c - pthread synchronization on two consumers one producer -

i have worker thread processing queue of work items.

//producer void push_into_queue(char *item) {     pthread_mutex_lock (&queuemutex);     if(workqueue.full) { // full }     else{         add_item_into_queue(item);         pthread_cond_signal (&queuesignalpush);     }        pthread_mutex_unlock(&queuemutex); } // consumer1 void* worker(void* arg) {     while(true) {         pthread_mutex_lock(&queuemutex);         while(workqueue.empty)             pthread_cond_wait(&queuesignalpush, &queuemutex);          item = workqueue.front; // pop queue         add_item_into_list(item);          // need signal here thread2?         pthread_cond_signal(&queuesignalpop);         pthread_mutex_unlock(&queuemutex);     }        return null; } pthread_create (&thread1, null, (void *) &worker, null); 

now have thread2 consume data inserted in add_item_into_list() if items have been added list. note list permanent , can't emptied nor freed entire duration of program.

so question is: need pthread_cond_signal?, if yes, signal go? , how other worker (canonical form)?

i see 2 possible ways of solving problem:

a. introduce condition variable (e.g. signallist) list, consumer2 thread wait events on it. in case consumer1 have signal twice: once on queuesignalpop , once on signallist:

// consumer1 void* worker(void* arg) {     while(true) {         // ...         pthread_cond_signal(&queuesignalpop);         pthread_cond_signal(&signallist);         pthread_mutex_unlock(&queuemutex);     }        return null; } 

b. use existing condition queuesignalpop variable inside consumer2 wait events, , use broadcast instead of signal inside consumer1. broadcast means waiting threads on condition variable wake up:

// consumer1 void* worker(void* arg) {     while(true) {         // ...         pthread_cond_broadcast(&queuesignalpop);         pthread_mutex_unlock(&queuemutex);     }        return null; } // consumer2 void* worker2(void* arg) {     while(true) {         while(list.empty)             pthread_cond_wait(&queuesignalpop, &queuemutex);         // ...     }        return null; } 

i propose go first approach, since better distinguish purpose of each condition variable.