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Fix segfault awaiting JS promises on Python 3.14.0–3.14.3 #516

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Fix segfault awaiting JS promises on Python 3.14.0–3.14.3 #516

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Copilot Nov 9, 2026
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28 changes: 28 additions & 0 deletions src/PyEventLoop.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -142,6 +142,26 @@ PyEventLoop PyEventLoop::_loopNotFound() {
PyEventLoop PyEventLoop::_getLoopOnThread(PyThreadState *tstate) {
// Modified from Python 3.9 `get_running_loop` https://github.com/python/cpython/blob/7cb3a44/Modules/_asynciomodule.c#L241-L278

// For the current thread, ask asyncio itself instead of reading CPython's private thread-state layout,
// which differs between patch releases (e.g. 3.14.3 vs 3.14.4).
if (tstate == PyThreadState_Get()) {
PyObject *asyncio = PyImport_ImportModule("asyncio");
if (asyncio == NULL) {
return _loopNotFound();
}
PyObject *loop = PyObject_CallMethod(asyncio, "_get_running_loop", NULL);
Py_DECREF(asyncio);
if (loop == NULL) {
PyErr_Clear();
return _loopNotFound();
}
if (loop == Py_None) {
Py_DECREF(loop);
return _loopNotFound();
}
return PyEventLoop(loop); // takes the new reference
}

PyObject *ts_dict;
#if PY_VERSION_HEX >= 0x030d0000 // Python version is greater than 3.13
// The private `_PyThreadState_GetDict(tstate)` API gets removed in Python 3.13.
Expand Down Expand Up @@ -204,6 +224,14 @@ PyEventLoop PyEventLoop::_getLoopOnThread(PyThreadState *tstate) {
// (we only need the first few fields of `_PyThreadStateImpl`)
};

#if PY_VERSION_HEX >= 0x030e0000 && PY_VERSION_HEX < 0x030f0000
// Python 3.14.4 added a pointer field to the public `PyThreadState`, shifting the offsets of the private fields.
// Refuse to read another thread's state when the runtime and build-time layouts differ.
if ((PY_VERSION_HEX >= 0x030e0400) != (Py_Version >= 0x030e0400)) {
return _loopNotFound();
}
#endif

// Modified from https://github.com/python/cpython/blob/v3.13.0rc1/Modules/_asynciomodule.c#L3205-L3210
PyObject *loop = ((PyThreadStateHolder *)tstate)->asyncio_running_loop;
if (loop == NULL) {
Expand Down