mirror of
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114 lines
2.7 KiB
C
114 lines
2.7 KiB
C
/* The classic producer-consumer example.
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Illustrates mutexes and conditions.
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All integers between 0 and 9999 should be printed exactly twice,
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once to the right of the arrow and once to the left. */
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#include <stdio.h>
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#include "pthread.h"
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#define BUFFER_SIZE 16
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/* Circular buffer of integers. */
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struct prodcons {
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int buffer[BUFFER_SIZE]; /* the actual data */
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pthread_mutex_t lock; /* mutex ensuring exclusive access to buffer */
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int readpos, writepos; /* positions for reading and writing */
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pthread_cond_t notempty; /* signaled when buffer is not empty */
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pthread_cond_t notfull; /* signaled when buffer is not full */
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};
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/* Initialize a buffer */
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void init(struct prodcons * b)
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{
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pthread_mutex_init(&b->lock, NULL);
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pthread_cond_init(&b->notempty, NULL);
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pthread_cond_init(&b->notfull, NULL);
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b->readpos = 0;
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b->writepos = 0;
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}
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/* Store an integer in the buffer */
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void put(struct prodcons * b, int data)
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{
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pthread_mutex_lock(&b->lock);
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/* Wait until buffer is not full */
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while ((b->writepos + 1) % BUFFER_SIZE == b->readpos) {
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pthread_cond_wait(&b->notfull, &b->lock);
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/* pthread_cond_wait reacquired b->lock before returning */
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}
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/* Write the data and advance write pointer */
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b->buffer[b->writepos] = data;
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b->writepos++;
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if (b->writepos >= BUFFER_SIZE) b->writepos = 0;
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/* Signal that the buffer is now not empty */
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pthread_cond_signal(&b->notempty);
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pthread_mutex_unlock(&b->lock);
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}
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/* Read and remove an integer from the buffer */
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int get(struct prodcons * b)
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{
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int data;
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pthread_mutex_lock(&b->lock);
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/* Wait until buffer is not empty */
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while (b->writepos == b->readpos) {
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pthread_cond_wait(&b->notempty, &b->lock);
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}
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/* Read the data and advance read pointer */
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data = b->buffer[b->readpos];
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b->readpos++;
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if (b->readpos >= BUFFER_SIZE) b->readpos = 0;
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/* Signal that the buffer is now not full */
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pthread_cond_signal(&b->notfull);
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pthread_mutex_unlock(&b->lock);
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return data;
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}
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/* A test program: one thread inserts integers from 1 to 10000,
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the other reads them and prints them. */
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#define OVER (-1)
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struct prodcons buffer;
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void * producer(void * data)
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{
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int n;
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for (n = 0; n < 10000; n++) {
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printf("%d --->\n", n);
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put(&buffer, n);
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}
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put(&buffer, OVER);
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return NULL;
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}
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void * consumer(void * data)
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{
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int d;
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while (1) {
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d = get(&buffer);
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if (d == OVER) break;
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printf("---> %d\n", d);
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}
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return NULL;
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}
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int main(void)
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{
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pthread_t th_a, th_b;
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void * retval;
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init(&buffer);
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/* Create the threads */
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pthread_create(&th_a, NULL, producer, 0);
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pthread_create(&th_b, NULL, consumer, 0);
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/* Wait until producer and consumer finish. */
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pthread_join(th_a, &retval);
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pthread_join(th_b, &retval);
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return 0;
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}
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