#!/usr/bin/env python
     # encoding: utf-8
     #
     # Copyright (c) 2009 Doug Hellmann All rights reserved.
     #
     """
     """
     #end_pymotw_header
     
     import multiprocessing
     import time
     
     class Consumer(multiprocessing.Process):
         
         def __init__(self, task_queue, result_queue):
             multiprocessing.Process.__init__(self)
             self.task_queue = task_queue
             self.result_queue = result_queue
     
         def run(self):
             proc_name = self.name
             while True:
                 next_task = self.task_queue.get()
                 if next_task is None:
                     # Poison pill means shutdown
                     print '%s: Exiting' % proc_name
                     self.task_queue.task_done()
                     break
                 print '%s: %s' % (proc_name, next_task)
                 answer = next_task()
                 self.task_queue.task_done()
                 self.result_queue.put(answer)
             return
     
     
     class Task(object):
         def __init__(self, a, b):
             self.a = a
             self.b = b
         def __call__(self):
             time.sleep(0.1) # pretend to take some time to do the work
             return '%s * %s = %s' % (self.a, self.b, self.a * self.b)
         def __str__(self):
             return '%s * %s' % (self.a, self.b)
     
     
     if __name__ == '__main__':
         # Establish communication queues
         tasks = multiprocessing.JoinableQueue()
         results = multiprocessing.Queue()
         
         # Start consumers
         num_consumers = multiprocessing.cpu_count() * 2
         print 'Creating %d consumers' % num_consumers
         consumers = [ Consumer(tasks, results)
                       for i in xrange(num_consumers) ]
         for w in consumers:
             w.start()
         
         # Enqueue jobs
         num_jobs = 10
         for i in xrange(num_jobs):
             tasks.put(Task(i, i))
         
         # Add a poison pill for each consumer
         for i in xrange(num_consumers):
             tasks.put(None)
     
         # Wait for all of the tasks to finish
         tasks.join()
         
         # Start printing results
         while num_jobs:
             result = results.get()
             print 'Result:', result
             num_jobs -= 1