Best thread pool approach

[fguy817817]

I have written a demo program below for a thread pool. Do you guys think this is the best approach for initializing a thread pool, using it to do work, and then cancelling it? I have tested this code and it appears to work. I was just wondering if there is a better approach or if I should change anything.

#define num_workers 5
pthread_t workers[num_workers];
pthread_cond_t  available;;		
pthread_mutex_t lock;

void* doing_stuff();

void cleanup_handler(void *arg) 
{
  pthread_mutex_unlock(&lock);
}

int main(int argc, char *argv[])
{
	while(1)
	{
		pthread_cond_init(&available, NULL);
	    
	                if (pthread_mutex_init(&lock, NULL) != 0)
		{
			exit(EXIT_FAILURE);
		}
		
		system("clear");
		
		printf("\n\n----- Creating threads -----\n\n");
		int x;
		for(x =0; x<num_workers; x++)
		{
			pthread_create(&workers[x], NULL, doing_stuff, NULL);
		}
		
		sleep(5);
		
		printf("\n\n----- Cancelling threads -----\n\n");
		
		for(x =0; x<num_workers; x++)
		{
			printf("Canceling thread %lu.\n", workers[x]);
			pthread_cancel(workers[x]);
		}
		
		for(x =0; x<num_workers; x++)
		{
			printf("Joining thread %lu.\n", workers[x]);
			pthread_join(workers[x], NULL);
		}
		
		pthread_mutex_unlock(&lock);
		pthread_cond_destroy(&available);
		pthread_mutex_destroy(&lock);
		
		sleep(5);
	}
	
	return 0;
}

void *doing_stuff()
{
	printf("Thread %lu has started.\n", pthread_self());
	pthread_cleanup_push(cleanup_handler, NULL);
	
	while(1)
	{
		pthread_mutex_lock(&lock);
		
		printf("Thread %lu is at wait condition.\n", pthread_self());
		pthread_cond_wait(&available, &lock); 

                                /* Perform the work */
		
		pthread_mutex_unlock(&lock);
		
		sleep(5);
	}
	pthread_cleanup_pop(0);

	return NULL;
}