import threading

import time

import random

class 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()