Python学习笔记——多线程编程(三)

@信号量

    #是一个计数器，当资源消耗时递减，当资源释放时递增。

 

@两种信号量类

    #Semaphore

    #BoundedSemaphore， 一个有界信号量会确保它当前的值不超过它的初始值。如果超过，则引发ValueError。

 

@事例：

    #!/usr/bin/env python

 

    from atexit import register

    from random import randrange

    from threading import BoundedSemaphore, Lock, Thread

    from time import sleep, ctime

 

    lock = Lock()

    MAX = 5

    candytray = BoundedSemaphore(MAX)

 

    def refill():

        lock.acquire()

        print("Refilling candy...")

        try:

            candytray.release()

        except ValueError:

            print('full, skipping')

        else:

            print('OK')

        lock.release()

 

    def buy():

        lock.acquire()

        print('Buying candy...')

        if candytray.acquire(False):

            print('OK')

        else:

            print('empty, skipping')

        lock.release()

 

    def producer(loops):

        for i in range(loops):

            refill()

            sleep(randrange(3))

 

    def consumer(loops):

        for i in range(loops):

            buy()

            sleep(randrange(3))

 

    def _main():

        print('starting at:', ctime())

        nloops = randrange(2, 6)

        print('THE CANDY MACHINE (full with %d bars)!' % MAX)

        Thread(target=consumer, args=(randrange(nloops, nloops+ MAX + 2),)).start()

        Thread(target=producer, args=(nloops,)).start()

 

    @register

    def _atexit():

        print('all DONE at:', ctime())

 

    if __name__ == '__main__':

        _main()