While trying to make sense of some static analysis warnings for the Windows console IO module, I Ctrl+C'd in the middle of an intentionally absurd __repr__ output, and on proceeding in the debugger (which treated it as an exception), I immediately hit the assertion right here: /* Get the Python thread state using PyGILState API, since _PyThreadState_GET() returns NULL if the GIL is released. For example, signal.raise_signal() releases the GIL. */ PyThreadState *tstate = PyGILState_GetThisThreadState(); assert(tstate != NULL); ...With the stacktrace:	ucrtbased.dll!issue_debug_notification(const wchar_t * const message) Line 28	C++	ucrtbased.dll!__acrt_report_runtime_error(const wchar_t * message) Line 154	C++	ucrtbased.dll!abort() Line 51	C++	ucrtbased.dll!common_assert_to_stderr_direct(const wchar_t * const expression, const wchar_t * const file_name, const unsigned int line_number) Line 161	C++	ucrtbased.dll!common_assert_to_stderr<wchar_t>(const wchar_t * const expression, const wchar_t * const file_name, const unsigned int line_number) Line 175	C++	ucrtbased.dll!common_assert<wchar_t>(const wchar_t * const expression, const wchar_t * const file_name, const unsigned int line_number, void * const return_address) Line 420	C++	ucrtbased.dll!_wassert(const wchar_t * expression, const wchar_t * file_name, unsigned int line_number) Line 443	C++ >	python39_d.dll!trip_signal(int sig_num) Line 266	C	python39_d.dll!signal_handler(int sig_num) Line 342	C	ucrtbased.dll!ctrlevent_capture(const unsigned long ctrl_type) Line 206	C++	KernelBase.dll!_CtrlRoutine@4()	Unknown	kernel32.dll!@BaseThreadInitThunk@12()	Unknown	ntdll.dll!__RtlUserThreadStart()	Unknown	ntdll.dll!__RtlUserThreadStart@8()	Unknown ...I'm not entirely sure why this happened, but I can tell a few things. _PyRuntime.gilstate.autoInterpreterState is NOT null, in fact the gilstate object is as displayed in my watch window: -	_PyRuntime.gilstate	{check_enabled=1 tstate_current={_value=0 } getframe=0x79e3a570 {python39_d.dll!threadstate_getframe(_ts *)} ...}	_gilstate_runtime_state	check_enabled	1	int +	tstate_current	{_value=0 }	_Py_atomic_address	getframe	0x79e3a570 {python39_d.dll!threadstate_getframe(_ts *)}	_frame *(*)(_ts *) -	autoInterpreterState	0x00e5eff8 {next=0x00000000 <NULL> tstate_head=0x00e601c0 {prev=0x00000000 <NULL> next=0x00000000 <NULL> ...} ...}	_is * +	next	0x00000000 <NULL>	_is * +	tstate_head	0x00e601c0 {prev=0x00000000 <NULL> next=0x00000000 <NULL> interp=0x00e5eff8 {next=0x00000000 <NULL> ...} ...}	_ts * +	runtime	0x7a0e2118 {python39_d.dll!pyruntimestate _PyRuntime} {preinitializing=0 preinitialized=1 core_initialized=...}	pyruntimestate *	id	0	__int64	id_refcount	-1	__int64	requires_idref	0	int	id_mutex	0x00000000	void *	finalizing	0	int +	ceval	{tracing_possible=0 eval_breaker={_value=0 } pending={finishing=0 lock=0x00e59390 calls_to_do={_value=...} ...} }	_ceval_state +	gc	{trash_delete_later=0x00000000 <NULL> trash_delete_nesting=0 enabled=1 ...}	_gc_runtime_state +	modules	0x00bf1228 {ob_refcnt=3 ob_type=0x7a0b1178 {python39_d.dll!_typeobject PyDict_Type} {ob_base={ob_base=...} ...} }	_object * +	modules_by_index	0x00750058 {ob_refcnt=1 ob_type=0x7a0b8210 {python39_d.dll!_typeobject PyList_Type} {ob_base={ob_base=...} ...} }	_object * +	sysdict	0x00bf1298 {ob_refcnt=2 ob_type=0x7a0b1178 {python39_d.dll!_typeobject PyDict_Type} {ob_base={ob_base=...