[FIXED] Python multiprocessing module: join processes with timeout

Issue

I'm doing an optimization of parameters of a complex simulation. I'm using the multiprocessing module for enhancing the performance of the optimization algorithm. The basics of multiprocessing I learned at http://pymotw.com/2/multiprocessing/basics.html. The complex simulation lasts different times depending on the given parameters from the optimization algorithm, around 1 to 5 minutes. If the parameters are chosen very badly, the simulation can last 30 minutes or more and the results are not useful. So I was thinking about build in a timeout to the multiprocessing, that terminates all simulations that last more than a defined time. Here is an abstracted version of the problem:

import numpy as np
import time
import multiprocessing

def worker(num):
    
    time.sleep(np.random.random()*20)

def main():
    
    pnum = 10    
    
    procs = []
    for i in range(pnum):
        p = multiprocessing.Process(target=worker, args=(i,), name = ('process_' + str(i+1)))
        procs.append(p)
        p.start()
        print('starting', p.name)
        
    for p in procs:
        p.join(5)
        print('stopping', p.name)
     
if __name__ == "__main__":
    main()

The line p.join(5) defines the timeout of 5 seconds. Because of the for-loop for p in procs: the program waits 5 seconds until the first process is finished and then again 5 seconds until the second process is finished and so on, but i want the program to terminate all processes that last more than 5 seconds. Additionally, if none of the processes last longer than 5 seconds the program must not wait this 5 seconds.

Solution

You can do this by creating a loop that will wait for some timeout amount of seconds, frequently checking to see if all processes are finished. If they don't all finish in the allotted amount of time, then terminate all of the processes:

TIMEOUT = 5 
start = time.time()
while time.time() - start <= TIMEOUT:
    if not any(p.is_alive() for p in procs):
        # All the processes are done, break now.
        break

    time.sleep(.1)  # Just to avoid hogging the CPU
else:
    # We only enter this if we didn't 'break' above.
    print("timed out, killing all processes")
    for p in procs:
        p.terminate()
        p.join()

Answered By - dano