use signaling instead of polling in thpool_wait

thpool.c

@@ -79,6 +79,7 @@ typedef struct thpool_{
 	volatile int num_threads_alive;      /* threads currently alive   */
 	volatile int num_threads_working;    /* threads currently working */
 	pthread_mutex_t  thcount_lock;       /* used for thread count etc */
+	pthread_cond_t  threads_all_idle;    /* signal to thpool_wait     */
 	jobqueue*  jobqueue_p;               /* pointer to the job queue  */    
 } thpool_;
 
@@ -192,46 +193,11 @@ int thpool_add_work(thpool_* thpool_p, void *(*function_p)(void*), void* arg_p){
 
 /* Wait until all jobs have finished */
 void thpool_wait(thpool_* thpool_p){
-
-	/* Continuous polling */
-	double timeout = 1.0;
-	time_t start, end;
-	double tpassed = 0.0;
-	time (&start);
-	while (tpassed < timeout && 
-			(thpool_p->jobqueue_p->len || thpool_p->num_threads_working))
-	{
-		time (&end);
-		tpassed = difftime(end,start);
-	}
-
-	/* Exponential polling */
-	long init_nano =  1; /* MUST be above 0 */
-	long new_nano;
-	double multiplier =  1.01;
-	int  max_secs   = 20;
-
-	struct timespec polling_interval;
-	polling_interval.tv_sec  = 0;
-	polling_interval.tv_nsec = init_nano;
-
-	while (thpool_p->jobqueue_p->len || thpool_p->num_threads_working)
-	{
-		nanosleep(&polling_interval, NULL);
-		if ( polling_interval.tv_sec < max_secs ){
-			new_nano = CEIL(polling_interval.tv_nsec * multiplier);
-			polling_interval.tv_nsec = new_nano % MAX_NANOSEC;
-			if ( new_nano > MAX_NANOSEC ) {
-				polling_interval.tv_sec ++;
-			}
-		}
-		else break;
-	}
-
-	/* Fall back to max polling */
-	while (thpool_p->jobqueue_p->len || thpool_p->num_threads_working){
-		sleep(max_secs);
+	pthread_mutex_lock(&thpool_p->thcount_lock);
+	while (thpool_p->jobqueue_p->len || thpool_p->num_threads_working) {
+		pthread_cond_wait(&thpool_p->threads_all_idle, &thpool_p->thcount_lock);
 	}
+	pthread_mutex_unlock(&thpool_p->thcount_lock);
 }
 
 
@@ -382,6 +348,9 @@ static void* thread_do(struct thread* thread_p){
 
 			pthread_mutex_lock(&thpool_p->thcount_lock);
 			thpool_p->num_threads_working--;
+			if (!thpool_p->num_threads_working) {
+				pthread_cond_signal(&thpool_p->threads_all_idle);
+			}
 			pthread_mutex_unlock(&thpool_p->thcount_lock);
 
 		}