+class StressTests(TestBase):
+
+    # In these tests we generally want a lot of interpreters,
+    # but not so many that any test takes too long.
+
+    @support.requires_resource('cpu')
+    def test_create_many_sequential(self):
+        alive = []
+        for _ in range(100):
+            interp = interpreters.create()
+            alive.append(interp)
+
+    @support.requires_resource('cpu')
+    def test_create_many_threaded(self):
+        alive = []
+        def task():
+            interp = interpreters.create()
+            alive.append(interp)
+        threads = (threading.Thread(target=task) for _ in range(200))
+        with threading_helper.start_threads(threads):
+            pass
+
+
+if __name__ == '__main__':
+    # Test needs to be a package, so we can do relative imports.
+    unittest.main()
diff --git a/Lib/test/test_interpreters/utils.py b/Lib/test/test_interpreters/utils.py
new file mode 100644
index 00000000000000..623c8737b79831
--- /dev/null
+++ b/Lib/test/test_interpreters/utils.py
@@ -0,0 +1,73 @@
+import contextlib
+import os
+import threading
+from textwrap import dedent
+import unittest
+
+from test.support import interpreters
+
+
+def _captured_script(script):
+    r, w = os.pipe()
+    indented = script.replace('\n', '\n                ')
+    wrapped = dedent(f"""
+        import contextlib
+        with open({w}, 'w', encoding='utf-8') as spipe:
+            with contextlib.redirect_stdout(spipe):
+                {indented}
+        """)
+    return wrapped, open(r, encoding='utf-8')
+
+
+def clean_up_interpreters():
+    for interp in interpreters.list_all():
+        if interp.id == 0:  # main
+            continue
+        try:
+            interp.close()
+        except RuntimeError:
+            pass  # already destroyed
+
+
+def _run_output(interp, request, channels=None):
+    script, rpipe = _captured_script(request)
+    with rpipe:
+        interp.exec_sync(script, channels=channels)
+        return rpipe.read()
+
+
+@contextlib.contextmanager
+def _running(interp):
+    r, w = os.pipe()
+    def run():
+        interp.exec_sync(dedent(f"""
+            # wait for "signal"
+            with open({r}) as rpipe:
+                rpipe.read()
+            """))
+
+    t = threading.Thread(target=run)
+    t.start()
+
+    yield
+
+    with open(w, 'w') as spipe:
+        spipe.write('done')
+    t.join()
+
+
+class TestBase(unittest.TestCase):
+
+    def pipe(self):
+        def ensure_closed(fd):
+            try:
+                os.close(fd)
+            except OSError:
+                pass
+        r, w = os.pipe()
+        self.addCleanup(lambda: ensure_closed(r))
+        self.addCleanup(lambda: ensure_closed(w))
+        return r, w
+
+    def tearDown(self):
+        clean_up_interpreters()

From 8ca303fe7fe79bdb161530ed4832625efb328113 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Tue, 28 Nov 2023 16:51:32 -0700
Subject: [PATCH 11/26] Add interpreters.Queue.

---
 Lib/test/support/interpreters/__init__.py |   7 +-
 Lib/test/support/interpreters/queue.py    | 156 +++++++++++++++
 Lib/test/test_interpreters/test_queue.py  | 233 ++++++++++++++++++++++
 3 files changed, 394 insertions(+), 2 deletions(-)
 create mode 100644 Lib/test/support/interpreters/queue.py
 create mode 100644 Lib/test/test_interpreters/test_queue.py

diff --git a/Lib/test/support/interpreters/__init__.py b/Lib/test/support/interpreters/__init__.py
index 86b625640a439f..f7a7b7053eeec6 100644
--- a/Lib/test/support/interpreters/__init__.py
+++ b/Lib/test/support/interpreters/__init__.py
@@ -8,14 +8,17 @@
     InterpreterError, InterpreterNotFoundError,
     is_shareable,
 )
-from .channel import create as create_channel
+from .queue import (
+    create as create_queue,
+    Queue, QueueEmpty, QueueFull,
+)
 
 
 __all__ = [
     'get_current', 'get_main', 'create', 'list_all', 'is_shareable',
     'Interpreter',
     'InterpreterError', 'InterpreterNotFoundError', 'ExecFailure',
-    'create_channel',
+    'create_queue', 'QueueEmpty', 'QueueFull',
 ]
 
