[glib] Simplify checks for CLOCK_MONOTONIC

[Dan Winship <danw src gnome org>]

commit 71cf70b39cd3859ac4cb4954c369bda731a61171
Author: Dan Winship <danw gnome org>
Date:   Tue Oct 11 15:38:37 2011 -0400

    Simplify checks for CLOCK_MONOTONIC
    
    Remove the complicated configure-time and runtime checks, and just use
    CLOCK_MONOTONIC if it's defined.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=661421

 configure.ac |   15 ----------
 glib/gmain.c |   84 +++++++++++++++++++++++----------------------------------
 2 files changed, 34 insertions(+), 65 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 4a9e723..e6feb1d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2402,21 +2402,6 @@ AC_CHECK_FUNCS(clock_gettime, [], [
 ])
 AC_SUBST(GLIB_RT_LIBS)
 
-AC_CACHE_CHECK(for monotonic clocks,
-    glib_cv_monotonic_clock,AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
-#include <time.h>
-#include <unistd.h>
-int main() {
-#if !(defined(_POSIX_MONOTONIC_CLOCK) && _POSIX_MONOTONIC_CLOCK >= 0 && defined(CLOCK_MONOTONIC))
-        #error No monotonic clock
-#endif
-	return 0;
-}
-]])],glib_cv_monotonic_clock=yes,glib_cv_monotonic_clock=no))
-if test "$glib_cv_monotonic_clock" = "yes"; then
-  AC_DEFINE(HAVE_MONOTONIC_CLOCK,1,[Have a monotonic clock])
-fi
-
 
 dnl ************************
 dnl *** g_atomic_* tests ***
diff --git a/glib/gmain.c b/glib/gmain.c
index 5250453..3cf1fa8 100644
--- a/glib/gmain.c
+++ b/glib/gmain.c
@@ -2013,66 +2013,50 @@ g_get_monotonic_time (void)
 {
 #ifdef HAVE_CLOCK_GETTIME
   /* librt clock_gettime() is our first choice */
-  {
-#ifdef HAVE_MONOTONIC_CLOCK
-    static volatile gsize clockid = 0;
+  struct timespec ts;
+
+#ifdef CLOCK_MONOTONIC
+  clock_gettime (CLOCK_MONOTONIC, &ts);
 #else
-    static clockid_t clockid = CLOCK_REALTIME;
-#endif
-    struct timespec ts;
-
-#ifdef HAVE_MONOTONIC_CLOCK
-    if (g_once_init_enter (&clockid))
-      {
-	clockid_t best_clockid;
-
-	if (sysconf (_SC_MONOTONIC_CLOCK) >= 0)
-	  best_clockid = CLOCK_MONOTONIC;
-	else
-	  best_clockid = CLOCK_REALTIME;
-	g_once_init_leave (&clockid, (gsize)best_clockid);
-      }
+  clock_gettime (CLOCK_REALTIME, &ts);
 #endif
 
-    clock_gettime (clockid, &ts);
-
-    /* In theory monotonic time can have any epoch.
-     *
-     * glib presently assumes the following:
-     *
-     *   1) The epoch comes some time after the birth of Jesus of Nazareth, but
-     *      not more than 10000 years later.
-     *
-     *   2) The current time also falls sometime within this range.
-     *
-     * These two reasonable assumptions leave us with a maximum deviation from
-     * the epoch of 10000 years, or 315569520000000000 seconds.
-     *
-     * If we restrict ourselves to this range then the number of microseconds
-     * will always fit well inside the constraints of a int64 (by a factor of
-     * about 29).
-     *
-     * If you actually hit the following assertion, probably you should file a
-     * bug against your operating system for being excessively silly.
-     **/
-    g_assert (G_GINT64_CONSTANT (-315569520000000000) < ts.tv_sec &&
-              ts.tv_sec < G_GINT64_CONSTANT (315569520000000000));
-
-    return (((gint64) ts.tv_sec) * 1000000) + (ts.tv_nsec / 1000);
-  }
-#else
+  /* In theory monotonic time can have any epoch.
+   *
+   * glib presently assumes the following:
+   *
+   *   1) The epoch comes some time after the birth of Jesus of Nazareth, but
+   *      not more than 10000 years later.
+   *
+   *   2) The current time also falls sometime within this range.
+   *
+   * These two reasonable assumptions leave us with a maximum deviation from
+   * the epoch of 10000 years, or 315569520000000000 seconds.
+   *
+   * If we restrict ourselves to this range then the number of microseconds
+   * will always fit well inside the constraints of a int64 (by a factor of
+   * about 29).
+   *
+   * If you actually hit the following assertion, probably you should file a
+   * bug against your operating system for being excessively silly.
+   **/
+  g_assert (G_GINT64_CONSTANT (-315569520000000000) < ts.tv_sec &&
+            ts.tv_sec < G_GINT64_CONSTANT (315569520000000000));
+
+  return (((gint64) ts.tv_sec) * 1000000) + (ts.tv_nsec / 1000);
+
+#else /* !HAVE_CLOCK_GETTIME */
+
   /* It may look like we are discarding accuracy on Windows (since its
    * current time is expressed in 100s of nanoseconds) but according to
    * many sources, the time is only updated 64 times per second, so
    * microsecond accuracy is more than enough.
    */
-  {
-    GTimeVal tv;
+  GTimeVal tv;
 
-    g_get_current_time (&tv);
+  g_get_current_time (&tv);
 
-    return (((gint64) tv.tv_sec) * 1000000) + tv.tv_usec;
-  }
+  return (((gint64) tv.tv_sec) * 1000000) + tv.tv_usec;
 #endif
 }