[PATCH xserver v2] xwayland: Use the CLOCK_MONOTONIC clock

[Olivier Fourdan]

Hi Jonas,

> By default the X server will try CLOCK_MONOTONIC_COARSE before
> CLOCK_MONOTONIC, while A Wayland compositor may only support getting
> their timestamps from the CLOCK_MONOTONIC clock. This causes various
> issues since it may happen that a timestamp from CLOCK_MONOTONIC
> retrieved before a sending an X request will still be "later" than the
> timestamp the X server than gets after receiving the request, due to the
> fact that CLOCK_MONOTONIC_COARSE has a lower resolution.
> 
> To avoid these issues, make Xwayland always use CLOCK_MONOTONIC, so
> that it becomes possible for Wayland compositor only supporting
> CLOCK_MONOTONIC and X server to use the same clock.
> 
> Signed-off-by: Jonas Ådahl <jadahl at gmail.com>
> Acked-by: Daniel Stone <daniels at collabora.com>
> ---
> 
> Here is a version that just simply forces it. I figured it would be annoynig
> to
> have to detect the Xwayland version and append a command line given the
> version.
> 
> Let me know if a command line argument version of the patch is preferred by
> anyone.

I agree it's better to have it on by default for Xwayland, not all compositors make it easy to change Xwayland options without rebuilding.

I reckon this patch is much needed, I'd be happy to see this merged in 1.18 and master.

Cheers,
Olivier


>  configure.ac           |  4 ++++
>  hw/xwayland/xwayland.c |  2 ++
>  include/os.h           |  7 +++++++
>  os/utils.c             | 24 ++++++++++++++++++++++--
>  4 files changed, 35 insertions(+), 2 deletions(-)
> 
> diff --git a/configure.ac b/configure.ac
> index f4de90f..8cc508c 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -2471,6 +2471,10 @@ if test "x$XWAYLAND" = xyes; then
>  	AC_SUBST([XWAYLAND_LIBS])
>  	AC_SUBST([XWAYLAND_SYS_LIBS])
>  
> +	if test "x$MONOTONIC_CLOCK" != xyes; then
> +		AC_MSG_ERROR([Xwayland requires CLOCK_MONOTONIC support.])
> +	fi
> +
>  	WAYLAND_PREFIX=`$PKG_CONFIG --variable=prefix wayland-client`
>  	AC_PATH_PROG([WAYLAND_SCANNER], [wayland-scanner],,
>  		     [${WAYLAND_PREFIX}/bin$PATH_SEPARATOR$PATH])
> diff --git a/hw/xwayland/xwayland.c b/hw/xwayland/xwayland.c
> index 3d36205..cad4e9d 100644
> --- a/hw/xwayland/xwayland.c
> +++ b/hw/xwayland/xwayland.c
> @@ -32,6 +32,7 @@
>  #include <misyncshm.h>
>  #include <compositeext.h>
>  #include <glx_extinit.h>
> +#include <os.h>
>  
>  void
>  ddxGiveUp(enum ExitCode error)
> @@ -47,6 +48,7 @@ AbortDDX(enum ExitCode error)
>  void
>  OsVendorInit(void)
>  {
> +    ForceClockId(CLOCK_MONOTONIC);
>  }
>  
>  void
> diff --git a/include/os.h b/include/os.h
> index 461d5d6..f37ad5d 100644
> --- a/include/os.h
> +++ b/include/os.h
> @@ -51,6 +51,9 @@ SOFTWARE.
>  #include <stdarg.h>
>  #include <stdint.h>
>  #include <string.h>
> +#ifdef MONOTONIC_CLOCK
> +#include <time.h>
> +#endif
>  
>  #define SCREEN_SAVER_ON   0
>  #define SCREEN_SAVER_OFF  1
> @@ -180,6 +183,10 @@ extern _X_EXPORT void ListenOnOpenFD(int /* fd */ , int
> /* noxauth */ );
>  
>  extern _X_EXPORT Bool AddClientOnOpenFD(int /* fd */ );
>  
> +#ifdef MONOTONIC_CLOCK
> +extern _X_EXPORT void ForceClockId(clockid_t /* forced_clockid */);
> +#endif
> +
>  extern _X_EXPORT CARD32 GetTimeInMillis(void);
>  extern _X_EXPORT CARD64 GetTimeInMicros(void);
>  
> diff --git a/os/utils.c b/os/utils.c
> index e48d9f8..2c4a588 100644
> --- a/os/utils.c
> +++ b/os/utils.c
> @@ -210,6 +210,10 @@ sig_atomic_t inSignalContext = FALSE;
>  #define HAS_SAVED_IDS_AND_SETEUID
>  #endif
>  
> +#ifdef MONOTONIC_CLOCK
> +static clockid_t clockid;
> +#endif
> +
>  OsSigHandlerPtr
>  OsSignal(int sig, OsSigHandlerPtr handler)
>  {
> @@ -427,6 +431,24 @@ GiveUp(int sig)
>      errno = olderrno;
>  }
>  
> +#ifdef MONOTONIC_CLOCK
> +void
> +ForceClockId(clockid_t forced_clockid)
> +{
> +    struct timespec tp;
> +
> +    BUG_RETURN (clockid);
> +
> +    clockid = forced_clockid;
> +
> +    if (clock_gettime(clockid, &tp) != 0) {
> +        FatalError("Forced clock id failed to retrieve current time: %s\n",
> +                   strerror(errno));
> +        return;
> +    }
> +}
> +#endif
> +
>  #if (defined WIN32 && defined __MINGW32__) || defined(__CYGWIN__)
>  CARD32
>  GetTimeInMillis(void)
> @@ -446,7 +468,6 @@ GetTimeInMillis(void)
>  
>  #ifdef MONOTONIC_CLOCK
>      struct timespec tp;
> -    static clockid_t clockid;
>  
>      if (!clockid) {
>  #ifdef CLOCK_MONOTONIC_COARSE
> @@ -475,7 +496,6 @@ GetTimeInMicros(void)
>      struct timeval tv;
>  #ifdef MONOTONIC_CLOCK
>      struct timespec tp;
> -    static clockid_t clockid;
>  
>      if (!clockid) {
>          if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
> --
> 2.4.3
> 
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