 
diff --git a/Lib/test/support/interpreters/queue.py b/Lib/test/support/interpreters/queue.py
new file mode 100644
index 00000000000000..ed6b0d551dd890
--- /dev/null
+++ b/Lib/test/support/interpreters/queue.py
@@ -0,0 +1,156 @@
+"""Cross-interpreter Queues High Level Module."""
+
+import queue
+import time
+import weakref
+import _xxinterpchannels as _channels
+import _xxinterpchannels as _queues
+
+# aliases:
+from _xxinterpchannels import (
+    ChannelError as QueueError,
+    ChannelNotFoundError as QueueNotFoundError,
+)
+
+__all__ = [
+    'create', 'list_all',
+    'Queue',
+    'QueueError', 'QueueNotFoundError', 'QueueEmpty', 'QueueFull',
+]
+
+
+def create(maxsize=0):
+    """Return a new cross-interpreter queue.
+
+    The queue may be used to pass data safely between interpreters.
+    """
+    # XXX honor maxsize
+    qid = _queues.create()
+    return Queue._with_maxsize(qid, maxsize)
+
+
+def list_all():
+    """Return a list of all open queues."""
+    return [Queue(qid)
+            for qid in _queues.list_all()]
+
+
+class QueueEmpty(queue.Empty):
+    """Raised from get_nowait() when the queue is empty.
+
+    It is also raised from get() if it times out.
+    """
+
+
+class QueueFull(queue.Full):
+    """Raised from put_nowait() when the queue is full.
+
+    It is also raised from put() if it times out.
+    """
+
+
+_known_queues = weakref.WeakValueDictionary()
+
+class Queue:
+    """A cross-interpreter queue."""
+
+    @classmethod
+    def _with_maxsize(cls, id, maxsize):
+        if not isinstance(maxsize, int):
+            raise TypeError(f'maxsize must be an int, got {maxsize!r}')
+        elif maxsize < 0:
+            maxsize = 0
+        else:
+            maxsize = int(maxsize)
+        self = cls(id)
+        self._maxsize = maxsize
+        return self
+
+    def __new__(cls, id, /):
+        # There is only one instance for any given ID.
+        if isinstance(id, int):
+            id = _channels._channel_id(id, force=False)
+        elif not isinstance(id, _channels.ChannelID):
+            raise TypeError(f'id must be an int, got {id!r}')
+        key = int(id)
+        try:
+            self = _known_queues[key]
+        except KeyError:
+            self = super().__new__(cls)
+            self._id = id
+            self._maxsize = 0
+            _known_queues[key] = self
+        return self
+
+    def __repr__(self):
+        return f'{type(self).__name__}({self.id})'
+
+    def __hash__(self):
+        return hash(self._id)
+
+    @property
+    def id(self):
+        return int(self._id)
+
+    @property
+    def maxsize(self):
+        return self._maxsize
+
+    @property
+    def _info(self):
+        return _channels.get_info(self._id)
+
+    def empty(self):
+        return self._info.count == 0
+
+    def full(self):
+        if self._maxsize <= 0:
+            return False
+        return self._info.count >= self._maxsize
+
+    def qsize(self):
+        return self._info.count
+
+    def put(self, obj, timeout=None):
+        # XXX block if full
+        _channels.send(self._id, obj, blocking=False)
+
+    def put_nowait(self, obj):
+        # XXX raise QueueFull if full
+        return _channels.send(self._id, obj, blocking=False)
+
+    def get(self, timeout=None, *,
+             _sentinel=object(),
+             _delay=10 / 1000,  # 10 milliseconds
+             ):
+        """Return the next object from the queue.
+
+        This blocks while the queue is empty.
+        """
+        if timeout is not None:
+            timeout = int(timeout)
+            if timeout < 0:
+                raise ValueError(f'timeout value must be non-negative')
+            end = time.time() + timeout
+        obj = _channels.recv(self._id, _sentinel)
+        while obj is _sentinel:
+            time.sleep(_delay)
+            if timeout is not None and time.time() >= end:
+                raise QueueEmpty
+            obj = _channels.recv(self._id, _sentinel)
+        return obj
+
+    def get_nowait(self, *, _sentinel=object()):
+        """Return the next object from the channel.
+
+        If the queue is empty then raise QueueEmpty.  Otherwise this
+        is the same as get().
+        """
+        obj = _channels.recv(self._id, _sentinel)
+        if obj is _sentinel:
+            raise QueueEmpty
+        return obj
+
+
+# XXX add this:
+#_channels._register_queue_type(Queue)
diff --git a/Lib/test/test_interpreters/test_queue.py b/Lib/test/test_interpreters/test_queue.py
new file mode 100644
index 00000000000000..cf6ac5f0990d2f
--- /dev/null
+++ b/Lib/test/test_interpreters/test_queue.py
@@ -0,0 +1,233 @@
+import threading
+from textwrap import dedent
+import unittest
+import time
+
+from test.support import import_helper
+# Raise SkipTest if subinterpreters not supported.
+import_helper.import_module('_xxinterpchannels')
+#import_helper.import_module('_xxinterpqueues')
+from test.support import interpreters
+import test.support.interpreters.queue as queues
+from .utils import _run_output, TestBase
+
+
+class QueueTests(TestBase):
+
+    def test_create(self):
+        with self.subTest('vanilla'):
+            queue = queues.create()
+            self.assertEqual(queue.maxsize, 0)
+
+        with self.subTest('small maxsize'):
+            queue = queues.create(3)
+            self.assertEqual(queue.maxsize, 3)
+
+        with self.subTest('big maxsize'):
+            queue = queues.create(100)
+            self.assertEqual(queue.maxsize, 100)
+
+        with self.subTest('no maxsize'):
+            queue = queues.create(0)
+            self.assertEqual(queue.maxsize, 0)
+
+        with self.subTest('negative maxsize'):
+            queue = queues.create(-1)
+            self.assertEqual(queue.maxsize, 0)
+
+        with self.subTest('bad maxsize'):
+            with self.assertRaises(TypeError):
+                queues.create('1')
+
+    @unittest.expectedFailure
+    def test_shareable(self):
+        queue1 = queues.create()
+        queue2 = queues.create()
+        queue1.put(queue2)
+        queue3 = queue1.get()
+        self.assertIs(queue3, queue1)
+
+    def test_id_type(self):
+        queue = queues.create()
+        self.assertIsInstance(queue.id, int)
+
+    def test_custom_id(self):
+        with self.assertRaises(queues.QueueNotFoundError):
+            queues.Queue(1_000_000)
+
+    def test_id_readonly(self):
+        queue = queues.create()
+        with self.assertRaises(AttributeError):
+            queue.id = 1_000_000
+
+    def test_maxsize_readonly(self):
+        queue = queues.create(10)
+        with self.assertRaises(AttributeError):
+            queue.maxsize = 1_000_000
+
+    def test_hashable(self):
+        queue = queues.create()
+        expected = hash(queue.id)
+        actual = hash(queue)
+        self.assertEqual(actual, expected)
+
+    def test_equality(self):
+        queue1 = queues.create()
+        queue2 = queues.create()
+        self.assertEqual(queue1, queue1)
+        self.assertNotEqual(queue1, queue2)
+
+
+class TestQueueOps(TestBase):
+
+    def test_empty(self):
+        queue = queues.create()
+        before = queue.empty()
+        queue.put(None)
+        during = queue.empty()
+        queue.get()
+        after = queue.empty()
+
+        self.assertIs(before, True)
+        self.assertIs(during, False)
+        self.assertIs(after, True)
+
+    def test_full(self):
+        expected = [False, False, False, True, False, False, False]
+        actual = []
+        queue = queues.create(3)
+        for _ in range(3):
+            actual.append(queue.full())
+            queue.put(None)
+        actual.append(queue.full())
+        for _ in range(3):
+            queue.get()
+            actual.append(queue.full())
+
+        self.assertEqual(actual, expected)
+
+    def test_qsize(self):
+        expected = [0, 1, 2, 3, 2, 3, 2, 1, 0, 1, 0]
+        actual = []
+        queue = queues.create()
+        for _ in range(3):
+            actual.append(queue.qsize())
+            queue.put(None)
+        actual.append(queue.qsize())
+        queue.get()
+        actual.append(queue.qsize())
+        queue.put(None)
+        actual.append(queue.qsize())
+        for _ in range(3):
+            queue.get()
+            actual.append(queue.qsize())
+        queue.put(None)
+        actual.append(queue.qsize())
+        queue.get()
+        actual.append(queue.qsize())
+
+        self.assertEqual(actual, expected)
+
+    def test_put_get_main(self):
+        expected = list(range(20))
+        queue = queues.create()
+        for i in range(20):
+            queue.put(i)
+        actual = [queue.get() for _ in range(20)]
+
+        self.assertEqual(actual, expected)
+
+    @unittest.expectedFailure
+    def test_put_timeout(self):
+        queue = queues.create(2)
+        queue.put(None)
+        queue.put(None)
+        with self.assertRaises(queues.QueueFull):
+            queue.put(None, timeout=0.1)
+        queue.get()
+        queue.put(None)
+
+    @unittest.expectedFailure
+    def test_put_nowait(self):
+        queue = queues.create(2)
+        queue.put_nowait(None)
+        queue.put_nowait(None)
+        with self.assertRaises(queues.QueueFull):
+            queue.put_nowait(None)
+        queue.get()
+        queue.put_nowait(None)
+
+    def test_get_timeout(self):
+        queue = queues.create()
+        with self.assertRaises(queues.QueueEmpty):
+            queue.get(timeout=0.1)
+
+    def test_get_nowait(self):
+        queue = queues.create()
+        with self.assertRaises(queues.QueueEmpty):
+            queue.get_nowait()
+
+    def test_put_get_same_interpreter(self):
+        interp = interpreters.create()
+        interp.exec_sync(dedent("""
+            import test.support.interpreters.queue as queues
+            queue = queues.create()
+            orig = b'spam'
+            queue.put(orig)
+            obj = queue.get()
+            assert obj == orig, 'expected: obj == orig'
+            assert obj is not orig, 'expected: obj is not orig'
+            """))
+
+    @unittest.expectedFailure
+    def test_put_get_different_interpreters(self):
+        queue1 = queues.create()
+        queue2 = queues.create()
+        obj1 = b'spam'
+        queue1.put(obj1)
+        out = _run_output(
+            interpreters.create(),
+            dedent(f"""
+                import test.support.interpreters.queue as queues
+                queue1 = queues.Queue({queue1.id})
+                queue2 = queues.Queue({queue2.id})
+                obj = queue1.get()
+                assert obj == b'spam', 'expected: obj == obj1'
+                # When going to another interpreter we get a copy.
+                assert id(obj) != {id(obj1)}, 'expected: obj is not obj1'
+                obj2 = b'eggs'
+                print(id(obj2))
+                queue2.put(obj2)
+                """))
+        obj2 = queue2.get()
+
+        self.assertEqual(obj2, b'eggs')
+        self.assertNotEqual(id(obj2), int(out))
+
+    def test_put_get_different_threads(self):
+        queue1 = queues.create()
+        queue2 = queues.create()
+
+        def f():
+            while True:
+                try:
+                    obj = queue1.get(timeout=0.1)
+                    break
+                except queues.QueueEmpty:
+                    continue
+            queue2.put(obj)
+        t = threading.Thread(target=f)
+        t.start()
+
+        orig = b'spam'
+        queue1.put(orig)
+        obj = queue2.get()
+        t.join()
+
+        self.assertEqual(obj, orig)
+        self.assertIsNot(obj, orig)
+
+
+if __name__ == '__main__':
+    # Test needs to be a package, so we can do relative imports.
+    unittest.main()

