producer consumer problem

producer_consumer.c

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

#define BUFFER_SIZE 10
sem_t fill_count, empty_count;
pthread_mutex_t lock;

int p;

void *producer(void *param)
{
    for(;;)
    {
        sem_wait(&empty_count);
        pthread_mutex_lock(&lock);
        p++;
        pthread_mutex_unlock(&lock);
        sem_post(&fill_count);

    }
}

void *consumer(void *param)
{
    for(;;)
    {
        sem_wait(&fill_count);
        pthread_mutex_lock(&lock);
        p--;
        pthread_mutex_unlock(&lock);
        sem_post(&empty_count);
    }
}

int main(void)
{
    pthread_t t[3];
    sem_init(&fill_count, 0, 0);
    sem_init(&empty_count, 0, BUFFER_SIZE);
    pthread_mutex_init(&lock, NULL);

    pthread_create(&t[0], NULL, consumer, NULL);
    pthread_create(&t[1], NULL, producer, NULL);
    pthread_create(&t[2], NULL, producer, NULL);
    for(;;)
    {
        printf("p = %d\n", p);
    }

    pthread_cancel(t[0]);
    pthread_cancel(t[1]);
    pthread_cancel(t[2]);

    sem_destroy(&fill_count);
    sem_destroy(&empty_count);
    pthread_mutex_destroy(&lock);

}