threading_semaphore.py

#!/usr/bin/env python3
# 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


class ActivePool:

    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.current_thread().getName()
        pool.makeActive(name)
        time.sleep(0.1)
        pool.makeInactive(name)


logging.basicConfig(
    level=logging.DEBUG,
    format='%(asctime)s (%(threadName)-2s) %(message)s',
)

pool = ActivePool()
s = threading.Semaphore(2)
for i in range(4):
    t = threading.Thread(
        target=worker,
        name=str(i),
        args=(s, pool),
    )
    t.start()