} ...} }	_object * +	builtins	0x00bf1f48 {ob_refcnt=88 ob_type=0x7a0b1178 {python39_d.dll!_typeobject PyDict_Type} {ob_base={ob_base=...} ...} }	_object * +	importlib	0x00c0df60 {ob_refcnt=28 ob_type=0x7a0b92d0 {python39_d.dll!_typeobject PyModule_Type} {ob_base={ob_base=...} ...} }	_object *	num_threads	0	long	pythread_stacksize	0	unsigned int +	codec_search_path	0x00c4a260 {ob_refcnt=1 ob_type=0x7a0b8210 {python39_d.dll!_typeobject PyList_Type} {ob_base={ob_base=...} ...} }	_object * +	codec_search_cache	0x00c1f0d8 {ob_refcnt=1 ob_type=0x7a0b1178 {python39_d.dll!_typeobject PyDict_Type} {ob_base={ob_base=...} ...} }	_object * +	codec_error_registry	0x00c14f10 {ob_refcnt=1 ob_type=0x7a0b1178 {python39_d.dll!_typeobject PyDict_Type} {ob_base={ob_base=...} ...} }	_object *	codecs_initialized	1	int +	fs_codec	{encoding=0x00e5aa40 "utf-8" utf8=1 errors=0x00e89ea8 "surrogatepass" ...}	<unnamed-tag> +	config	{_config_init=2 isolated=0 use_environment=1 ...}	PyConfig +	dict	0x00000000 <NULL>	_object * +	builtins_copy	0x00c00a08 {ob_refcnt=1 ob_type=0x7a0b1178 {python39_d.dll!_typeobject PyDict_Type} {ob_base={ob_base=...} ...} }	_object * +	import_func	0x00bfd900 {ob_refcnt=4 ob_type=0x7a0b90d0 {python39_d.dll!_typeobject PyCFunction_Type} {ob_base={ob_base=...} ...} }	_object *	eval_frame	0x79a52577 {python39_d.dll!__PyEval_EvalFrameDefault}	_object *(*)(_ts *, _frame *, int)	co_extra_user_count	0	int +	co_extra_freefuncs	0x00e5f308 {0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, ...}	void(*)(void *)[255]	pyexitfunc	0x79af7320 {python39_d.dll!atexit_callfuncs(_object *)}	void(*)(_object *) +	pyexitmodule	0x00f5d690 {ob_refcnt=16 ob_type=0x7a0b92d0 {python39_d.dll!_typeobject PyModule_Type} {ob_base={ob_base=...} ...} }	_object *	tstate_next_unique_id	1	unsigned __int64 +	warnings	{filters=0x0078edc8 {ob_refcnt=3 ob_type=0x7a0b8210 {python39_d.dll!_typeobject PyList_Type} {ob_base=...} } ...}	_warnings_runtime_state +	audit_hooks	0x00000000 <NULL>	_object * +	parser	{listnode={level=0 atbol=0 } }	<unnamed-tag> +	small_ints	0x00e5f734 {0x00755868 {ob_base={ob_base={ob_refcnt=2 ob_type=0x7a0b8738 {python39_d.dll!_typeobject PyLong_Type} {...} } ...} ...}, ...}	_longobject *[262] +	autoTSSkey	{_is_initialized=1 _key=5 }	_Py_tss_t This looks to me like there's some kind of race condition in the thread local storage. Later, when TlsGetValue is called in PyThread_tss_get with the value of 5, the error code is lost, so I don't even know the exact reported error, and apparently 0 (nullptr) is a valid return anyways *shrug*. If I'm correctly decoding the address of the TLS slot in the TEB (I think *(unsigned int*)(void*)((@fs+0xe10)+ (20)) is the correct address for the 5th item? 4 bytes, key=5?), then there is actually a null tstate there. Not sure why. This is in a relatively recent (<1wk old) branch of the code, with some non-behavioral tweaks to add annotations in while I'm bug hunting, so it shouldn't matter. I'm not sure if I can reproduce this, but it happened, so there's a bug somewhere. What else? The signal number that tripped this was 2, sig interrupt, which makes sense. There are other threads active, so maybe that's why? The TLS was never initialized for that thread? Here's the dump from the visual studio threads window, 22316 is the active thread. Not Flagged	10360	0	Main Thread	Main Thread	python39_d.dll!