1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
6 // Windows Timer Primer
8 // A good article: http://www.ddj.com/windows/184416651
9 // A good mozilla bug: http://bugzilla.mozilla.org/show_bug.cgi?id=363258
11 // The default windows timer, GetSystemTimeAsFileTime is not very precise.
12 // It is only good to ~15.5ms.
14 // QueryPerformanceCounter is the logical choice for a high-precision timer.
15 // However, it is known to be buggy on some hardware. Specifically, it can
16 // sometimes "jump". On laptops, QPC can also be very expensive to call.
17 // It's 3-4x slower than timeGetTime() on desktops, but can be 10x slower
18 // on laptops. A unittest exists which will show the relative cost of various
19 // timers on any system.
21 // The next logical choice is timeGetTime(). timeGetTime has a precision of
22 // 1ms, but only if you call APIs (timeBeginPeriod()) which affect all other
23 // applications on the system. By default, precision is only 15.5ms.
24 // Unfortunately, we don't want to call timeBeginPeriod because we don't
25 // want to affect other applications. Further, on mobile platforms, use of
26 // faster multimedia timers can hurt battery life. See the intel
27 // article about this here:
28 // http://softwarecommunity.intel.com/articles/eng/1086.htm
30 // To work around all this, we're going to generally use timeGetTime(). We
31 // will only increase the system-wide timer if we're not running on battery
34 #include "base/time/time.h"
36 #pragma comment(lib, "winmm.lib")
40 #include "base/basictypes.h"
42 #include "base/lazy_instance.h"
43 #include "base/logging.h"
44 #include "base/synchronization/lock.h"
47 using base::TimeDelta;
48 using base::TimeTicks;
52 // From MSDN, FILETIME "Contains a 64-bit value representing the number of
53 // 100-nanosecond intervals since January 1, 1601 (UTC)."
54 int64 FileTimeToMicroseconds(const FILETIME& ft) {
55 // Need to bit_cast to fix alignment, then divide by 10 to convert
56 // 100-nanoseconds to milliseconds. This only works on little-endian
58 return bit_cast<int64, FILETIME>(ft) / 10;
61 void MicrosecondsToFileTime(int64 us, FILETIME* ft) {
62 DCHECK_GE(us, 0LL) << "Time is less than 0, negative values are not "
63 "representable in FILETIME";
65 // Multiply by 10 to convert milliseconds to 100-nanoseconds. Bit_cast will
66 // handle alignment problems. This only works on little-endian machines.
67 *ft = bit_cast<FILETIME, int64>(us * 10);
70 int64 CurrentWallclockMicroseconds() {
72 ::GetSystemTimeAsFileTime(&ft);
73 return FileTimeToMicroseconds(ft);
76 // Time between resampling the un-granular clock for this API. 60 seconds.
77 const int kMaxMillisecondsToAvoidDrift = 60 * Time::kMillisecondsPerSecond;
79 int64 initial_time = 0;
80 TimeTicks initial_ticks;
82 void InitializeClock() {
83 initial_ticks = TimeTicks::Now();
84 initial_time = CurrentWallclockMicroseconds();
87 // The two values that ActivateHighResolutionTimer uses to set the systemwide
88 // timer interrupt frequency on Windows. It controls how precise timers are
89 // but also has a big impact on battery life.
90 const int kMinTimerIntervalHighResMs = 1;
91 const int kMinTimerIntervalLowResMs = 4;
92 // Track if kMinTimerIntervalHighResMs or kMinTimerIntervalLowResMs is active.
93 bool g_high_res_timer_enabled = false;
94 // How many times the high resolution timer has been called.
95 uint32_t g_high_res_timer_count = 0;
96 // The lock to control access to the above two variables.
97 base::LazyInstance<base::Lock>::Leaky g_high_res_lock =
98 LAZY_INSTANCE_INITIALIZER;
102 // Time -----------------------------------------------------------------------
104 // The internal representation of Time uses FILETIME, whose epoch is 1601-01-01
105 // 00:00:00 UTC. ((1970-1601)*365+89)*24*60*60*1000*1000, where 89 is the
106 // number of leap year days between 1601 and 1970: (1970-1601)/4 excluding
107 // 1700, 1800, and 1900.
109 const int64 Time::kTimeTToMicrosecondsOffset = GG_INT64_C(11644473600000000);
113 if (initial_time == 0)
116 // We implement time using the high-resolution timers so that we can get
117 // timeouts which are smaller than 10-15ms. If we just used
118 // CurrentWallclockMicroseconds(), we'd have the less-granular timer.
120 // To make this work, we initialize the clock (initial_time) and the
121 // counter (initial_ctr). To compute the initial time, we can check
122 // the number of ticks that have elapsed, and compute the delta.
