How to know if threading.Condition.wait(timeout) has timed out or has been notified?

Question

I'm developing an application with some threads, each one running an infinite loop with a time sleep. What I want is to finish all threads once the main one has finished, here an example:

def main():

    display_res_stop = threading.Condition()
    display_result_t = threading.Thread(target=sample_t, args=(display_res_stop, ))
    display_result_t.start()

    time.sleep(4)

    display_res_stop.acquire()
    display_res_stop.notify()
    display_res_stop.release()


def sample_t(stop_cond):
    stop_cond.acquire()

    while True:
        print 5
        c = stop_cond.wait(10)

    stop_cond.release()

if __name__ == '__main__':
    main()

The problem with this solution is that I don't know if condition.wait has finished because the timeout or because has been notified. In the second case while loop should finish.

At first I was doing a time.sleep(t) and using threading events but then the application has to wait until t on all threads has passed.

I'm thinking about a mixed solution using threading.Condition and Event but I don't know if it's the nicest thing to do (Condition for the 'sleep' and Event to replace while True).

Answer 1

After all it was very simple, I was just focusing on the wrong thing: I just needed a sleep that could be stopped with an event and thats what Event.wait(t) does. The problem then, can be solved just with Events.

import threading
import time

def sample_thread(stop_ev):
    while not stop_ev.is_set():
        print 'Thread iteration'
        stop_ev.wait(0.1)

def main():
    stop_ev = threading.Event()
    sample_t = threading.Thread(target=sample_thread, args=(stop_ev, ))
    sample_t.start()

    # Other stuff here, sleep is just dummy
    time.sleep(14)

    stop_ev.set()

    print 'End reached.'

if __name__ == '__main__':
    main()

Answer 2

The easy way to do this is to use Python 3.2 or later, or get the backport of the current threading to 3.1/2.7/etc. from PyPI, or just copy the code for that method from, say, 3.4's source.

As the docs for Condition.wait explain:

The return value is True unless a given timeout expired, in which case it is False.

Changed in version 3.2: Previously, the method always returned None.

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As a side note, I'm not sure you need a Condition here at all; you're not checking a flag inside the loop, or doing anything else that should be susceptible to a race condition, you're just waiting to be notified. That implies that, as long as you don't need magic auto-reset, an Event should be just fine. And Event.wait has had the True/False return since 2.7/3.1+, rather than 3.2+.