pthread_mutex_timedlock

函数pthread_mutex_timedlock
当线程试图获取一个已加锁的互斥变量时，pthread_mutex_timedlock互斥量原语允许绑定线程
阻塞的时间。pthread_mutex_timedlock函数与pthread_mutex_lock是基本等价的，但是在达到超时
时间值时，pthread_mutex_timedlock不会对互斥量进行加锁，而是返回错误码ETIMEDOUT。
#include<pthread.h>
#include<time.h>
int pthread_mutex_timedlock(pthread_mutex_t *restrict mutex,const struct timespec 

*restrict tsptr);
超时指定愿意等待的绝对时间（与相对时间对比而言，指定在时间x之前可以阻塞等待，而不是说愿

意阻塞Y秒）。这个超时时间是用timespec结构来表示的，它用秒和纳秒来描述时间。

#include"apue.h"
#include <pthread.h>
#include<time.h>

int
main(void)
{
    int err;
    struct timespec tout;
    struct tm *tmp;
    char buf[64];
    pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;

    pthread_mutex_lock(&lock);
    printf("mutex is locked
");
    clock_gettime(CLOCK_REALTIME, &tout);
    tmp = localtime(&tout.tv_sec);
    strftime(buf, sizeof(buf), "%r", tmp);
    printf("current time is %s
", buf);
    pthread_mutex_unlock(&lock);//这个是我自己加的，为了测试这个程序
    tout.tv_sec += 10;    /* 10 seconds from now */
    /* caution: this could lead to deadlock */
    err = pthread_mutex_timedlock(&lock, &tout);
    clock_gettime(CLOCK_REALTIME, &tout);
    tmp = localtime(&tout.tv_sec);
    strftime(buf, sizeof(buf), "%r", tmp);
    printf("the time is now %s
", buf);
    if (err == 0)
        printf("mutex locked again!
");
    else
        printf("can't lock mutex again: %s
", strerror(err));
    exit(0);
}