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