/*
 * Synchronization via POSIX Semaphores
 */
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdbool.h>
#include <semaphore.h>

int coin_flip;
sem_t coin_flip_done;   // semaphore for thread 1 to signal coin flip

static void *
thread1(void *_)
{
    coin_flip = rand() % 2;
    sem_post(&coin_flip_done);  // raise semaphore, increment, 'up'

    printf("Thread 1: flipped coin %d\n", coin_flip);
    return NULL;
}

static void *
thread2(void *_)
{
    sem_wait(&coin_flip_done);  // wait until semaphore is raised, 
                                // then decrement, 'down'
    printf("Thread 2: flipped coin %d\n", coin_flip);
    return NULL;
}

int
main()
{
    int i, N = 2;
    pthread_t t[N];
    srand(getpid());

    sem_init(&coin_flip_done, 0, 0);
    pthread_create(&t[1], NULL, thread2, NULL);
    pthread_create(&t[0], NULL, thread1, NULL);

    for (i = 0; i < N; i++)
        pthread_join(t[i], NULL);
    return 0;
}