------------------------ Code

------ Threads A/B

{
  pthread_mutex_lock(mutex)
  while (m_size == 0)
      pthread_cond_wait(cond);

  m_size--
  pthread_mutex_unlock(mutex)
}

------ Threads C
{
  .. do some work ..
  pthread_mutex_lock(mutex)
  m_size = 5;
  pthread_mutex_signal(cond);
  pthread_mutex_unlock(mutex);
}


Thread A            Thread B            Thread C

pthread_mutex_lock(mutex)
while (m_size == 0)
pthread_cond_wait(cond)
                pthread_mutex_lock(mutex)
                while (m_size == 0)
                pthread_cond_wait(cond)
                                .. do some work ..
                                pthread_mutex_lock(mutex)
                                m_size = 1;
                                pthread_cond_signal(cond);
                                pthread_mutex_unlock(mutex);
while (m_size > 0)
                while (m_size > 0)
m_size--
                m_size--
pthread_mutex_unlock(mutex)
                pthread_mutex_unlock(mutex)