root/base/time/time_win.cc

DEFINITIONS

1. FileTimeToMicroseconds
2. MicrosecondsToFileTime
3. CurrentWallclockMicroseconds
4. InitializeClock
5. Now
6. NowFromSystemTime
7. FromFileTime
8. ToFileTime
9. EnableHighResolutionTimer
10. ActivateHighResolutionTimer
11. IsHighResolutionTimerInUse
12. FromExploded
13. Explode
14. timeGetTimeWrapper
15. RolloverProtectedNow
16. IsBuggyAthlon
17. GetInstance
18. IsUsingHighResClock
19. DisableHighResClock
20. Now
21. GetQPCDriftMicroseconds
22. QPCValueToMicroseconds
23. skew_
24. InitializeClock
25. UnreliableNow
26. ReliableNow
27. HighResNowWrapper
28. CPUReliablySupportsHighResTime
29. SetMockTickFunction
30. SetNowIsHighResNowIfSupported
31. Now
32. HighResNow
33. IsHighResNowFastAndReliable
34. ThreadNow
35. NowFromSystemTraceTime
36. GetQPCDriftMicroseconds
37. FromQPCValue
38. IsHighResClockWorking
39. UnprotectedNow
40. FromQPCValue

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.


// Windows Timer Primer
//
// A good article:  http://www.ddj.com/windows/184416651
// A good mozilla bug:  http://bugzilla.mozilla.org/show_bug.cgi?id=363258
//
// The default windows timer, GetSystemTimeAsFileTime is not very precise.
// It is only good to ~15.5ms.
//
// QueryPerformanceCounter is the logical choice for a high-precision timer.
// However, it is known to be buggy on some hardware.  Specifically, it can
// sometimes "jump".  On laptops, QPC can also be very expensive to call.
// It's 3-4x slower than timeGetTime() on desktops, but can be 10x slower
// on laptops.  A unittest exists which will show the relative cost of various
// timers on any system.
//
// The next logical choice is timeGetTime().  timeGetTime has a precision of
// 1ms, but only if you call APIs (timeBeginPeriod()) which affect all other
// applications on the system.  By default, precision is only 15.5ms.
// Unfortunately, we don't want to call timeBeginPeriod because we don't
// want to affect other applications.  Further, on mobile platforms, use of
// faster multimedia timers can hurt battery life.  See the intel
// article about this here:
// http://softwarecommunity.intel.com/articles/eng/1086.htm
//
// To work around all this, we're going to generally use timeGetTime().  We
// will only increase the system-wide timer if we're not running on battery
// power.  Using timeBeginPeriod(1) is a requirement in order to make our
// message loop waits have the same resolution that our time measurements
// do.  Otherwise, WaitForSingleObject(..., 1) will no less than 15ms when
// there is nothing else to waken the Wait.

#include "base/time/time.h"

#pragma comment(lib, "winmm.lib")
#include <windows.h>
#include <mmsystem.h>

#include "base/basictypes.h"
#include "base/cpu.h"
#include "base/logging.h"
#include "base/memory/singleton.h"
#include "base/synchronization/lock.h"

using base::Time;
using base::TimeDelta;
using base::TimeTicks;

namespace {

// From MSDN, FILETIME "Contains a 64-bit value representing the number of
// 100-nanosecond intervals since January 1, 1601 (UTC)."
int64 FileTimeToMicroseconds(const FILETIME& ft) {
  // Need to bit_cast to fix alignment, then divide by 10 to convert
  // 100-nanoseconds to milliseconds. This only works on little-endian
  // machines.
  return bit_cast<int64, FILETIME>(ft) / 10;
}

void MicrosecondsToFileTime(int64 us, FILETIME* ft) {
  DCHECK_GE(us, 0LL) << "Time is less than 0, negative values are not "
      "representable in FILETIME";

  // Multiply by 10 to convert milliseconds to 100-nanoseconds. Bit_cast will
  // handle alignment problems. This only works on little-endian machines.
  *ft = bit_cast<FILETIME, int64>(us * 10);
}

int64 CurrentWallclockMicroseconds() {
  FILETIME ft;
  ::GetSystemTimeAsFileTime(&ft);
  return FileTimeToMicroseconds(ft);
}

// Time between resampling the un-granular clock for this API.  60 seconds.
const int kMaxMillisecondsToAvoidDrift = 60 * Time::kMillisecondsPerSecond;

int64 initial_time = 0;
TimeTicks initial_ticks;

void InitializeClock() {
  initial_ticks = TimeTicks::Now();
  initial_time = CurrentWallclockMicroseconds();
}

