René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"race condition in threading when interpreter finalized while daemon thread runs (thread sanitizer identified)","articleBody":"# Bug report\n\n### Bug description:\n\nUsing the code in #105805 with the newly added `test.test_threading.ThreadTests.test_finalize_daemon_thread_hang` test enabled you can reproduce this thread sanitizer crash as follows (I used clang 18):\n\nThis also happens if I just take the new test and corresponding Modules/_testcapimodule.c change and patch it on top of `main` - it's a pre-existing bug not related to my PR adding the new test.  _(Filing now before I check this in decorated to be skipped under sanitizers so I can reference the issue number in a comment)_\n\n```\nCC=clang LD=lld ./configure --with-thread-sanitizer --with-pydebug \u0026\u0026 make -j8\n./python -m test test_threading -v\n...\n======================================================================\nFAIL: test_finalize_daemon_thread_hang (test.test_threading.ThreadTests.test_finalize_daemon_thread_hang)\n----------------------------------------------------------------------\nTraceback (most recent call last):\n  File \"/home/greg/oss/cpython/Lib/test/test_threading.py\", line 1236, in test_finalize_daemon_thread_hang\n    assert_python_ok(\"-c\", script)\n    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^\n  File \"/home/greg/oss/cpython/Lib/test/support/script_helper.py\", line 182, in assert_python_ok\n    return _assert_python(True, *args, **env_vars)\n  File \"/home/greg/oss/cpython/Lib/test/support/script_helper.py\", line 167, in _assert_python\n    res.fail(cmd_line)\n    ~~~~~~~~^^^^^^^^^^\n  File \"/home/greg/oss/cpython/Lib/test/support/script_helper.py\", line 80, in fail\n    raise AssertionError(f\"Process return code is {exitcode}\\n\"\n    ...\u003c10 lines\u003e...\n                         f\"---\")\nAssertionError: Process return code is 66\ncommand line: ['/home/greg/oss/b/python', '-X', 'faulthandler', '-I', '-c', \"\\nimport os\\nimport sys\\nimport threading\\nimport time\\nimport _testcapi\\n\\nlock = threa\nding.Lock()\\nlock.acquire()\\nthread_started_event = threading.Event()\\ndef thread_func():\\n    try:\\n        thread_started_event.set()\\n        _testcapi.finalize_t\nhread_hang(lock.acquire)\\n    finally:\\n        # Control must not reach here.\\n        os._exit(2)\\n\\nt = threading.Thread(target=thread_func)\\nt.daemon = True\\nt.s\ntart()\\nthread_started_event.wait()\\n# Sleep to ensure daemon thread is blocked on `lock.acquire`\\n#\\n# Note: This test is designed so that in the unlikely case that\n\\n# `0.1` seconds is not sufficient time for the thread to become\\n# blocked on `lock.acquire`, the test will still pass, it just\\n# won't be properly testing the th\nread behavior during\\n# finalization.\\ntime.sleep(0.1)\\n\\ndef run_during_finalization():\\n    # Wake up daemon thread\\n    lock.release()\\n    # Sleep to give the da\nemon thread time to crash if it is going\\n    # to.\\n    #\\n    # Note: If due to an exceptionally slow execution this delay is\\n    # insufficient, the test will st\nill pass but will simply be\\n    # ineffective as a test.\\n    time.sleep(0.1)\\n    # If control reaches here, the test succeeded.\\n    os._exit(0)\\n\\n# Replace sys.\nstderr.flush as a way to run code during finalization\\norig_flush = sys.stderr.flush\\ndef do_flush(*args, **kwargs):\\n    orig_flush(*args, **kwargs)\\n    if not sys\n.is_finalizing:\\n        return\\n    sys.stderr.flush = orig_flush\\n    run_during_finalization()\\n\\nsys.stderr.flush = do_flush\\n\\n# If the follow exit code is reta\nined, `run_during_finalization`\\n# did not run.