Internal time differences now use monotonic time source if available.

This also implies the removal of the winmm.lib dependency for WIN32.

17 files changed, 176 insertions, 208 deletions

diff --git a/CHANGES b/CHANGES
index d0e41a5d4..8372bd37b 100644
--- a/CHANGES
+++ b/CHANGES
@@ -7,6 +7,10 @@
                                   Changelog
 
 
+Yang Tse (9 May 2008)
+- Internal time differences now use monotonic time source if available.
+  This also implies the removal of the winmm.lib dependency for WIN32.
+
 Daniel Stenberg (9 May 2008)
 - Stefan Krause reported a busy-looping case when using the multi interface
   and doing CONNECT to a proxy. The app would then busy-loop until the proxy
diff --git a/RELEASE-NOTES b/RELEASE-NOTES
index 1e85e25fc..15781b3ea 100644
--- a/RELEASE-NOTES
+++ b/RELEASE-NOTES
@@ -33,6 +33,7 @@ This release includes the following bugfixes:
  o microsecond resolution keys for internal splay trees
  o krb4 and krb5 ftp segfault
  o multi interface busy loop for CONNECT requests
+ o internal time differences now use monotonic time source if available
 
 This release includes the following known bugs:
 
diff --git a/configure.ac b/configure.ac
index 910a8d160..8a5988959 100644
--- a/configure.ac
+++ b/configure.ac
@@ -675,36 +675,6 @@ if test x$CURL_DISABLE_LDAP != x1 ; then
 fi
 
 dnl **********************************************************************
-dnl Check for the presence of the winmm library.
-dnl **********************************************************************
-
-case $host in
-  *-*-cygwin*)
-    dnl Under Cygwin, winmm exists but is not needed as WIN32 is not #defined
-    dnl and gettimeofday() will be used regardless of the outcome of this test.
-    dnl Skip this test, otherwise -lwinmm will be needlessly added to LIBS
-    dnl (and recorded as such in the .la file, potentially affecting downstream
-    dnl clients of the library.)
-    ;;
-  *)
-    AC_MSG_CHECKING([for timeGetTime in winmm])
-    my_ac_save_LIBS=$LIBS
-    LIBS="-lwinmm $LIBS"
-    AC_TRY_LINK([#include <windef.h>
-                 #include <mmsystem.h>
-                 ],
-                 [timeGetTime();],
-                 [ dnl worked!
-                 AC_MSG_RESULT([yes])
-                 ],
-                 [ dnl failed, restore LIBS
-                 LIBS=$my_ac_save_LIBS
-                 AC_MSG_RESULT(no)]
-               )
-    ;;
-esac
-
-dnl **********************************************************************
 dnl Checks for IPv6
 dnl **********************************************************************
 
@@ -2006,6 +1976,7 @@ AC_CHECK_FUNCS( strtoll \
                 strcmpi \
                 gethostbyaddr \
                 gettimeofday \
+                clock_gettime \
                 inet_addr \
                 inet_ntoa \
                 inet_pton \
diff --git a/docs/INSTALL.devcpp b/docs/INSTALL.devcpp
index 8ff4144cc..ed5ed9150 100644
--- a/docs/INSTALL.devcpp
+++ b/docs/INSTALL.devcpp
@@ -239,7 +239,7 @@ Linker Links
 checked.
 
 3- Include in the white space immediately below the box referred in 2 -lcurl
--lws2_32 -lwinmm.
+-lws2_32.
 
 SSL Files
 ---------
diff --git a/docs/examples/Makefile.m32 b/docs/examples/Makefile.m32
index 470061c4c..5107c04fe 100644
--- a/docs/examples/Makefile.m32
+++ b/docs/examples/Makefile.m32
@@ -106,7 +106,7 @@ ifndef USE_LDAP_OPENLDAP
 curl_LDADD += -lwldap32
 endif
 endif
-curl_LDADD += -lws2_32 -lwinmm
+curl_LDADD += -lws2_32
 COMPILE = $(CC) $(INCLUDES) $(CFLAGS)
 
 # Makefile.inc provides the check_PROGRAMS and COMPLICATED_EXAMPLES defines
diff --git a/lib/Makefile.Watcom b/lib/Makefile.Watcom
index 8e5118ecb..ed564c111 100644
--- a/lib/Makefile.Watcom
+++ b/lib/Makefile.Watcom
@@ -10,7 +10,7 @@ CC = wcc386
 
