STINNER Victor <vstin...@python.org> added the comment:
When I reproduce test_cancel_make_subprocess_transport_exec() hang, the problem is that the C signal handler is called with SIGCHLD when the child process completes, but the Python signal handler is not called. Python is "blocked" in a selector (maybe select.select(), it doesn't matter). I guess that the selector is interrupted by a signal (even if asyncio calls signal.setinterrupt(SIGCHLD, False)), but since the signal handler doesn't raise an exception, the syscall is restarted: see the PEP 475. I understood that the asyncio event loop only gets the opportunity to call the Python signal handler if there is a pending asyncio event (call_soon, call_timer, event on a tracked FD, whatever). If the signal arrives when the event loop is idle, the Python signal handler will never be called since the selector is called with timeout=0 (blocking mode). MultiLoopChildWatcher must ensures that the event loop is awaken when it receives a signal by using signal.setwakeup(). This is done by _UnixSelectorEventLoop.add_signal_handler(). Maybe MultiLoopChildWatcher could reuse this function, rather than calling directly signal.signal(). ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue38323> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
