#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
    Python 線程同步機制:Semaphore
"""

import time
import threading
import random

#  信號量同步基於內部計數器，每調用一次acquire()，計數器減1；每調用一次release()，計數器加1.當計數器為0時，acquire()調用被阻塞。
sema = threading.Semaphore(3)

def foo(param):
    with sema:
        print ‘
 
%d acquire sema‘ % (param,)
        n = random.random() * 3
        time.sleep(5)
    print ‘%d releas sema‘ % (param,)


if __name__ == ‘__main__‘:
    threads = []
    for i in range(5):
        t = threading.Thread(target=foo, args=(i,))
        t.start()
        threads.append(t)

    
 
print ‘------------‘
    for t in threads:
        t.join()

    print ‘main End‘

輸出：

python t_Semaphore.py

0 acquire sema
1 acquire sema
2 acquire sema
------------
1 releas sema
2 releas sema
0 releas sema3 acquire sema

4 acquire sema
4 releas sema
3 releas sema
main End

Process finished with exit code 0

python多線程同步機制Semaphore