\\nsys.exit(1)\\n\"]\n\nstdout:\n---\n\n---\n\nstderr:\n---\n==================\nWARNING: ThreadSanitizer: data race (pid=2184927)\n  Write of size 8 at 0x724800000028 by main thread:\n    #0 __tsan_memset \u003cnull\u003e (python+0xdc23d) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #1 fill_mem_debug /home/greg/oss/b/../cpython/Objects/obmalloc.c:2637:5 (python+0x31bc3a) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #2 _PyMem_DebugRawFree /home/greg/oss/b/../cpython/Objects/obmalloc.c:2766:5 (python+0x31bc3a)\n    #3 PyMem_RawFree /home/greg/oss/b/../cpython/Objects/obmalloc.c:971:5 (python+0x319498) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #4 free_threadstate /home/greg/oss/b/../cpython/Python/pystate.c:1455:9 (python+0x54ba27) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #5 _PyThreadState_DeleteList /home/greg/oss/b/../cpython/Python/pystate.c:1933:9 (python+0x54ba27)\n    #6 _Py_Finalize /home/greg/oss/b/../cpython/Python/pylifecycle.c:2043:5 (python+0x522649) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #7 Py_Exit /home/greg/oss/b/../cpython/Python/pylifecycle.c:3390:9 (python+0x5253a5) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #8 handle_system_exit /home/greg/oss/b/../cpython/Python/pythonrun.c:635:9 (python+0x550ae6) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #9 _PyErr_PrintEx /home/greg/oss/b/../cpython/Python/pythonrun.c:644:5 (python+0x550ae6)\n    #10 PyErr_PrintEx /home/greg/oss/b/../cpython/Python/pythonrun.c:721:5 (python+0x55027c) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #11 PyErr_Print /home/greg/oss/b/../cpython/Python/pythonrun.c:727:5 (python+0x55027c)\n    #12 _PyRun_SimpleStringFlagsWithName /home/greg/oss/b/../cpython/Python/pythonrun.c:552:9 (python+0x55027c)\n    #13 pymain_run_command /home/greg/oss/b/../cpython/Modules/main.c:253:11 (python+0x58f2e4) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #14 pymain_run_python /home/greg/oss/b/../cpython/Modules/main.c:687:21 (python+0x58f2e4)\n    #15 Py_RunMain /home/greg/oss/b/../cpython/Modules/main.c:775:5 (python+0x58f2e4)\n    #16 pymain_main /home/greg/oss/b/../cpython/Modules/main.c:805:12 (python+0x58f8e9) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #17 Py_BytesMain /home/greg/oss/b/../cpython/Modules/main.c:829:12 (python+0x58f969) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #18 main /home/greg/oss/b/../cpython/Programs/python.c:15:12 (python+0x15e810) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n\n  Previous atomic read of size 8 at 0x724800000028 by thread T1:\n    #0 _Py_atomic_load_uintptr_relaxed /home/greg/oss/b/../cpython/Include/cpython/pyatomic_gcc.h:347:10 (python+0x4de525) (BuildId: f07474199a50b9dfeeb5b474be4e3a40\n79af30a5)\n    #1 _Py_eval_breaker_bit_is_set /home/greg/oss/b/../cpython/Include/internal/pycore_ceval.h:307:19 (python+0x4de525)\n    #2 drop_gil /home/greg/oss/b/../cpython/Python/ceval_gil.c:259:9 (python+0x4de525)\n    #3 _PyEval_ReleaseLock /home/greg/oss/b/../cpython/Python/ceval_gil.c:596:5 (python+0x4de6fb) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #4 detach_thread /home/greg/oss/b/../cpython/Python/pystate.c:2144:5 (python+0x54c1ec) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #5 _PyThreadState_Detach /home/greg/oss/b/../cpython/Python/pystate.c:2150:5 (python+0x548adb) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #6 PyEval_SaveThread /home/greg/oss/b/../cpython/Python/ceval_gil.c:640:5 (python+0x4de922) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #7 PyThread_acquire_lock_timed_with_retries /home/greg/oss/b/../cpython/Python/thread.c:148:13 (python+0x573cbc) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30\na5)\n    #8 acquire_timed /home/greg/oss/b/../cpython/Modules/_threadmodule.c:737:12 (python+0x61dbc0) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #9 lock_PyThread_acquire_lock /home/greg/oss/b/../cpython/Modules/_threadmodule.c:793:22 (python+0x61dbc0)\n    #10 cfunction_call /home/greg/oss/b/../cpython/Objects/methodobject.c:540:18 (python+0x2e9488) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #11 _PyObject_MakeTpCall /home/greg/oss/b/../cpython/Objects/call.c:242:18 (python+0x2539d2) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #12 _PyObject_VectorcallTstate /home/greg/oss/b/../cpython/Include/internal/pycore_call.h:165:16 (python+0x2532ed) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af\n30a5)\n    #13 PyObject_CallNoArgs /home/greg/oss/b/../cpython/Objects/call.c:106:12 (python+0x2531bd) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #14 finalize_thread_hang /home/greg/oss/b/../cpython/Modules/_testcapimodule.c:3332:5 (_testcapi.cpython-314d-x86_64-linux-gnu.so+0x1e204) (BuildId: 4bdac866b639\ncba10e0265b34477a0f6dd6d394c)\n    #15 cfunction_vectorcall_O /home/greg/oss/b/../cpython/Objects/methodobject.c:512:24 (python+0x2e873d) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #16 _PyObject_VectorcallTstate /home/greg/oss/b/../cpython/Include/internal/pycore_call.h:167:11 (python+0x25328b) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af\n30a5)\n    #17 PyObject_Vectorcall /home/greg/oss/b/../cpython/Objects/call.c:327:12 (python+0x2549a0) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #18 _PyEval_EvalFrameDefault /home/greg/oss/b/../cpython/Python/generated_cases.c.h:920:35 (python+0x459d5a) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #19 _PyEval_EvalFrame /home/greg/oss/b/../cpython/Include/internal/pycore_ceval.h:119:16 (python+0x453c62) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #20 _PyEval_Vector /home/greg/oss/b/../cpython/Python/ceval.c:1852:12 (python+0x453c62)\n    #21 _PyFunction_Vectorcall /home/greg/oss/b/../cpython/Objects/call.c (python+0x254ebc) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #22 _PyObject_VectorcallTstate /home/greg/oss/b/../cpython/Include/internal/pycore_call.h:167:11 (python+0x25a35b) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af\n30a5)\n    #23 method_vectorcall /home/greg/oss/b/../cpython/Objects/classobject.c:70:20 (python+0x258a85) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #24 _PyVectorcall_Call /home/greg/oss/b/../cpython/Objects/call.c:273:16 (python+0x2548a7) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #25 _PyObject_Call /home/greg/oss/b/../cpython/Objects/call.c:348:16 (python+0x254abb) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #26 PyObject_Call /home/greg/oss/b/../cpython/Objects/call.c:373:12 (python+0x254ce7) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #27 thread_run /home/greg/oss/b/../cpython/Modules/_threadmodule.c:337:21 (python+0x61c1e8) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #28 pythread_wrapper /home/greg/oss/b/../cpython/Python/thread_pthread.h:242:5 (python+0x5740bb) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n\n  Location is heap block of size 360 at 0x724800000000 allocated by main thread:\n    #0 calloc \u003cnull\u003e (python+0xdeaaa) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #1 _PyMem_RawCalloc /home/greg/oss/b/../cpython/Objects/obmalloc.c:76:12 (python+0x3174cb) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #2 _PyMem_DebugRawAlloc /home/greg/oss/b/../cpython/Objects/obmalloc.c:2696:24 (python+0x31babe) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #3 _PyMem_DebugRawCalloc /home/greg/oss/b/../cpython/Objects/obmalloc.c:2741:12 (python+0x31babe)\n    #4 PyMem_RawCalloc /home/greg/oss/b/../cpython/Objects/obmalloc.c:957:12 (python+0x3193cb) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #5 alloc_threadstate /home/greg/oss/b/../cpython/Python/pystate.c:1440:12 (python+0x549de1) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #6 new_threadstate /home/greg/oss/b/../cpython/Python/pystate.c:1549:38 (python+0x549de1)\n    #7 _PyThreadState_New /home/greg/oss/b/../cpython/Python/pystate.c:1632:12 (python+0x54a7de) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #8 ThreadHandle_start /home/greg/oss/b/../cpython/Modules/_threadmodule.c:405:20 (python+0x61bb6a) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #9 do_start_new_thread /home/greg/oss/b/../cpython/Modules/_threadmodule.c:1882:9 (python+0x61bb6a)\n    #10 thread_PyThread_start_joinable_thread /home/greg/oss/b/../cpython/Modules/_threadmodule.c:2005:14 (python+0x61aacc) (BuildId: f07474199a50b9dfeeb5b474be4e3a4\n079af30a5)\n    #11 cfunction_call /home/greg/oss/b/../cpython/Objects/methodobject.c:540:18 (python+0x2e9488) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #12 _PyObject_MakeTpCall /home/greg/oss/b/../cpython/Objects/call.c:242:18 (python+0x2539d2) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #13 _PyObject_VectorcallTstate /home/greg/oss/b/../cpython/Include/internal/pycore_call.h:165:16 (python+0x2532ed) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af\n30a5)\n    #14 PyObject_Vectorcall /home/greg/oss/b/../cpython/Objects/call.c:327:12 (python+0x2549a0) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #15 _PyEval_EvalFrameDefault /home/greg/oss/b/../cpython/Python/generated_cases.c.h:1831:35 (python+0x45ec3e) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #16 _PyEval_EvalFrame /home/greg/oss/b/../cpython/Include/internal/pycore_ceval.h:119:16 (python+0x453a19) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #17 _PyEval_Vector /home/greg/oss/b/../cpython/Python/ceval.c:1852:12 (python+0x453a19)\n    #18 PyEval_EvalCode /home/greg/oss/b/../cpython/Python/ceval.c:650:21 (python+0x453a19)\n    #19 run_eval_code_obj /home/greg/oss/b/../cpython/Python/pythonrun.c:1323:9 (python+0x55356d) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #20 run_mod /home/greg/oss/b/../cpython/Python/pythonrun.c:1408:19 (python+0x552f7e) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #21 _PyRun_StringFlagsWithName /home/greg/oss/b/../cpython/Python/pythonrun.c:1207:15 (python+0x550012) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #22 _PyRun_SimpleStringFlagsWithName /home/greg/oss/b/../cpython/Python/pythonrun.c:547:15 (python+0x550012)\n    #23 pymain_run_command /home/greg/oss/b/../cpython/Modules/main.c:253:11 (python+0x58f2e4) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #24 pymain_run_python /home/greg/oss/b/../cpython/Modules/main.c:687:21 (python+0x58f2e4)\n    #25 Py_RunMain /home/greg/oss/b/../cpython/Modules/main.c:775:5 (python+0x58f2e4)\n    #26 pymain_main /home/greg/oss/b/../cpython/Modules/main.c:805:12 (python+0x58f8e9) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #27 Py_BytesMain /home/greg/oss/b/../cpython/Modules/main.c:829:12 (python+0x58f969) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #28 main /home/greg/oss/b/../cpython/Programs/python.c:15:12 (python+0x15e810) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n\n  Thread T1 (tid=2184929, running) created by main thread at:\n    #0 pthread_create \u003cnull\u003e (python+0xe01ff) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #1 do_start_joinable_thread /home/greg/oss/b/../cpython/Python/thread_pthread.h:289:14 (python+0x572deb) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #2 PyThread_start_joinable_thread /home/greg/oss/b/../cpython/Python/thread_pthread.h:313:9 (python+0x572c0a) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #3 ThreadHandle_start /home/greg/oss/b/../cpython/Modules/_threadmodule.c:422:9 (python+0x61bc7b) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #4 do_start_new_thread /home/greg/oss/b/../cpython/Modules/_threadmodule.c:1882:9 (python+0x61bc7b)\n    #5 thread_PyThread_start_joinable_thread /home/greg/oss/b/../cpython/Modules/_threadmodule.c:2005:14 (python+0x61aacc) (BuildId: f07474199a50b9dfeeb5b474be4e3a40\n79af30a5)\n    #6 cfunction_call /home/greg/oss/b/../cpython/Objects/methodobject.c:540:18 (python+0x2e9488) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #7 _PyObject_MakeTpCall /home/greg/oss/b/../cpython/Objects/call.c:242:18 (python+0x2539d2) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #8 _PyObject_VectorcallTstate /home/greg/oss/b/../cpython/Include/internal/pycore_call.h:165:16 (python+0x2532ed) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af3\n0a5)\n    #9 PyObject_Vectorcall /home/greg/oss/b/../cpython/Objects/call.c:327:12 (python+0x2549a0) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #10 _PyEval_EvalFrameDefault /home/greg/oss/b/../cpython/Python/generated_cases.c.h:1831:35 (python+0x45ec3e) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #11 _PyEval_EvalFrame /home/greg/oss/b/../cpython/Include/internal/pycore_ceval.h:119:16 (python+0x453a19) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #12 _PyEval_Vector /home/greg/oss/b/../cpython/Python/ceval.c:1852:12 (python+0x453a19)\n    #13 PyEval_EvalCode /home/greg/oss/b/../cpython/Python/ceval.c:650:21 (python+0x453a19)\n    #14 run_eval_code_obj /home/greg/oss/b/../cpython/Python/pythonrun.c:1323:9 (python+0x55356d) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #15 run_mod /home/greg/oss/b/../cpython/Python/pythonrun.c:1408:19 (python+0x552f7e) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #16 _PyRun_StringFlagsWithName /home/greg/oss/b/../cpython/Python/pythonrun.c:1207:15 (python+0x550012) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #17 _PyRun_SimpleStringFlagsWithName /home/greg/oss/b/../cpython/Python/pythonrun.c:547:15 (python+0x550012)\n    #18 pymain_run_command /home/greg/oss/b/../cpython/Modules/main.c:253:11 (python+0x58f2e4) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #19 pymain_run_python /home/greg/oss/b/../cpython/Modules/main.c:687:21 (python+0x58f2e4)\n    #20 Py_RunMain /home/greg/oss/b/../cpython/Modules/main.c:775:5 (python+0x58f2e4)\n    #21 pymain_main /home/greg/oss/b/../cpython/Modules/main.c:805:12 (python+0x58f8e9) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #22 Py_BytesMain /home/greg/oss/b/../cpython/Modules/main.c:829:12 (python+0x58f969) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n    #23 main /home/greg/oss/b/../cpython/Programs/python.c:15:12 (python+0x15e810) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5)\n\nSUMMARY: ThreadSanitizer: data race (/home/greg/oss/b/python+0xdc23d) (BuildId: f07474199a50b9dfeeb5b474be4e3a4079af30a5) in __tsan_memset\n==================\nThreadSanitizer: reported 1 warnings\n```\n\nExamining the code in question where the race occurs... it's this block https://github.com/python/cpython/blob/v3.13.0rc3/Python/ceval_gil.c#L258\n\n```c\n#ifdef FORCE_SWITCHING\n    /* We might be releasing the GIL for the last time in this thread.  In that\n       case there's a possible race with tstate-\u003einterp getting deleted after\n       gil-\u003emutex is unlocked and before the following code runs, leading to a\n       crash.  We can use final_release to indicate the thread is done with the\n       GIL, and that's the only time we might delete the interpreter.  See\n       https://github.com/python/cpython/issues/104341. */\n    if (!final_release \u0026\u0026\n        _Py_eval_breaker_bit_is_set(tstate, _PY_GIL_DROP_REQUEST_BIT))\n```\n\nlooping in @ericsnowcurrently for #104341 context.\n\nThe `int final_release` value in that call stack is 0 so the next bit tries to load the eval breaker bit but the thread was woken up by python code executing **during finalization of the main thread** per the test.\n\nHow'd thread T1 ever obtain the GIL upon waking up in the first place given finalization had started?\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nLinux\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-130602\n* gh-130649\n* gh-130687\n* gh-135793\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/gpshead","@type":"Person","name":"gpshead"},"datePublished":"2024-10-02T04:12:19.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/124878/cpython/issues/124878"}