gettimeofday

　　调用gettimeofday()函数可以获取当前的格林尼治时间和当前时区。它的函数原型是：

int gettimeofday(struct timeval *restrict tp, void *restrict tzp);

　　gettimeofday的参数涉及两个结构体：

struct timeval{
       time_t           tv_sec;      //秒(从1970.1.1)
       suseconds_t      tv_usec;     //微秒
};

struct timezone{
       int     tz_minuteswest;
       int     tz_dsttime;
};

　　假设现在需要使用pthread_cond_timewait来阻塞一个线程，使用方法如下：

pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
pthread_mutex_t  lock = PTHREAD_MUTEAX_INITIALIZER;

struct timespec timeout;
get_timespec(&timeout, 500);
pthread_cond_timewait(&cond, &lock, &timeout);

void get_timespec(timespec *ts, int millisecond)
{
       struct timeval now;
       gettimeofday(&now,NULL);
       ts->tv_sec = now.tv_sec;
       ts->tv_nsec = now.tv_usec*1000;
       ts->tv_nsec += millisecond*1000;
}