python - threading.Condition.wait(timeout) ignores threading.Condition.notify() -

i have application uses 2 threads. want able shut down both threads waiting condition variable exitcondition. using python 3.3 unlike python 2.7 makes threading.condition.wait() return true when condition notified , false when timeout occured.

#!/usr/bin/python import threading time import sleep  exitcondition = threading.condition()  def inputactivity():     while true:         exitcondition.acquire()         exitconditionreached = exitcondition.wait(.1) #<-critical         print(exitconditionreached)         exitcondition.release()         if exitconditionreached: #exitcondition reached -> shutdown             return         else: #exitcondition not reached -> work             sleep(.1)  inthread = threading.thread(target = inputactivity) inthread.start()  sleep(.2) #<-critical  exitcondition.acquire() exitcondition.notify() print("exitcondition notified") exitcondition.release()  inthread.join() 

there 2 lines #<-critical comment in line 10 , 21. if sleeps "misaligned" (for example .25 , .1) program terminate. if sleeps "aligned" (for example .2 , .1) inthread run indefinitely printing false forever. looks race condition me, apparently if notify called @ same time wait notification not recognized. under impression exitcondition.acquire() , exitcondition.release() supposed prevent that. question why condition variable not thread safe , can it. ideally want write wait(0) guarantee no notification swallowed.

if call exitcondition.notify occurs when worker thread doing work (i.e., in sleep(.1) call (or anywhere else other .wait call), behaviour describe sounds i'd expect. wait call returns true if notification happened during wait.

it sounds me though use-case threading.event instead of threading.condition: replace threading.condition threading.event, replace notify call set call, , remove acquire , release calls altogether (in both threads).

that is, code should this:

#!/usr/bin/python import threading time import sleep  exitcondition = threading.event()  def inputactivity():     while true:         exitconditionreached = exitcondition.wait(.1) #<-critical         print(exitconditionreached)         if exitconditionreached: #exitcondition reached -> shutdown             return         else: #exitcondition not reached -> work             sleep(.1)  inthread = threading.thread(target = inputactivity) inthread.start()  sleep(.2) #<-critical  exitcondition.set() print("exitcondition set")  inthread.join() 

once you've got far, don't need first .wait: can replace direct is_set call see if exit condition has been set yet:

#!/usr/bin/python import threading time import sleep  exitcondition = threading.event()  def inputactivity():     while true:         if exitcondition.is_set(): #exitcondition reached -> shutdown             return         else: #exitcondition not reached -> work             sleep(.1)  inthread = threading.thread(target = inputactivity) inthread.start()  sleep(.2) #<-critical  exitcondition.set() print("exitcondition set")  inthread.join()