Can pthread_cond_wait() always win the competition in locking a mutex?

Question

This question is regarding the pthread tutorial in llnl. Say there are three threads.

Thread 1:

pthread_mutex_lock(&mutex)
do_s         


        

Answer 1

There is no guarantee. Returning from pthread_cond_wait() should be treated as implying that the condition might have changed, not that it definitely has - so you need to re-check the condition, and may need to wait again. This is exactly why pthread_cond_wait() should be called within a loop that checks the condition.