From 8b9737347f1a8c638ba646271d8b9b51c47bed83 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 14:35:22 -0700
Subject: [PATCH 12/26] Add memoryview XID with _xxsubinterpreters import.

---
 Modules/_xxinterpchannelsmodule.c  | 157 -----------------------
 Modules/_xxsubinterpretersmodule.c | 197 +++++++++++++++++++++++++++++
 2 files changed, 197 insertions(+), 157 deletions(-)

diff --git a/Modules/_xxinterpchannelsmodule.c b/Modules/_xxinterpchannelsmodule.c
index 1c9ae3b87adf7c..97729ec269cb62 100644
--- a/Modules/_xxinterpchannelsmodule.c
+++ b/Modules/_xxinterpchannelsmodule.c
@@ -8,7 +8,6 @@
 #include "Python.h"
 #include "interpreteridobject.h"
 #include "pycore_crossinterp.h"   // struct _xid
-#include "pycore_pybuffer.h"      // _PyBuffer_ReleaseInInterpreterAndRawFree()
 #include "pycore_interp.h"        // _PyInterpreterState_LookUpID()
 
 #ifdef MS_WINDOWS
@@ -263,136 +262,6 @@ wait_for_lock(PyThread_type_lock mutex, PY_TIMEOUT_T timeout)
 }
 
 
-/* Cross-interpreter Buffer Views *******************************************/
-
-// XXX Release when the original interpreter is destroyed.
-
-typedef struct {
-    PyObject_HEAD
-    Py_buffer *view;
-    int64_t interpid;
-} XIBufferViewObject;
-
-static PyObject *
-xibufferview_from_xid(PyTypeObject *cls, _PyCrossInterpreterData *data)
-{
-    assert(data->data != NULL);
-    assert(data->obj == NULL);
-    assert(data->interpid >= 0);
-    XIBufferViewObject *self = PyObject_Malloc(sizeof(XIBufferViewObject));
-    if (self == NULL) {
-        return NULL;
-    }
-    PyObject_Init((PyObject *)self, cls);
-    self->view = (Py_buffer *)data->data;
-    self->interpid = data->interpid;
-    return (PyObject *)self;
-}
-
-static void
-xibufferview_dealloc(XIBufferViewObject *self)
-{
-    PyInterpreterState *interp = _PyInterpreterState_LookUpID(self->interpid);
-    /* If the interpreter is no longer alive then we have problems,
-       since other objects may be using the buffer still. */
-    assert(interp != NULL);
-
-    if (_PyBuffer_ReleaseInInterpreterAndRawFree(interp, self->view) < 0) {
-        // XXX Emit a warning?
-        PyErr_Clear();
-    }
-
-    PyTypeObject *tp = Py_TYPE(self);
-    tp->tp_free(self);
-    /* "Instances of heap-allocated types hold a reference to their type."
-     * See: https://docs.python.org/3.11/howto/isolating-extensions.html#garbage-collection-protocol
-     * See: https://docs.python.org/3.11/c-api/typeobj.html#c.PyTypeObject.tp_traverse
-    */
-    // XXX Why don't we implement Py_TPFLAGS_HAVE_GC, e.g. Py_tp_traverse,
-    // like we do for _abc._abc_data?
-    Py_DECREF(tp);
-}
-
-static int
-xibufferview_getbuf(XIBufferViewObject *self, Py_buffer *view, int flags)
-{
-    /* Only PyMemoryView_FromObject() should ever call this,
-       via _memoryview_from_xid() below. */
-    *view = *self->view;
-    view->obj = (PyObject *)self;
-    // XXX Should we leave it alone?
-    view->internal = NULL;
-    return 0;
-}
-
-static PyType_Slot XIBufferViewType_slots[] = {
-    {Py_tp_dealloc, (destructor)xibufferview_dealloc},
-    {Py_bf_getbuffer, (getbufferproc)xibufferview_getbuf},
-    // We don't bother with Py_bf_releasebuffer since we don't need it.
-    {0, NULL},
-};
-
-static PyType_Spec XIBufferViewType_spec = {
-    .name = MODULE_NAME ".CrossInterpreterBufferView",
-    .basicsize = sizeof(XIBufferViewObject),
-    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
-              Py_TPFLAGS_DISALLOW_INSTANTIATION | Py_TPFLAGS_IMMUTABLETYPE),
-    .slots = XIBufferViewType_slots,
-};
-
-
-/* extra XID types **********************************************************/
-
-static PyTypeObject * _get_current_xibufferview_type(void);
-
-static PyObject *
-_memoryview_from_xid(_PyCrossInterpreterData *data)
-{
-    PyTypeObject *cls = _get_current_xibufferview_type();
-    if (cls == NULL) {
-        return NULL;
-    }
-    PyObject *obj = xibufferview_from_xid(cls, data);
-    if (obj == NULL) {
-        return NULL;
-    }
-    return PyMemoryView_FromObject(obj);
-}
-
-static int
-_memoryview_shared(PyThreadState *tstate, PyObject *obj,
-                   _PyCrossInterpreterData *data)
-{
-    Py_buffer *view = PyMem_RawMalloc(sizeof(Py_buffer));
-    if (view == NULL) {
-        return -1;
-    }
-    if (PyObject_GetBuffer(obj, view, PyBUF_FULL_RO) < 0) {
-        PyMem_RawFree(view);
-        return -1;
-    }
-    _PyCrossInterpreterData_Init(data, tstate->interp, view, NULL,
-                                 _memoryview_from_xid);
-    return 0;
-}
-
-static int
-register_builtin_xid_types(struct xid_class_registry *classes)
-{
-    PyTypeObject *cls;
-    crossinterpdatafunc func;
-
-    // builtin memoryview
-    cls = &PyMemoryView_Type;
-    func = _memoryview_shared;
-    if (register_xid_class(cls, func, classes)) {
-        return -1;
-    }
-
-    return 0;
-}
-
-
 /* module state *************************************************************/
 
