import threadingimport timeimport randomclass Worker(threading.Thread):    '''售票员'''    def __init__(self, wait_num=5, index=0):        super().__init__()        self.wait_num = wait_num          # 当前排队人数        self.setName('窗口' + str(index)) # 窗口号     def run(self):        global counter, mutex                while counter and self.wait_num: # 若有余票且有人排队            # ============================            # 窗口问询            # ============================            time.sleep(random.randrange(2,10)) # 比较耗时，时间随机                        # ============================            # 出票            # ============================            mutex.acquire()         # 锁住①            if counter == 0:        # 如果票数为0                mutex.release()     # 解锁③ -----> 这句很重要！！！                print(self.getName(), '：抱歉，票已售完')                break                            counter = counter - 1   # 票数减一            print('{}：当前余票 {} 张'.format(self.getName(), counter))            mutex.release()         # 解锁③                        # ============================            # 排队人数变化            # ============================            self.wait_num -= 1                      # 排队人数减一            self.wait_num += random.randrange(0,2)  # 排队人数随机增加    if __name__ == '__main__':    # 剩余车票数    counter = 20        # 创建锁    mutex = threading.Lock()        # 开4个售票窗口    workers = []    for i in range(4):        wait_num = random.randrange(2,10) # 窗口前排队人数随机        workers.append(Worker(wait_num, i+1))         # 开始售票    for w in workers:        w.start()        # 阻塞主程/后台静默？自己选    #for w in workers:    #    w.join()