How can I catch SIGINT in threading python program?

Question

When using threading module and Thread() class, SIGINT (Ctrl+C in console) could not be catched.

Why and what can I do?

Simple test program:

#!/usr/bin/env python

import threading

def test(suffix):
    while True:
        print "test", suffix

def main():
    for i in (1, 2, 3, 4, 5):
        threading.Thread(target=test, args=(i, )).start()

if __name__ == "__main__":
    main()

Try hitting Ctrl-C - nothing happens.

Answer 1

Threads and signals don't mix. In Python this is even more so the case than outside: signals only ever get delivered to one thread (the main thread); other threads won't get the message. There's nothing you can do to interrupt threads other than the main thread. They're out of your control.

The only thing you can do here is introduce a communication channel between the main thread and whatever threads you start, using the queue module. You can then send a message to the thread and have it terminate (or do whatever else you want) when it sees the message.

Alternatively, and it's often a very good alternative, is to not use threads. What to use instead depends greatly on what you're trying to achieve, however.