From 0d9b55f773b13dc1d44651163888b6a5037a2c7d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20P=C3=ADsa=C5=99?= <address@hidden>
Date: Wed, 30 Nov 2016 17:13:16 +0100
Subject: [PATCH 2/2] Prefer clock_gettime(CLOCK_MONOTONIC)
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gettimeofday() reports wrong elapsed real time if a time step was
inserted while running a program. This can happen on initial time
adjustment from NTP server or by manual adjustement by date command.

This patch uses clock_gettime(CLOCK_MONOTONIC) instead (if available)
that does not suffer from the issue.

<http://lists.gnu.org/archive/html/bug-gnu-utils/2013-09/msg00008.html>

Signed-off-by: Petr Písař <address@hidden>
---
 configure.ac |  2 ++
 resuse.c     | 27 +++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index 2380b76..558d112 100644
--- a/configure.ac
+++ b/configure.ac
@@ -29,6 +29,8 @@ dnl Checks for library functions.
 AC_FUNC_VPRINTF
 AC_FUNC_WAIT3
 AC_CHECK_FUNCS(strerror)
+AC_SEARCH_LIBS(clock_gettime, [rt])
+test "$ac_cv_search_clock_gettime" != "no" && AC_DEFINE(HAVE_CLOCK_GETTIME)
 
 AC_MSG_CHECKING(for getpagesize)
 AC_TRY_LINK([#include <sys/param.h>],
diff --git a/resuse.c b/resuse.c
index 4133941..da0da64 100644
--- a/resuse.c
+++ b/resuse.c
@@ -23,7 +23,14 @@
 #include "wait.h"
 #include "port.h"
 
-#if !HAVE_WAIT3
+#if HAVE_WAIT3
+# if HAVE_CLOCK_GETTIME
+#  ifndef _POSIX_C_SOURCE
+#   define _POSIX_C_SOURCE 199309L
+#  endif
+#  include <time.h>
+# endif
+#else
 # include <sys/times.h>
 # ifndef HZ
 #  include <sys/param.h>
@@ -48,7 +55,14 @@ resuse_start (resp)
      RESUSE *resp;
 {
 #if HAVE_WAIT3
+#if HAVE_CLOCK_GETTIME
+  struct timespec res;
+  clock_gettime(CLOCK_MONOTONIC, &res);
+  resp->start.tv_sec = res.tv_sec;
+  resp->start.tv_usec = res.tv_nsec / 1000;
+#else
   gettimeofday (&resp->start, (struct timezone *) 0);
+#endif /* !HAVE_CLOCK_GETTIME */
 #else
   long value;
   struct tms tms;
@@ -56,7 +70,7 @@ resuse_start (resp)
   value = times (&tms);
   resp->start.tv_sec = value / HZ;
   resp->start.tv_usec = value % HZ * (1000000 / HZ);
-#endif
+#endif /* !HAVE_WAIT3 */
 }
 
 /* Wait for and fill in data on child process PID.
@@ -76,6 +90,9 @@ resuse_end (pid, resp)
   int status;
 
 #if HAVE_WAIT3
+#if HAVE_CLOCK_GETTIME
+  struct timespec res;
+#endif
   pid_t caught;
 
   /* Ignore signals, but don't ignore the children.  When wait3
@@ -86,7 +103,13 @@ resuse_end (pid, resp)
 	return 0;
     }
 
+#if HAVE_CLOCK_GETTIME
+  clock_gettime(CLOCK_MONOTONIC, &res);
+  resp->elapsed.tv_sec = res.tv_sec;
+  resp->elapsed.tv_usec = res.tv_nsec / 1000;
+#else
   gettimeofday (&resp->elapsed, (struct timezone *) 0);
+#endif
 #else  /* !HAVE_WAIT3 */
   long value;
   struct tms tms;
-- 
2.7.4