mirror of
https://github.com/classilla/tenfourfox.git
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557 lines
18 KiB
C++
557 lines
18 KiB
C++
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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// Windows Timer Primer
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//
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// A good article: http://www.ddj.com/windows/184416651
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// A good mozilla bug: http://bugzilla.mozilla.org/show_bug.cgi?id=363258
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//
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// The default windows timer, GetSystemTimeAsFileTime is not very precise.
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// It is only good to ~15.5ms.
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//
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// QueryPerformanceCounter is the logical choice for a high-precision timer.
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// However, it is known to be buggy on some hardware. Specifically, it can
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// sometimes "jump". On laptops, QPC can also be very expensive to call.
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// It's 3-4x slower than timeGetTime() on desktops, but can be 10x slower
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// on laptops. A unittest exists which will show the relative cost of various
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// timers on any system.
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//
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// The next logical choice is timeGetTime(). timeGetTime has a precision of
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// 1ms, but only if you call APIs (timeBeginPeriod()) which affect all other
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// applications on the system. By default, precision is only 15.5ms.
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// Unfortunately, we don't want to call timeBeginPeriod because we don't
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// want to affect other applications. Further, on mobile platforms, use of
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// faster multimedia timers can hurt battery life. See the intel
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// article about this here:
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// http://softwarecommunity.intel.com/articles/eng/1086.htm
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//
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// To work around all this, we're going to generally use timeGetTime(). We
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// will only increase the system-wide timer if we're not running on battery
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// power.
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#include "base/time/time.h"
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#pragma comment(lib, "winmm.lib")
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#include <windows.h>
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#include <mmsystem.h>
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#include "base/basictypes.h"
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#include "base/cpu.h"
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#include "base/lazy_instance.h"
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#include "base/logging.h"
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#include "base/synchronization/lock.h"
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using base::Time;
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using base::TimeDelta;
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using base::TimeTicks;
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namespace {
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// From MSDN, FILETIME "Contains a 64-bit value representing the number of
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// 100-nanosecond intervals since January 1, 1601 (UTC)."
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int64 FileTimeToMicroseconds(const FILETIME& ft) {
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// Need to bit_cast to fix alignment, then divide by 10 to convert
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// 100-nanoseconds to milliseconds. This only works on little-endian
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// machines.
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return bit_cast<int64, FILETIME>(ft) / 10;
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}
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void MicrosecondsToFileTime(int64 us, FILETIME* ft) {
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DCHECK_GE(us, 0LL) << "Time is less than 0, negative values are not "
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"representable in FILETIME";
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// Multiply by 10 to convert milliseconds to 100-nanoseconds. Bit_cast will
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// handle alignment problems. This only works on little-endian machines.
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*ft = bit_cast<FILETIME, int64>(us * 10);
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}
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int64 CurrentWallclockMicroseconds() {
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FILETIME ft;
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::GetSystemTimeAsFileTime(&ft);
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return FileTimeToMicroseconds(ft);
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}
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// Time between resampling the un-granular clock for this API. 60 seconds.
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const int kMaxMillisecondsToAvoidDrift = 60 * Time::kMillisecondsPerSecond;
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int64 initial_time = 0;
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TimeTicks initial_ticks;
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void InitializeClock() {
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initial_ticks = TimeTicks::Now();
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initial_time = CurrentWallclockMicroseconds();
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}
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// The two values that ActivateHighResolutionTimer uses to set the systemwide
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// timer interrupt frequency on Windows. It controls how precise timers are
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// but also has a big impact on battery life.
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const int kMinTimerIntervalHighResMs = 1;
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const int kMinTimerIntervalLowResMs = 4;
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// Track if kMinTimerIntervalHighResMs or kMinTimerIntervalLowResMs is active.
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bool g_high_res_timer_enabled = false;
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// How many times the high resolution timer has been called.
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uint32_t g_high_res_timer_count = 0;
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// The lock to control access to the above two variables.
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base::LazyInstance<base::Lock>::Leaky g_high_res_lock =
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LAZY_INSTANCE_INITIALIZER;
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} // namespace
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// Time -----------------------------------------------------------------------
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// The internal representation of Time uses FILETIME, whose epoch is 1601-01-01
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// 00:00:00 UTC. ((1970-1601)*365+89)*24*60*60*1000*1000, where 89 is the
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// number of leap year days between 1601 and 1970: (1970-1601)/4 excluding
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// 1700, 1800, and 1900.