 typedef struct {
@@ -405,7 +274,6 @@ typedef struct {
     /* heap types */
     PyTypeObject *ChannelInfoType;
     PyTypeObject *ChannelIDType;
-    PyTypeObject *XIBufferViewType;
 
     /* exceptions */
     PyObject *ChannelError;
@@ -449,7 +317,6 @@ traverse_module_state(module_state *state, visitproc visit, void *arg)
     /* heap types */
     Py_VISIT(state->ChannelInfoType);
     Py_VISIT(state->ChannelIDType);
-    Py_VISIT(state->XIBufferViewType);
 
     /* exceptions */
     Py_VISIT(state->ChannelError);
@@ -474,7 +341,6 @@ clear_module_state(module_state *state)
         (void)_PyCrossInterpreterData_UnregisterClass(state->ChannelIDType);
     }
     Py_CLEAR(state->ChannelIDType);
-    Py_CLEAR(state->XIBufferViewType);
 
     /* exceptions */
     Py_CLEAR(state->ChannelError);
@@ -487,17 +353,6 @@ clear_module_state(module_state *state)
 }
 
 
-static PyTypeObject *
-_get_current_xibufferview_type(void)
-{
-    module_state *state = _get_current_module_state();
-    if (state == NULL) {
-        return NULL;
-    }
-    return state->XIBufferViewType;
-}
-
-
 /* channel-specific code ****************************************************/
 
 #define CHANNEL_SEND 1
@@ -3463,18 +3318,6 @@ module_exec(PyObject *mod)
         goto error;
     }
 
-    // XIBufferView
-    state->XIBufferViewType = add_new_type(mod, &XIBufferViewType_spec, NULL,
-                                           xid_classes);
-    if (state->XIBufferViewType == NULL) {
-        goto error;
-    }
-
-    // Register external types.
-    if (register_builtin_xid_types(xid_classes) < 0) {
-        goto error;
-    }
-
     /* Make sure chnnels drop objects owned by this interpreter. */
     PyInterpreterState *interp = _get_current_interp();
     PyUnstable_AtExit(interp, clear_interpreter, (void *)interp);
diff --git a/Modules/_xxsubinterpretersmodule.c b/Modules/_xxsubinterpretersmodule.c
index 5954d47e2555ec..8205fa78820581 100644
--- a/Modules/_xxsubinterpretersmodule.c
+++ b/Modules/_xxsubinterpretersmodule.c
@@ -12,6 +12,7 @@
 #include "pycore_initconfig.h"    // _PyErr_SetFromPyStatus()
 #include "pycore_long.h"          // _PyLong_IsNegative()
 #include "pycore_modsupport.h"    // _PyArg_BadArgument()
+#include "pycore_pybuffer.h"      // _PyBuffer_ReleaseInInterpreterAndRawFree()
 #include "pycore_pyerrors.h"      // _Py_excinfo
 #include "pycore_pystate.h"       // _PyInterpreterState_SetRunningMain()
 
@@ -121,11 +122,169 @@ get_interpid_obj(PyInterpreterState *interp)
     return interpid_to_pylong(id);
 }
 
