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/* The classic producer-consumer example, implemented with semaphores.
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"
#include "semaphore.h"
#define BUFFER_SIZE 16
/* Circular buffer of integers. */
struct prodcons
{
int buffer[BUFFER_SIZE]; /* the actual data */
int readpos, writepos; /* positions for reading and writing */
sem_t sem_read; /* number of elements available for reading */
sem_t sem_write; /* number of locations available for writing */
};
/* Initialize a buffer */
static void
init (struct prodcons *b)
{
sem_init (&b->sem_write, 0, BUFFER_SIZE - 1);
sem_init (&b->sem_read, 0, 0);
b->readpos = 0;
b->writepos = 0;
}
/* Store an integer in the buffer */
static void
put (struct prodcons *b, int data)
{
/* Wait until buffer is not full */
sem_wait (&b->sem_write);
/* 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 contains one more element for reading */
sem_post (&b->sem_read);
}
/* Read and remove an integer from the buffer */
static int
get (struct prodcons *b)
{
int data;
/* Wait until buffer is not empty */
sem_wait (&b->sem_read);
/* 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 has now one more location for writing */
sem_post (&b->sem_write);
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
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;
}
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