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// static
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const int64 Time::kTimeTToMicrosecondsOffset = GG_INT64_C(11644473600000000);
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// static
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Time Time::Now() {
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if (initial_time == 0)
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InitializeClock();
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// We implement time using the high-resolution timers so that we can get
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// timeouts which are smaller than 10-15ms. If we just used
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// CurrentWallclockMicroseconds(), we'd have the less-granular timer.
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//
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// To make this work, we initialize the clock (initial_time) and the
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// counter (initial_ctr). To compute the initial time, we can check
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// the number of ticks that have elapsed, and compute the delta.
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//
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// To avoid any drift, we periodically resync the counters to the system
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// clock.
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while (true) {
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TimeTicks ticks = TimeTicks::Now();
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// Calculate the time elapsed since we started our timer
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TimeDelta elapsed = ticks - initial_ticks;
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// Check if enough time has elapsed that we need to resync the clock.
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if (elapsed.InMilliseconds() > kMaxMillisecondsToAvoidDrift) {
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InitializeClock();
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continue;
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}
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return Time(elapsed + Time(initial_time));
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}
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}
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// static
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Time Time::NowFromSystemTime() {
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// Force resync.
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InitializeClock();
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return Time(initial_time);
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}
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// static
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Time Time::FromFileTime(FILETIME ft) {
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if (bit_cast<int64, FILETIME>(ft) == 0)
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return Time();
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if (ft.dwHighDateTime == std::numeric_limits<DWORD>::max() &&
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ft.dwLowDateTime == std::numeric_limits<DWORD>::max())
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return Max();
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return Time(FileTimeToMicroseconds(ft));
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}
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FILETIME Time::ToFileTime() const {
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if (is_null())
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return bit_cast<FILETIME, int64>(0);
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if (is_max()) {
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FILETIME result;
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result.dwHighDateTime = std::numeric_limits<DWORD>::max();
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result.dwLowDateTime = std::numeric_limits<DWORD>::max();
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return result;
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}
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FILETIME utc_ft;
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MicrosecondsToFileTime(us_, &utc_ft);
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return utc_ft;
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}
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// static
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void Time::EnableHighResolutionTimer(bool enable) {
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base::AutoLock lock(g_high_res_lock.Get());
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if (g_high_res_timer_enabled == enable)
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return;
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g_high_res_timer_enabled = enable;
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if (!g_high_res_timer_count)
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return;
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// Since g_high_res_timer_count != 0, an ActivateHighResolutionTimer(true)
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// was called which called timeBeginPeriod with g_high_res_timer_enabled
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// with a value which is the opposite of |enable|. With that information we
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// call timeEndPeriod with the same value used in timeBeginPeriod and
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// therefore undo the period effect.
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if (enable) {
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timeEndPeriod(kMinTimerIntervalLowResMs);
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timeBeginPeriod(kMinTimerIntervalHighResMs);
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} else {
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timeEndPeriod(kMinTimerIntervalHighResMs);
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timeBeginPeriod(kMinTimerIntervalLowResMs);
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}
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}
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// static
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bool Time::ActivateHighResolutionTimer(bool activating) {
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// We only do work on the transition from zero to one or one to zero so we
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// can easily undo the effect (if necessary) when EnableHighResolutionTimer is
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// called.
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const uint32_t max = std::numeric_limits<uint32_t>::max();
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base::AutoLock lock(g_high_res_lock.Get());
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UINT period = g_high_res_timer_enabled ? kMinTimerIntervalHighResMs
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: kMinTimerIntervalLowResMs;
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if (activating) {
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DCHECK(g_high_res_timer_count != max);
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++g_high_res_timer_count;
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if (g_high_res_timer_count == 1)
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timeBeginPeriod(period);
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} else {
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DCHECK(g_high_res_timer_count != 0);
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--g_high_res_timer_count;
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if (g_high_res_timer_count == 0)
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timeEndPeriod(period);
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}
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return (period == kMinTimerIntervalHighResMs);
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}
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// static
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bool Time::IsHighResolutionTimerInUse() {
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base::AutoLock lock(g_high_res_lock.Get());
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return g_high_res_timer_enabled && g_high_res_timer_count > 0;
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}
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// static
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Time Time::FromExploded(bool is_local, const Exploded& exploded) {
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// Create the system struct representing our exploded time. It will either be
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// in local time or UTC.
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SYSTEMTIME st;
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st.wYear = static_cast<WORD>(exploded.year);
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st.wMonth = static_cast<WORD>(exploded.month);
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st.wDayOfWeek = static_cast<WORD>(exploded.day_of_week);
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st.wDay = static_cast<WORD>(exploded.day_of_month);
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st.wHour = static_cast<WORD>(exploded.hour);
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st.wMinute = static_cast<WORD>(exploded.minute);
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st.wSecond = static_cast<WORD>(exploded.second);
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st.wMilliseconds = static_cast<WORD>(exploded.millisecond);
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FILETIME ft;
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bool success = true;
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// Ensure that it's in UTC.
