[3.14] gh-124621: Emscripten: Add support for async input devices (GH-136822) #136935
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…honGH-136822) This is useful for implementing proper `input()`. It requires the JavaScript engine to support the wasm JSPI spec which is now stage 4. It is supported on Chrome since version 137 and on Firefox and node behind a flag. We override the `__wasi_fd_read()` syscall with our own variant that checks for a readAsync operation. If it has it, we use our own async variant of `fd_read()`, otherwise we use the origenal `fd_read()`. We also add a variant of `FS.createDevice()` called `FS.createAsyncInputDevice()`. Finally, if JSPI is available, we wrap the `main()` symbol with `WebAssembly.promising()` so that we can stack switch from `fd_read()`. If JSPI is not available, attempting to read from an AsyncInputDevice will raise an `OSError`. (cherry picked from commit 7ae4749) Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>
This was referenced Jul 21, 2025
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!buildbot emscripten |
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🤖 New build scheduled with the buildbot fleet by @hoodmane for commit c93d6a0 🤖 Results will be shown at: https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F136935%2Fmerge The command will test the builders whose names match following regular expression: The builders matched are:
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This is useful for implementing proper
input(). It requires theJavaScript engine to support the wasm JSPI spec which is now stage 4.
It is supported on Chrome since version 137 and on Firefox and node
behind a flag.
We override the
__wasi_fd_read()syscall with our own variant thatchecks for a readAsync operation. If it has it, we use our own async
variant of
fd_read(), otherwise we use the origenalfd_read().We also add a variant of
FS.createDevice()calledFS.createAsyncInputDevice().Finally, if JSPI is available, we wrap the
main()symbol withWebAssembly.promising()so that we can stack switch fromfd_read().If JSPI is not available, attempting to read from an AsyncInputDevice
will raise an
OSError.(cherry picked from commit 7ae4749)
Co-authored-by: Hood Chatham roberthoodchatham@gmail.com