无名信号量实现三个线程的同步互斥实例

代码

#include
sem_t sem1;
sem_t sem2;
sem_t sem3;
int c=10000;
void *task1(void *arg)
{
   int num=5;
   while (num--)
   {
    sleep(1);
    sem_wait(&sem3);
    c-=3000;
    printf("此时线程1,临界资源减少3000为c=%d\n",c);
    sem_post(&sem1);
   }
   pthread_exit(NULL);
}
void *task2(void *arg)
{
int num=5;
   while (num--)
   {
    sleep(1);
    sem_wait(&sem1);
    c+=3000;
    printf("此时线程2,临界资源加3000为c=%d\n",c);
    sem_post(&sem2);
   }
   pthread_exit(NULL);
}
void *task3(void *arg)
{
int num=5;
   while (num--)
   {
    sleep(1);
    sem_wait(&sem2);
    c*=3;
    printf("此时线程3,临界资源扩大三倍为c=%d\n",c);
    sem_post(&sem3);
   }
   pthread_exit(NULL);
}
int main(int argc, char const *argv[])
{
    pthread_t tid1,tid2,tid3;
    //无名信号量初始化
    //sem_init的第三个参数可以影响无名信号量申请和释放的顺序
    //越大越先，越小越后
    sem_init(&sem1,0,0);
    sem_init(&sem2,0,0);
    sem_init(&sem3,0,1);
    printf("c的值本来是%d\n",c);
    //线程创建
    pthread_create(&tid1,NULL,task1,NULL);
    pthread_create(&tid2,NULL,task2,NULL);
    pthread_create(&tid3,NULL,task3,NULL);
    //线程回收
    pthread_join(tid1,NULL);
    pthread_join(tid2,NULL);
    pthread_join(tid3,NULL);
    //无名信号量销毁
    sem_destroy(&sem1);
    sem_destroy(&sem2);
    sem_destroy(&sem3);
    return 0;
}

运行结果