124 // To avoid any drift, we periodically resync the counters to the system
127 TimeTicks ticks = TimeTicks::Now();
129 // Calculate the time elapsed since we started our timer
130 TimeDelta elapsed = ticks - initial_ticks;
132 // Check if enough time has elapsed that we need to resync the clock.
133 if (elapsed.InMilliseconds() > kMaxMillisecondsToAvoidDrift) {
138 return Time(elapsed + Time(initial_time));
143 Time Time::NowFromSystemTime() {
146 return Time(initial_time);
150 Time Time::FromFileTime(FILETIME ft) {
151 if (bit_cast<int64, FILETIME>(ft) == 0)
153 if (ft.dwHighDateTime == std::numeric_limits<DWORD>::max() &&
154 ft.dwLowDateTime == std::numeric_limits<DWORD>::max())
156 return Time(FileTimeToMicroseconds(ft));
159 FILETIME Time::ToFileTime() const {
161 return bit_cast<FILETIME, int64>(0);
164 result.dwHighDateTime = std::numeric_limits<DWORD>::max();
165 result.dwLowDateTime = std::numeric_limits<DWORD>::max();
169 MicrosecondsToFileTime(us_, &utc_ft);
174 void Time::EnableHighResolutionTimer(bool enable) {
175 base::AutoLock lock(g_high_res_lock.Get());
176 if (g_high_res_timer_enabled == enable)
178 g_high_res_timer_enabled = enable;
179 if (!g_high_res_timer_count)
181 // Since g_high_res_timer_count != 0, an ActivateHighResolutionTimer(true)
182 // was called which called timeBeginPeriod with g_high_res_timer_enabled
183 // with a value which is the opposite of |enable|. With that information we
184 // call timeEndPeriod with the same value used in timeBeginPeriod and
185 // therefore undo the period effect.
187 timeEndPeriod(kMinTimerIntervalLowResMs);
188 timeBeginPeriod(kMinTimerIntervalHighResMs);
190 timeEndPeriod(kMinTimerIntervalHighResMs);
191 timeBeginPeriod(kMinTimerIntervalLowResMs);
196 bool Time::ActivateHighResolutionTimer(bool activating) {
197 // We only do work on the transition from zero to one or one to zero so we
198 // can easily undo the effect (if necessary) when EnableHighResolutionTimer is
200 const uint32_t max = std::numeric_limits<uint32_t>::max();
202 base::AutoLock lock(g_high_res_lock.Get());
203 UINT period = g_high_res_timer_enabled ? kMinTimerIntervalHighResMs
204 : kMinTimerIntervalLowResMs;
206 DCHECK(g_high_res_timer_count != max);
207 ++g_high_res_timer_count;
208 if (g_high_res_timer_count == 1)
209 timeBeginPeriod(period);
211 DCHECK(g_high_res_timer_count != 0);
212 --g_high_res_timer_count;
213 if (g_high_res_timer_count == 0)
214 timeEndPeriod(period);
216 return (period == kMinTimerIntervalHighResMs);
220 bool Time::IsHighResolutionTimerInUse() {
221 base::AutoLock lock(g_high_res_lock.Get());
222 return g_high_res_timer_enabled && g_high_res_timer_count > 0;
226 Time Time::FromExploded(bool is_local, const Exploded& exploded) {
227 // Create the system struct representing our exploded time. It will either be
228 // in local time or UTC.
230 st.wYear = exploded.year;
231 st.wMonth = exploded.month;
232 st.wDayOfWeek = exploded.day_of_week;
233 st.wDay = exploded.day_of_month;
234 st.wHour = exploded.hour;
235 st.wMinute = exploded.minute;
236 st.wSecond = exploded.second;
237 st.wMilliseconds = exploded.millisecond;
241 // Ensure that it's in UTC.
244 success = TzSpecificLocalTimeToSystemTime(NULL, &st, &utc_st) &&
245 SystemTimeToFileTime(&utc_st, &ft);
247 success = !!SystemTimeToFileTime(&st, &ft);
251 NOTREACHED() << "Unable to convert time";
254 return Time(FileTimeToMicroseconds(ft));
257 void Time::Explode(bool is_local, Exploded* exploded) const {
259 // We are not able to convert it to FILETIME.
260 ZeroMemory(exploded, sizeof(*exploded));
266 MicrosecondsToFileTime(us_, &utc_ft);
268 // FILETIME in local time if necessary.
270 // FILETIME in SYSTEMTIME (exploded).
274 // We don't use FileTimeToLocalFileTime here, since it uses the current
275 // settings for the time zone and daylight saving time. Therefore, if it is
276 // daylight saving time, it will take daylight saving time into account,
277 // even if the time you are converting is in standard time.
