From c46a14c2078cc7e99592b89c6747c5f44e208f01 Mon Sep 17 00:00:00 2001 From: Sam Gross Date: Wed, 4 Jun 2025 03:35:56 -0400 Subject: [PATCH] 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. (cherry picked from commit cc581f32bf5f15e9f2f89b830ec64ea25684d0cd) Co-authored-by: Sam Gross --- ...-06-03-18-26-54.gh-issue-135099.Q9usKm.rst | 2 ++ Python/parking_lot.c | 22 ++++++++++++++----- 2 files changed, 18 insertions(+), 6 deletions(-) create mode 100644 Misc/NEWS.d/next/Windows/2025-06-03-18-26-54.gh-issue-135099.Q9usKm.rst 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; }