如何阻止时间在Linux上向后运行? [英] How to stop time from running backwards on Linux?

问题描述

这里我做了一个小测试，以验证时间确实只在Linux中向前运行.

Here's a little test I've written to verify that time does indeed only run forwards in Linux.

#include <time.h>
#include <sys/time.h>  

bool timeGoesForwardTest2()
{
   timeval tv1, tv2;   
   double startTime = getTimeSeconds();  // my function

   while ( getTimeSeconds() - startTime < 5 )
   {
      gettimeofday( &tv1, NULL );  
      gettimeofday( &tv2, NULL );  

      if ( tv2.tv_usec == tv1.tv_usec &&
           tv2.tv_sec == tv1.tv_sec )
      {
         continue;  // Equal times are allowed.
      }

      // tv2 should be greater than tv1
      if ( !( tv2.tv_usec>tv1.tv_usec ||
              tv2.tv_sec-1 == tv1.tv_sec ) )
      {
         printf( "tv1: %d %d\n", int( tv1.tv_sec ), int( tv1.tv_usec ) );
         printf( "tv2: %d %d\n", int( tv2.tv_sec ), int( tv2.tv_usec ) );
         return false;
      }         
   }
   return true;
}

测试失败并显示结果.

 tv1: 1296011067 632550
 tv2: 1296011067 632549

ummm ....

ummm....

为什么会这样?

这是我的设置:

Linux version 2.6.35-22-generic (buildd@rothera) (gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu4) ) #33-Ubuntu SMP Sun Sep 19 20:34:50 UTC 2010 (Ubuntu 2.6.35-22.33-generic 2.6.35.4)
... running inside VirtualBox 3.2.12, in Windows 7.

推荐答案

VirtualBox上有一个公开问题错误跟踪器.他们链接到博客文章，说明为什么您不应该使用gettimeofday()来衡量时间的流逝:

There is an open issue at the VirtualBox Bug Tracker. They link to a blog post stating why you shouldn't use gettimeofday() to measure the passage of time:

最便捷的时间测量方式正确地似乎是clock_gettime(CLOCK_MONOTONIC，...)

The most portable way to measure time correctly seems to be clock_gettime(CLOCK_MONOTONIC, ...)

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