_PyOS_WindowsConsoleReadline	ntdll.dll!_NtDeviceIoControlFile@40()	KernelBase.dll!ConsoleCallServerGeneric()	KernelBase.dll!_ReadConsoleInternal@24()	KernelBase.dll!_ReadConsoleW@20()	python39_d.dll!_PyOS_WindowsConsoleReadline(void * hStdIn) Line 120	python39_d.dll!PyOS_StdioReadline(_iobuf * sys_stdin, _iobuf * sys_stdout, const char * prompt) Line 253	python39_d.dll!PyOS_Readline(_iobuf * sys_stdin, _iobuf * sys_stdout, const char * prompt) Line 358	python39_d.dll!tok_nextc(tok_state * tok) Line 856	python39_d.dll!tok_get(tok_state * tok, const char * * p_start, const char * * p_end) Line 1166	python39_d.dll!PyTokenizer_Get(tok_state * tok, const char * * p_start, const char * * p_end) Line 1813	python39_d.dll!parsetok(tok_state * tok, grammar * g, int start, perrdetail * err_ret, int * flags) Line 253	python39_d.dll!PyParser_ParseFileObject(_iobuf * fp, _object * filename, const char * enc, grammar * g, int start, const char * ps1, const char * ps2, perrdetail * err_ret, int * flags) Line 188	python39_d.dll!PyParser_ASTFromFileObject(_iobuf * fp, _object * filename, const char * enc, int start, const char * ps1, const char * ps2, PyCompilerFlags * flags, int * errcode, _arena * arena) Line 1388	python39_d.dll!PyRun_InteractiveOneObjectEx(_iobuf * fp, _object * filename, PyCompilerFlags * flags) Line 240	python39_d.dll!PyRun_InteractiveLoopFlags(_iobuf * fp, const char * filename_str, PyCompilerFlags * flags) Line 122	python39_d.dll!PyRun_AnyFileExFlags(_iobuf * fp, const char * filename, int closeit, PyCompilerFlags * flags) Line 81	python39_d.dll!pymain_run_stdin(PyConfig * config, PyCompilerFlags * cf) Line 467	python39_d.dll!pymain_run_python(int * exitcode) Line 556	python39_d.dll!Py_RunMain() Line 632	python39_d.dll!pymain_main(_PyArgv * args) Line 663	python39_d.dll!Py_Main(int argc, wchar_t * * argv) Line 674	python_d.exe!wmain(int argc, wchar_t * * argv) Line 10	python_d.exe!invoke_main() Line 90	python_d.exe!__scrt_common_main_seh() Line 288	python_d.exe!__scrt_common_main() Line 331	python_d.exe!wmainCRTStartup() Line 17	kernel32.dll!@BaseThreadInitThunk@12()	ntdll.dll!__RtlUserThreadStart()	ntdll.dll!__RtlUserThreadStart@8() Not Flagged	14944	0	Worker Thread	ntdll.dll!_TppWorkerThread@4()	ntdll.dll!_NtWaitForWorkViaWorkerFactory@20	ntdll.dll!_NtWaitForWorkViaWorkerFactory@20()	ntdll.dll!_TppWorkerThread@4()	kernel32.dll!@BaseThreadInitThunk@12()	ntdll.dll!__RtlUserThreadStart()	ntdll.dll!__RtlUserThreadStart@8() Not Flagged	>	22316	0	Worker Thread	KernelBase.dll!_CtrlRoutine@4()	ucrtbased.dll!issue_debug_notification	ucrtbased.dll!issue_debug_notification(const wchar_t * const message) Line 28	ucrtbased.dll!__acrt_report_runtime_error(const wchar_t * message) Line 154	ucrtbased.dll!abort() Line 51	ucrtbased.dll!common_assert_to_stderr_direct(const wchar_t * const expression, const wchar_t * const file_name, const unsigned int line_number) Line 161	ucrtbased.dll!common_assert_to_stderr<wchar_t>(const wchar_t * const expression, const wchar_t * const file_name, const unsigned int line_number) Line 175	ucrtbased.dll!common_assert<wchar_t>(const wchar_t * const expression, const wchar_t * const file_name, const unsigned int line_number, void * const return_address) Line 420	ucrtbased.dll!