}  // namespace

// Time -----------------------------------------------------------------------

// The internal representation of Time uses FILETIME, whose epoch is 1601-01-01
// 00:00:00 UTC.  ((1970-1601)*365+89)*24*60*60*1000*1000, where 89 is the
// number of leap year days between 1601 and 1970: (1970-1601)/4 excluding
// 1700, 1800, and 1900.
// static
const int64 Time::kTimeTToMicrosecondsOffset = GG_INT64_C(11644473600000000);

bool Time::high_resolution_timer_enabled_ = false;
int Time::high_resolution_timer_activated_ = 0;

// static
Time Time::Now() {
  if (initial_time == 0)
    InitializeClock();

  // We implement time using the high-resolution timers so that we can get
  // timeouts which are smaller than 10-15ms.  If we just used
  // CurrentWallclockMicroseconds(), we'd have the less-granular timer.
  //
  // To make this work, we initialize the clock (initial_time) and the
  // counter (initial_ctr).  To compute the initial time, we can check
  // the number of ticks that have elapsed, and compute the delta.
  //
  // To avoid any drift, we periodically resync the counters to the system
  // clock.
  while (true) {
    TimeTicks ticks = TimeTicks::Now();

    // Calculate the time elapsed since we started our timer
    TimeDelta elapsed = ticks - initial_ticks;

    // Check if enough time has elapsed that we need to resync the clock.
    if (elapsed.InMilliseconds() > kMaxMillisecondsToAvoidDrift) {
      InitializeClock();
      continue;
    }

    return Time(elapsed + Time(initial_time));
  }
}

// static
Time Time::NowFromSystemTime() {
  // Force resync.
  InitializeClock();
  return Time(initial_time);
}

// static
Time Time::FromFileTime(FILETIME ft) {
  if (bit_cast<int64, FILETIME>(ft) == 0)
    return Time();
  if (ft.dwHighDateTime == std::numeric_limits<DWORD>::max() &&
      ft.dwLowDateTime == std::numeric_limits<DWORD>::max())
    return Max();
  return Time(FileTimeToMicroseconds(ft));
}

FILETIME Time::ToFileTime() const {
  if (is_null())
    return bit_cast<FILETIME, int64>(0);
  if (is_max()) {
    FILETIME result;
    result.dwHighDateTime = std::numeric_limits<DWORD>::max();
    result.dwLowDateTime = std::numeric_limits<DWORD>::max();
    return result;
  }
  FILETIME utc_ft;
  MicrosecondsToFileTime(us_, &utc_ft);
  return utc_ft;
}

// static
void Time::EnableHighResolutionTimer(bool enable) {
  // Test for single-threaded access.
  static PlatformThreadId my_thread = PlatformThread::CurrentId();
  DCHECK(PlatformThread::CurrentId() == my_thread);

  if (high_resolution_timer_enabled_ == enable)
    return;

  high_resolution_timer_enabled_ = enable;
}

// static
bool Time::ActivateHighResolutionTimer(bool activating) {
  if (!high_resolution_timer_enabled_ && activating)
    return false;

  // Using anything other than 1ms makes timers granular
  // to that interval.
  const int kMinTimerIntervalMs = 1;
  MMRESULT result;
  if (activating) {
    result = timeBeginPeriod(kMinTimerIntervalMs);
    high_resolution_timer_activated_++;
  } else {
    result = timeEndPeriod(kMinTimerIntervalMs);
    high_resolution_timer_activated_--;
  }
  return result == TIMERR_NOERROR;
}

// static
bool Time::IsHighResolutionTimerInUse() {
  // Note:  we should track the high_resolution_timer_activated_ value
  // under a lock if we want it to be accurate in a system with multiple
  // message loops.  We don't do that - because we don't want to take the
  // expense of a lock for this.  We *only* track this value so that unit
  // tests can see if the high resolution timer is on or off.
  return high_resolution_timer_enabled_ &&
      high_resolution_timer_activated_ > 0;
}

// static
Time Time::FromExploded(bool is_local, const Exploded& exploded) {
  // Create the system struct representing our exploded time. It will either be
  // in local time or UTC.
  SYSTEMTIME st;
  st.wYear = exploded.year;
  st.wMonth = exploded.month;
  st.wDayOfWeek = exploded.day_of_week;
  st.wDay = exploded.day_of_month;
  st.wHour = exploded.hour;
  st.wMinute = exploded.minute;
  st.wSecond = exploded.second;
  st.wMilliseconds = exploded.millisecond;

