Question

I create 100 child processes

proc_list = [
    Process(target = simulator, args=(result_queue,))
    for i in xrange(100)]

and start them

for proc in proc_list: proc.start()

Each process puts into the result_queue (instance of multiprocessing.Queue) 10000 tuples after doing some processing.

def simulate(alg_instance, image_ids, gamma, results,
                     simulations, sim_semaphore):
  (rs, qs, t_us) =  alg_instance.simulate_multiple(image_ids, gamma,
                                             simulations)
  all_tuples = zip(rs, qs, t_us)
  for result in all_tuples:
    results.put(result)
  sim_semaphore.release()

I should be (?) getting 1000000 tuples at the queue, but after various runs I get these (sample) sizes:
14912
19563
12952
13524
7487
18350
15986
11928
14281
14282
7317

Any suggestions?

Answer 1

My solution to multiprocessing issues is almost always to use the Manager objects. While the exposed interface is the same, the underlying implementation is much simpler and has less bugs.

from multiprocessing import Manager
manager = Manager()
result_queue = manager.Queue()

Try it out and see if it doesn’t fix your issues.