/* Compile with cc -Og -o thread_sleeps -pthread thread_sleeps.c */

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

int main(int argc, char *argv[]);
void* sender(void*);
void* receiver(void*);

static pthread_mutex_t  mutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t   slept = PTHREAD_COND_INITIALIZER;

int                     nsleeps = 0;

#define NPASSES         20

int main(int argc, char *argv[])
{
    pthread_t sender_tid;
    pthread_t receiver_tid;

    if (pthread_create (&sender_tid, NULL, sender, NULL) != 0)
        {
        fprintf(stderr, "Couldn't create sender thread\n");
        return 1;
        }
    if (pthread_create (&receiver_tid, NULL, receiver, NULL) != 0)
        {
        fprintf(stderr, "Couldn't create receiver thread\n");
        return 1;
        }
    if (pthread_join (sender_tid, NULL) != 0)
        {
        fprintf(stderr, "Couldn't join with sender thread\n");
        return 1;
        }
    if (pthread_join (receiver_tid, NULL) != 0)
        {
        fprintf(stderr, "Couldn't join with receiver thread\n");
        return 1;
        }
    return 0;

}

void* sender(void* data)
{
    int i;

    for (i = 0;  i < NPASSES;  i++) {
        sleep(1);
        printf("Sender slept %d time(s)\n", i + 1);
        pthread_mutex_lock(&mutex);
        ++nsleeps;
        pthread_mutex_unlock(&mutex);
        pthread_cond_signal(&slept);
    }
    return NULL;
}

void* receiver(void* data)
{
    int total_sleeps = 1;
    int sleep_time;

    while (1) {
        pthread_mutex_lock(&mutex);
        if (nsleeps >= NPASSES) {
            pthread_mutex_unlock(&mutex);
            printf("\tReceiver saw %d total sleeps\n", total_sleeps);
            return NULL;
        }
        while (nsleeps < total_sleeps) {
            pthread_cond_wait(&slept, &mutex);
        }
        pthread_mutex_unlock(&mutex);
        printf("\tReceiver saw sleep number %d...", total_sleeps);
        ++total_sleeps;
        if (nsleeps < total_sleeps) {
            sleep_time = random() % 4;
            printf("sleeping %d second(s)\n", sleep_time);
            sleep(sleep_time);
        }
        else
            printf("continuing\n");
    }
}