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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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