Why does using threading.Event result in SIGTERM not being caught?

From Python documentation on signals:

Although Python signal handlers are called asynchronously as far as the Python user is concerned, they can only occur between the “atomic” instructions of the Python interpreter. This means that signals arriving during long calculations implemented purely in C (such as regular expression matches on large bodies of text) may be delayed for an arbitrary amount of time.

I tested various threading and thread classes and none of them work the way you want it -- this is probably because of how Python handles signals.

In signal, however, there is a pause() function that sleeps until a signal is received by the process. Your modified example would look like this:

import signalRUN = Truedef handle(a, b):    global RUN    print "handled"    RUN = Falsesignal.signal(signal.SIGTERM, handle)signal.signal(signal.SIGINT, handle)signal.signal(signal.SIGHUP, handle)while RUN:    signal.pause()print "Stopping"

I checked it on Linux, it works. I don't think it classifies as poll-and-sleep anymore if your application doesn't use a lot of other signals.

It's good to handle SIGINT and SIGHUP too, to properly handle user interruption (usually by pressing Ctrl+C) and user disconnection (closing the parent terminal) respectively.

Also, note that signal.pause() is not available on Windows systems.

In Python 3, this works:

from threading import Eventfrom os import getpidfrom signal import SIGTERM, SIGINT, SIGHUP, signalstop_event = Event()def handler(signum, frame):    stop_event.set()def main():    signal(SIGTERM, handler)    signal(SIGINT, handler)    signal(SIGHUP, handler)    print('start, pid:', getpid())    stop_event.wait()    print('done')if __name__ == '__main__':    main()

It looks that in Python 2.7 it works only if you specify wait interval: stop_event.wait(number_of_seconds)