 CFLAGS = -3r -mf -d3 -hc -zff -zgf -zq -zm -zc -s -fr=con -w2 -fpi -oilrtfm -bt=nt &
          -bd -d+ -dWIN32 -dCURL_CA_BUNDLE=getenv("CURL_CA_BUNDLE")                 &
-         -dBUILDING_LIBCURL -dWITHOUT_MM_LIB -dHAVE_SPNEGO=1 -dENABLE_IPV6         &
+         -dBUILDING_LIBCURL -dHAVE_SPNEGO=1 -dENABLE_IPV6                          &
          -dDEBUG_THREADING_GETADDRINFO -dDEBUG=1 -dCURLDEBUG -d_WIN32_WINNT=0x0501 &
          -dWINBERAPI=__declspec(cdecl) -dWINLDAPAPI=__declspec(cdecl)              &
          -I. -I..\include
diff --git a/lib/Makefile.m32 b/lib/Makefile.m32
index 6fd8b9b7c..615d07805 100644
--- a/lib/Makefile.m32
+++ b/lib/Makefile.m32
@@ -96,7 +96,7 @@ ifndef USE_LDAP_OPENLDAP
 DLL_LIBS += -lwldap32
 endif
 endif
-DLL_LIBS += -lws2_32 -lwinmm
+DLL_LIBS += -lws2_32
 COMPILE = $(CC) $(INCLUDES) $(CFLAGS)
 
 # Makefile.inc provides the CSOURCES and HHEADERS defines
diff --git a/lib/Makefile.vc6 b/lib/Makefile.vc6
index bce42a6a0..5652cb499 100644
--- a/lib/Makefile.vc6
+++ b/lib/Makefile.vc6
@@ -66,10 +66,6 @@ WINDOWS_SDK_PATH = "C:\Program Files\Microsoft SDK"
 !ENDIF

 !ENDIF

 

-# Use the high resolution time by default.  Comment this out to use low

-# resolution time and not require winmm.lib

-USEMM_LIBS = YES

-

 #############################################################

 ## Nothing more to do below this line!

 

@@ -85,13 +81,9 @@ LFLAGS     = /nologo /machine:$(MACHINE)
 SSLLIBS    = libeay32.lib ssleay32.lib

 ZLIBLIBSDLL= zdll.lib

 ZLIBLIBS   = zlib.lib

-!IFDEF USEMM_LIBS

-WINLIBS    = wsock32.lib wldap32.lib winmm.lib

-!ELSE

 WINLIBS    = wsock32.lib wldap32.lib

-CFLAGS     = $(CFLAGS) /DWITHOUT_MM_LIB

-!ENDIF

-#  RSAglue.lib was formerly needed in the SSLLIBS

+CFLAGS     = $(CFLAGS)

+

 CFGSET     = FALSE

 

 !IFDEF WINDOWS_SSPI

diff --git a/lib/config-win32ce.h b/lib/config-win32ce.h
index 6c0fb411f..b3f6c74ff 100644
--- a/lib/config-win32ce.h
+++ b/lib/config-win32ce.h
@@ -350,7 +350,6 @@
 #define CURL_DISABLE_FILE 1
 #define CURL_DISABLE_TELNET 1
 #define CURL_DISABLE_LDAP 1
-#define WITHOUT_MM_LIB 1
 
 #ifdef HAVE_WINDOWS_H
 #  ifndef WIN32_LEAN_AND_MEAN
diff --git a/lib/msvcproj.head b/lib/msvcproj.head
index cfc7b5aa8..703598059 100644
--- a/lib/msvcproj.head
+++ b/lib/msvcproj.head
@@ -54,7 +54,7 @@ BSC32=bscmake.exe
 # ADD BSC32 /nologo

 LINK32=link.exe

 # ADD BASE LINK32 kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib /nologo /dll /machine:I386

-# ADD LINK32 kernel32.lib ws2_32.lib wldap32.lib winmm.lib /nologo /dll /map /debug /machine:I386 /out:"Release/libcurl.dll"

+# ADD LINK32 kernel32.lib ws2_32.lib wldap32.lib /nologo /dll /map /debug /machine:I386 /out:"Release/libcurl.dll"

