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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 */
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
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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