_wassert(const wchar_t * expression, const wchar_t * file_name, unsigned int line_number) Line 443	python39_d.dll!trip_signal(int sig_num) Line 266	python39_d.dll!signal_handler(int sig_num) Line 342	ucrtbased.dll!ctrlevent_capture(const unsigned long ctrl_type) Line 206	KernelBase.dll!_CtrlRoutine@4()	kernel32.dll!@BaseThreadInitThunk@12()	ntdll.dll!__RtlUserThreadStart()	ntdll.dll!__RtlUserThreadStart@8() Not Flagged	10180	0	Worker Thread	ntdll.dll!_TppWorkerThread@4()	ntdll.dll!_NtWaitForWorkViaWorkerFactory@20	ntdll.dll!_NtWaitForWorkViaWorkerFactory@20()	ntdll.dll!_TppWorkerThread@4()	kernel32.dll!@BaseThreadInitThunk@12()	ntdll.dll!__RtlUserThreadStart()	ntdll.dll!__RtlUserThreadStart@8() Not Flagged	28940	0	Worker Thread	ntdll.dll!_TppWorkerThread@4()	ntdll.dll!_NtWaitForWorkViaWorkerFactory@20	ntdll.dll!_NtWaitForWorkViaWorkerFactory@20()	ntdll.dll!_TppWorkerThread@4()	kernel32.dll!@BaseThreadInitThunk@12()	ntdll.dll!__RtlUserThreadStart()	ntdll.dll!__RtlUserThreadStart@8() Not Flagged	9396	0	Worker Thread	ntdll.dll!_TppWorkerThread@4()	ntdll.dll!_NtWaitForWorkViaWorkerFactory@20	ntdll.dll!_NtWaitForWorkViaWorkerFactory@20()	ntdll.dll!_TppWorkerThread@4()	kernel32.dll!@BaseThreadInitThunk@12()	ntdll.dll!__RtlUserThreadStart()	ntdll.dll!__RtlUserThreadStart@8() Not Flagged	28960	0	Worker Thread	ntdll.dll!_TppWorkerThread@4()	ntdll.dll!_NtWaitForWorkViaWorkerFactory@20	ntdll.dll!_NtWaitForWorkViaWorkerFactory@20()	ntdll.dll!_TppWorkerThread@4()	kernel32.dll!@BaseThreadInitThunk@12()	ntdll.dll!__RtlUserThreadStart()	ntdll.dll!__RtlUserThreadStart@8() Anyways, I hope that's a useful report for an obscure bug.

Lmao the name mangling comes up as a mailto. That's interesting.

Hmmm, happens every time I interrupt while attached. Is there some obvious gotcha in the docs that I'm missing?

On Windows, PyGILState_GetThisThreadState() returns NULL when ^C-interrupt occurs. It is from TlsGetValue() winAPI and I don't think the os's behevior is wrong. In trip_signal(), crash can be avoided by skipping PyEval_SignalReceived() if tstate is invalid. But I'm not sure the skip itself is ok.

Oh oh. This issue is quite annoying for my work on subinterpreters. I introduced this bug when I moved pending calls from _PyRuntimeState to PyInterpreterState in bpo-39984. _PyEval_AddPendingCall() now requires tstate to add a function to pending calls of the proper interpreter. The problem on Windows is that each CTRL+c is executed in a different thread. Here is a modified Python 3.8 which dumps the thread identifier ("tid") at startup and when trip_signal() is triggered by CTRL+C: vstinner@WIN C:\vstinner\python\3.8>python Running Release|x64 interpreter... pymain_main: tid=1788 Python 3.8.1+ (heads/3.8-dirty:19be85c765, Apr 8 2020, 19:35:20) [MSC v.1916 64 bit (AMD64)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> ^C trip_signal: tid=6996 tstate=0000000000000000 KeyboardInterrupt >>> ^C trip_signal: tid=2384 tstate=0000000000000000 KeyboardInterrupt >>> ^C trip_signal: tid=32 tstate=0000000000000000 KeyboardInterrupt When trip_signal() is called, PyGILState_GetThisThreadState() returns NULL.

 New changeset b54a99d6432de93de85be2b42a63774f8b4581a0 by Victor Stinner in branch 'master': bpo-40082: trip_signal() uses the main interpreter (GH-19441) https://github.com/python/cpython/commit/b54a99d6432de93de85be2b42a63774f8b4581a0 

Thanks for the bug report Alexander Riccio. I fixed bug in master. Python 3.8 is not affected.