c++線程間依賴啟動

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; /*初始化互斥鎖*/
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;  //初始化條件變量 

void *thread1(void *);
void *thread2(void *);

int i=1;
int main(void)
{
        pthread_t t_a;
        pthread_t t_b;
        pthread_create(&t_a,NULL,thread1,(void *)NULL);/*創建進程t_a*/
        pthread_create(&t_b,NULL,thread2,(void *)NULL); /*創建進程t_b*/
        pthread_join(t_b, NULL);/*等待進程t_b結束*/
        pthread_mutex_destroy(&mutex);
        pthread_cond_destroy(&cond);
         exit(0);
}

void *thread1(void *junk)
{
        for(i=1;i<=9;i++)
        {
             pthread_mutex_lock(&mutex);//
             if(i%3==0)
                 pthread_cond_signal(&cond);/*條件改變，發送信號，通知t_b進程*/
              else       
                  printf("thead1:%d\n",i);
              pthread_mutex_unlock(&mutex);//*解鎖互斥量*/
              printf("Up Unlock Mutex\n");      
              sleep(1.5);
        }

}

void *thread2(void *junk)
{
        while(i<9)
        {
              pthread_mutex_lock(&mutex);

            if(i%3!=0)
                   pthread_cond_wait(&cond,&mutex);/*等待*/
            printf("thread2:%d\n",i);
            pthread_mutex_unlock(&mutex);
            printf("Down Ulock Mutex\n");

            sleep(1);
                }

}

調試後得知，其中pthread_cond_wait(&cond,&mutex);一定要鎖住的mutex才有效。 pthread_cond_signal(&cond);而這裡可以與mutex沒有任何關系，一般用法是。兩個線程全局一個cond和mutex，key。cond是條件變量。而mutex唯一目的是可以達到 當一個線程，執行到某一句話後，再執行另一個線程。

static void *work(void *pthis)
 {
 duan->lock();
 communication *handle= (communication *)pthis;
 std::cout<<"deng dai xinhao12!\n";
 key=10;//改變key，
 duan->unlock();
 handle->ComPos->signal();
 std::cout<<"deng dai xinhao!\n";

duan->lock();
 position *handle = (position *)pthis;
 if(handle->mut==NULL)
 //handle->mut=new Mutex();

// std::cout<<"position dengdai!\n"; 
 std::cout<<"position dengdai!\n";
 while(key==0)  
 handle->ComPos->wait(*(duan));//線程 等待另一個消息。就是先執行上一個線程。有了線程的先後關系
 duan->unlock(); 
 //handle->mut->unlock();
 std::cout<<"position dengdai jieshu!\n";
// }
}