https://github.com/python/cpython/commit/cc581f32bf5f15e9f2f89b830ec64ea25684d0cd
commit: cc581f32bf5f15e9f2f89b830ec64ea25684d0cd
branch: main
author: Sam Gross <colesb...@gmail.com>
committer: encukou <encu...@gmail.com>
date: 2025-06-04T09:35:56+02:00
summary:
gh-135099: Only wait on `_PyOS_SigintEvent()` in main thread (GH-135100)
On Windows, the `_PyOS_SigintEvent()` event handle is used to interrupt
the main thread when Ctrl-C is pressed. Previously, we also waited on
the event from other threads, but ignored the result. However, this can
race with interpreter shutdown because the main thread closes the handle
in `_PySignal_Fini` and threads may still be running and using mutexes
during interpreter shtudown.
Only use `_PyOS_SigintEvent()` in the main thread in parking_lot.c, like
we do in other places in the CPython codebase.
files:
A Misc/NEWS.d/next/Windows/2025-06-03-18-26-54.gh-issue-135099.Q9usKm.rst
M Python/parking_lot.c
diff --git
a/Misc/NEWS.d/next/Windows/2025-06-03-18-26-54.gh-issue-135099.Q9usKm.rst
b/Misc/NEWS.d/next/Windows/2025-06-03-18-26-54.gh-issue-135099.Q9usKm.rst
new file mode 100644
index 00000000000000..36e70b1c0d8cb6
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2025-06-03-18-26-54.gh-issue-135099.Q9usKm.rst
@@ -0,0 +1,2 @@
+Fix a crash that could occur on Windows when a background thread waits on a
+:c:type:`PyMutex` while the main thread is shutting down the interpreter.
diff --git a/Python/parking_lot.c b/Python/parking_lot.c
index 8edf43235942ab..e896dea02712f2 100644
--- a/Python/parking_lot.c
+++ b/Python/parking_lot.c
@@ -112,17 +112,27 @@ _PySemaphore_PlatformWait(_PySemaphore *sema, PyTime_t
timeout)
}
}
- // NOTE: we wait on the sigint event even in non-main threads to match the
- // behavior of the other platforms. Non-main threads will ignore the
- // Py_PARK_INTR result.
- HANDLE sigint_event = _PyOS_SigintEvent();
- HANDLE handles[2] = { sema->platform_sem, sigint_event };
- DWORD count = sigint_event != NULL ? 2 : 1;
+ HANDLE handles[2] = { sema->platform_sem, NULL };
+ HANDLE sigint_event = NULL;
+ DWORD count = 1;
+ if (_Py_IsMainThread()) {
+ // gh-135099: Wait on the SIGINT event only in the main thread. Other
+ // threads would ignore the result anyways, and accessing
+ // `_PyOS_SigintEvent()` from non-main threads may race with
+ // interpreter shutdown, which closes the event handle. Note that
+ // non-main interpreters will ignore the result.
+ sigint_event = _PyOS_SigintEvent();
+ if (sigint_event != NULL) {
+ handles[1] = sigint_event;
+ count = 2;
+ }
+ }
wait = WaitForMultipleObjects(count, handles, FALSE, millis);
if (wait == WAIT_OBJECT_0) {
res = Py_PARK_OK;
}
else if (wait == WAIT_OBJECT_0 + 1) {
+ assert(sigint_event != NULL);
ResetEvent(sigint_event);
res = Py_PARK_INTR;
}
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