// 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.
#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/lazy_instance.h"
#include "base/logging.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();
}
// The two values that ActivateHighResolutionTimer uses to set the systemwide
// timer interrupt frequency on Windows. It controls how precise timers are
// but also has a big impact on battery life.
const int kMinTimerIntervalHighResMs = 1;
const int kMinTimerIntervalLowResMs = 4;
// Track if kMinTimerIntervalHighResMs or kMinTimerIntervalLowResMs is active.
bool g_high_res_timer_enabled = false;
// How many times the high resolution timer has been called.
uint32_t g_high_res_timer_count = 0;
// The lock to control access to the above two variables.
base::LazyInstance<base::Lock>::Leaky g_high_res_lock =
LAZY_INSTANCE_INITIALIZER;
} // 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);
// 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) {
base::AutoLock lock(g_high_res_lock.Get());
if (g_high_res_timer_enabled == enable)
return;
g_high_res_timer_enabled = enable;
if (!g_high_res_timer_count)
return;
// Since g_high_res_timer_count != 0, an ActivateHighResolutionTimer(true)
// was called which called timeBeginPeriod with g_high_res_timer_enabled
// with a value which is the opposite of |enable|. With that information we
// call timeEndPeriod with the same value used in timeBeginPeriod and
// therefore undo the period effect.
if (enable) {
timeEndPeriod(kMinTimerIntervalLowResMs);
timeBeginPeriod(kMinTimerIntervalHighResMs);
} else {
timeEndPeriod(kMinTimerIntervalHighResMs);
timeBeginPeriod(kMinTimerIntervalLowResMs);
}
}
// static
bool Time::ActivateHighResolutionTimer(bool activating) {
// We only do work on the transition from zero to one or one to zero so we
// can easily undo the effect (if necessary) when EnableHighResolutionTimer is
// called.
const uint32_t max = std::numeric_limits<uint32_t>::max();
base::AutoLock lock(g_high_res_lock.Get());
UINT period = g_high_res_timer_enabled ? kMinTimerIntervalHighResMs
: kMinTimerIntervalLowResMs;
if (activating) {
DCHECK(g_high_res_timer_count != max);
++g_high_res_timer_count;
if (g_high_res_timer_count == 1)
timeBeginPeriod(period);
} else {
DCHECK(g_high_res_timer_count != 0);
--g_high_res_timer_count;
if (g_high_res_timer_count == 0)
timeEndPeriod(period);
}
return (period == kMinTimerIntervalHighResMs);
}
// static
bool Time::IsHighResolutionTimerInUse() {
base::AutoLock lock(g_high_res_lock.Get());
return g_high_res_timer_enabled && g_high_res_timer_count > 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 = {0};
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:
HighResNowSingleton()
: ticks_per_second_(0),
skew_(0) {
base::CPU cpu;
if (IsBuggyAthlon(cpu))
return;
// Synchronize the QPC clock with GetSystemTimeAsFileTime.
LARGE_INTEGER ticks_per_sec = {0};
if (!QueryPerformanceFrequency(&ticks_per_sec))
return; // QPC is not available.
ticks_per_second_ = ticks_per_sec.QuadPart;
skew_ = UnreliableNow() - ReliableNow();
}
bool IsUsingHighResClock() {
return ticks_per_second_ != 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;
// 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));
}