#include <pthread.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>

#define N 1 

struct msg {
  int value;
};

struct port {
  struct msg messages[N];
  pthread_mutex_t m;
  pthread_cond_t empty;
  pthread_cond_t full;
  int count;
  int head;
  int tail;
};

void msg_send(struct port *p, struct msg *m)
{
  pthread_mutex_lock(&p->m);
  while (p->count == N) {
    pthread_cond_wait(&p->full, &p->m);
  }
  memcpy(&p->messages[p->tail], m, sizeof(struct msg));
  p->tail = (p->tail + 1) % N;
  p->count = p->count + 1;
  pthread_cond_signal(&p->empty);
  pthread_mutex_unlock(&p->m);
}

void msg_receive(struct port *p, struct msg *m)
{
  pthread_mutex_lock(&p->m);
  while (p->count == 0) {
    pthread_cond_wait(&p->empty, &p->m);
  }
  memcpy(m, &p->messages[p->head], sizeof(struct msg));
  p->head = (p->head + 1) % N;
  p->count = p->count - 1;
  pthread_cond_signal(&p->full);
  pthread_mutex_unlock(&p->m);
}

struct port *port_init(void)
{
  struct port *p;

  p = malloc(sizeof(struct port));
  if (p == NULL) {
    return NULL;
  }

  p->head = 0;
  p->tail = 0;
  p->count = 0;
  pthread_mutex_init(&p->m, NULL);
  pthread_cond_init(&p->empty, NULL);
  pthread_cond_init(&p->full, NULL);

  return p;
}



struct port *p;

void *thread1(void *v)
{
  struct msg m;

  m.value = 1;
  printf("Sending %d\n", m.value);
  msg_send(p, &m);
  m.value = 2;
  printf("Sending %d\n", m.value);
  msg_send(p, &m);
  m.value = 3;
  printf("Sending %d\n", m.value);
  msg_send(p, &m);
  m.value = 4;
  printf("Sending %d\n", m.value);
  msg_send(p, &m);

  return NULL;
}

void *thread2(void *v)
{
  struct msg m;

  sleep(5);
  msg_receive(p, &m);
  printf("Received %d\n", m.value);

  sleep(1);
  msg_receive(p, &m);
  printf("Received %d\n", m.value);

  sleep(1);
  msg_receive(p, &m);
  printf("Received %d\n", m.value);

  sleep(1);
  msg_receive(p, &m);
  printf("Received %d\n", m.value);

  return NULL;
}

int main(int argc, char *argv[])
{
  int err;
  pthread_t id1, id2;

  p = port_init();
  err = pthread_create(&id1, NULL, thread1, NULL);
  if (err) {
    perror("PThread Create");
  }

  err = pthread_create(&id2, NULL, thread2, NULL);
  if (err) {
    perror("PThread Create");
  }

  pthread_join(id1, NULL);
  pthread_join(id2, NULL);

  return 0;
}