  FILETIME ft;
  bool success = true;
  // Ensure that it's in UTC.
  if (is_local) {
    SYSTEMTIME utc_st;
    success = TzSpecificLocalTimeToSystemTime(NULL, &st, &utc_st) &&
              SystemTimeToFileTime(&utc_st, &ft);
  } else {
    success = !!SystemTimeToFileTime(&st, &ft);
  }

  if (!success) {
    NOTREACHED() << "Unable to convert time";
    return Time(0);
  }
  return Time(FileTimeToMicroseconds(ft));
}

void Time::Explode(bool is_local, Exploded* exploded) const {
  if (us_ < 0LL) {
    // We are not able to convert it to FILETIME.
    ZeroMemory(exploded, sizeof(*exploded));
    return;
  }

  // FILETIME in UTC.
  FILETIME utc_ft;
  MicrosecondsToFileTime(us_, &utc_ft);

  // FILETIME in local time if necessary.
  bool success = true;
  // FILETIME in SYSTEMTIME (exploded).
  SYSTEMTIME st;
  if (is_local) {
    SYSTEMTIME utc_st;
    // We don't use FileTimeToLocalFileTime here, since it uses the current
    // settings for the time zone and daylight saving time. Therefore, if it is
    // daylight saving time, it will take daylight saving time into account,
    // even if the time you are converting is in standard time.
    success = FileTimeToSystemTime(&utc_ft, &utc_st) &&
              SystemTimeToTzSpecificLocalTime(NULL, &utc_st, &st);
  } else {
    success = !!FileTimeToSystemTime(&utc_ft, &st);
  }

  if (!success) {
    NOTREACHED() << "Unable to convert time, don't know why";
    ZeroMemory(exploded, sizeof(*exploded));
    return;
  }

  exploded->year = st.wYear;
  exploded->month = st.wMonth;
  exploded->day_of_week = st.wDayOfWeek;
  exploded->day_of_month = st.wDay;
  exploded->hour = st.wHour;
  exploded->minute = st.wMinute;
  exploded->second = st.wSecond;
  exploded->millisecond = st.wMilliseconds;
}

// TimeTicks ------------------------------------------------------------------
namespace {

// We define a wrapper to adapt between the __stdcall and __cdecl call of the
// mock function, and to avoid a static constructor.  Assigning an import to a
// function pointer directly would require setup code to fetch from the IAT.
DWORD timeGetTimeWrapper() {
  return timeGetTime();
}

DWORD (*tick_function)(void) = &timeGetTimeWrapper;

// Accumulation of time lost due to rollover (in milliseconds).
int64 rollover_ms = 0;

// The last timeGetTime value we saw, to detect rollover.
DWORD last_seen_now = 0;

// Lock protecting rollover_ms and last_seen_now.
// Note: this is a global object, and we usually avoid these. However, the time
// code is low-level, and we don't want to use Singletons here (it would be too
// easy to use a Singleton without even knowing it, and that may lead to many
// gotchas). Its impact on startup time should be negligible due to low-level
// nature of time code.
base::Lock rollover_lock;

// We use timeGetTime() to implement TimeTicks::Now().  This can be problematic
// because it returns the number of milliseconds since Windows has started,
// which will roll over the 32-bit value every ~49 days.  We try to track
// rollover ourselves, which works if TimeTicks::Now() is called at least every
// 49 days.
TimeDelta RolloverProtectedNow() {
  base::AutoLock locked(rollover_lock);
  // We should hold the lock while calling tick_function to make sure that
  // we keep last_seen_now stay correctly in sync.
  DWORD now = tick_function();
  if (now < last_seen_now)
    rollover_ms += 0x100000000I64;  // ~49.7 days.
  last_seen_now = now;
  return TimeDelta::FromMilliseconds(now + rollover_ms);
}

bool IsBuggyAthlon(const base::CPU& cpu) {
  // On Athlon X2 CPUs (e.g. model 15) QueryPerformanceCounter is
  // unreliable.  Fallback to low-res clock.
  return cpu.vendor_name() == "AuthenticAMD" && cpu.family() == 15;
}

