1 # 2 # Simple example which uses a pool of workers to carry out some tasks. 3 # 4 # Notice that the results will probably not come out of the output 5 # queue in the same in the same order as the corresponding tasks were 6 # put on the input queue. If it is important to get the results back 7 # in the original order then consider using `Pool.map()` or 8 # `Pool.imap()` (which will save on the amount of code needed anyway). 9 # 10 # Copyright (c) 2006-2008, R Oudkerk 11 # All rights reserved. 12 # 13 14 import time 15 import random 16 17 from multiprocessing import Process, Queue, current_process, freeze_support 18 19 # 20 # Function run by worker processes 21 # 22 23 def worker(input, output): 24 for func, args in iter(input.get, 'STOP'): 25 result = calculate(func, args) 26 output.put(result) 27 28 # 29 # Function used to calculate result 30 # 31 32 def calculate(func, args): 33 result = func(*args) 34 return '%s says that %s%s = %s' % \ 35 (current_process().name, func.__name__, args, result) 36 37 # 38 # Functions referenced by tasks 39 # 40 41 def mul(a, b): 42 time.sleep(0.5*random.random()) 43 return a * b 44 45 def plus(a, b): 46 time.sleep(0.5*random.random()) 47 return a + b 48 49 # 50 # 51 # 52 53 def test(): 54 NUMBER_OF_PROCESSES = 4 55 TASKS1 = [(mul, (i, 7)) for i in range(20)] 56 TASKS2 = [(plus, (i, 8)) for i in range(10)] 57 58 # Create queues 59 task_queue = Queue() 60 done_queue = Queue() 61 62 # Submit tasks 63 for task in TASKS1: 64 task_queue.put(task) 65 66 # Start worker processes 67 for i in range(NUMBER_OF_PROCESSES): 68 Process(target=worker, args=(task_queue, done_queue)).start() 69 70 # Get and print results 71 print 'Unordered results:' 72 for i in range(len(TASKS1)): 73 print '\t', done_queue.get() 74 75 # Add more tasks using `put()` 76 for task in TASKS2: 77 task_queue.put(task) 78 79 # Get and print some more results 80 for i in range(len(TASKS2)): 81 print '\t', done_queue.get() 82 83 # Tell child processes to stop 84 for i in range(NUMBER_OF_PROCESSES): 85 task_queue.put('STOP') 86 87 88 if __name__ == '__main__': 89 freeze_support() 90 test() 91
