gh-145235: Make dict watcher API thread-safe for free-threaded builds#145233
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yoney wants to merge 3 commits intopython:mainfrom
Open
gh-145235: Make dict watcher API thread-safe for free-threaded builds#145233yoney wants to merge 3 commits intopython:mainfrom
yoney wants to merge 3 commits intopython:mainfrom
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colesbury
reviewed
Feb 25, 2026
Python/optimizer_analysis.c
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| PyInterpreterState *interp = _PyInterpreterState_GET(); | ||
| if (interp->dict_state.watchers[GLOBALS_WATCHER_ID] == NULL) { | ||
| interp->dict_state.watchers[GLOBALS_WATCHER_ID] = globals_watcher_callback; | ||
| if (FT_ATOMIC_LOAD_PTR_RELAXED(interp->dict_state.watchers[GLOBALS_WATCHER_ID]) == NULL) { |
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A _PyOnceFlag (maybe in JitOptContext) might be a better fit here.
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After looking into it (with Claude), JitOptContext seems to be per-optimization-run so _PyOnceFlag might not the right place. I put it in _Py_dict_state as I couldn't find a better place. It fits in the struct packing without extra space.
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@colesbury Thank you for the review. I’ve addressed the comments. |
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In free-threaded builds, concurrent calls to
PyDict_AddWatcher,PyDict_ClearWatcher,PyDict_Watch, andPyDict_Unwatchcan race on the shared callback array and the per-dict watcher tags. This change adds a mutex to serialize watcher registration and removal, atomic operations for tag updates, and atomic acquire/release synchronization for callback dispatch in_PyDict_SendEvent.Note: Before this change, running
test.test_free_threading.test_dict_watcheremitted tsan warnings in the free-threaded tsan build.cc: @colesbury @mpage @DinoV