+static PyObject *
+_get_current_module(void)
+{
+    PyObject *name = PyUnicode_FromString(MODULE_NAME);
+    if (name == NULL) {
+        return NULL;
+    }
+    PyObject *mod = PyImport_GetModule(name);
+    Py_DECREF(name);
+    if (mod == NULL) {
+        return NULL;
+    }
+    assert(mod != Py_None);
+    return mod;
+}
+
+
+/* Cross-interpreter Buffer Views *******************************************/
+
+// XXX Release when the original interpreter is destroyed.
+
+typedef struct {
+    PyObject_HEAD
+    Py_buffer *view;
+    int64_t interpid;
+} XIBufferViewObject;
+
+static PyObject *
+xibufferview_from_xid(PyTypeObject *cls, _PyCrossInterpreterData *data)
+{
+    assert(data->data != NULL);
+    assert(data->obj == NULL);
+    assert(data->interpid >= 0);
+    XIBufferViewObject *self = PyObject_Malloc(sizeof(XIBufferViewObject));
+    if (self == NULL) {
+        return NULL;
+    }
+    PyObject_Init((PyObject *)self, cls);
+    self->view = (Py_buffer *)data->data;
+    self->interpid = data->interpid;
+    return (PyObject *)self;
+}
+
+static void
+xibufferview_dealloc(XIBufferViewObject *self)
+{
+    PyInterpreterState *interp = _PyInterpreterState_LookUpID(self->interpid);
+    /* If the interpreter is no longer alive then we have problems,
+       since other objects may be using the buffer still. */
+    assert(interp != NULL);
+
+    if (_PyBuffer_ReleaseInInterpreterAndRawFree(interp, self->view) < 0) {
+        // XXX Emit a warning?
+        PyErr_Clear();
+    }
+
+    PyTypeObject *tp = Py_TYPE(self);
+    tp->tp_free(self);
+    /* "Instances of heap-allocated types hold a reference to their type."
+     * See: https://docs.python.org/3.11/howto/isolating-extensions.html#garbage-collection-protocol
+     * See: https://docs.python.org/3.11/c-api/typeobj.html#c.PyTypeObject.tp_traverse
+    */
+    // XXX Why don't we implement Py_TPFLAGS_HAVE_GC, e.g. Py_tp_traverse,
+    // like we do for _abc._abc_data?
+    Py_DECREF(tp);
+}
+
+static int
+xibufferview_getbuf(XIBufferViewObject *self, Py_buffer *view, int flags)
+{
+    /* Only PyMemoryView_FromObject() should ever call this,
+       via _memoryview_from_xid() below. */
+    *view = *self->view;
+    view->obj = (PyObject *)self;
+    // XXX Should we leave it alone?
+    view->internal = NULL;
+    return 0;
+}
+
+static PyType_Slot XIBufferViewType_slots[] = {
+    {Py_tp_dealloc, (destructor)xibufferview_dealloc},
+    {Py_bf_getbuffer, (getbufferproc)xibufferview_getbuf},
+    // We don't bother with Py_bf_releasebuffer since we don't need it.
+    {0, NULL},
+};
+
+static PyType_Spec XIBufferViewType_spec = {
+    .name = MODULE_NAME ".CrossInterpreterBufferView",
+    .basicsize = sizeof(XIBufferViewObject),
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
+              Py_TPFLAGS_DISALLOW_INSTANTIATION | Py_TPFLAGS_IMMUTABLETYPE),
+    .slots = XIBufferViewType_slots,
+};
+
+
+static PyTypeObject * _get_current_xibufferview_type(void);
+
+static PyObject *
+_memoryview_from_xid(_PyCrossInterpreterData *data)
+{
+    PyTypeObject *cls = _get_current_xibufferview_type();
+    if (cls == NULL) {
+        return NULL;
+    }
+    PyObject *obj = xibufferview_from_xid(cls, data);
+    if (obj == NULL) {
+        return NULL;
+    }
+    return PyMemoryView_FromObject(obj);
+}
+
+static int
+_memoryview_shared(PyThreadState *tstate, PyObject *obj,
+                   _PyCrossInterpreterData *data)
+{
+    Py_buffer *view = PyMem_RawMalloc(sizeof(Py_buffer));
+    if (view == NULL) {
+        return -1;
+    }
+    if (PyObject_GetBuffer(obj, view, PyBUF_FULL_RO) < 0) {
+        PyMem_RawFree(view);
+        return -1;
+    }
+    _PyCrossInterpreterData_Init(data, tstate->interp, view, NULL,
+                                 _memoryview_from_xid);
+    return 0;
+}
+
+static int
+register_memoryview_xid(PyObject *mod, PyTypeObject **p_state)
+{
+    // XIBufferView
+    assert(*p_state == NULL);
+    PyTypeObject *cls = (PyTypeObject *)PyType_FromModuleAndSpec(
+                mod, &XIBufferViewType_spec, NULL);
+    if (cls == NULL) {
+        return -1;
+    }
+    if (PyModule_AddType(mod, cls) < 0) {
+        Py_DECREF(cls);
+        return -1;
+    }
+    *p_state = cls;
+
+    // Register XID for the builtin memoryview type.
+    if (_PyCrossInterpreterData_RegisterClass(
+                &PyMemoryView_Type, _memoryview_shared) < 0) {
+        return -1;
+    }
+    // We don't ever bother un-registering memoryview.
+
+    return 0;
+}
+
+
 
 /* module state *************************************************************/
 
 typedef struct {
     int _notused;
+
+    /* heap types */
+    PyTypeObject *XIBufferViewType;
 } module_state;
 
 static inline module_state *
@@ -137,19 +296,51 @@ get_module_state(PyObject *mod)
     return state;
 }
 
+static module_state *
+_get_current_module_state(void)
+{
+    PyObject *mod = _get_current_module();
+    if (mod == NULL) {
+        // XXX import it?
+        PyErr_SetString(PyExc_RuntimeError,
+                        MODULE_NAME " module not imported yet");
+        return NULL;
+    }
+    module_state *state = get_module_state(mod);
+    Py_DECREF(mod);
+    return state;
+}
+
 static int
 traverse_module_state(module_state *state, visitproc visit, void *arg)
 {
+    /* heap types */
+    Py_VISIT(state->XIBufferViewType);
+
     return 0;
 }
 
 static int
 clear_module_state(module_state *state)
 {
+    /* heap types */
+    Py_CLEAR(state->XIBufferViewType);
+
     return 0;
 }
 
 
+static PyTypeObject *
+_get_current_xibufferview_type(void)
+{
+    module_state *state = _get_current_module_state();
+    if (state == NULL) {
+        return NULL;
+    }
+    return state->XIBufferViewType;
+}
+
+
 /* Python code **************************************************************/
 
 static const char *
@@ -863,6 +1054,8 @@ The 'interpreters' module provides a more convenient interface.");
 static int
 module_exec(PyObject *mod)
 {
+    module_state *state = get_module_state(mod);
+
     // exceptions
     if (PyModule_AddType(mod, (PyTypeObject *)PyExc_InterpreterError) < 0) {
         goto error;
@@ -871,6 +1064,10 @@ module_exec(PyObject *mod)
         goto error;
     }
 
+    if (register_memoryview_xid(mod, &state->XIBufferViewType) < 0) {
+        goto error;
+    }
+
     return 0;
 
 error:

From cc20f1f10c65d5a28930c8a283e6a28a385ee5e1 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 15:27:06 -0700
Subject: [PATCH 13/26] Update CODEOWNERS.

---
 .github/CODEOWNERS | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index 1925363cbeb46e..84eceb5089c819 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -78,6 +78,11 @@ Python/traceback.c            @iritkatriel
 **/*importlib/resources/*      @jaraco @warsaw @FFY00
 **/importlib/metadata/*       @jaraco @warsaw
 
+# Subinterpreters
+Lib/test/support/interpreters/**  @ericsnowcurrently
+Modules/_xx*interp*module.c   @ericsnowcurrently
+Lib/test/test_interpreters/**  @ericsnowcurrently
+
 # Dates and times
 **/*datetime*                 @pganssle @abalkin
 **/*str*time*                 @pganssle @abalkin

From cb0a6059c980a5cef413935e12d3b16fbd9e8543 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 15:32:38 -0700
Subject: [PATCH 14/26] Ignore static builtin exception types.