// Overview of time counters:
// (1) CPU cycle counter. (Retrieved via RDTSC)
// The CPU counter provides the highest resolution time stamp and is the least
// expensive to retrieve. However, the CPU counter is unreliable and should not
// be used in production. Its biggest issue is that it is per processor and it
// is not synchronized between processors. Also, on some computers, the counters
// will change frequency due to thermal and power changes, and stop in some
// states.
//
// (2) QueryPerformanceCounter (QPC). The QPC counter provides a high-
// resolution (100 nanoseconds) time stamp but is comparatively more expensive
// to retrieve. What QueryPerformanceCounter actually does is up to the HAL.
// (with some help from ACPI).
// According to http://blogs.msdn.com/oldnewthing/archive/2005/09/02/459952.aspx
// in the worst case, it gets the counter from the rollover interrupt on the
// programmable interrupt timer. In best cases, the HAL may conclude that the
// RDTSC counter runs at a constant frequency, then it uses that instead. On
// multiprocessor machines, it will try to verify the values returned from
// RDTSC on each processor are consistent with each other, and apply a handful
// of workarounds for known buggy hardware. In other words, QPC is supposed to
// give consistent result on a multiprocessor computer, but it is unreliable in
// reality due to bugs in BIOS or HAL on some, especially old computers.
// With recent updates on HAL and newer BIOS, QPC is getting more reliable but
// it should be used with caution.
//
// (3) System time. The system time provides a low-resolution (typically 10ms
// to 55 milliseconds) time stamp but is comparatively less expensive to
// retrieve and more reliable.
class HighResNowSingleton {
 public:
  static HighResNowSingleton* GetInstance() {
    return Singleton<HighResNowSingleton>::get();
  }

  bool IsUsingHighResClock() {
    return ticks_per_second_ != 0.0;
  }

  void DisableHighResClock() {
    ticks_per_second_ = 0.0;
  }

  TimeDelta Now() {
    if (IsUsingHighResClock())
      return TimeDelta::FromMicroseconds(UnreliableNow());

    // 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;

    // Intentionally calculate microseconds in a round about manner to avoid
    // overflow and precision issues. Think twice before simplifying!
    int64 whole_seconds = qpc_value / ticks_per_second_;
    int64 leftover_ticks = qpc_value % ticks_per_second_;
    int64 microseconds = (whole_seconds * Time::kMicrosecondsPerSecond) +
                         ((leftover_ticks * Time::kMicrosecondsPerSecond) /
                          ticks_per_second_);
    return microseconds;
  }

 private:
  HighResNowSingleton()
    : ticks_per_second_(0),
      skew_(0) {
    InitializeClock();

    base::CPU cpu;
    if (IsBuggyAthlon(cpu))
      DisableHighResClock();
  }

  // Synchronize the QPC clock with GetSystemTimeAsFileTime.
  void InitializeClock() {
    LARGE_INTEGER ticks_per_sec = {0};
    if (!QueryPerformanceFrequency(&ticks_per_sec))
      return;  // Broken, we don't guarantee this function works.
    ticks_per_second_ = ticks_per_sec.QuadPart;

    skew_ = UnreliableNow() - ReliableNow();
  }

  // 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).

  friend struct DefaultSingletonTraits<HighResNowSingleton>;
};

TimeDelta HighResNowWrapper() {
  return HighResNowSingleton::GetInstance()->Now();
}

typedef TimeDelta (*NowFunction)(void);
NowFunction now_function = RolloverProtectedNow;

bool CPUReliablySupportsHighResTime() {
  base::CPU cpu;
  if (!cpu.has_non_stop_time_stamp_counter())
    return false;

  if (IsBuggyAthlon(cpu))
    return false;

  return true;
}

}  // 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
bool TimeTicks::SetNowIsHighResNowIfSupported() {
  if (!CPUReliablySupportsHighResTime()) {
    return false;
  }

  now_function = HighResNowWrapper;
  return true;
}

// static
TimeTicks TimeTicks::Now() {
  return TimeTicks() + now_function();
}

// static
TimeTicks TimeTicks::HighResNow() {
  return TimeTicks() + HighResNowSingleton::GetInstance()->Now();
}

// static
bool TimeTicks::IsHighResNowFastAndReliable() {
  return CPUReliablySupportsHighResTime();
}

// static
TimeTicks TimeTicks::ThreadNow() {
  NOTREACHED();
  return TimeTicks();
}

// static
TimeTicks TimeTicks::NowFromSystemTraceTime() {
  return HighResNow();
}

// static
int64 TimeTicks::GetQPCDriftMicroseconds() {
  return HighResNowSingleton::GetInstance()->GetQPCDriftMicroseconds();
}

// static
TimeTicks TimeTicks::FromQPCValue(LONGLONG qpc_value) {
  return TimeTicks(
      HighResNowSingleton::GetInstance()->QPCValueToMicroseconds(qpc_value));
}

// static
bool TimeTicks::IsHighResClockWorking() {
  return HighResNowSingleton::GetInstance()->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(
      HighResNowSingleton::GetInstance()->QPCValueToMicroseconds(qpc_value));
}