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Implement fast/precise monotonic clocks on Windows

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This uses code from libutp, which was released under the MIT
license; see evutil_time.c and LICENSE changes.
This commit is contained in:
Nick Mathewson 2012-04-23 13:33:25 -04:00
parent a2598ec6bd
commit 2c470452fb
3 changed files with 168 additions and 27 deletions
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25
LICENSE
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@ -72,3 +72,28 @@ The arc4module is available under the following, sometimes called the
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
==============================
The Windows timer code is based on code from libutp, which is
distributed under this license, sometimes called the "MIT" license.
Copyright (c) 2010 BitTorrent, Inc.
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

155
evutil_time.c
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@ -133,7 +133,6 @@ evutil_usleep_(const struct timeval *tv)
#endif #endif
} }
/* /*
This function assumes it's called repeatedly with a This function assumes it's called repeatedly with a
not-actually-so-monotonic time source whose outputs are in 'tv'. It not-actually-so-monotonic time source whose outputs are in 'tv'. It
@ -283,57 +282,163 @@ evutil_gettime_monotonic_(struct evutil_monotonic_timer *base,
Windows has QueryPerformanceCounter(), which gives time most high- Windows has QueryPerformanceCounter(), which gives time most high-
resolution time. It's a pity it's not so monotonic in practice; it's resolution time. It's a pity it's not so monotonic in practice; it's
also got some fun bugs, especially with older Windowses, under also got some fun bugs, especially: with older Windowses, under
virtualizations, with funny hardware, on multiprocessor systems, and so virtualizations, with funny hardware, on multiprocessor systems, and so
on. PEP418 [1] has a nice roundup here. on. PEP418 [1] has a nice roundup of the issues here.
There's GetTickCount64(), which gives a number of 1-msec ticks since There's GetTickCount64() on Vista and later, which gives a number of 1-msec
startup. The accuracy here might be as bad as 10-20 msec, I hear. ticks since startup. The accuracy here might be as bad as 10-20 msec, I
There's an undocumented function (NtSetTimerResolution) that allegedly hear. There's an undocumented function (NtSetTimerResolution) that
increases the accuracy. Good luck! allegedly increases the accuracy. Good luck!
There's also GetTickCount(), which is only 32 bits, but seems to be There's also GetTickCount(), which is only 32 bits, but seems to be
supported on pre-Vista versions of Windows. supported on pre-Vista versions of Windows. Apparently, you can coax
another 14 bits out of it, giving you 2231 years before rollover.
The less said about timeGetTime() the better. The less said about timeGetTime() the better.
"We don't care. We don't have to. We're the Phone Company." "We don't care. We don't have to. We're the Phone Company."
-- Lily Tomlin, SNL -- Lily Tomlin, SNL
Our strategy, if precise timers are turned off, is to just use the best
GetTickCount equivalent available. If we've been asked for precise timing,
then we mostly[2] assume that GetTickCount is monotonic, and correct
GetPerformanceCounter to approximate it.
[1] http://www.python.org/dev/peps/pep-0418 [1] http://www.python.org/dev/peps/pep-0418
[2] Of course, we feed the Windows stuff into adjust_monotonic_time()
anyway, just in case it isn't.
*/ */
/*
Parts of our logic in the win32 timer code here are closely based on
BitTorrent's libUTP library. That code is subject to the following
license:
Copyright (c) 2010 BitTorrent, Inc.
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
static ev_uint64_t
evutil_GetTickCount_(struct evutil_monotonic_timer *base)
{
if (base->GetTickCount64_fn) {
/* Let's just use GetTickCount64 if we can. */
return base->GetTickCount64_fn();
} else if (base->GetTickCount_fn) {
/* Greg Hazel assures me that this works, that BitTorrent has
* done it for years, and this it won't turn around and
* bite us. He says they found it on some game programmers'
* forum some time around 2007.
*/
ev_uint64_t v = base->GetTickCount_fn();
return (DWORD)v | ((v >> 18) & 0xFFFFFFFF00000000);
} else {
/* Here's the fallback implementation. We have to use
* GetTickCount() with its given signature, so we only get
* 32 bits worth of milliseconds, which will roll ove every
* 49 days or so. */
DWORD ticks = GetTickCount();
if (ticks < base->last_tick_count) {
base->adjust_tick_count += ((ev_uint64_t)1) << 32;
}
base->last_tick_count = ticks;
return ticks + base->adjust_tick_count;
}
}
int int
evutil_configure_monotonic_time_(struct evutil_monotonic_timer *base, evutil_configure_monotonic_time_(struct evutil_monotonic_timer *base,
int precise) int precise)
{ {
HANDLE h;
memset(base, 0, sizeof(*base)); memset(base, 0, sizeof(*base));
base->last_tick_count = GetTickCount();
h = evutil_load_windows_system_library_(TEXT("kernel32.dll"));
if (h != NULL) {
base->GetTickCount64_fn = (ev_GetTickCount_func)GetProcAddress(h, "GetTickCount64");
base->GetTickCount_fn = (ev_GetTickCount_func)GetProcAddress(h, "GetTickCount");
}
base->first_tick = base->last_tick_count = evutil_GetTickCount_(base);
if (precise) {
LARGE_INTEGER freq;
if (QueryPerformanceFrequency(&freq)) {
LARGE_INTEGER counter;
QueryPerformanceCounter(&counter);
base->first_counter = counter.QuadPart;
base->usec_per_count = 1.0e6 / freq.QuadPart;
base->use_performance_counter = 1;
}
}
return 0; return 0;
} }
static inline ev_int64_t
abs64(ev_int64_t i)
{
return i < 0 ? -i : i;
}
int int
evutil_gettime_monotonic_(struct evutil_monotonic_timer *base, evutil_gettime_monotonic_(struct evutil_monotonic_timer *base,
struct timeval *tp) struct timeval *tp)
{ {
/* TODO: Support GetTickCount64. */ ev_uint64_t ticks = evutil_GetTickCount_(base);
/* TODO: Support alternate timer backends if the user asked if (base->use_performance_counter) {
* for a high-precision timer. QueryPerformanceCounter is /* Here's a trick we took from BitTorrent's libutp, at Greg
* possibly a good idea, but it is also supposed to have * Hazel's recommendation. We use QueryPerformanceCounter for
* reliability issues under various circumstances. */ * our high-resolution timer, but use GetTickCount*() to keep
DWORD ticks = GetTickCount(); * it sane, and adjust_monotonic_time() to keep it monotonic.
if (ticks < base->last_tick_count) { */
/* The 32-bit timer rolled over. Let's assume it only LARGE_INTEGER counter;
* happened once. Add 2**32 msec to adjust_tick_count. */ ev_int64_t counter_elapsed, counter_usec_elapsed, ticks_elapsed;
const struct timeval tv_rollover = { 4294967, 296000 }; QueryPerformanceCounter(&counter);
evutil_timeradd(&tv_rollover, &base->adjust_tick_count, &base->adjust_tick_count); counter_elapsed = (ev_int64_t)
} (counter.QuadPart - base->first_counter);
base->last_tick_count = ticks; ticks_elapsed = ticks - base->first_tick;
tp->tv_sec = ticks / 1000; /* TODO: This may upset VC6. If you need this to work with
tp->tv_usec = (ticks % 1000) * 1000; * VC6, please supply an appropriate patch. */
evutil_timeradd(tp, &base->adjust_tick_count, tp); counter_usec_elapsed = (ev_int64_t)
(counter_elapsed * base->usec_per_count);
if (abs64(ticks_elapsed*1000 - counter_usec_elapsed) > 1000000) {
/* It appears that the QueryPerformanceCounter()
* result is more than 1 second away from
* GetTickCount() result. Let's adjust it to be as
* accurate as we can; adjust_monotnonic_time() below
* will keep it monotonic. */
counter_usec_elapsed = ticks_elapsed * 1000;
base->first_counter = counter.QuadPart - counter_usec_elapsed / base->usec_per_count;
}
tp->tv_sec = counter_usec_elapsed / 1000000;
tp->tv_usec = counter_usec_elapsed % 1000000;
} else {
/* We're just using GetTickCount(). */
tp->tv_sec = ticks / 1000;
tp->tv_usec = (ticks % 1000) * 1000;
}
adjust_monotonic_time(base, tp); adjust_monotonic_time(base, tp);
return 0; return 0;

