Python-多线程注意事项

# encoding: UTF-8

import threading
import time


def show_fun(sem, n):
    # 不能放在这里
    # sem_lock.acquire()
    print("{0} start -- {1}".format(time.ctime(), n))
    print "working"
    time.sleep(2)
    print("{0} end -- {1}".format(time.ctime(), n))
    sem.release()


if __name__ == '__main__':
    max_connections = 5
    semaphore = threading.BoundedSemaphore(max_connections)
    thread_list = list()
    for i in range(8):
        # 锁申请必须在外部申请，而不是在show_fun内部，因为t.start()会实例化所有对象
        # 锁在show_fun内部对象内，会导致所有对象被实例化，实例化后再被acquire，并发越大，资源暂用率明显
        semaphore.acquire()
        t = threading.Thread(target=show_fun, args=(semaphore, i,))
        thread_list.append(t)
        t.start()
    # 等待所有子进程结束
    for t in thread_list:
        t.join()