278 success = FileTimeToSystemTime(&utc_ft, &utc_st) &&
279 SystemTimeToTzSpecificLocalTime(NULL, &utc_st, &st);
281 success = !!FileTimeToSystemTime(&utc_ft, &st);
285 NOTREACHED() << "Unable to convert time, don't know why";
286 ZeroMemory(exploded, sizeof(*exploded));
290 exploded->year = st.wYear;
291 exploded->month = st.wMonth;
292 exploded->day_of_week = st.wDayOfWeek;
293 exploded->day_of_month = st.wDay;
294 exploded->hour = st.wHour;
295 exploded->minute = st.wMinute;
296 exploded->second = st.wSecond;
297 exploded->millisecond = st.wMilliseconds;
300 // TimeTicks ------------------------------------------------------------------
303 // We define a wrapper to adapt between the __stdcall and __cdecl call of the
304 // mock function, and to avoid a static constructor. Assigning an import to a
305 // function pointer directly would require setup code to fetch from the IAT.
306 DWORD timeGetTimeWrapper() {
307 return timeGetTime();
310 DWORD (*tick_function)(void) = &timeGetTimeWrapper;
312 // Accumulation of time lost due to rollover (in milliseconds).
313 int64 rollover_ms = 0;
315 // The last timeGetTime value we saw, to detect rollover.
316 DWORD last_seen_now = 0;
318 // Lock protecting rollover_ms and last_seen_now.
319 // Note: this is a global object, and we usually avoid these. However, the time
320 // code is low-level, and we don't want to use Singletons here (it would be too
321 // easy to use a Singleton without even knowing it, and that may lead to many
322 // gotchas). Its impact on startup time should be negligible due to low-level
323 // nature of time code.
324 base::Lock rollover_lock;
326 // We use timeGetTime() to implement TimeTicks::Now(). This can be problematic
327 // because it returns the number of milliseconds since Windows has started,
328 // which will roll over the 32-bit value every ~49 days. We try to track
329 // rollover ourselves, which works if TimeTicks::Now() is called at least every
331 TimeDelta RolloverProtectedNow() {
332 base::AutoLock locked(rollover_lock);
333 // We should hold the lock while calling tick_function to make sure that
334 // we keep last_seen_now stay correctly in sync.
335 DWORD now = tick_function();
336 if (now < last_seen_now)
337 rollover_ms += 0x100000000I64; // ~49.7 days.
339 return TimeDelta::FromMilliseconds(now + rollover_ms);
342 bool IsBuggyAthlon(const base::CPU& cpu) {
343 // On Athlon X2 CPUs (e.g. model 15) QueryPerformanceCounter is
344 // unreliable. Fallback to low-res clock.
345 return cpu.vendor_name() == "AuthenticAMD" && cpu.family() == 15;
348 // Overview of time counters:
349 // (1) CPU cycle counter. (Retrieved via RDTSC)
350 // The CPU counter provides the highest resolution time stamp and is the least
351 // expensive to retrieve. However, the CPU counter is unreliable and should not
352 // be used in production. Its biggest issue is that it is per processor and it
353 // is not synchronized between processors. Also, on some computers, the counters
354 // will change frequency due to thermal and power changes, and stop in some
357 // (2) QueryPerformanceCounter (QPC). The QPC counter provides a high-
358 // resolution (100 nanoseconds) time stamp but is comparatively more expensive
359 // to retrieve. What QueryPerformanceCounter actually does is up to the HAL.
360 // (with some help from ACPI).
361 // According to http://blogs.msdn.com/oldnewthing/archive/2005/09/02/459952.aspx
362 // in the worst case, it gets the counter from the rollover interrupt on the
363 // programmable interrupt timer. In best cases, the HAL may conclude that the
364 // RDTSC counter runs at a constant frequency, then it uses that instead. On
365 // multiprocessor machines, it will try to verify the values returned from
366 // RDTSC on each processor are consistent with each other, and apply a handful
367 // of workarounds for known buggy hardware. In other words, QPC is supposed to
368 // give consistent result on a multiprocessor computer, but it is unreliable in
369 // reality due to bugs in BIOS or HAL on some, especially old computers.
370 // With recent updates on HAL and newer BIOS, QPC is getting more reliable but
371 // it should be used with caution.
373 // (3) System time. The system time provides a low-resolution (typically 10ms
374 // to 55 milliseconds) time stamp but is comparatively less expensive to
375 // retrieve and more reliable.
376 class HighResNowSingleton {
378 HighResNowSingleton()
379 : ticks_per_second_(0),
383 if (IsBuggyAthlon(cpu))
386 // Synchronize the QPC clock with GetSystemTimeAsFileTime.
387 LARGE_INTEGER ticks_per_sec = {0};
388 if (!QueryPerformanceFrequency(&ticks_per_sec))
389 return; // QPC is not available.
