This patch significantly increases the precision of gettimeofday() on
Windows 8 or later. It is then similar to Cygwin or Linux.
It also affects C++11 std::chrono:*_clock as _GLIBCXX_USE_GETTIMEOFDAY
is defined but not _GLIBCXX_USE_CLOCK_*.
A similar change (or a call to getntptimeofday()) would possibly also
make sense for clock_gettime(CLOCK_REALTIME,...).
Drawback: GetSystemTimePreciseAsFileTime() is slower than the legacy
function.
But it is still reasonably fast. Average time per call on an old machine
with i7-2600K:
GetSystemTimePreciseAsFileTime(): 23ns
GetSystemTimeAsFileTime(): <3ns
--
Regards,
Christian
From f3366a524643067b7adb0d535c38bb106bda42e2 Mon Sep 17 00:00:00 2001
From: Christian Franke <christian.fra...@t-online.de>
Date: Thu, 22 Apr 2021 13:47:30 +0200
Subject: [PATCH] crt: Increase precision of gettimeofday() if possible.
Use GetSystemTimePreciseAsFileTime() if available.
Signed-off-by: Christian Franke <christian.fra...@t-online.de>
---
mingw-w64-crt/misc/gettimeofday.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/mingw-w64-crt/misc/gettimeofday.c
b/mingw-w64-crt/misc/gettimeofday.c
index 50ffcfc7..8e016f9c 100644
--- a/mingw-w64-crt/misc/gettimeofday.c
+++ b/mingw-w64-crt/misc/gettimeofday.c
@@ -41,8 +41,23 @@ int getntptimeofday (struct timespec *tp, struct timezone *z)
}
if (tp != NULL) {
- GetSystemTimeAsFileTime (&_now.ft); /* 100-nanoseconds since
1-1-1601 */
- /* The actual accuracy on XP seems to be 125,000 nanoseconds = 125
microseconds = 0.125 milliseconds */
+ typedef void (WINAPI * GetSystemTimeAsFileTime_t)(LPFILETIME);
+ static volatile GetSystemTimeAsFileTime_t GetSystemTimeAsFileTime_p = NULL;
+
+ /* Set function pointer during first call */
+ GetSystemTimeAsFileTime_t get_time = GetSystemTimeAsFileTime_p;
+ if (get_time == NULL) {
+ /* Use GetSystemTimePreciseAsFileTime() if available (Windows 8 or
later) */
+ get_time = (void *) GetProcAddress (GetModuleHandle ("kernel32.dll"),
+ "GetSystemTimePreciseAsFileTime"); /* <1us precision on Windows 10 */
+ if (get_time == NULL)
+ get_time = GetSystemTimeAsFileTime; /* >15ms precision on Windows 10 */
+ /* First thread wins */
+ InterlockedCompareExchangePointer ((void * volatile *)
&GetSystemTimeAsFileTime_p,
+ get_time, NULL);
+ }
+
+ get_time (&_now.ft); /* 100 nano-seconds since 1-1-1601 */
_now.ns100 -= FILETIME_1970; /* 100 nano-seconds since 1-1-1970 */
tp->tv_sec = _now.ns100 / HECTONANOSEC_PER_SEC; /* seconds since
1-1-1970 */
tp->tv_nsec = (long) (_now.ns100 % HECTONANOSEC_PER_SEC) * 100; /*
nanoseconds */
--
2.31.1
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