[PATCH xserver 3/4] os: Make CLOCK_REALTIME the CLOCK_MONOTONIC fallback

[Mark Kettenis]

> From: Jeff Smith <whydoubt at gmail.com>
> Date: Tue, 26 Dec 2017 22:10:54 -0600
> 
> When clock_gettime(CLOCK_MONOTONIC) fails, xserver falls back on
> gettimeofday().  However, gettimeofday() is deprecated in favor of
> clock_gettime(CLOCK_REALTIME).
> 
> Fall back on CLOCK_REALTIME if CLOCK_MONOTONIC fails.  As long as
> clock_gettime() is available, passing CLOCK_REALTIME can be expected to
> work.  Leave the gettimeofday() implementation available for
> configurations that do not try to obtain a monotonic clock.

What problem are you trying to fix?  Are there any modern systems
where CLOCK_MONOTONIC isn't available?  Adding more "legacy" codepaths
isn't going to improve the quality of the code!  Especially if those codepaths are redundant.


> diff --git a/os/utils.c b/os/utils.c
> index 876841c..f3d0f71 100644
> --- a/os/utils.c
> +++ b/os/utils.c
> @@ -200,8 +200,8 @@ sig_atomic_t inSignalContext = FALSE;
>  #endif
>  
>  #ifdef MONOTONIC_CLOCK
> -static clockid_t clockid;
> -static clockid_t clockid_micro;
> +static clockid_t clockid = ~0L;
> +static clockid_t clockid_micro = ~0L;
>  #endif
>  
>  OsSigHandlerPtr
> @@ -427,8 +427,8 @@ ForceClockId(clockid_t forced_clockid)
>  {
>      struct timespec tp;
>  
> -    BUG_RETURN(clockid);
> -    BUG_RETURN(clockid_micro);
> +    BUG_RETURN(clockid != ~0L);
> +    BUG_RETURN(clockid_micro != ~0L);
>  
>      if (clock_gettime(forced_clockid, &tp) != 0) {
>          FatalError("Forced clock id failed to retrieve current time: %s\n",
> @@ -452,16 +452,13 @@ GetTimeInMicros(void)
>  {
>      return (CARD64) GetTickCount() * 1000;
>  }
> -#else
> +#elif defined(MONOTONIC_CLOCK)
>  CARD32
>  GetTimeInMillis(void)
>  {
> -    struct timeval tv;
> -
> -#ifdef MONOTONIC_CLOCK
>      struct timespec tp;
>  
> -    if (!clockid) {
> +    if (clockid == ~0L) {
>  #ifdef CLOCK_MONOTONIC_COARSE
>          if (clock_getres(CLOCK_MONOTONIC_COARSE, &tp) == 0 &&
>              (tp.tv_nsec / 1000) <= 1000 &&
> @@ -472,32 +469,38 @@ GetTimeInMillis(void)
>          if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
>              clockid = CLOCK_MONOTONIC;
>          else
> -            clockid = ~0L;
> +            clockid = CLOCK_REALTIME;
>      }
> -    if (clockid != ~0L && clock_gettime(clockid, &tp) == 0)
> -        return (tp.tv_sec * 1000) + (tp.tv_nsec / 1000000L);
> -#endif
> -
> -    X_GETTIMEOFDAY(&tv);
> -    return (tv.tv_sec * 1000) + (tv.tv_usec / 1000);
> +    clock_gettime(clockid, &tp);
> +    return (tp.tv_sec * 1000) + (tp.tv_nsec / 1000000L);
>  }
> -
>  CARD64
>  GetTimeInMicros(void)
>  {
> -    struct timeval tv;
> -#ifdef MONOTONIC_CLOCK
>      struct timespec tp;
>  
> -    if (!clockid_micro) {
> +    if (clockid_micro == ~0L) {
>          if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
>              clockid_micro = CLOCK_MONOTONIC;
>          else
> -            clockid_micro = ~0L;
> +            clockid_micro = CLOCK_REALTIME;
>      }
> -    if (clockid_micro != ~0L && clock_gettime(clockid_micro, &tp) == 0)
> -        return (CARD64) tp.tv_sec * (CARD64)1000000 + tp.tv_nsec / 1000;
> -#endif
> +    clock_gettime(clockid_micro, &tp);
> +    return (CARD64) tp.tv_sec * (CARD64)1000000 + tp.tv_nsec / 1000;
> +}
> +#else
> +CARD32
> +GetTimeInMillis(void)
> +{
> +    struct timeval tv;
> +
> +    X_GETTIMEOFDAY(&tv);
> +    return (tv.tv_sec * 1000) + (tv.tv_usec / 1000);
> +}
> +CARD64
> +GetTimeInMicros(void)
> +{
> +    struct timeval tv;
>  
>      X_GETTIMEOFDAY(&tv);
>      return (CARD64) tv.tv_sec * (CARD64)1000000 + (CARD64) tv.tv_usec;
> -- 
> 2.9.4
> 
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