linux 條件變數

 

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

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

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,thread2,(void *)NULL);/*建立進程t_a*/
    pthread_create(&t_b,NULL,thread1,(void *)NULL); /*建立進程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);/*鎖住互斥量*/
        if(i%3==0)
             pthread_cond_signal(&cond);/*條件改變，發送訊號，通知t_b進程*/
        else       
             printf("thead1:%d\n",i);
        pthread_mutex_unlock(&mutex);/*解鎖互斥量*/

sleep(1);
}

}

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

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

sleep(1);
}

}

 

pthread_cond_wait:  

get cond àwake up;lock;

unget cond->unlock, then sleep