Linux下system_uptime函数

ReMeppo 2012-02-07 10:39:56

看这个函数有点头晕, 哪位热心的大哥大姐帮解释解释... 感激不尽



#define WRAPAROUND_VALUE (0xffffffffUL / HZ + 1) /* HZ = frequency of ticks

                                                    per second. */



/* Static function to get current sec and usec.  */

static int

system_uptime (struct pal_timeval *tv, struct pal_tzval *tz)

{

  struct sysinfo info;

  static unsigned long prev = 0;

  static unsigned long wraparound_count = 0;

  unsigned long uptime;

  static long base = 0;

  static long offset = 0;

  long leap;

  long diff;

  

  /* Get sysinfo.  */

  if (sysinfo (&info) < 0)   //得到系统信息包括启动时间

    return RESULT_ERROR;



  /* Check for wraparound. */

  if (prev > info.uptime)

    wraparound_count++;	//这个有什么用? 这个count是代表什么, 这里表达意思是什么? 怎么样count才++

  

  /* System uptime.  */

  uptime = wraparound_count * WRAPAROUND_VALUE + info.uptime;  //这里算的是什么? 

  prev = info.uptime;      

  

  /* Get tv_sec and tv_usec.  */

  gettimeofday (tv, tz);



//下面一连串的调整 都不知道是什么意思了. 几个静态变量和临时变量混和在一起... 

  /* Deffernce between gettimeofday sec and uptime.  */

  leap = tv->tv_sec - uptime;



  /* Remember base diff for adjustment.  */

  if (! base)

    base = leap;



  /* Basically we use gettimeofday's return value because it is the

     only way to get required granularity.  But when diff is very

     different we adjust the value using base value.  */

  diff = (leap - base) + offset;



  /* When system time go forward than 2 sec.  */

  if (diff > 2 || diff < -2)

    offset -= diff;



  /* Adjust second.  */

  tv->tv_sec += offset;



  return RESULT_OK;

}

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ReMeppo 2012-02-14

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帅得不敢出门 2012-02-11

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WRAPAROUND_VALUE (0xffffffffUL / HZ + 1) 溢出一次需要的时间



 /* Check for wraparound. */

  if (prev > info.uptime)

    wraparound_count++;    //溢出一次 wraparound_count++ 

  

  /* System uptime.  */

  uptime = wraparound_count * WRAPAROUND_VALUE + info.uptime;  所有溢出时间相加+info.uptime就是总uptime

  prev = info.uptime;      



// 溢出的例子    比如总量为10 ,此时prev = 10  那么info.uptime为 1而不是11,此时prev > info.uptime

那么此时wraparound_count=1  ，然后再算出现在的uptime

下面的代码都有英文注释，我就不解释了。

ReMeppo 2012-02-10