Shutting worker threads down gracefully after signal, portably

Duncan Findlay duncan at
Mon Jan 9 23:43:43 EST 2012

Suppose I've got a Python daemon that spawns a bunch of worker threads, waits for a singal (e.g. SIGTERM) and then shuts down the worker threads gracefully. What's the simplest way to do the signal handling portably across as many operating systems as possible (at least Linux and FreeBSD). Specifically, I'm interested in solutions where the main thread consumes no CPU, so no time.sleep(n) loops.

The most obvious solution (below) does not work with on FreeBSD, because the signal gets delivered to a different thread and signal.pause() doesn't return.

_shutdown = False

def sig_handler(signum, frame):
    print 'handled'
    global _shutdown
    _shutdown = True

if __name__ == '__main__':

    # Set up signal handling.
    signal.signal(signal.SIGTERM, sig_handler)

    # Start worker threads.
    workers = [Worker() for i in xrange(NUM_THREADS)]
    for worker in workers:

    # Sleep until woken by a signal.
    while not _shutdown:

    # Shutdown work threads gracefully.
    for worker in workers:

Any ideas? I've attached a more complete code sample.

Duncan Findlay

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