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if (is_local) {
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SYSTEMTIME utc_st;
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success = TzSpecificLocalTimeToSystemTime(NULL, &st, &utc_st) &&
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SystemTimeToFileTime(&utc_st, &ft);
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} else {
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success = !!SystemTimeToFileTime(&st, &ft);
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}
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if (!success) {
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NOTREACHED() << "Unable to convert time";
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return Time(0);
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}
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return Time(FileTimeToMicroseconds(ft));
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}
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void Time::Explode(bool is_local, Exploded* exploded) const {
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if (us_ < 0LL) {
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// We are not able to convert it to FILETIME.
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ZeroMemory(exploded, sizeof(*exploded));
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return;
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}
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// FILETIME in UTC.
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FILETIME utc_ft;
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MicrosecondsToFileTime(us_, &utc_ft);
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// FILETIME in local time if necessary.
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bool success = true;
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// FILETIME in SYSTEMTIME (exploded).
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SYSTEMTIME st = {0};
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if (is_local) {
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SYSTEMTIME utc_st;
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// We don't use FileTimeToLocalFileTime here, since it uses the current
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// settings for the time zone and daylight saving time. Therefore, if it is
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// daylight saving time, it will take daylight saving time into account,
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// even if the time you are converting is in standard time.
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success = FileTimeToSystemTime(&utc_ft, &utc_st) &&
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SystemTimeToTzSpecificLocalTime(NULL, &utc_st, &st);
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} else {
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success = !!FileTimeToSystemTime(&utc_ft, &st);
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}
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if (!success) {
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NOTREACHED() << "Unable to convert time, don't know why";
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ZeroMemory(exploded, sizeof(*exploded));
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return;
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}
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exploded->year = st.wYear;
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exploded->month = st.wMonth;
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exploded->day_of_week = st.wDayOfWeek;
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exploded->day_of_month = st.wDay;
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exploded->hour = st.wHour;
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exploded->minute = st.wMinute;
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exploded->second = st.wSecond;
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exploded->millisecond = st.wMilliseconds;
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}
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// TimeTicks ------------------------------------------------------------------
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namespace {
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// We define a wrapper to adapt between the __stdcall and __cdecl call of the
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// mock function, and to avoid a static constructor. Assigning an import to a
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// function pointer directly would require setup code to fetch from the IAT.
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DWORD timeGetTimeWrapper() {
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return timeGetTime();
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}
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DWORD (*tick_function)(void) = &timeGetTimeWrapper;
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// Accumulation of time lost due to rollover (in milliseconds).
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int64 rollover_ms = 0;
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// The last timeGetTime value we saw, to detect rollover.
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DWORD last_seen_now = 0;
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// Lock protecting rollover_ms and last_seen_now.
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// Note: this is a global object, and we usually avoid these. However, the time
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// code is low-level, and we don't want to use Singletons here (it would be too
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// easy to use a Singleton without even knowing it, and that may lead to many
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// gotchas). Its impact on startup time should be negligible due to low-level
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// nature of time code.
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base::Lock rollover_lock;
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// We use timeGetTime() to implement TimeTicks::Now(). This can be problematic
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// because it returns the number of milliseconds since Windows has started,
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// which will roll over the 32-bit value every ~49 days. We try to track
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// rollover ourselves, which works if TimeTicks::Now() is called at least every
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// 49 days.
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TimeDelta RolloverProtectedNow() {
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base::AutoLock locked(rollover_lock);
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// We should hold the lock while calling tick_function to make sure that
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// we keep last_seen_now stay correctly in sync.
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DWORD now = tick_function();
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if (now < last_seen_now)
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rollover_ms += 0x100000000I64; // ~49.7 days.
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last_seen_now = now;
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return TimeDelta::FromMilliseconds(now + rollover_ms);
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}
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bool IsBuggyAthlon(const base::CPU& cpu) {
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// On Athlon X2 CPUs (e.g. model 15) QueryPerformanceCounter is
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// unreliable. Fallback to low-res clock.
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return cpu.vendor_name() == "AuthenticAMD" && cpu.family() == 15;
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}
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// Overview of time counters:
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// (1) CPU cycle counter. (Retrieved via RDTSC)
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// The CPU counter provides the highest resolution time stamp and is the least
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// expensive to retrieve. However, the CPU counter is unreliable and should not
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// be used in production. Its biggest issue is that it is per processor and it
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// is not synchronized between processors. Also, on some computers, the counters
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// will change frequency due to thermal and power changes, and stop in some
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// states.