---
 Tools/c-analyzer/cpython/globals-to-fix.tsv | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Tools/c-analyzer/cpython/globals-to-fix.tsv b/Tools/c-analyzer/cpython/globals-to-fix.tsv
index aa8ce49ae86376..e3a1b5d532bda2 100644
--- a/Tools/c-analyzer/cpython/globals-to-fix.tsv
+++ b/Tools/c-analyzer/cpython/globals-to-fix.tsv
@@ -290,6 +290,10 @@ Objects/exceptions.c	-	PyExc_UnicodeWarning	-
 Objects/exceptions.c	-	PyExc_BytesWarning	-
 Objects/exceptions.c	-	PyExc_ResourceWarning	-
 Objects/exceptions.c	-	PyExc_EncodingWarning	-
+Python/crossinterp.c	-	_PyExc_InterpreterError	-
+Python/crossinterp.c	-	_PyExc_InterpreterNotFoundError	-
+Python/crossinterp.c	-	PyExc_InterpreterError	-
+Python/crossinterp.c	-	PyExc_InterpreterNotFoundError	-
 
 ##-----------------------
 ## singletons

From 62a9bacb5051f8c3318907182ced1b6a459d4449 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 15:45:25 -0700
Subject: [PATCH 15/26] Make CODEOWNERS more specific.

---
 .github/CODEOWNERS | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index 84eceb5089c819..f8ebeb4181da00 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -153,7 +153,15 @@ Doc/c-api/stable.rst          @encukou
 **/*itertools*                @rhettinger
 **/*collections*              @rhettinger
 **/*random*                   @rhettinger
-**/*queue*                    @rhettinger
+Doc/**/*queue*                @rhettinger
+PCbuild/**/*queue*            @rhettinger
+Modules/_queuemodule.c        @rhettinger
+Lib/*queue*.py                @rhettinger
+Lib/asyncio/*queue*.py        @rhettinger
+Lib/multiprocessing/*queue*.py  @rhettinger
+Lib/test/*queue*.py           @rhettinger
+Lib/test_asyncio/*queue*.py   @rhettinger
+Lib/test_multiprocessing/*queue*.py  @rhettinger
 **/*bisect*                   @rhettinger
 **/*heapq*                    @rhettinger
 **/*functools*                @rhettinger

From 6c7101856587976884d1455976ccc0efeb2ca9cc Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 16:05:59 -0700
Subject: [PATCH 16/26] Fix submodule names.

---
 Lib/test/support/interpreters/__init__.py                   | 2 +-
 Lib/test/support/interpreters/{channel.py => channels.py}   | 0
 Lib/test/support/interpreters/{queue.py => queues.py}       | 0
 .../test_interpreters/{test_channel.py => test_channels.py} | 6 +++---
 .../test_interpreters/{test_queue.py => test_queues.py}     | 4 ++--
 5 files changed, 6 insertions(+), 6 deletions(-)
 rename Lib/test/support/interpreters/{channel.py => channels.py} (100%)
 rename Lib/test/support/interpreters/{queue.py => queues.py} (100%)
 rename Lib/test/test_interpreters/{test_channel.py => test_channels.py} (98%)
 rename Lib/test/test_interpreters/{test_queue.py => test_queues.py} (98%)

diff --git a/Lib/test/support/interpreters/__init__.py b/Lib/test/support/interpreters/__init__.py
index f7a7b7053eeec6..e54982e16439e5 100644
--- a/Lib/test/support/interpreters/__init__.py
+++ b/Lib/test/support/interpreters/__init__.py
@@ -8,7 +8,7 @@
     InterpreterError, InterpreterNotFoundError,
     is_shareable,
 )
-from .queue import (
+from .queues import (
     create as create_queue,
     Queue, QueueEmpty, QueueFull,
 )
diff --git a/Lib/test/support/interpreters/channel.py b/Lib/test/support/interpreters/channels.py
similarity index 100%
rename from Lib/test/support/interpreters/channel.py
rename to Lib/test/support/interpreters/channels.py
diff --git a/Lib/test/support/interpreters/queue.py b/Lib/test/support/interpreters/queues.py
similarity index 100%
rename from Lib/test/support/interpreters/queue.py
rename to Lib/test/support/interpreters/queues.py
diff --git a/Lib/test/test_interpreters/test_channel.py b/Lib/test/test_interpreters/test_channels.py
similarity index 98%
rename from Lib/test/test_interpreters/test_channel.py
rename to Lib/test/test_interpreters/test_channels.py
index f38237e0b153b9..3c3e18832d4168 100644
--- a/Lib/test/test_interpreters/test_channel.py
+++ b/Lib/test/test_interpreters/test_channels.py
@@ -7,7 +7,7 @@
 # Raise SkipTest if subinterpreters not supported.
 _channels = import_helper.import_module('_xxinterpchannels')
 from test.support import interpreters
-import test.support.interpreters.channel as channels
+from test.support.interpreters import channels
 from .utils import _run_output, TestBase
 
 
@@ -121,7 +121,7 @@ def test_send_recv_main(self):
     def test_send_recv_same_interpreter(self):
         interp = interpreters.create()
         interp.exec_sync(dedent("""
-            import test.support.interpreters.channel as channels
+            from test.support.interpreters import channels
             r, s = channels.create()
             orig = b'spam'
             s.send_nowait(orig)
@@ -194,7 +194,7 @@ def test_send_recv_nowait_main_with_default(self):
     def test_send_recv_nowait_same_interpreter(self):
         interp = interpreters.create()
         interp.exec_sync(dedent("""
-            import test.support.interpreters.channel as channels
+            from test.support.interpreters import channels
             r, s = channels.create()
             orig = b'spam'
             s.send_nowait(orig)
diff --git a/Lib/test/test_interpreters/test_queue.py b/Lib/test/test_interpreters/test_queues.py
similarity index 98%
rename from Lib/test/test_interpreters/test_queue.py
rename to Lib/test/test_interpreters/test_queues.py
index cf6ac5f0990d2f..2af90b14d3e3c4 100644
--- a/Lib/test/test_interpreters/test_queue.py
+++ b/Lib/test/test_interpreters/test_queues.py
@@ -8,7 +8,7 @@
 import_helper.import_module('_xxinterpchannels')
 #import_helper.import_module('_xxinterpqueues')
 from test.support import interpreters
-import test.support.interpreters.queue as queues
+from test.support.interpreters import queues
 from .utils import _run_output, TestBase
 
 
@@ -170,7 +170,7 @@ def test_get_nowait(self):
     def test_put_get_same_interpreter(self):
         interp = interpreters.create()
         interp.exec_sync(dedent("""
-            import test.support.interpreters.queue as queues
+            from test.support.interpreters import queues
             queue = queues.create()
             orig = b'spam'
             queue.put(orig)

From 13a44e353bb9cbee1f5bb26d4ea74c7200db39fc Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Thu, 7 Dec 2023 13:45:09 -0700
Subject: [PATCH 17/26] Use interpreters.__getattr__() for submodule aliases.

