线程2——条件变量

动态创建条件变量

int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *cond_attr);

---

注销一个条件变量

int pthread_cond_destroy(pthread_cond_t *cond);

---

无条件等待

int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);

---

计时等待

int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec*abstime);

---

发送单个条件变量成立信号

int pthread_cond_signal(pthread_cond_t *cond)

---

 广播条件变量成立信号

int pthread_cond_ broadcast (pthread_cond_t *cond)

---

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/time.h>
//声明两个线程
void* task1(void *arg);
void* task2(void *arg);
pthread_t tid[3];                    //线程的3个指针
pthread_mutex_t lock;                //互斥锁指针
pthread_cond_t cond;                //条件变量指针
int main(void)
{
    int ret;
    
    //初始化互斥锁和条件变量
    pthread_mutex_init(&lock,NULL);
    pthread_cond_init(&cond,NULL);
    //创建2个线程
    pthread_create(&tid[0],NULL,task1,NULL);
    pthread_create(&tid[1],NULL,task2,NULL);
    //等待
    pthread_join(tid[0],NULL);
    pthread_join(tid[1],NULL);

    printf("Main:ALL new threads end
");
    //销毁互斥锁
    pthread_mutex_destroy(&lock);
    pthread_exit(NULL);
}

void* task1(void *arg)
{
    struct timeval now;
    /*
     struct timeval 
        {
          time_t       tv_sec;    //  seconds 秒
          suseconds_t   tv_usec; // microseconds 毫秒
        };
    */
    struct timespec outtime;
    /*
    struct timespec 
        {
            time_t tv_sec; // seconds 秒
            long tv_nsec; // and nanoseconds 纳秒 
        };
    */
    printf("I am task1
");
    pthread_mutex_lock(&lock);        //上锁
    printf("task1: wait max time is 5s
");
    gettimeofday(&now, NULL);        //返回自1970-01-01 00:00:00到现在经历的秒数
    outtime.tv_sec = now.tv_sec + 5; 
    outtime.tv_nsec = now.tv_usec * 1000;
    pthread_cond_timedwait(&cond, &lock, &outtime);//线程1等待条件变量，最多等待5s
    printf("task1: coutinue run
");
    printf("task1: ready to pthread_exit
");
    
    pthread_exit(NULL);
}


void* task2(void *arg)
{
    printf("I am task2
");
    sleep(3);      //线程2休眠3s后激活条件变量
    printf("task2: ready to signal the cond
");
    pthread_cond_signal(&cond);    //发送变量成立信号 用来激活条件变量
    printf("task2: ready to pthread_exit
");
    pthread_exit(NULL);
}

运行后代码如下

k1: wait max time is 5s
I am task2
task2: ready to signal the cond
task2: ready to pthread_exit
task1: coutinue run
task1: ready to pthread_exit
Main:ALL new threads end

先运行task1，触发条件变量，跳到task2激活，执行task2的两句话，然后再回到task1执行两句话，最后回到主函数

计时等待：pthread_cond_timedwait()；用法：

struct timeval now;
struct timespec outtime;
gettimeofday(&now, NULL);//获取当前时间
outtime.tv_sec = now.tv_sec + 5; //设定唤醒的绝对时间是当前时间+5s
outtime.tv_nsec = now.tv_usec * 1000;
pthread_cond_timedwait(&cond, &lock, &outtime);

用到的两个结构体

struct timeval{  
    long int tv_sec; // 秒数  
    long int tv_usec; // 微秒数  
}  



struct timespec {
    time_t tv_sec; // seconds 秒 
    long tv_nsec; // and nanoseconds 毫秒 
};