thread-condition.c

// C Threading demo

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define NUM_THREADS 3
#define TCOUNT 10
#define COUNT_LIMIT 8

int count = 0;
int thread_ids[3] = {0, 1, 2};
pthread_mutex_t count_mutex;
pthread_cond_t count_threshold_cv;

void *inc_count(void *t)
{
        int i;
        long my_id = (long)t;

        for (i = 0; i < TCOUNT; i++)
        {
                pthread_mutex_lock(&count_mutex);
                count++;

                if (COUNT_LIMIT == count)
                {
                        pthread_cond_signal(&count_threshold_cv);
                        printf("inc_count(): thread %ld, count = %d Threshold reached.\n", my_id, count);
                }
                printf("inc_count(): thread %ld, count = %d, unlocking mutex\n", my_id, count);
                pthread_mutex_unlock(&count_mutex);
                sleep(1);
        }
        pthread_exit(NULL);
}

void *watch_count(void *t)
{
        long my_id = (long)t;
        printf("Starting watch_count(): thread %ld\n", my_id);

        pthread_mutex_lock(&count_mutex);
        while (count < COUNT_LIMIT)
        {
                pthread_cond_wait(&count_threshold_cv, &count_mutex);
                printf("watch_count(): thread %ld Condition signal received.\n", my_id);
                count += 125;
                printf("watch_count(): thread %ld count now = %d.\n", my_id, count);        
        }
        pthread_mutex_unlock(&count_mutex);
        pthread_exit(NULL);
}

int main(int argc, char *argv[])
{
        int i, rc;
        long t1 = 1, t2 = 2, t3 = 3;
        pthread_t threads[3];
        pthread_attr_t attr;

        pthread_mutex_init(&count_mutex, NULL);
        pthread_cond_init(&count_threshold_cv, NULL);

        pthread_attr_init(&attr);
        pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
        pthread_create(&threads[0], &attr, watch_count, (void *)t1);
        pthread_create(&threads[1], &attr, inc_count, (void *)t2);
        pthread_create(&threads[2], &attr, inc_count, (void *)t3);

        for (i = 0; i < NUM_THREADS; i++)
        {
                pthread_join(threads[i], NULL);
        }

        printf ("Main(): Waited on %d  threads. Done.\n", NUM_THREADS);
        pthread_attr_destroy(&attr);
        pthread_mutex_destroy(&count_mutex);
        pthread_cond_destroy(&count_threshold_cv);
        pthread_exit(NULL);
}