Catch Ctrl+C / SIGINT and exit multiprocesses gracefully in python [duplicate]

Question

How do I catch a Ctrl+C in multiprocess python program and exit all processes gracefully, I need the solution to work both on unix and windows. I've tried the following:

import multiprocessing import time import signal import sys  jobs = []  def worker():     signal.signal(signal.SIGINT, signal_handler)     while(True):         time.sleep(1.1234)         print "Working..."  def signal_handler(signal, frame):     print 'You pressed Ctrl+C!'     # for p in jobs:     #     p.terminate()     sys.exit(0)  if __name__ == "__main__":     for i in range(50):         p = multiprocessing.Process(target=worker)         jobs.append(p)         p.start() 

And it's kind of working, but I don't think it's the right solution.

Answer 1

The previously accepted solution has race conditions and it does not work with map and async functions.

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The correct way to handle Ctrl+C/SIGINT with multiprocessing.Pool is to:

1. Make the process ignore SIGINT before a process Pool is created. This way created child processes inherit SIGINT handler.
2. Restore the original SIGINT handler in the parent process after a Pool has been created.
3. Use map_async and apply_async instead of blocking map and apply.
4. Wait on the results with timeout because the default blocking waits to ignore all signals. This is Python bug https://bugs.python.org/issue8296.

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Putting it together:

#!/bin/env python from __future__ import print_function  import multiprocessing import os import signal import time  def run_worker(delay):     print("In a worker process", os.getpid())     time.sleep(delay)  def main():     print("Initializng 2 workers")     original_sigint_handler = signal.signal(signal.SIGINT, signal.SIG_IGN)     pool = multiprocessing.Pool(2)     signal.signal(signal.SIGINT, original_sigint_handler)     try:         print("Starting 2 jobs of 5 seconds each")         res = pool.map_async(run_worker, [5, 5])         print("Waiting for results")         res.get(60) # Without the timeout this blocking call ignores all signals.     except KeyboardInterrupt:         print("Caught KeyboardInterrupt, terminating workers")         pool.terminate()     else:         print("Normal termination")         pool.close()     pool.join()  if __name__ == "__main__":     main() 

As @YakovShklarov noted, there is a window of time between ignoring the signal and unignoring it in the parent process, during which the signal can be lost. Using pthread_sigmask instead to temporarily block the delivery of the signal in the parent process would prevent the signal from being lost, however, it is not available in Python-2.