New submission from Bohuslav "Slavek" Kabrda: Reproducer attached. To describe the problem in words, one needs to do this to reproduce this issue: - Create a signal handler and register it using signal.signal to SIGCHLD. - Create a thread that invokes a subprocess, e.g. "sleep 1" and then continues to do something for time period longer than the subprocess is running. - Run this thread from main thread and call signal.pause() in the main thread. - The pause() call is never interrupted and the signal handler is never run.
This happens because: - Python adds signal_handler as a handler to the specified signal and stores the passed Python function in structure Handlers. - When signal.pause() is run, the main thread releases the GIL, so that other threads can run. - The non-main thread gets to lease and actually invokes the subprocess and then continues to do something. - When subprocess finishes, it sends the signal *to the thread that invoked it* (assuming this thread is still running). This means that the signal.pause() call is not interrupted and main thread continues to sleep. - The non-main thread adds handler call to the list of pending calls using Py_AddPendingCall. - Pending calls are checked in Py_MakePendingCalls, which is called in every iteration of the bytecode evaluation loop in PyEval_EvalFrameEx. - The problem is that since pause() isn't un-paused and hangs forever, the evaluation loop never gets to another iteration, hence can't do any pending call. This happens on all Python versions I've tried, using pthread threading. I think this could *possibly* be solved by issuing a pthread_kill from the non-main thread to the main thread to wake it up, but I'm not sure what all the implications of such a change would be. ---------- components: Interpreter Core files: signal_pause_doesnt_wake_up.py messages: 222021 nosy: bkabrda priority: normal severity: normal status: open title: signal.pause() doesn't wake up on SIGCHLD in non-main thread versions: Python 2.7, Python 3.4, Python 3.5 Added file: http://bugs.python.org/file35815/signal_pause_doesnt_wake_up.py _______________________________________ 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
