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/* The classic producer-consumer example.

   Illustrates mutexes and conditions.

   All integers between 0 and 9999 should be printed exactly twice,

   once to the right of the arrow and once to the left. */

#include <stdio.h>

#include "pthread.h"

#define BUFFER_SIZE 16

/* Circular buffer of integers. */

struct prodcons {

  int buffer[BUFFER_SIZE];      /* the actual data */

  pthread_mutex_t lock;         /* mutex ensuring exclusive access to buffer */

  int readpos, writepos;        /* positions for reading and writing */

  pthread_cond_t notempty;      /* signaled when buffer is not empty */

  pthread_cond_t notfull;       /* signaled when buffer is not full */

};

/* Initialize a buffer */

void init(struct prodcons * b)

{

  pthread_mutex_init(&b->lock, NULL);

  pthread_cond_init(&b->notempty, NULL);

  pthread_cond_init(&b->notfull, NULL);

  b->readpos = 0;

  b->writepos = 0;

}

/* Store an integer in the buffer */

void put(struct prodcons * b, int data)

{

  pthread_mutex_lock(&b->lock);

  /* Wait until buffer is not full */

  while ((b->writepos + 1) % BUFFER_SIZE == b->readpos) {

    pthread_cond_wait(&b->notfull, &b->lock);

    /* pthread_cond_wait reacquired b->lock before returning */

  }

  /* Write the data and advance write pointer */

  b->buffer[b->writepos] = data;

  b->writepos++;

  if (b->writepos >= BUFFER_SIZE) b->writepos = 0;

  /* Signal that the buffer is now not empty */

  pthread_cond_signal(&b->notempty);

  pthread_mutex_unlock(&b->lock);

}

/* Read and remove an integer from the buffer */

int get(struct prodcons * b)

{

  int data;

  pthread_mutex_lock(&b->lock);

  /* Wait until buffer is not empty */

  while (b->writepos == b->readpos) {

    pthread_cond_wait(&b->notempty, &b->lock);

  }

  /* Read the data and advance read pointer */

  data = b->buffer[b->readpos];

  b->readpos++;

  if (b->readpos >= BUFFER_SIZE) b->readpos = 0;

  /* Signal that the buffer is now not full */

  pthread_cond_signal(&b->notfull);

  pthread_mutex_unlock(&b->lock);

  return data;

}

/* A test program: one thread inserts integers from 1 to 10000,

   the other reads them and prints them. */

#define OVER (-1)

struct prodcons buffer;

void * producer(void * data)

{

  int n;

  for (n = 0; n < 10000; n++) {

    printf("%d --->\n", n);

    put(&buffer, n);

  }

  put(&buffer, OVER);

  return NULL;

}

void * consumer(void * data)

{

  int d;

  while (1) {

    d = get(&buffer);

    if (d == OVER) break;

    printf("---> %d\n", d);

  }

  return NULL;

}

int main(void)

{

  pthread_t th_a, th_b;

  void * retval;

  init(&buffer);

  /* Create the threads */

  pthread_create(&th_a, NULL, producer, 0);

  pthread_create(&th_b, NULL, consumer, 0);

  /* Wait until producer and consumer finish. */

  pthread_join(th_a, &retval);

  pthread_join(th_b, &retval);

  return 0;

}