参考资料：https://blog.****.net/cd_xuyue/article/details/52052893
1使用两个循环分别处理start和join函数.即可实现并发.
threads = [Thread() for i in range(5)]
for thread in threads:
thread.start()
for thread in threads:
thread.join()
2 要保证锁对于多个子线程来说是共用的,即不要在Thread的子类内部创建锁.