#!/usr/bin/env python
     # encoding: utf-8
     #
     # Copyright (c) 2008 Doug Hellmann All rights reserved.
     #
     """Multiple concurrent access to a resource
     """
     #end_pymotw_header
     import random
     import multiprocessing
     import time
     
     class ActivePool(object):
         def __init__(self):
             super(ActivePool, self).__init__()
             self.mgr = multiprocessing.Manager()
             self.active = self.mgr.list()
             self.lock = multiprocessing.Lock()
         def makeActive(self, name):
             with self.lock:
                 self.active.append(name)
         def makeInactive(self, name):
             with self.lock:
                 self.active.remove(name)
         def __str__(self):
             with self.lock:
                 return str(self.active)
     
     def worker(s, pool):
         name = multiprocessing.current_process().name
         with s:
             pool.makeActive(name)
             print 'Now running: %s' % str(pool)
             time.sleep(random.random())
             pool.makeInactive(name)
     
     if __name__ == '__main__':
         pool = ActivePool()
         s = multiprocessing.Semaphore(3)
         jobs = [
             multiprocessing.Process(target=worker, name=str(i), args=(s, pool))
             for i in range(10)
             ]
     
         for j in jobs:
             j.start()
     
         for j in jobs:
             j.join()
             print 'Now running: %s' % str(pool)