 

 !ELSEIF  "$(CFG)" == "curllib - Win32 Debug"

 

@@ -81,7 +81,7 @@ BSC32=bscmake.exe
 # ADD BSC32 /nologo

 LINK32=link.exe

 # ADD BASE LINK32 kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib /nologo /dll /debug /machine:I386 /pdbtype:sept

-# ADD LINK32 kernel32.lib ws2_32.lib wldap32.lib winmm.lib /nologo /dll /incremental:no /map /debug /machine:I386 /out:"Debug/libcurl.dll" /pdbtype:sept

+# ADD LINK32 kernel32.lib ws2_32.lib wldap32.lib /nologo /dll /incremental:no /map /debug /machine:I386 /out:"Debug/libcurl.dll" /pdbtype:sept

 # SUBTRACT LINK32 /nodefaultlib

 

 !ENDIF 

diff --git a/lib/select.c b/lib/select.c
index c305bc9fa..847933ee9 100644
--- a/lib/select.c
+++ b/lib/select.c
@@ -184,7 +184,7 @@ int Curl_socket_ready(curl_socket_t readfd, curl_socket_t writefd,
     return r;
   }
 
-  /* Avoid initial timestamp, avoid gettimeofday() call, when elapsed
+  /* Avoid initial timestamp, avoid curlx_tvnow() call, when elapsed
      time in this function does not need to be measured. This happens
      when function is called with a zero timeout or a negative timeout
      value indicating a blocking call should be performed. */
@@ -368,7 +368,7 @@ int Curl_poll(struct pollfd ufds[], unsigned int nfds, int timeout_ms)
     return r;
   }
 
-  /* Avoid initial timestamp, avoid gettimeofday() call, when elapsed
+  /* Avoid initial timestamp, avoid curlx_tvnow() call, when elapsed
      time in this function does not need to be measured. This happens
      when function is called with a zero timeout or a negative timeout
      value indicating a blocking call should be performed. */
diff --git a/lib/timeval.c b/lib/timeval.c
index bb9c0a174..b36633384 100644
--- a/lib/timeval.c
+++ b/lib/timeval.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2005, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2008, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -23,69 +23,70 @@
 
 #include "timeval.h"
 
-#ifndef HAVE_GETTIMEOFDAY
+#if defined(WIN32) && !defined(MSDOS)
 
-#ifdef WIN32
-#include <mmsystem.h>
-
-static int gettimeofday(struct timeval *tp, void *nothing)
+struct timeval curlx_tvnow(void)
 {
-#ifdef WITHOUT_MM_LIB
-  SYSTEMTIME st;
-  time_t tt;
-  struct tm tmtm;
-  /* mktime converts local to UTC */
-  GetLocalTime (&st);
-  tmtm.tm_sec = st.wSecond;
-  tmtm.tm_min = st.wMinute;
-  tmtm.tm_hour = st.wHour;
-  tmtm.tm_mday = st.wDay;
-  tmtm.tm_mon = st.wMonth - 1;
-  tmtm.tm_year = st.wYear - 1900;
-  tmtm.tm_isdst = -1;
-  tt = mktime (&tmtm);
-  tp->tv_sec = tt;
-  tp->tv_usec = st.wMilliseconds * 1000;
-#else
-  /**
-   ** The earlier time calculations using GetLocalTime
-   ** had a time resolution of 10ms.The timeGetTime, part
-   ** of multimedia apis offer a better time resolution
-   ** of 1ms.Need to link against winmm.lib for this
-   **/
-  unsigned long Ticks = 0;
-  unsigned long Sec =0;
-  unsigned long Usec = 0;
-  Ticks = timeGetTime();
-
-  Sec = Ticks/1000;
-  Usec = (Ticks - (Sec*1000))*1000;
-  tp->tv_sec = Sec;
-  tp->tv_usec = Usec;
-#endif /* WITHOUT_MM_LIB */
-  (void)nothing;
-  return 0;
+  /*
+  ** 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;
 }
-#else /* WIN32 */
-/* non-win32 version of Curl_gettimeofday() */
-static int gettimeofday(struct timeval *tp, void *nothing)
+
+#elif defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC)
+
+struct timeval curlx_tvnow(void)
 {
-  (void)nothing; /* we don't support specific time-zones */
-  tp->tv_sec = (long)time(NULL);
-  tp->tv_usec = 0;
-  return 0;
+  /*
+  ** 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;
 }
-#endif /* WIN32 */
-#endif /* HAVE_GETTIMEOFDAY */
 
