STINNER Victor added the comment: Hum, maybe I found the root issue: the C signal handler calls Py_AddPendingCall() which uses a lock to protect a global static pendingcalls array (of 32 items). The function tries 100 times in a row to acquire to lock, or does nothing (returns -1) if it fails to acquire the lock.
If we start to allow signals from any thread, this shared pendingcalls array can quickly become a source of race conditions like deadlocks or ignored callbacks. To avoid deadlocks, IMHO the best is to have a per-thread array which consumes 512 bytes (on 64-bit, 32 items made of 2 pointers). -- The _thread module has a strange _thread.interrupt_main() function. -- >From the point of view of the Python signal handler, the current "if >(PyThread_get_thread_ident() != main_thread) return 0;" code in the C signal >handler is somehow an implicit pthread_sigmask(signal.SIG_BLOCK, range(1, >signal.NSIG)) on all threads except of the main thread, whereas Unix gives a >fine control on these masks with the pthread_sigmask() function. -- The Windows part is more tricky. A Windows Event object (created by CreateEvent() and retrieved by _PyOS_SigintEvent()) is used to interrupt a few blocking functions: * my_fgets() used by PyOS_StdioReadline() to implemented "readline" (especially for the REPL) * _PyOS_WindowsConsoleReadline() * read_console_w() of Modules/_io/winconsole.c * time.sleep() -- only if it's the main thread and delay != 0 seconds * _multiprocessing.SemLock.acquire() -- only if called from the main thread * _winapi.WaitForMultipleObjects() The event is set by the SIGINT signal handler set by Python. Extract of pysleep() comment: /* Allow sleep(0) to maintain win32 semantics, and as decreed * by Guido, only the main thread can be interrupted. */ ---------- nosy: +pitrou _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue21895> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
