Something about conditional variables in PThread

Step to use conditional variables:

1.  Declare and initialize global data/variables which require synchronization (such as "count")
2. Declare and initialize a condition variable object
3. Declare and initialize an associated mutex
4. Create threads A and B to do work

Step for thread A:

1. Lock the mutex
2. Check the global data (e.g., counter), if not fulfilled, call pthread_cond_wait(). pthread_cond_wait() will automatically release the lock and put the thread into block state.
3. Get the signal from thread B and wake up. After waking up, the thread will automatically grab the mutex.
4. Unlock the mutex and proceed.

Step for thread B:

1. Lock the mutex
2. modify the global data (e.g., counter), if certain threshold is met, call pthread_cond_signal() or pthread_cond_broadcast to notify the blocked thread(s). pthread_cond_singal() is for one thread and pthread_cond_broadcast() assume there are multiple threads waiting. 
3. Unlock the mutex and proceed.

See Also: POSIX Threads Programming