15
time-internal.h
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@ -56,6 +56,10 @@ extern "C" {
long evutil_tv_to_msec_(const struct timeval *tv); long evutil_tv_to_msec_(const struct timeval *tv);
void evutil_usleep_(const struct timeval *tv); void evutil_usleep_(const struct timeval *tv);
#ifdef _WIN32
typedef ULONGLONG (WINAPI *ev_GetTickCount_func)(void);
#endif
struct evutil_monotonic_timer { struct evutil_monotonic_timer {
#ifdef HAVE_MACH_MONOTONIC #ifdef HAVE_MACH_MONOTONIC
@ -67,8 +71,15 @@ struct evutil_monotonic_timer {
#endif #endif
#ifdef HAVE_WIN32_MONOTONIC #ifdef HAVE_WIN32_MONOTONIC
DWORD last_tick_count; ev_GetTickCount_func GetTickCount64_fn;
struct timeval adjust_tick_count; ev_GetTickCount_func GetTickCount_fn;
ev_uint64_t last_tick_count;
ev_uint64_t adjust_tick_count;
ev_uint64_t first_tick;
ev_uint64_t first_counter;
double usec_per_count;
int use_performance_counter;
#endif #endif
struct timeval adjust_monotonic_clock; struct timeval adjust_monotonic_clock;