c-ares/ares__timeval.c

/* $Id$ */

/* 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_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;
  if(0 == clock_gettime(CLOCK_MONOTONIC, &tsnow)) {
    now.tv_sec = tsnow.tv_sec;
    now.tv_usec = tsnow.tv_nsec / 1000;
  }
  /*
  ** Even when the configure process has truly detected monotonic clock
  ** availability, it might happen that it is not actually available at
  ** run-time. When this occurs simply fallback to other time source.
  */
#ifdef HAVE_GETTIMEOFDAY
  else
    (void)gettimeofday(&now, NULL);
#else
  else {
    now.tv_sec = (long)time(NULL);
    now.tv_usec = 0;
  }
#endif
  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

#if 0 /* Not used */
/*
 * 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;
}
#endif