Discussion:
gettimeofday: improve for native Windows
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Bruno Haible
2017-04-30 17:42:06 UTC
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Raw Message
gettimeofday should provide the same time resolution as utime.


2017-04-30 Bruno Haible <***@clisp.org>

gettimeofday: Provide higher resolution on native Windows.
* lib/gettimeofday.c: Don't include <sys/timeb.h>.
(GetSystemTimePreciseAsFileTimeFuncType): New variable.
(initialize): Initialize it.
(gettimeofday) [WINDOWS_NATIVE]: Use it, and convert from FILETIME to
'struct timeval'. Don't use _ftime().
* m4/gettimeofday.m4 (gl_PREREQ_GETTIMEOFDAY): Don't test for
<sys/timeb.h> and _ftime.

diff --git a/lib/gettimeofday.c b/lib/gettimeofday.c
index d6117bd..a4a71a7 100644
--- a/lib/gettimeofday.c
+++ b/lib/gettimeofday.c
@@ -24,8 +24,9 @@

#include <time.h>

-#if HAVE_SYS_TIMEB_H
-# include <sys/timeb.h>
+#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
+# define WINDOWS_NATIVE
+# include <windows.h>
#endif

#if GETTIMEOFDAY_CLOBBERS_LOCALTIME || TZSET_CLOBBERS_LOCALTIME
@@ -92,6 +93,28 @@ rpl_tzset (void)
tzset ();
*localtime_buffer_addr = save;
}
+
+#endif
+
+#ifdef WINDOWS_NATIVE
+
+/* GetSystemTimePreciseAsFileTime was introduced only in Windows 8. */
+typedef void (WINAPI * GetSystemTimePreciseAsFileTimeFuncType) (FILETIME *lpTime);
+static GetSystemTimePreciseAsFileTimeFuncType GetSystemTimePreciseAsFileTimeFunc = NULL;
+static BOOL initialized = FALSE;
+
+static void
+initialize (void)
+{
+ HMODULE kernel32 = LoadLibrary ("kernel32.dll");
+ if (kernel32 != NULL)
+ {
+ GetSystemTimePreciseAsFileTimeFunc =
+ (GetSystemTimePreciseAsFileTimeFuncType) GetProcAddress (kernel32, "GetSystemTimePreciseAsFileTime");
+ }
+ initialized = TRUE;
+}
+
#endif

/* This is a wrapper for gettimeofday. It is used only on systems
@@ -130,12 +153,35 @@ gettimeofday (struct timeval *restrict tv, void *restrict tz)

#else

-# if HAVE__FTIME
-
- struct _timeb timebuf;
- _ftime (&timebuf);
- tv->tv_sec = timebuf.time;
- tv->tv_usec = timebuf.millitm * 1000;
+# ifdef WINDOWS_NATIVE
+
+ /* On native Windows, there are two ways to get the current time:
+ GetSystemTimeAsFileTime
+ <https://msdn.microsoft.com/en-us/library/ms724397.aspx>
+ or
+ GetSystemTimePreciseAsFileTime
+ <https://msdn.microsoft.com/en-us/library/hh706895.aspx>. */
+ FILETIME current_time;
+
+ if (!initialized)
+ initialize ();
+ if (GetSystemTimePreciseAsFileTimeFunc != NULL)
+ GetSystemTimePreciseAsFileTimeFunc (&current_time);
+ else
+ GetSystemTimeAsFileTime (&current_time);
+
+ /* Convert from FILETIME to 'struct timeval'. */
+ /* FILETIME: <https://msdn.microsoft.com/en-us/library/ms724284.aspx> */
+ ULONGLONG since_1601 =
+ ((ULONGLONG) current_time.dwHighDateTime << 32)
+ | (ULONGLONG) current_time.dwLowDateTime;
+ /* Between 1601-01-01 and 1970-01-01 there were 280 normal years and 89 leap
+ years, in total 134774 days. */
+ ULONGLONG since_1970 =
+ since_1601 - (ULONGLONG) 134774 * (ULONGLONG) 86400 * (ULONGLONG) 10000000;
+ ULONGLONG microseconds_since_1970 = since_1970 / (ULONGLONG) 10;
+ tv->tv_sec = microseconds_since_1970 / (ULONGLONG) 1000000;
+ tv->tv_usec = microseconds_since_1970 % (ULONGLONG) 1000000;

# else

diff --git a/m4/gettimeofday.m4 b/m4/gettimeofday.m4
index 4f501e5..742b6c9 100644
--- a/m4/gettimeofday.m4
+++ b/m4/gettimeofday.m4
@@ -1,4 +1,4 @@
-# serial 21
+# serial 22

# Copyright (C) 2001-2003, 2005, 2007, 2009-2017 Free Software Foundation, Inc.
# This file is free software; the Free Software Foundation
@@ -132,7 +132,4 @@ AC_DEFUN([gl_GETTIMEOFDAY_REPLACE_LOCALTIME], [
])

# Prerequisites of lib/gettimeofday.c.
-AC_DEFUN([gl_PREREQ_GETTIMEOFDAY], [
- AC_CHECK_HEADERS([sys/timeb.h])
- AC_CHECK_FUNCS([_ftime])
-])
+AC_DEFUN([gl_PREREQ_GETTIMEOFDAY], [:])

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