gh-124621: Emscripten: Add support for async input devices #136822
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🤖 New build scheduled with the buildbot fleet by @hoodmane for commit 3d573d5 🤖 Results will be shown at: https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F136822%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 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 original `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`.
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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 offd_read(), otherwise we use the originalfd_read(). We also add a variant ofFS.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 anOSError.