---
 Lib/test/support/interpreters/__init__.py | 21 ++++++++++++++++-----
 Lib/test/test_interpreters/test_api.py    | 18 ++++++++++++++++++
 2 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/Lib/test/support/interpreters/__init__.py b/Lib/test/support/interpreters/__init__.py
index e54982e16439e5..f2a86023a83be6 100644
--- a/Lib/test/support/interpreters/__init__.py
+++ b/Lib/test/support/interpreters/__init__.py
@@ -8,20 +8,31 @@
     InterpreterError, InterpreterNotFoundError,
     is_shareable,
 )
-from .queues import (
-    create as create_queue,
-    Queue, QueueEmpty, QueueFull,
-)
 
 
 __all__ = [
     'get_current', 'get_main', 'create', 'list_all', 'is_shareable',
     'Interpreter',
     'InterpreterError', 'InterpreterNotFoundError', 'ExecFailure',
-    'create_queue', 'QueueEmpty', 'QueueFull',
+    'create_queue', 'Queue', 'QueueEmpty', 'QueueFull',
 ]
 
 
+_queuemod = None
+
+def __getattr__(name):
+    if name in ('Queue', 'QueueEmpty', 'QueueFull', 'create_queue'):
+        global create_queue, Queue, QueueEmpty, QueueFull
+        ns = globals()
+        from .queues import (
+            create as create_queue,
+            Queue, QueueEmpty, QueueFull,
+        )
+        return ns[name]
+    else:
+        raise AttributeError(name)
+
+
 class ExecFailure(RuntimeError):
 
     def __init__(self, excinfo):
diff --git a/Lib/test/test_interpreters/test_api.py b/Lib/test/test_interpreters/test_api.py
index d94a03bccf2e97..53e5db3e30a8e1 100644
--- a/Lib/test/test_interpreters/test_api.py
+++ b/Lib/test/test_interpreters/test_api.py
@@ -12,6 +12,24 @@
 from .utils import _captured_script, _run_output, _running, TestBase
 
 
+class ModuleTests(TestBase):
+
+    def test_queue_aliases(self):
+        first = [
+            interpreters.create_queue,
+            interpreters.Queue,
+            interpreters.QueueEmpty,
+            interpreters.QueueFull,
+        ]
+        second = [
+            interpreters.create_queue,
+            interpreters.Queue,
+            interpreters.QueueEmpty,
+            interpreters.QueueFull,
+        ]
+        self.assertEqual(second, first)
+
+
 class CreateTests(TestBase):
 
     def test_in_main(self):

From c9d15d2c56f4a688269ee51da34f4d9e30b5e444 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 16:18:03 -0700
Subject: [PATCH 18/26] Fix InterpreterIDTests.

---
 Lib/test/test_capi/test_misc.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_capi/test_misc.py b/Lib/test/test_capi/test_misc.py
index dec68977a6ba45..3d8c7886a7cb2e 100644
--- a/Lib/test/test_capi/test_misc.py
+++ b/Lib/test/test_capi/test_misc.py
@@ -2079,7 +2079,7 @@ def test_does_not_exist(self):
         with self.assertRaises(_interpreters.InterpreterNotFoundError):
             self.InterpreterID(int(id) + 1)  # unforced
 
-    def test_does_not_exist(self):
+    def test_destroyed(self):
         id = _interpreters.create()
         _interpreters.destroy(id)
         with self.assertRaises(_interpreters.InterpreterNotFoundError):

From 1c76c4a702be612208a94e5849c6d5b4661a07fe Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 16:20:16 -0700
Subject: [PATCH 19/26] LONG_LONG_MAX -> LLONG_MAX

---
 Modules/_xxsubinterpretersmodule.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Modules/_xxsubinterpretersmodule.c b/Modules/_xxsubinterpretersmodule.c
index 8205fa78820581..37959e953ee4f5 100644
--- a/Modules/_xxsubinterpretersmodule.c
+++ b/Modules/_xxsubinterpretersmodule.c
@@ -54,7 +54,7 @@ pylong_to_interpid(PyObject *idobj)
         // For now, we don't worry about if LLONG_MAX < INT64_MAX.
         goto bad_id;
     }
-#if LONG_LONG_MAX > INT64_MAX
+#if LLONG_MAX > INT64_MAX
     if (id > INT64_MAX) {
         goto bad_id;
     }
@@ -105,7 +105,7 @@ look_up_interp(PyObject *arg)
 static PyObject *
 interpid_to_pylong(int64_t id)
 {
-    assert(id < LONG_LONG_MAX);
+    assert(id < LLONG_MAX);
     return PyLong_FromLongLong(id);
 }
 

From cfae15f4e3742b7eaf39e4dce2d7f5c843dbf2eb Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 16:50:04 -0700
Subject: [PATCH 20/26] Fix Interpreter.run().

---
 Lib/test/support/interpreters/__init__.py |  1 +
 Lib/test/test_interpreters/test_api.py    | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/Lib/test/support/interpreters/__init__.py b/Lib/test/support/interpreters/__init__.py
index f2a86023a83be6..2d6376deb5907e 100644
--- a/Lib/test/support/interpreters/__init__.py
+++ b/Lib/test/support/interpreters/__init__.py
@@ -1,5 +1,6 @@
 """Subinterpreters High Level Module."""
 
+import threading
 import weakref
 import _xxsubinterpreters as _interpreters
 
diff --git a/Lib/test/test_interpreters/test_api.py b/Lib/test/test_interpreters/test_api.py
index 53e5db3e30a8e1..7f4014c28c70ef 100644
--- a/Lib/test/test_interpreters/test_api.py
+++ b/Lib/test/test_interpreters/test_api.py
@@ -557,6 +557,24 @@ def task():
     # Interpreter.exec_sync() behavior.
 
 
+class TestInterpreterRun(TestBase):
+
+    def test_success(self):
+        interp = interpreters.create()
+        script, file = _captured_script('print("it worked!", end="")')
+        with file:
+            t = interp.run(script)
+            t.join()
+            out = file.read()
+
+        self.assertEqual(out, 'it worked!')
+
+    def test_failure(self):
+        interp = interpreters.create()
+        t = interp.run('raise Exception')
+        t.join()
+
+
 class TestIsShareable(TestBase):
 
     def test_default_shareables(self):

From 3f98ce1e572c36b972dd0f4b425ca8bfa85a04a9 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 16:54:54 -0700
Subject: [PATCH 21/26] Use exec_sync() in test_sys.

