多线程中互斥量与条件变量的使用

现在的位置: 首页 > 综合 > 正文

RSS

多线程中互斥量与条件变量的使用

2013年09月11日 ⁄ 综合 ⁄ 共 3453字 ⁄ 字号小中大 ⁄ 评论关闭

多线程中利用互斥量与条件变量进行线程间同步的过程如下：

1.线程入口处先get locker

2.判断条件变量的值

3条件变量为真进行相应的出来

4条件变量为假，调用pthread_cond_wait释放锁，并拥塞线程，此时执行流转到另一线程判断条件变量的真假。

5进行相应的处理之后，再次判读是否有必要更改条件变量的状态

6释放互斥锁

#include <stdio.h> 
#include <stdlib.h> 
#include <unistd.h> 
#include <pthread.h> 
#define MUTEX_COND_DEBUG 
#ifdef MUTEX_COND_DEBUG 
#define DB(x) x 
#else 
#define DB(x) 
#endif 
#define BUFFER_SIZE 8 
struct Products 
{ 
int buffer[BUFFER_SIZE]; 
pthread_mutex_t locker; //保证存取操作的互斥性 
pthread_cond_t notEmpty; //是否可读 
pthread_cond_t notFull; //是否可写 
int posReadFrom; 	 //消费 
int posWriteTo; //生产 
}; 
int BufferIsFull(struct Products* products) 
{ 
if ((products->posWriteTo + 1) % BUFFER_SIZE == products->posReadFrom) 
{ 
return (1); 
} 
return (0); 
} 
int BufferIsEmpty(struct Products* products) 
{ 
if (products->posWriteTo == products->posReadFrom) 
{ 
return (1); 
} 
return (0); 
} 
//制造产品 
void Produce(struct Products* products, int item) 
{ 
int empty; 
//原子操作！ 错！！ 应该是得不到锁，进入阻塞状态，等待其他线程释放该锁。 
pthread_mutex_lock(&products->locker); 
DB(printf("Produce get the locker/n");) 
//释放锁，这样消费线程才可以访问资源，并消费，之后通知notfull消息 
while (BufferIsFull(products)) 
{ 
DB(printf("buffer is full, can not produce/n");) 
DB(printf("Produce release the locker/n");) 
/*如果条件不真，解互斥量锁，拥塞线程，知道条件为真，等条件为真时，再次将互斥量锁住*/ 
pthread_cond_wait(&products->notFull, &products->locker); 
DB(printf("notFull is true and it will write/n");) 
} //无空间可写入
 //判断是否为空，设置empty标志 
empty = BufferIsEmpty( products); 
//写入数据 
products->buffer[products->posWriteTo] = item; 
DB(printf("done! producer: %d/n", item);) 
products->posWriteTo++; 
if (products->posWriteTo >= BUFFER_SIZE) 
products->posWriteTo = 0; 
//如果之前为空，则发通知给消费线程,新数据被写入，可以消费 
if(empty) 
{ 
DB(printf("buffer is empty,can not consume/n");) 
DB(printf("buffer is writed,consume it/n");) 
pthread_cond_signal(&products->notEmpty); 
} 
pthread_mutex_unlock(&products->locker); //解锁 
DB(printf("produce release the locker/n");) 
} 
//消费产品 
int Consume(struct Products* products) 
{ 
int item, full; 
pthread_mutex_lock(&products->locker); 
DB(printf("Consume get the locker/n");) 
// 为空时持续等待,无数据可读, 
// 进入等待状态，不占用CPU，同时，释放占用的互斥锁，一旦被唤醒则再次锁定互斥量，即锁定product结构体的读写。 
while (BufferIsEmpty(products)) 
{ 
DB(printf("buffer is empty, can not consume/n");) 
DB(printf("Consume release the locker/n");) 
pthread_cond_wait(&products->notEmpty, &products->locker); 
DB(printf("notEmpty is true and it will read/n");) 
} 
//判断是否为满，设置full标志 
full = BufferIsFull(products); 
//提取数据 
item = products->buffer[products->posReadFrom]; 
DB(printf("done! consume: %d/n", item);) 
products->posReadFrom++; 
if (products->posReadFrom >= BUFFER_SIZE) //如果到末尾,从头读取 
products->posReadFrom = 0; 
 //如果之前是full的，则发信号通知生产线程 
if(full) 
 { 
 DB(printf("buffer is full,can not produce/n");) 
 DB(printf("buffer is consume, produce it/n");) 
pthread_cond_signal(&products->notFull); 
} 
pthread_mutex_unlock(&products->locker); 
DB(printf("consume release the locker/n");) 
return item; 
} 
#define END_FLAG (-1) 
struct Products products; 
void* ProducerThread(void* data) 
{ 
int i; 
for (i = 0; i < 16; ++i) 
{ 
printf("producer: %d/n", i); 
Produce(&products, i); 
} 
Produce(&products, END_FLAG); 
return NULL; 
} 
void* ConsumerThread(void* data) 
{ 
int item; 
while (1) 
{ 
item = Consume(&products); 
if (END_FLAG == item) 
break; 
printf("consumer: %d/n", item); 
} 
return (NULL); 
} 
int main(int argc, char* argv[]) 
{ 
pthread_t producer; 
pthread_t consumer; 
int result; 
pthread_cond_init((pthread_cond_t * __restrict__)&products.notEmpty,NULL); 
pthread_cond_init((pthread_cond_t * __restrict__)&products.notFull,NULL); 
pthread_cond_init((pthread_cond_t * __restrict__)&products.locker,NULL); 
pthread_create(&producer, NULL, &ProducerThread, NULL); 
pthread_create(&consumer, NULL, &ConsumerThread, NULL); 
pthread_join(producer, (void *)&result); 
DB(printf("producer complete/n");) 
pthread_join(consumer, (void *)&result); 
DB(printf("consume complete/n");)
return 0; 
}

【上篇】ORACLE函数大全
【下篇】Android 读取元素的数据

作者: raglan

该日志由 raglan 于11年前发表在综合分类下，最后更新于 2013年09月11日.
转载请注明: 多线程中互斥量与条件变量的使用 | 学步园 +复制链接

抱歉!评论已关闭.

学步园

多线程中互斥量与条件变量的使用

作者: raglan

书签

最新文章New

本站推荐

返回首页