[PThread] condition variable usage pattern

producer/consumer model. The return value for each pthread function call need to be checked too.

Producer:

while(/* condition for producer to contintue */)
{
  pthread_mutex_lock(&mutex);

  // do something for producer

  // the order of the two following call is not important
  // unlock before signal may more efficient than signal before unlock
  pthread_mutex_unlock(&mutex);
  pthread_cond_signal(&cond);
}

Consumer:

while(/* condition for consumer to continue */)
{
  // must  contain lock before calling condition wait
  pthread_mutex_lock(&mutex);

  // the condition wait need to be recheck for
  // 1. spurious wakeup
  // 2. other thread can be waken early
  while(/* condition to check for state not valid */)
  {
    s = pthread_cond_wait(&cond, &mutex);
  }
  // do consumer work, now under mutex protection
  pthread_mutex_unlock(&mutex);
  // some other work which don't need mutex
}

Spurious wakeup:
Some condition wait implementation can cause the thread to be waken up when no signal to the condition variable.
man pthreadconidsignal for further detail.