Mutex and Condvar

• Inefficient

  • pthread_cond_broadcast() wakes up everyone, but they all have to immediately block on the mutex

• Not Safe

        T1: mutex_lock(&mutex)
        T1: cond_wait(&cond, &mutex)                    /* down */
                        T2: mutex_lock(&mutex)
                        T2: cond_signal(&cond)          /* up */
                        T2: cond_wait(&cond, &mutex)    /* down */

• pthread_cond_signal() could consume its own signal

  • non-compliant

  • programs *do* depend on that not happening