Using pthread apis

gistfile1.c

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

long state = 0;
pthread_mutex_t state_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t state_cond = PTHREAD_COND_INITIALIZER;

void* compute(void* arg) {
    pthread_mutex_lock(&state_mutex);
    printf("child: %lu\n", state);
    while (state == 0) {
        pthread_cond_wait(&state_cond, &state_mutex);
    }
    state = (long)arg;
    printf("child: %lu\n", state);
    pthread_mutex_unlock(&state_mutex);
    pthread_exit(NULL);
}

int main() {
    pthread_t child;
    printf("parent: begin\n");
    pthread_create(&child, NULL, compute, (void*)1729);

    sleep(1);
    pthread_mutex_lock(&state_mutex);
    printf("parent: %lu\n", state);
    state = 1000;
    pthread_cond_signal(&state_cond);
    printf("parent: %lu\n", state);
    pthread_mutex_unlock(&state_mutex);

    void* ret;
    pthread_join(child, &ret);
    printf("parent: end\n");
}