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//
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// (2) QueryPerformanceCounter (QPC). The QPC counter provides a high-
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// resolution (100 nanoseconds) time stamp but is comparatively more expensive
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// to retrieve. What QueryPerformanceCounter actually does is up to the HAL.
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// (with some help from ACPI).
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// According to http://blogs.msdn.com/oldnewthing/archive/2005/09/02/459952.aspx
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// in the worst case, it gets the counter from the rollover interrupt on the
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// programmable interrupt timer. In best cases, the HAL may conclude that the
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// RDTSC counter runs at a constant frequency, then it uses that instead. On
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// multiprocessor machines, it will try to verify the values returned from
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// RDTSC on each processor are consistent with each other, and apply a handful
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// of workarounds for known buggy hardware. In other words, QPC is supposed to
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// give consistent result on a multiprocessor computer, but it is unreliable in
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// reality due to bugs in BIOS or HAL on some, especially old computers.
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// With recent updates on HAL and newer BIOS, QPC is getting more reliable but
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// it should be used with caution.
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//
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// (3) System time. The system time provides a low-resolution (typically 10ms
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// to 55 milliseconds) time stamp but is comparatively less expensive to
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// retrieve and more reliable.
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class HighResNowSingleton {
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public:
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HighResNowSingleton()
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: ticks_per_second_(0),
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skew_(0) {
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base::CPU cpu;
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if (IsBuggyAthlon(cpu))
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return;
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// Synchronize the QPC clock with GetSystemTimeAsFileTime.
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LARGE_INTEGER ticks_per_sec = {0};
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if (!QueryPerformanceFrequency(&ticks_per_sec))
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return; // QPC is not available.
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ticks_per_second_ = ticks_per_sec.QuadPart;
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skew_ = UnreliableNow() - ReliableNow();
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}
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bool IsUsingHighResClock() {
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return ticks_per_second_ != 0;
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}
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TimeDelta Now() {
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if (IsUsingHighResClock())
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return TimeDelta::FromMicroseconds(UnreliableNow());
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// Just fallback to the slower clock.
|
||
|
return RolloverProtectedNow();
|
||
|
}
|
||
|
|
||
|
int64 GetQPCDriftMicroseconds() {
|
||
|
if (!IsUsingHighResClock())
|
||
|
return 0;
|
||
|
return abs((UnreliableNow() - ReliableNow()) - skew_);
|
||
|
}
|
||
|
|
||
|
int64 QPCValueToMicroseconds(LONGLONG qpc_value) {
|
||
|
if (!ticks_per_second_)
|
||
|
return 0;
|
||
|
// If the QPC Value is below the overflow threshold, we proceed with
|
||
|
// simple multiply and divide.
|
||
|
if (qpc_value < Time::kQPCOverflowThreshold)
|
||
|
return qpc_value * Time::kMicrosecondsPerSecond / ticks_per_second_;
|
||
|
// Otherwise, calculate microseconds in a round about manner to avoid
|
||
|
// overflow and precision issues.
|
||
|
int64 whole_seconds = qpc_value / ticks_per_second_;
|
||
|
int64 leftover_ticks = qpc_value - (whole_seconds * ticks_per_second_);
|
||
|
int64 microseconds = (whole_seconds * Time::kMicrosecondsPerSecond) +
|
||
|
((leftover_ticks * Time::kMicrosecondsPerSecond) /
|
||
|
ticks_per_second_);
|
||
|
return microseconds;
|
||
|
}
|
||
|
|
||
|
private:
|
||
|
// Get the number of microseconds since boot in an unreliable fashion.
|
||
|
int64 UnreliableNow() {
|
||
|
LARGE_INTEGER now;
|
||
|
QueryPerformanceCounter(&now);
|
||
|
return QPCValueToMicroseconds(now.QuadPart);
|
||
|
}
|
||
|
|
||
|
// Get the number of microseconds since boot in a reliable fashion.
|
||
|
int64 ReliableNow() {
|
||
|
return RolloverProtectedNow().InMicroseconds();
|
||
|
}
|
||
|
|
||
|
int64 ticks_per_second_; // 0 indicates QPF failed and we're broken.
|
||
|
int64 skew_; // Skew between lo-res and hi-res clocks (for debugging).
