Example program for producer-consumer implementation using pthread apis

producer-consumer.c

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

#define MAX 1024

int shared_buffer[MAX];
int producer_index;
int consumer_index;
int num_items;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
int global_id = 1;

void* producer(void* data) {
  while (1) {
    pthread_mutex_lock(&mutex);
    while (num_items == MAX) {
      printf("%p(P): Waiting on full\n", pthread_self());
      pthread_cond_wait(&cond, &mutex);
    }
    shared_buffer[producer_index] = global_id;
    global_id++;
    producer_index = (producer_index + 1) % MAX;
    num_items++;
    printf("%p(P:%d:%d): Produced %d\n", pthread_self(), num_items, producer_index, global_id - 1);
    if (num_items == 1) { pthread_cond_signal(&cond); }
    pthread_mutex_unlock(&mutex);
  }
}

void* consumer(void* data) {
  while (1) {
    pthread_mutex_lock(&mutex);
    while (num_items == 0) {
      printf("%p(C): Waiting on empty\n", pthread_self());
      pthread_cond_wait(&cond, &mutex);
    }
    int x = shared_buffer[consumer_index];
    printf("%p(C:%d:%d): Consumed %d\n", pthread_self(), num_items, consumer_index, x);
    consumer_index = (consumer_index + 1) % MAX;
    num_items--;
    if (num_items == MAX - 1) { pthread_cond_signal(&cond); }
    pthread_mutex_unlock(&mutex);
  }
}

#define PRODUCERS 20
#define CONSUMERS 10

int main() {
  pthread_t producer_threads[PRODUCERS];
  pthread_t consumer_threads[CONSUMERS];
  for (int i = 0; i < PRODUCERS; ++i) {
    pthread_create(&producer_threads[i], NULL, producer, NULL);
  }
  for (int i = 0; i < CONSUMERS; ++i) {
    pthread_create(&consumer_threads[i], NULL, consumer, NULL);
  }
  void* ret;
  for (int i = 0; i < PRODUCERS; ++i) {
    pthread_join(producer_threads[i], &ret);
  }
  for (int i = 0; i < CONSUMERS; ++i) {
    pthread_join(consumer_threads[i], &ret);
  }
}