LinuxC多线程编程第五篇：线程通信(Condition)

        线程同步还有一种情况，线程1需要等某个条件成立才能继续往下执行，如果这个条件不成立，线程1就阻塞等待，线程2在执行某个条件成立了就唤醒线程1。这个和Java中的wait()和notify()其实是一样的

注意：最下面有本文演示的源码的链接地址

初始化与销毁通信条件

#include
int pthread_cond_destroy(pthread_cond_t *cond);
int pthread_cond_init(pthread_cond_t *restrict cond, const pthread_condattr_t *restrict attr);
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
以上和上一篇中Mutex锁比较类似，我就不再重复。

具体实现函数

#include
int pthread_cond_timedwait(pthread_cond_t *restrict cond, pthread_mutex_t *restrict mutex, const struct timespec *restrict abstime);
int pthread_cond_wait(pthread_cond_t *restrict cond, pthread_mutex_t *restrict mutex);
int pthread_cond_broadcast(pthread_cond_t *cond);
int pthread_cond_signal(pthread_cond_t *cond);
这几个函数更加函数名就可以理解它的意思了，我就不多说。pthread_cond_signal、pthread_cond_broadcast与Java中notify、notifyAll()也是一样的。

pthread_cond_wait在一个conditon上阻塞等待，这个函数要做3个步骤：

• 释放Mutex
• 阻塞等待
• 当其它线程调用pthread_cond_signal或pthread_cond_signal,它会重写获取锁。

我简单的写了一个阻塞栈，方便大家理解：

#include 
#include 
#include 
struct node{
     struct node* next;
     int number;
}; 

pthread_cond_t hasNode = PTHREAD_COND_INITIALIZER;
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
struct node* head = NULL;
void* get(void *arg)
{
 struct node *node;
 while(1) 
 {  	
   pthread_mutex_lock(&lock); 
   if(head == NULL)
  {        
    printf("has no data...\n");
     pthread_cond_wait(&hasNode,&lock);
   }
   node = head;
   head = node->next;
   printf("get the head node number:%d\n",node->number);
   pthread_mutex_unlock(&lock);
   free(node); //移除获取到的节点
   sleep(rand()%5);
   }
}


void* put(void *p) 
{
 struct node* node; 
  while(1)
 {     
  node = malloc(sizeof(struct node));
  node->number = rand()%1000 +1;
  printf("put the head node number:%d\n",node->number);    
  pthread_mutex_lock(&lock);
  node->next = head;
  head = node;
  pthread_mutex_unlock(&lock);
  pthread_cond_signal(&hasNode);
  sleep(rand()%5);   	
}

}


int main(){
pthread_t pid,cid;
srand(time(NULL));
pthread_create(&pid,NULL,get,NULL);
pthread_create(&cid,NULL,put,NULL);
pthread_join(pid,NULL);
pthread_join(cid,NULL);
return 0;
}

 

编译运行结果如下

 

 

源码下载：http://download.csdn.net/detail/jefry_xdz/4246164