-/* Return the current time in a timeval struct */
+#elif defined(HAVE_GETTIMEOFDAY)
+
 struct timeval curlx_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 curlx_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...
diff --git a/src/Makefile.Watcom b/src/Makefile.Watcom
index 8f75233a6..942443848 100644
--- a/src/Makefile.Watcom
+++ b/src/Makefile.Watcom
@@ -7,7 +7,7 @@
 CC = wcc386
 
 CFLAGS = -3r -mf -d3 -hc -zff -zgf -zq -zm -s -fr=con -w2 -fpi -oilrtfm     &
-         -bt=nt -d+ -dWIN32 -dHAVE_STRTOLL -dWITHOUT_MM_LIB                 &
+         -bt=nt -d+ -dWIN32 -dHAVE_STRTOLL                                  &
          -dSIZEOF_CURL_OFF_T=8 -dCURLDEBUG -dENABLE_IPV6 -dHAVE_WINSOCK2_H  &
          -I..\include -I..\lib
 
diff --git a/src/Makefile.m32 b/src/Makefile.m32
index 32817e915..3ecd99971 100644
--- a/src/Makefile.m32
+++ b/src/Makefile.m32
@@ -104,7 +104,7 @@ ifndef USE_LDAP_OPENLDAP
 curl_LDADD += -lwldap32
 endif
 endif
-curl_LDADD += -lws2_32 -lwinmm
+curl_LDADD += -lws2_32
 COMPILE = $(CC) $(INCLUDES) $(CFLAGS)
 
 # Makefile.inc provides the CSOURCES and HHEADERS defines
diff --git a/src/Makefile.vc6 b/src/Makefile.vc6
index 233242252..49438d1e3 100644
--- a/src/Makefile.vc6
+++ b/src/Makefile.vc6
@@ -10,8 +10,6 @@
 ## Comments to: Troy Engel <tengel@sonic.net>

 ## Updated by: Craig Davison <cd@securityfocus.com>

 ## release-ssl added by Miklos Nemeth <mnemeth@kfkisystems.com>

-## winmm.lib added by Miklos Nemeth <mnemeth@kfkisystems.com> to

-## support timeGetTime() in curlutil.c

 #

 #############################################################

 

@@ -221,8 +219,8 @@ LFLAGS         = $(LFLAGS) $(SSL_IMP_LFLAGS) $(ZLIB_LFLAGS)
 !ENDIF

 

 

-LINKLIBS       = $(LINKLIBS) wsock32.lib wldap32.lib winmm.lib

-LINKLIBS_DEBUG = $(LINKLIBS_DEBUG) wsock32.lib wldap32.lib winmm.lib

+LINKLIBS       = $(LINKLIBS) wsock32.lib wldap32.lib

+LINKLIBS_DEBUG = $(LINKLIBS_DEBUG) wsock32.lib wldap32.lib

 

 all : release

 

diff --git a/src/curlutil.c b/src/curlutil.c
index 0394d80e2..12a7d2e06 100644
--- a/src/curlutil.c
+++ b/src/curlutil.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2007, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2008, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -25,69 +25,70 @@
 
 #include "curlutil.h"
 
-#ifndef HAVE_GETTIMEOFDAY
+#if defined(WIN32) && !defined(MSDOS)
 
