text: /* 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 */
  
  static 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 */
  static 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 */
  
  static 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;
  
  static void * producer(void * data)
  {
    int n;
    for (n = 0; n < 10000; n++) {
      printf("%d --->\n", n);
      put(&buffer, n);
    }
    put(&buffer, OVER);
    return NULL;
  }
  
  static void * consumer(void * data)
  {
    int d;
    while (1) {
      d = get(&buffer);
      if (d == OVER) break;
      printf("---> %d\n", d);
    }
    return NULL;
  }
  
  int libc_ex2(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;
  }
  #include <finsh.h>
  FINSH_FUNCTION_EXPORT(libc_ex2, example 2 for libc);
  