线程中的 条件变量 pthread_cond_t

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;/*初始化互斥锁*/
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;/*初始化条件变量*/
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);/*创建进程t_a*/
    pthread_create(&t_b,NULL,thread2,(void *)NULL); /*创建进程t_b*/
    pthread_join(t_a, NULL);/*等待进程t_a结束*/
    pthread_join(t_b, NULL);/*等待进程t_b结束*/
    pthread_mutex_destroy(&mutex);
    pthread_cond_destroy(&cond);
    exit(0);
}
void *thread1(void *junk)
{
    for(i=1;i<=6;i++)
    {
		printf("\n1111111111     i is %d         111111111111\n",i);
        pthread_mutex_lock(&mutex);/*锁住互斥量*/
		printf("thread1: lock %d\n", __LINE__);
        if(i%3==0){
			printf("thread1:signal 1  line:%d   i is %d \n", __LINE__,i);
            pthread_cond_signal(&cond);/*条件改变，发送信号，通知t_b进程*/
			printf("thread1:signal 2  %d\n", __LINE__);
			sleep(1);
		}
        pthread_mutex_unlock(&mutex);/*解锁互斥量*/
		printf("thread1: unlock %d\n\n", __LINE__);
		sleep(1);
	}
}
void *thread2(void *junk)
{
    while(i<6)
    {
		
		printf("2222222222222 in pthread2 i is %d 222222222222222222 \n",i);
        pthread_mutex_lock(&mutex);
		printf("thread2: lock line:%d   i is %d\n", __LINE__,i);
		if(i%3!=0){
			printf("thread2: wait 1  %d\n", __LINE__);
            pthread_cond_wait(&cond,&mutex);/*解锁mutex，并等待cond改变*/
			
			
			
			printf("thread2: wait 2  %d\n", __LINE__);
			printf("thread2: i is  %d\n\n", i);
		}
        pthread_mutex_unlock(&mutex);
		printf("thread2: unlock %d\n\n", __LINE__);
		sleep(1);
	}
}