Links are:
(1) C language mutex pthread_mutex_t
https://blog.csdn.net/baidu_36649389/article/details/54573825
(2) linux multithreaded operation, the mutex lock condition
https://blog.csdn.net/wangqing_12345/article/details/68490842
(3) pthread thread locks and lock condition
https://www.cnblogs.com/csun/p/6297729.html