Acquire the GIL when not owned.

ericsnowcurrently · ericsnowcurrently · commit ad1e40b332c3 · 2023-05-05T11:33:59.000-06:00
diff --git a/Python/ceval_gil.c b/Python/ceval_gil.c
@@ -499,42 +499,56 @@ PyEval_ThreadsInitialized(void)
     return _PyEval_ThreadsInitialized();
 }
 
+static void
+init_shared_gil(PyInterpreterState *interp, struct _gil_runtime_state *gil)
+{
+    assert(gil_created(gil));
+    interp->ceval.gil = gil;
+    interp->ceval.own_gil = 0;
+}
+
+static void
+init_own_gil(PyInterpreterState *interp, struct _gil_runtime_state *gil)
+{
+    assert(!gil_created(gil));
+    create_gil(gil);
+    assert(gil_created(gil));
+    interp->ceval.gil = gil;
+    interp->ceval.own_gil = 1;
+}
+
 PyStatus
 _PyEval_InitGIL(PyThreadState *tstate, int own_gil)
 {
     assert(tstate->interp->ceval.gil == NULL);
+    int locked;
     if (!own_gil) {
         PyInterpreterState *main_interp = _PyInterpreterState_Main();
         assert(tstate->interp != main_interp);
-        struct _gil_runtime_state *gil = main_interp->ceval.gil;
-        assert(gil_created(gil));
-        tstate->interp->ceval.gil = gil;
-        tstate->interp->ceval.own_gil = 0;
-        return _PyStatus_OK();
+        init_shared_gil(tstate->interp, main_interp->ceval.gil);
+        locked = _Py_atomic_load_relaxed(&main_interp->ceval.gil->locked);
     }
-
     /* XXX per-interpreter GIL */
-    struct _gil_runtime_state *gil = &tstate->interp->runtime->ceval.gil;
-    if (!_Py_IsMainInterpreter(tstate->interp)) {
+    else if (!_Py_IsMainInterpreter(tstate->interp)) {
         /* Currently, the GIL is shared by all interpreters,
            and only the main interpreter is responsible to create
            and destroy it. */
-        assert(gil_created(gil));
-        tstate->interp->ceval.gil = gil;
+        struct _gil_runtime_state *main_gil = _PyInterpreterState_Main()->ceval.gil;
+        init_shared_gil(tstate->interp, main_gil);
         // XXX For now we lie.
         tstate->interp->ceval.own_gil = 1;
-        return _PyStatus_OK();
+        locked = _Py_atomic_load_relaxed(&main_gil->locked);
+    }
+    else {
+        PyThread_init_thread();
+        // XXX per-interpreter GIL: switch to interp->ceval._gil.
+        init_own_gil(tstate->interp, &tstate->interp->runtime->ceval.gil);
+        locked = 0;
+    }
+    if (!locked) {
+        take_gil(tstate);
     }
-    assert(own_gil);
-
-    assert(!gil_created(gil));
 
-    PyThread_init_thread();
-    create_gil(gil);
-    assert(gil_created(gil));
-    tstate->interp->ceval.gil = gil;
-    tstate->interp->ceval.own_gil = 1;
-    take_gil(tstate);
     return _PyStatus_OK();
 }
 
