pythonマルチスレッドノート(4)--駅の切符販売シミュレーション

import threading
import time
import random

class Worker(threading.Thread):
    '''   '''
    def __init__(self, wait_num=5, index=0):
        super().__init__()
        self.wait_num = wait_num          #       
        self.setName('  ' + str(index)) #    
 
    def run(self):
        global counter, mutex
        
        while counter and self.wait_num: #          
            # ============================
            #     
            # ============================
            time.sleep(random.randrange(2,10)) #     ，    
            
            # ============================
            #   
            # ============================
            mutex.acquire()         #   ①
            if counter == 0:        #      0
                mutex.release()     #   ③ ----->      ！！！
                print(self.getName(), '：  ，    ')
                break
                
            counter = counter - 1   #     
            print('{}：     {}  '.format(self.getName(), counter))
            mutex.release()         #   ③
            
            # ============================
            #       
            # ============================
            self.wait_num -= 1                      #       
            self.wait_num += random.randrange(0,2)  #         

    
if __name__ == '__main__':
    #      
    counter = 20
    
    #    
    mutex = threading.Lock()
    
    #  4     
    workers = []
    for i in range(4):
        wait_num = random.randrange(2,10) #          
        workers.append(Worker(wait_num, i+1)) 
    
    #     
    for w in workers:
        w.start()
    
    #     /    ？   
    #for w in workers:
    #    w.join()