Use monotonic time source if available.

ares__timeval.c

@@ -0,0 +1,95 @@
+/* $Id$ */
+
+/* Copyright (C) 2008 by Daniel Stenberg et al
+ *
+ * Permission to use, copy, modify, and distribute this software and its
+ * documentation for any purpose and without fee is hereby granted, provided
+ * that the above copyright notice appear in all copies and that both that
+ * copyright notice and this permission notice appear in supporting
+ * documentation, and that the name of M.I.T. not be used in advertising or
+ * publicity pertaining to distribution of the software without specific,
+ * written prior permission.  M.I.T. makes no representations about the
+ * suitability of this software for any purpose.  It is provided "as is"
+ * without express or implied warranty.
+ */
+
+#include "setup.h"
+#include "ares.h"
+#include "ares_private.h"
+
+#if defined(WIN32) && !defined(MSDOS)
+
+struct timeval ares__tvnow(void)
+{
+  /*
+  ** GetTickCount() is available on _all_ Windows versions from W95 up
+  ** to nowadays. Returns milliseconds elapsed since last system boot,
+  ** increases monotonically and wraps once 49.7 days have elapsed.
+  */
+  struct timeval now;
+  DWORD milliseconds = GetTickCount();
+  now.tv_sec = milliseconds / 1000;
+  now.tv_usec = (milliseconds % 1000) * 1000;
+  return now;
+}
+
+#elif defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC)
+
+struct timeval ares__tvnow(void)
+{
+  /*
+  ** clock_gettime() is granted to be increased monotonically when the
+  ** monotonic clock is queried. Time starting point is unspecified, it
+  ** could be the system start-up time, the Epoch, or something else,
+  ** in any case the time starting point does not change once that the
+  ** system has started up.
+  */
+  struct timeval now;
+  struct timespec tsnow;
+  (void)clock_gettime(CLOCK_MONOTONIC, &tsnow)
+  now.tv_sec = tsnow.tv_sec;
+  now.tv_usec = tsnow.tv_nsec / 1000;
+  return now;
+}
+
+#elif defined(HAVE_GETTIMEOFDAY)
+
+struct timeval ares__tvnow(void)
+{
+  /*
+  ** gettimeofday() is not granted to be increased monotonically, due to
+  ** clock drifting and external source time synchronization it can jump
+  ** forward or backward in time.
+  */
+  struct timeval now;
+  (void)gettimeofday(&now, NULL);
+  return now;
+}
+
+#else
+
+struct timeval ares__tvnow(void)
+{
+  /*
+  ** time() returns the value of time in seconds since the Epoch.
+  */
+  struct timeval now;
+  now.tv_sec = (long)time(NULL);
+  now.tv_usec = 0;
+  return now;
+}
+
+#endif
+
+/*
+ * Make sure that the first argument is the more recent time, as otherwise
+ * we'll get a weird negative time-diff back...
+ *
+ * Returns: the time difference in number of milliseconds.
+ */
+long ares__tvdiff(struct timeval newer, struct timeval older)
+{
+  return (newer.tv_sec-older.tv_sec)*1000+
+    (newer.tv_usec-older.tv_usec)/1000;
+}
+