Question

At one point in my function it would reach

pthread_cond_wait(&cond_state, &b_state);

When a signal is send and wake up this thread. Does it immediately try to do a lock on mutex before it calls Enter?

    void Enter(int g, int timer){
     pthread_mutex_lock(&b_state);

     if (room.state == 2 || room.state == g)
     {
       pthread_mutex_unlock(&b_state);
       Leave();
     }
     else 
     {  
       pthread_cond_wait(&cond_state, &b_state);
       Enter(g, timer);         //Try to enter again
     }
    }

I am having a problem when if a thread went to sleep, once it woke up it will get stuck at mutex_lock after called Enter.

Answer 1

Yes, the manpage for pthread_cond_wait says:

The waiting thread unblocks only after another thread calls
pthread_cond_signal(3), or pthread_cond_broadcast(3) with the same
condition variable, and the current thread reacquires the lock on
mutex.