-#ifdef WIN32
-#include <mmsystem.h>
-
-static int gettimeofday(struct timeval *tp, void *nothing)
+struct timeval cutil_tvnow(void)
 {
-#ifdef WITHOUT_MM_LIB
-  SYSTEMTIME st;
-  time_t tt;
-  struct tm tmtm;
-  /* mktime converts local to UTC */
-  GetLocalTime (&st);
-  tmtm.tm_sec = st.wSecond;
-  tmtm.tm_min = st.wMinute;
-  tmtm.tm_hour = st.wHour;
-  tmtm.tm_mday = st.wDay;
-  tmtm.tm_mon = st.wMonth - 1;
-  tmtm.tm_year = st.wYear - 1900;
-  tmtm.tm_isdst = -1;
-  tt = mktime (&tmtm);
-  tp->tv_sec = tt;
-  tp->tv_usec = st.wMilliseconds * 1000;
-#else
-  /**
-   ** The earlier time calculations using GetLocalTime
-   ** had a time resolution of 10ms.The timeGetTime, part
-   ** of multimedia apis offer a better time resolution
-   ** of 1ms.Need to link against winmm.lib for this
-   **/
-  unsigned long Ticks = 0;
-  unsigned long Sec =0;
-  unsigned long Usec = 0;
-  Ticks = timeGetTime();
-
-  Sec = Ticks/1000;
-  Usec = (Ticks - (Sec*1000))*1000;
-  tp->tv_sec = Sec;
-  tp->tv_usec = Usec;
-#endif /* WITHOUT_MM_LIB */
-  (void)nothing;
-  return 0;
+  /*
+  ** 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;
 }
-#else /* WIN32 */
-/* non-win32 version of Curl_gettimeofday() */
-static int gettimeofday(struct timeval *tp, void *nothing)
+
+#elif defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC)
+
+struct timeval cutil_tvnow(void)
 {
-  (void)nothing; /* we don't support specific time-zones */
-  tp->tv_sec = (long)time(NULL);
-  tp->tv_usec = 0;
-  return 0;
+  /*
+  ** 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;
 }
-#endif /* WIN32 */
-#endif /* HAVE_GETTIMEOFDAY */
 
-/* Return the current time in a timeval struct */
+#elif defined(HAVE_GETTIMEOFDAY)
+
 struct timeval cutil_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 cutil_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...
diff --git a/tests/libtest/testutil.c b/tests/libtest/testutil.c
index 146660c71..8ed2b2f08 100644
--- a/tests/libtest/testutil.c
+++ b/tests/libtest/testutil.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2007, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2008, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -25,69 +25,70 @@
 
 #include "testutil.h"
 
-#ifndef HAVE_GETTIMEOFDAY
+#if defined(WIN32) && !defined(MSDOS)
 
-#ifdef WIN32
-#include <mmsystem.h>
-
-static int gettimeofday(struct timeval *tp, void *nothing)
+struct timeval tutil_tvnow(void)
 {
-#ifdef WITHOUT_MM_LIB
-  SYSTEMTIME st;
-  time_t tt;
-  struct tm tmtm;
-  /* mktime converts local to UTC */
-  GetLocalTime (&st);
-  tmtm.tm_sec = st.wSecond;
-  tmtm.tm_min = st.wMinute;
-  tmtm.tm_hour = st.wHour;
-  tmtm.tm_mday = st.wDay;
-  tmtm.tm_mon = st.wMonth - 1;
-  tmtm.tm_year = st.wYear - 1900;
-  tmtm.tm_isdst = -1;
-  tt = mktime (&tmtm);
-  tp->tv_sec = tt;
-  tp->tv_usec = st.wMilliseconds * 1000;
-#else
-  /**
-   ** The earlier time calculations using GetLocalTime
-   ** had a time resolution of 10ms.The timeGetTime, part
-   ** of multimedia apis offer a better time resolution
-   ** of 1ms.Need to link against winmm.lib for this
-   **/
-  unsigned long Ticks = 0;
-  unsigned long Sec =0;
-  unsigned long Usec = 0;
-  Ticks = timeGetTime();
-
-  Sec = Ticks/1000;
-  Usec = (Ticks - (Sec*1000))*1000;
-  tp->tv_sec = Sec;
-  tp->tv_usec = Usec;
-#endif /* WITHOUT_MM_LIB */
-  (void)nothing;
-  return 0;
+  /*
+  ** 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;
 }
-#else /* WIN32 */
-/* non-win32 version of Curl_gettimeofday() */
-static int gettimeofday(struct timeval *tp, void *nothing)
+
+#elif defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC)
+
+struct timeval tutil_tvnow(void)
 {
-  (void)nothing; /* we don't support specific time-zones */
-  tp->tv_sec = (long)time(NULL);
-  tp->tv_usec = 0;
-  return 0;
+  /*
+  ** 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;
 }
-#endif /* WIN32 */
-#endif /* HAVE_GETTIMEOFDAY */
 
-/* Return the current time in a timeval struct */
+#elif defined(HAVE_GETTIMEOFDAY)
+
 struct timeval tutil_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 tutil_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...