|
||
|
};
|
||
|
|
||
|
static base::LazyInstance<HighResNowSingleton>::Leaky
|
||
|
leaky_high_res_now_singleton = LAZY_INSTANCE_INITIALIZER;
|
||
|
|
||
|
HighResNowSingleton* GetHighResNowSingleton() {
|
||
|
return leaky_high_res_now_singleton.Pointer();
|
||
|
}
|
||
|
|
||
|
TimeDelta HighResNowWrapper() {
|
||
|
return GetHighResNowSingleton()->Now();
|
||
|
}
|
||
|
|
||
|
typedef TimeDelta (*NowFunction)(void);
|
||
|
|
||
|
bool CPUReliablySupportsHighResTime() {
|
||
|
base::CPU cpu;
|
||
|
if (!cpu.has_non_stop_time_stamp_counter() ||
|
||
|
!GetHighResNowSingleton()->IsUsingHighResClock())
|
||
|
return false;
|
||
|
|
||
|
if (IsBuggyAthlon(cpu))
|
||
|
return false;
|
||
|
|
||
|
return true;
|
||
|
}
|
||
|
|
||
|
TimeDelta InitialNowFunction();
|
||
|
|
||
|
volatile NowFunction now_function = InitialNowFunction;
|
||
|
|
||
|
TimeDelta InitialNowFunction() {
|
||
|
if (!CPUReliablySupportsHighResTime()) {
|
||
|
InterlockedExchangePointer(
|
||
|
reinterpret_cast<void* volatile*>(&now_function),
|
||
|
&RolloverProtectedNow);
|
||
|
return RolloverProtectedNow();
|
||
|
}
|
||
|
InterlockedExchangePointer(
|
||
|
reinterpret_cast<void* volatile*>(&now_function),
|
||
|
&HighResNowWrapper);
|
||
|
return HighResNowWrapper();
|
||
|
}
|
||
|
|
||
|
} // namespace
|
||
|
|
||
|
// static
|
||
|
TimeTicks::TickFunctionType TimeTicks::SetMockTickFunction(
|
||
|
TickFunctionType ticker) {
|
||
|
base::AutoLock locked(rollover_lock);
|
||
|
TickFunctionType old = tick_function;
|
||
|
tick_function = ticker;
|
||
|
rollover_ms = 0;
|
||
|
last_seen_now = 0;
|
||
|
return old;
|
||
|
}
|
||
|
|
||
|
// static
|
||
|
TimeTicks TimeTicks::Now() {
|
||
|
return TimeTicks() + now_function();
|
||
|
}
|
||
|
|
||
|
// static
|
||
|
TimeTicks TimeTicks::HighResNow() {
|
||
|
return TimeTicks() + HighResNowWrapper();
|
||
|
}
|
||
|
|
||
|
// static
|
||
|
bool TimeTicks::IsHighResNowFastAndReliable() {
|
||
|
return CPUReliablySupportsHighResTime();
|
||
|
}
|
||
|
|
||
|
// static
|
||
|
TimeTicks TimeTicks::ThreadNow() {
|
||
|
NOTREACHED();
|
||
|
return TimeTicks();
|
||
|
}
|
||
|
|
||
|
// static
|
||
|
TimeTicks TimeTicks::NowFromSystemTraceTime() {
|
||
|
return HighResNow();
|
||
|
}
|
||
|
|
||
|
// static
|
||
|
int64 TimeTicks::GetQPCDriftMicroseconds() {
|
||
|
return GetHighResNowSingleton()->GetQPCDriftMicroseconds();
|
||
|
}
|
||
|
|
||
|
// static
|
||
|
TimeTicks TimeTicks::FromQPCValue(LONGLONG qpc_value) {
|
||
|
return TimeTicks(GetHighResNowSingleton()->QPCValueToMicroseconds(qpc_value));
|
||
|
}
|
||
|
|
||
|
// static
|
||
|
bool TimeTicks::IsHighResClockWorking() {
|
||
|
return GetHighResNowSingleton()->IsUsingHighResClock();
|
||
|
}
|
||
|
|
||
|
TimeTicks TimeTicks::UnprotectedNow() {
|
||
|
if (now_function == HighResNowWrapper) {
|
||
|
return Now();
|
||
|
} else {
|
||
|
return TimeTicks() + TimeDelta::FromMilliseconds(timeGetTime());
|
||
|
}
|
||
|
}
|
||
|
|
||
|
// TimeDelta ------------------------------------------------------------------
|
||
|
|
||
|
// static
|
||
|
TimeDelta TimeDelta::FromQPCValue(LONGLONG qpc_value) {
|
||
|
return TimeDelta(GetHighResNowSingleton()->QPCValueToMicroseconds(qpc_value));
|
||
|
}
|