检测是否支持monotonic

最新推荐文章于 2025-01-02 16:03:04 发布

yongqingjiao

最新推荐文章于 2025-01-02 16:03:04 发布

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分类专栏： monotonic_time 文章标签： monotonic_time

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本文介绍了一个用于配置系统中单调时钟的函数evutil_configure_monotonic_time_。该函数检查并利用CLOCK_MONOTONIC_COARSE或CLOCK_MONOTONIC特性，以确保即使在较旧的内核版本中也能获取到稳定的系统时间。

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  int 
 
  evutil_configure_monotonic_time_ 
  ( 
  struct 
   evutil_monotonic_timer  
  * 
  base, 
 
  int 
   flags) 
 
  { 
 
  /* CLOCK_MONOTONIC exists on FreeBSD, Linux, and Solaris. You need to 
 
       * check for it at runtime, because some older kernel versions won't 
 
       * have it working. */ 
 
  #ifdef 
    
  CLOCK_MONOTONIC_COARSE 
 
  const 
    
  int 
   precise  
  = 
   flags  
  & 
   EV_MONOT_PRECISE; 
 
  #endif 
 
  const 
    
  int 
   fallback  
  = 
   flags  
  & 
   EV_MONOT_FALLBACK; 
 
  struct 
   timespec ts; 
 
  #ifdef 
    
  CLOCK_MONOTONIC_COARSE 
 
  if 
   (CLOCK_MONOTONIC_COARSE  
  < 
    
  0 
  ) { 
 
  /* Technically speaking, nothing keeps CLOCK_* from being 
 
           * negative (as far as I know). This check and the one below 
 
           * make sure that it's safe for us to use -1 as an "unset" 
 
           * value. */ 
 
  event_errx 
  ( 
  1 
  , 
  "I didn't expect CLOCK_MONOTONIC_COARSE to be < 0" 
  ); 
 
      } 
 
  if 
   ( 
  ! 
   precise  
  && 
    
  ! 
   fallback) { 
 
  if 
   ( 
  clock_gettime 
  (CLOCK_MONOTONIC_COARSE,  
  & 
  ts)  
  == 
    
  0 
  ) { 
 
              base-> 
  monotonic_clock 
    
  = 
   CLOCK_MONOTONIC_COARSE; 
 
  return 
    
  0 
  ; 
 
          } 
 
      } 
 
  #endif 
 
  if 
   ( 
  ! 
  fallback  
  && 
    
  clock_gettime 
  (CLOCK_MONOTONIC,  
  & 
  ts)  
  == 
    
  0 
  ) { 
 
          base-> 
  monotonic_clock 
    
  = 
   CLOCK_MONOTONIC; 
 
  return 
    
  0 
  ; 
 
      } 
 
  if 
   (CLOCK_MONOTONIC  
  < 
    
  0 
  ) { 
 
  event_errx 
  ( 
  1 
  , 
  "I didn't expect CLOCK_MONOTONIC to be < 0" 
  ); 
 
      } 
 
      base-> 
  monotonic_clock 
    
  = 
    
  - 
  1 
  ; 
 
  return 
    
  0 
  ; 
 
  }