multithreading - Python how to kill threads blocked on queue with signals?

Question

I start a bunch of threads working on a queue and I want to kill them when sending the SIGINT (Ctrl+C). What is the best way to handle this?

targets = Queue.Queue()
threads_num = 10
threads = []

for i in threads_num:
    t = MyThread()
    t.setDaemon(True)
    threads.append(t)
    t.start()

targets.join()

Answer 1

If you are not interested in letting the other threads shut down gracefully, simply start them in daemon mode and wrap the join of the queue in a terminator thread.

That way, you can make use of the join method of the thread -- which supports a timeout and does not block off exceptions -- instead of having to wait on the queue's join method.

In other words, do something like this:

term = Thread(target=someQueueVar.join)
term.daemon = True
term.start()
while (term.isAlive()):
    term.join(3600)

Now, Ctrl+C will terminate the MainThread whereupon the Python Interpreter hard-kills all threads marked as "daemons". Do note that this means that you have to set "Thread.daemon" for all the other threads or shut them down gracefully by catching the correct exception (KeyboardInterrupt or SystemExit) and doing whatever needs to be done for them to quit.

Do also note that you absolutely need to pass a number to term.join(), as otherwise it will, too, ignore all exceptions. You can select an arbitrarily high number, though.