From d285833290316cb5dd1e7f1e52c96be3e9cf21cd Mon Sep 17 00:00:00 2001
From: Daniel Stone <daniel@fooishbar.org>
Date: Wed, 25 Oct 2006 23:57:00 +0300
Subject: GetTimeInMillis: spuport monotonic clock Add support for
 CLOCK_MONOTONIC from clock_gettime, and use that in GetTimeInMillis() if
 available, falling back to the old gettimeofday() implementation.

This is _slightly_ faster on some 64-bit architectures, and _slightly_
slower on others (though barely measurable).
---
 os/utils.c | 39 +++++++++++++++++++++++++++++++++++----
 1 file changed, 35 insertions(+), 4 deletions(-)

(limited to 'os')

diff --git a/os/utils.c b/os/utils.c
index 31ae26a18..379291c9d 100644
--- a/os/utils.c
+++ b/os/utils.c
@@ -53,6 +53,19 @@ OR PERFORMANCE OF THIS SOFTWARE.
 #include <dix-config.h>
 #endif
 
+/* The world's most shocking hack, to ensure we get clock_gettime() and
+ * CLOCK_MONOTONIC. */
+#ifdef _POSIX_C_SOURCE
+#define _SAVED_POSIX_C_SOURCE _POSIX_C_SOURCE
+#undef _POSIX_C_SOURCE
+#endif
+#define _POSIX_C_SOURCE 199309L
+#include <time.h>
+#undef _POSIX_C_SOURCE
+#ifdef _SAVED_POSIX_C_SOURCE
+#define _POSIX_C_SOURCE _SAVED_POSIX_C_SOURCE
+#endif
+
 #ifdef __CYGWIN__
 #include <stdlib.h>
 #include <signal.h>
@@ -92,7 +105,6 @@ OR PERFORMANCE OF THIS SOFTWARE.
 #if !defined(SYSV) && !defined(WIN32) && !defined(Lynx) && !defined(QNX4)
 #include <sys/resource.h>
 #endif
-#include <time.h>
 #include <sys/stat.h>
 #include <ctype.h>    /* for isspace */
 #include <stdarg.h>
@@ -256,6 +268,8 @@ int auditTrailLevel = 1;
 
 _X_EXPORT Bool Must_have_memory = FALSE;
 
+static int monotonic_usable = -1;
+
 #ifdef AIXV3
 int SyncOn  = 0;
 extern int SelectWaitTime;
@@ -535,10 +549,27 @@ GiveUp(int sig)
 _X_EXPORT CARD32
 GetTimeInMillis(void)
 {
-    struct timeval  tp;
+    struct timeval tv;
+#ifdef MONOTONIC_CLOCK
+    struct timespec tp;
+    int spare = 0;
+
+    if (_X_UNLIKELY(monotonic_usable == -1)) {
+        if (clock_gettime(0, &tp) == 0 &&
+            clock_getcpuclockid(0, &spare) == 0)
+            monotonic_usable = 1;
+        else
+            monotonic_usable = 0;
+    }
+
+    if (_X_LIKELY(monotonic_usable == 1)) {
+        if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
+            return (tp.tv_sec * 1000) + (tp.tv_nsec / 1000000);
+    }
+#endif
 
-    X_GETTIMEOFDAY(&tp);
-    return(tp.tv_sec * 1000) + (tp.tv_usec / 1000);
+    X_GETTIMEOFDAY(&tv);
+    return(tv.tv_sec * 1000) + (tv.tv_usec / 1000);
 }
 
 _X_EXPORT void
-- 
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