---
 Lib/test/test_sys.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 7f49fb004272bb..3524aebca3deec 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -715,7 +715,7 @@ def test_subinterp_intern_dynamically_allocated(self):
         self.assertIs(t, s)
 
         interp = interpreters.create()
-        interp.run(textwrap.dedent(f'''
+        interp.exec_sync(textwrap.dedent(f'''
             import sys
             t = sys.intern({s!r})
             assert id(t) != {id(s)}, (id(t), {id(s)})
@@ -730,7 +730,7 @@ def test_subinterp_intern_statically_allocated(self):
         t = sys.intern(s)
 
         interp = interpreters.create()
-        interp.run(textwrap.dedent(f'''
+        interp.exec_sync(textwrap.dedent(f'''
             import sys
             t = sys.intern({s!r})
             assert id(t) == {id(t)}, (id(t), {id(t)})

From f8b1685b2c021057ab9c1feb12c23ebf7f1b28de Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 16:59:07 -0700
Subject: [PATCH 22/26] Fix test_capi.

---
 Lib/test/test_capi/test_misc.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Lib/test/test_capi/test_misc.py b/Lib/test/test_capi/test_misc.py
index 3d8c7886a7cb2e..9fea5376687d08 100644
--- a/Lib/test/test_capi/test_misc.py
+++ b/Lib/test/test_capi/test_misc.py
@@ -1527,6 +1527,7 @@ def test_isolated_subinterpreter(self):
         maxtext = 250
         main_interpid = 0
         interpid = _interpreters.create()
+        self.addCleanup(lambda: _interpreters.destroy(interpid))
         _interpreters.run_string(interpid, f"""if True:
             import json
             import os

From 0b34a83fa490c4859b9037a4156b4afb29719aee Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 17:05:00 -0700
Subject: [PATCH 23/26] Fix test_importlib.

---
 Lib/test/test_importlib/test_util.py | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_importlib/test_util.py b/Lib/test/test_importlib/test_util.py
index 914176559806f4..fe5e7b31d9c32b 100644
--- a/Lib/test/test_importlib/test_util.py
+++ b/Lib/test/test_importlib/test_util.py
@@ -657,14 +657,26 @@ class IncompatibleExtensionModuleRestrictionsTests(unittest.TestCase):
 
     def run_with_own_gil(self, script):
         interpid = _interpreters.create(isolated=True)
-        excsnap = _interpreters.run_string(interpid, script)
+        def ensure_destroyed():
+            try:
+                _interpreters.destroy(interpid)
+            except _interpreters.InterpreterNotFoundError:
+                pass
+        self.addCleanup(ensure_destroyed)
+        excsnap = _interpreters.exec(interpid, script)
         if excsnap is not None:
             if excsnap.type.__name__ == 'ImportError':
                 raise ImportError(excsnap.msg)
 
     def run_with_shared_gil(self, script):
         interpid = _interpreters.create(isolated=False)
-        excsnap = _interpreters.run_string(interpid, script)
+        def ensure_destroyed():
+            try:
+                _interpreters.destroy(interpid)
+            except _interpreters.InterpreterNotFoundError:
+                pass
+        self.addCleanup(ensure_destroyed)
+        excsnap = _interpreters.exec(interpid, script)
         if excsnap is not None:
             if excsnap.type.__name__ == 'ImportError':
                 raise ImportError(excsnap.msg)

From 68faf1aabb40adcefbf5f9b7840e05dc52049bd4 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 17:08:15 -0700
Subject: [PATCH 24/26] Fix test_import.

---
 Lib/test/test_import/__init__.py | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_import/__init__.py b/Lib/test/test_import/__init__.py
index 1ecac4f37fe1c1..d9dd897f928fc7 100644
--- a/Lib/test/test_import/__init__.py
+++ b/Lib/test/test_import/__init__.py
@@ -1968,6 +1968,7 @@ def test_disallowed_reimport(self):
             print(_testsinglephase)
             ''')
         interpid = _interpreters.create()
+        self.addCleanup(lambda: _interpreters.destroy(interpid))
 
         excsnap = _interpreters.run_string(interpid, script)
         self.assertIsNot(excsnap, None)
@@ -2102,12 +2103,18 @@ def re_load(self, name, mod):
 
     def add_subinterpreter(self):
         interpid = _interpreters.create(isolated=False)
-        _interpreters.run_string(interpid, textwrap.dedent('''
+        def ensure_destroyed():
+            try:
+                _interpreters.destroy(interpid)
+            except _interpreters.InterpreterNotFoundError:
+                pass
+        self.addCleanup(ensure_destroyed)
+        _interpreters.exec(interpid, textwrap.dedent('''
             import sys
             import _testinternalcapi
             '''))
         def clean_up():
-            _interpreters.run_string(interpid, textwrap.dedent(f'''
+            _interpreters.exec(interpid, textwrap.dedent(f'''
                 name = {self.NAME!r}
                 if name in sys.modules:
                     sys.modules.pop(name)._clear_globals()

From d161f760ae9df5563dee6db7ad85a6c687ef9290 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 17:11:50 -0700
Subject: [PATCH 25/26] Fix test_threading.

---
 Lib/test/test_threading.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index 146e2dbc0fc396..a5744a4037ecea 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -1365,7 +1365,7 @@ def test_threads_join_with_no_main(self):
         DONE = b'D'
 
         interp = interpreters.create()
-        interp.run(f"""if True:
+        interp.exec_sync(f"""if True:
             import os
             import threading
             import time

From 778276f962990cdadd828dc4eda5d255fd087fe2 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Dec 2023 18:42:07 -0700
Subject: [PATCH 26/26] Fix TestInterpreterRun.

---
 Lib/test/test_interpreters/test_api.py | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/Lib/test/test_interpreters/test_api.py b/Lib/test/test_interpreters/test_api.py
index 7f4014c28c70ef..e4ae9d005b5282 100644
--- a/Lib/test/test_interpreters/test_api.py
+++ b/Lib/test/test_interpreters/test_api.py
@@ -570,9 +570,19 @@ def test_success(self):
         self.assertEqual(out, 'it worked!')
 
     def test_failure(self):
-        interp = interpreters.create()
-        t = interp.run('raise Exception')
-        t.join()
+        caught = False
+        def excepthook(args):
+            nonlocal caught
+            caught = True
+        threading.excepthook = excepthook
+        try:
+            interp = interpreters.create()
+            t = interp.run('raise Exception')
+            t.join()
+
+            self.assertTrue(caught)
+        except BaseException:
+            threading.excepthook = threading.__excepthook__
 
 
 class TestIsShareable(TestBase):

<!DOCTYPE html PUBLIC '-//W3C//DTD XHTML 1.0 Transitional//EN' 'http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd'>
<html xmlns='http://www.w3.org/1999/xhtml'>
<head>
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