#!/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 logging
     import random
     import threading
     import time
     
     logging.basicConfig(level=logging.DEBUG,
                         format='%(asctime)s (%(threadName)-2s) %(message)s',
                         )
     
     class ActivePool(object):
         def __init__(self):
             super(ActivePool, self).__init__()
             self.active = []
             self.lock = threading.Lock()
         def makeActive(self, name):
             with self.lock:
                 self.active.append(name)
                 logging.debug('Running: %s', self.active)
         def makeInactive(self, name):
             with self.lock:
                 self.active.remove(name)
                 logging.debug('Running: %s', self.active)
     
     def worker(s, pool):
         logging.debug('Waiting to join the pool')
         with s:
             name = threading.currentThread().getName()
             pool.makeActive(name)
             time.sleep(0.1)
             pool.makeInactive(name)
     
     pool = ActivePool()
     s = threading.Semaphore(2)
     for i in range(4):
         t = threading.Thread(target=worker, name=str(i), args=(s, pool))
         t.start()