Producer consumer problem using semaphore

Program

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

#define BUFFER_SIZE 2

int buffer[BUFFER_SIZE];
int in = 0, out = 0;

sem_t empty, full;
pthread_mutex_t mutex;

void *producer(void *arg) {
  for (int i = 1; i <= 10; i++) {
    sem_wait(&empty);
    pthread_mutex_lock(&mutex);

    buffer[in] = i;
    printf("Produced: %d\n", i);
    in = (in + 1) % BUFFER_SIZE;

    pthread_mutex_unlock(&mutex);
    sem_post(&full);
    sleep(1);
  }
  return NULL;
}

void *consumer(void *arg) {
  for (int i = 1; i <= 10; i++) {
    sem_wait(&full);
    pthread_mutex_lock(&mutex);

    int item = buffer[out];
    printf("Consumed: %d\n", item);
    out = (out + 1) % BUFFER_SIZE;

    pthread_mutex_unlock(&mutex);
    sem_post(&empty);
    sleep(2);
  }
  return NULL;
}

int main() {
  pthread_t prod, cons;

  sem_init(&empty, 0, BUFFER_SIZE);
  sem_init(&full, 0, 0);
  pthread_mutex_init(&mutex, NULL);

  pthread_create(&prod, NULL, producer, NULL);
  pthread_create(&cons, NULL, consumer, NULL);

  pthread_join(prod, NULL);
  pthread_join(cons, NULL);

  sem_destroy(&empty);
  sem_destroy(&full);
  pthread_mutex_destroy(&mutex);

  return 0;
}