case 1: two Mutex are used: the 1st mutex is applied, and second mutex fails, and because of the poor design, the 1st mutex is not unlocked, and this causes all other threads (including the thread which holds the 2nd mutex) to halt. Thus, the 2nd mutex is locked perpetually, and so does the 1st mutex.

case 2: two mutex are used; the order of applying the mutex matters.

   void *function1()
    {
       ...
       pthread_mutex_lock(&lock1);           - Execution step 1
       pthread_mutex_lock(&lock2);           - Execution step 3 DEADLOCK!!!
       ...
       ...
       pthread_mutex_lock(&lock2);
       pthread_mutex_lock(&lock1);
       ...
    } 

    void *function2()
    {
       ...
       pthread_mutex_lock(&lock2);           - Execution step 2
       pthread_mutex_lock(&lock1);
       ...
       ...
       pthread_mutex_lock(&lock1);
       pthread_mutex_lock(&lock2);
       ...
    } 
  
    main()
    {
       ...

       pthread_create(&thread2, NULL, function1, NULL);
       ...
    }