/*
 * Synchronization via condition variables.
 *
 * This program contains a bug.  Find it and fix it.
 */
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdbool.h>
#include <semaphore.h>

int coin_flip;          // 0 or 1, heads or tails
bool coin_flip_done;    // states whether 'coin_flip' contains valid result
// protects coin_flip_done;
pthread_mutex_t coin_flip_done_lock = PTHREAD_MUTEX_INITIALIZER;    
pthread_cond_t coin_flip_done_cond = PTHREAD_COND_INITIALIZER;

static void *
producer(void *_items_to_produce)
{
    int i, n = *(int *)_items_to_produce;
    for (i = 0; i < n; i++) {
        pthread_mutex_lock(&coin_flip_done_lock);
        while (coin_flip_done)
            pthread_cond_wait(&coin_flip_done_cond, &coin_flip_done_lock);

        coin_flip = rand() % 2;
        coin_flip_done = true;
        printf("thread %p: flipping coin %d\n", 
            (void *)pthread_self(), coin_flip);
        pthread_cond_signal(&coin_flip_done_cond);
        pthread_mutex_unlock(&coin_flip_done_lock);
    }
    return NULL;
}

static void *
consumer(void *_items_to_consume)
{
    int i, n = *(int *)_items_to_consume;
    for (i = 0; i < n; i++) {
        pthread_mutex_lock(&coin_flip_done_lock);
        while (!coin_flip_done)
            pthread_cond_wait(&coin_flip_done_cond, &coin_flip_done_lock);

        coin_flip_done = false;
        printf("thread %p: coin flip outcome was %d\n", 
            (void *)pthread_self(), coin_flip);
        pthread_cond_signal(&coin_flip_done_cond);
        pthread_mutex_unlock(&coin_flip_done_lock);
    }
    return NULL;
}

int
main()
{
    int i, N = 4;
    pthread_t t[N];
    int items [N] =             { 3,        2,        4,        1 };
    void * (*func [N])(void*) = { consumer, consumer, producer, producer };
    srand(getpid());

    for (i = 0; i < N; i++)
        pthread_create(&t[i], NULL, func[i], items + i);

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