pthread-生产消费.c -----注释

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/************************************************
*
* The classic producer-consumer example.
* Illustrates mutexes and conditions.
* by Zou jian guo <ah_zou@tom.com>
* 2003-12-22
*
*************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <time.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 */
void init(struct prodcons * b)
{
pthread_mutex_init(&b->lock, NULL);/*初始化互斥锁*/
pthread_cond_init(&b->notempty, NULL);/*初始化条件变量notempty*/
pthread_cond_init(&b->notfull, NULL);/*初始化条件变量notfull*/
b->readpos = 0;/*初始化读位置*/
b->writepos = 0;/*初始化写位置*/
}
/*--------------------------------------------------------*/
/* Store an integer in the buffer */
void put(struct prodcons * b, int data)/*生产*/
{
pthread_mutex_lock(&b->lock); /*加锁*/
/* Wait until buffer is not full */ /*有一个空位就相当于满*/
while ((b->writepos + 1) % BUFFER_SIZE == b->readpos) { /*判断读写位置是否相等；+1防止两个进程都阻塞*/
printf("wait for not full\n");
pthread_cond_wait(&b->notfull, &b->lock);/*解lock互斥锁并阻塞，等待消费者notfull来解除阻塞,
被唤醒时再加lock锁*/
}
/* Write the data and advance write pointer */
b->buffer[b->writepos] = data; /*写入数据（产品放入共享区域）*/
b->writepos++; /*写位置+1 */
if (b->writepos >= BUFFER_SIZE) b->writepos = 0;
/* Signal that the buffer is now not empty */
pthread_cond_signal(&b->notempty); /*释放阻塞在notempty条件变量上的（消费者）线程*/
pthread_mutex_unlock(&b->lock); /*解锁*/
}
/*--------------------------------------------------------*/
/* Read and remove an integer from the buffer */
int get(struct prodcons * b)/*消费*/
{
int data;
pthread_mutex_lock(&b->lock);/*加锁*/
/* Wait until buffer is not empty */
while (b->writepos == b->readpos) { /*判断读写位置是否相等*/
printf("wait for not empty\n");
pthread_cond_wait(&b->notempty, &b->lock);/*解lock互斥锁并阻塞，等待消费者notempty来解除阻塞
被唤醒时，再加lock锁*/
}
/* Read the data and advance read pointer */
data = b->buffer[b->readpos]; /*读数据（消费产品）*/
b->readpos++; /*读位置+1*/
if (b->readpos >= BUFFER_SIZE) b->readpos = 0;
/* Signal that the buffer is now not full */
pthread_cond_signal(&b->notfull); /*释放阻塞在notfull条件变量上的（生产者）线程*/
pthread_mutex_unlock(&b->lock); /*解锁*/
return data;
}
/*--------------------------------------------------------*/
#define OVER (-1)
struct prodcons buffer;
/*--------------------------------------------------------*/
void * producer(void * data)/*生产者函数*/
{
int n;
for (n = 0; n < 1000; n++) {/*总产量为1000，生产1000个产品，停止生产*/
printf(" put-->%d\n", n);
put(&buffer, n);/*生产产品，放入共享区域*/
}
put(&buffer, OVER);/*生产结束标志*/
printf("producer stopped!\n");
return NULL;
}
/*--------------------------------------------------------*/
void * consumer(void * data)/*消费者函数*/
{
int d;
while (1) {
d = get(&buffer);/*消费产品*/
if (d == OVER ) break;
printf(" %d-->get\n", d);
}
printf("consumer stopped!\n");
return NULL;
}
/*--------------------------------------------------------*/
int main(void)
{
pthread_t th_a, th_b;
void * retval;
init(&buffer);/*初始化共享区域*/
pthread_create(&th_a, NULL, producer, 0);/*创建生产者线程*/
pthread_create(&th_b, NULL, consumer, 0);/*创建消费者线程*/
/* Wait until producer and consumer finish. */
pthread_join(th_a, &retval);/*主线程等该生产者线程*/
pthread_join(th_b, &retval);/*主线程等该消费者线程*/
return 0;
}

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