390 ticks_per_second_ = ticks_per_sec.QuadPart;
392 skew_ = UnreliableNow() - ReliableNow();
395 bool IsUsingHighResClock() {
396 return ticks_per_second_ != 0;
400 if (IsUsingHighResClock())
401 return TimeDelta::FromMicroseconds(UnreliableNow());
403 // Just fallback to the slower clock.
404 return RolloverProtectedNow();
407 int64 GetQPCDriftMicroseconds() {
408 if (!IsUsingHighResClock())
410 return abs((UnreliableNow() - ReliableNow()) - skew_);
413 int64 QPCValueToMicroseconds(LONGLONG qpc_value) {
414 if (!ticks_per_second_)
416 // If the QPC Value is below the overflow threshold, we proceed with
417 // simple multiply and divide.
418 if (qpc_value < Time::kQPCOverflowThreshold)
419 return qpc_value * Time::kMicrosecondsPerSecond / ticks_per_second_;
420 // Otherwise, calculate microseconds in a round about manner to avoid
421 // overflow and precision issues.
422 int64 whole_seconds = qpc_value / ticks_per_second_;
423 int64 leftover_ticks = qpc_value - (whole_seconds * ticks_per_second_);
424 int64 microseconds = (whole_seconds * Time::kMicrosecondsPerSecond) +
425 ((leftover_ticks * Time::kMicrosecondsPerSecond) /
431 // Get the number of microseconds since boot in an unreliable fashion.
432 int64 UnreliableNow() {
434 QueryPerformanceCounter(&now);
435 return QPCValueToMicroseconds(now.QuadPart);
438 // Get the number of microseconds since boot in a reliable fashion.
439 int64 ReliableNow() {
440 return RolloverProtectedNow().InMicroseconds();
443 int64 ticks_per_second_; // 0 indicates QPF failed and we're broken.
444 int64 skew_; // Skew between lo-res and hi-res clocks (for debugging).
447 static base::LazyInstance<HighResNowSingleton>::Leaky
448 leaky_high_res_now_singleton = LAZY_INSTANCE_INITIALIZER;
450 HighResNowSingleton* GetHighResNowSingleton() {
451 return leaky_high_res_now_singleton.Pointer();
454 TimeDelta HighResNowWrapper() {
455 return GetHighResNowSingleton()->Now();
458 typedef TimeDelta (*NowFunction)(void);
460 bool CPUReliablySupportsHighResTime() {
462 if (!cpu.has_non_stop_time_stamp_counter() ||
463 !GetHighResNowSingleton()->IsUsingHighResClock())
466 if (IsBuggyAthlon(cpu))
472 TimeDelta InitialNowFunction();
474 volatile NowFunction now_function = InitialNowFunction;
476 TimeDelta InitialNowFunction() {
477 if (!CPUReliablySupportsHighResTime()) {
478 InterlockedExchangePointer(
479 reinterpret_cast<void* volatile*>(&now_function),
480 &RolloverProtectedNow);
481 return RolloverProtectedNow();
483 InterlockedExchangePointer(
484 reinterpret_cast<void* volatile*>(&now_function),
486 return HighResNowWrapper();
492 TimeTicks::TickFunctionType TimeTicks::SetMockTickFunction(
493 TickFunctionType ticker) {
494 base::AutoLock locked(rollover_lock);
495 TickFunctionType old = tick_function;
496 tick_function = ticker;
503 TimeTicks TimeTicks::Now() {
504 return TimeTicks() + now_function();
508 TimeTicks TimeTicks::HighResNow() {
509 return TimeTicks() + HighResNowWrapper();
513 bool TimeTicks::IsHighResNowFastAndReliable() {
514 return CPUReliablySupportsHighResTime();
518 TimeTicks TimeTicks::ThreadNow() {
524 TimeTicks TimeTicks::NowFromSystemTraceTime() {
529 int64 TimeTicks::GetQPCDriftMicroseconds() {
530 return GetHighResNowSingleton()->GetQPCDriftMicroseconds();
534 TimeTicks TimeTicks::FromQPCValue(LONGLONG qpc_value) {
535 return TimeTicks(GetHighResNowSingleton()->QPCValueToMicroseconds(qpc_value));
539 bool TimeTicks::IsHighResClockWorking() {
540 return GetHighResNowSingleton()->IsUsingHighResClock();
543 TimeTicks TimeTicks::UnprotectedNow() {
544 if (now_function == HighResNowWrapper) {
547 return TimeTicks() + TimeDelta::FromMilliseconds(timeGetTime());
551 // TimeDelta ------------------------------------------------------------------
554 TimeDelta TimeDelta::FromQPCValue(LONGLONG qpc_value) {
555 return TimeDelta(GetHighResNowSingleton()->QPCValueToMicroseconds(qpc_value));