diff options
Diffstat (limited to 'security/sandbox/chromium/base/time/time_win.cc')
| -rw-r--r-- | security/sandbox/chromium/base/time/time_win.cc | 810 |
1 files changed, 810 insertions, 0 deletions
diff --git a/security/sandbox/chromium/base/time/time_win.cc b/security/sandbox/chromium/base/time/time_win.cc new file mode 100644 index 0000000000..c1976e64a6 --- /dev/null +++ b/security/sandbox/chromium/base/time/time_win.cc @@ -0,0 +1,810 @@ +// 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" + +#include <windows.foundation.h> +#include <windows.h> +#include <mmsystem.h> +#include <stdint.h> + +#include "base/atomicops.h" +#include "base/bit_cast.h" +#include "base/cpu.h" +#include "base/feature_list.h" +#include "base/logging.h" +#include "base/synchronization/lock.h" +#include "base/threading/platform_thread.h" +#include "base/time/time_override.h" +#include "base/time/time_win_features.h" + +namespace base { + +namespace { + +// From MSDN, FILETIME "Contains a 64-bit value representing the number of +// 100-nanosecond intervals since January 1, 1601 (UTC)." +int64_t FileTimeToMicroseconds(const FILETIME& ft) { + // Need to bit_cast to fix alignment, then divide by 10 to convert + // 100-nanoseconds to microseconds. This only works on little-endian + // machines. + return bit_cast<int64_t, FILETIME>(ft) / 10; +} + +void MicrosecondsToFileTime(int64_t us, FILETIME* ft) { + DCHECK_GE(us, 0LL) << "Time is less than 0, negative values are not " + "representable in FILETIME"; + + // Multiply by 10 to convert microseconds to 100-nanoseconds. Bit_cast will + // handle alignment problems. This only works on little-endian machines. + *ft = bit_cast<FILETIME, int64_t>(us * 10); +} + +int64_t CurrentWallclockMicroseconds() { + FILETIME ft; + ::GetSystemTimeAsFileTime(&ft); + return FileTimeToMicroseconds(ft); +} + +// Time between resampling the un-granular clock for this API. +constexpr TimeDelta kMaxTimeToAvoidDrift = TimeDelta::FromSeconds(60); + +int64_t g_initial_time = 0; +TimeTicks g_initial_ticks; + +void InitializeClock() { + g_initial_ticks = subtle::TimeTicksNowIgnoringOverride(); + g_initial_time = CurrentWallclockMicroseconds(); +} + +// Interval to use when on DC power. +UINT g_battery_power_interval_ms = 4; +// Track the last value passed to timeBeginPeriod so that we can cancel that +// call by calling timeEndPeriod with the same value. A value of zero means that +// the timer frequency is not currently raised. +UINT g_last_interval_requested_ms = 0; +// Track if MinTimerIntervalHighResMs() or MinTimerIntervalLowResMs() is active. +// For most purposes this could also be named g_is_on_ac_power. +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; +// Start time of the high resolution timer usage monitoring. This is needed +// to calculate the usage as percentage of the total elapsed time. +TimeTicks g_high_res_timer_usage_start; +// The cumulative time the high resolution timer has been in use since +// |g_high_res_timer_usage_start| moment. +TimeDelta g_high_res_timer_usage; +// Timestamp of the last activation change of the high resolution timer. This +// is used to calculate the cumulative usage. +TimeTicks g_high_res_timer_last_activation; +// The lock to control access to the above set of variables. +Lock* GetHighResLock() { + static auto* lock = new Lock(); + return lock; +} + +// The two values that ActivateHighResolutionTimer uses to set the systemwide +// timer interrupt frequency on Windows. These control how precise timers are +// but also have a big impact on battery life. + +// Used when a faster timer has been requested (g_high_res_timer_count > 0) and +// the computer is running on AC power (plugged in) so that it's okay to go to +// the highest frequency. +UINT MinTimerIntervalHighResMs() { + return 1; +} + +// Used when a faster timer has been requested (g_high_res_timer_count > 0) and +// the computer is running on DC power (battery) so that we don't want to raise +// the timer frequency as much. +UINT MinTimerIntervalLowResMs() { + return g_battery_power_interval_ms; +} + +// Calculate the desired timer interrupt interval. Note that zero means that the +// system default should be used. +UINT GetIntervalMs() { + if (!g_high_res_timer_count) + return 0; // Use the default, typically 15.625 + if (g_high_res_timer_enabled) + return MinTimerIntervalHighResMs(); + return MinTimerIntervalLowResMs(); +} + +// Compare the currently requested timer interrupt interval to the last interval +// requested and update if necessary (by cancelling the old request and making a +// new request). If there is no change then do nothing. +void UpdateTimerIntervalLocked() { + UINT new_interval = GetIntervalMs(); + if (new_interval == g_last_interval_requested_ms) + return; + if (g_last_interval_requested_ms) { + // Record how long the timer interrupt frequency was raised. + g_high_res_timer_usage += subtle::TimeTicksNowIgnoringOverride() - + g_high_res_timer_last_activation; + // Reset the timer interrupt back to the default. + timeEndPeriod(g_last_interval_requested_ms); + } + g_last_interval_requested_ms = new_interval; + if (g_last_interval_requested_ms) { + // Record when the timer interrupt was raised. + g_high_res_timer_last_activation = subtle::TimeTicksNowIgnoringOverride(); + timeBeginPeriod(g_last_interval_requested_ms); + } +} + +// Returns the current value of the performance counter. +uint64_t QPCNowRaw() { + LARGE_INTEGER perf_counter_now = {}; + // According to the MSDN documentation for QueryPerformanceCounter(), this + // will never fail on systems that run XP or later. + // https://msdn.microsoft.com/library/windows/desktop/ms644904.aspx + ::QueryPerformanceCounter(&perf_counter_now); + return perf_counter_now.QuadPart; +} + +bool SafeConvertToWord(int in, WORD* out) { + CheckedNumeric<WORD> result = in; + *out = result.ValueOrDefault(std::numeric_limits<WORD>::max()); + return result.IsValid(); +} + +} // namespace + +// Time ----------------------------------------------------------------------- + +namespace subtle { +Time TimeNowIgnoringOverride() { + if (g_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 (g_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 = TimeTicksNowIgnoringOverride(); + + // Calculate the time elapsed since we started our timer + TimeDelta elapsed = ticks - g_initial_ticks; + + // Check if enough time has elapsed that we need to resync the clock. + if (elapsed > kMaxTimeToAvoidDrift) { + InitializeClock(); + continue; + } + + return Time() + elapsed + TimeDelta::FromMicroseconds(g_initial_time); + } +} + +Time TimeNowFromSystemTimeIgnoringOverride() { + // Force resync. + InitializeClock(); + return Time() + TimeDelta::FromMicroseconds(g_initial_time); +} +} // namespace subtle + +// static +Time Time::FromFileTime(FILETIME ft) { + if (bit_cast<int64_t, 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_t>(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; +} + +void Time::ReadMinTimerIntervalLowResMs() { + AutoLock lock(*GetHighResLock()); + // Read the setting for what interval to use on battery power. + g_battery_power_interval_ms = + base::FeatureList::IsEnabled(base::kSlowDCTimerInterruptsWin) ? 8 : 4; + UpdateTimerIntervalLocked(); +} + +// static +// Enable raising of the system-global timer interrupt frequency to 1 kHz (when +// enable is true, which happens when on AC power) or some lower frequency when +// on battery power (when enable is false). If the g_high_res_timer_enabled +// setting hasn't actually changed or if if there are no outstanding requests +// (if g_high_res_timer_count is zero) then do nothing. +// TL;DR - call this when going from AC to DC power or vice-versa. +void Time::EnableHighResolutionTimer(bool enable) { + AutoLock lock(*GetHighResLock()); + g_high_res_timer_enabled = enable; + UpdateTimerIntervalLocked(); +} + +// static +// Request that the system-global Windows timer interrupt frequency be raised. +// How high the frequency is raised depends on the system's power state and +// possibly other options. +// TL;DR - call this at the beginning and end of a time period where you want +// higher frequency timer interrupts. Each call with activating=true must be +// paired with a subsequent activating=false call. +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(); + + AutoLock lock(*GetHighResLock()); + if (activating) { + DCHECK_NE(g_high_res_timer_count, max); + ++g_high_res_timer_count; + } else { + DCHECK_NE(g_high_res_timer_count, 0u); + --g_high_res_timer_count; + } + UpdateTimerIntervalLocked(); + return true; +} + +// static +// See if the timer interrupt interval has been set to the lowest value. +bool Time::IsHighResolutionTimerInUse() { + AutoLock lock(*GetHighResLock()); + return g_last_interval_requested_ms == MinTimerIntervalHighResMs(); +} + +// static +void Time::ResetHighResolutionTimerUsage() { + AutoLock lock(*GetHighResLock()); + g_high_res_timer_usage = TimeDelta(); + g_high_res_timer_usage_start = subtle::TimeTicksNowIgnoringOverride(); + if (g_high_res_timer_count > 0) + g_high_res_timer_last_activation = g_high_res_timer_usage_start; +} + +// static +double Time::GetHighResolutionTimerUsage() { + AutoLock lock(*GetHighResLock()); + TimeTicks now = subtle::TimeTicksNowIgnoringOverride(); + TimeDelta elapsed_time = now - g_high_res_timer_usage_start; + if (elapsed_time.is_zero()) { + // This is unexpected but possible if TimeTicks resolution is low and + // GetHighResolutionTimerUsage() is called promptly after + // ResetHighResolutionTimerUsage(). + return 0.0; + } + TimeDelta used_time = g_high_res_timer_usage; + if (g_high_res_timer_count > 0) { + // If currently activated add the remainder of time since the last + // activation. + used_time += now - g_high_res_timer_last_activation; + } + return used_time.InMillisecondsF() / elapsed_time.InMillisecondsF() * 100; +} + +// static +bool Time::FromExploded(bool is_local, const Exploded& exploded, Time* time) { + // Create the system struct representing our exploded time. It will either be + // in local time or UTC.If casting from int to WORD results in overflow, + // fail and return Time(0). + SYSTEMTIME st; + if (!SafeConvertToWord(exploded.year, &st.wYear) || + !SafeConvertToWord(exploded.month, &st.wMonth) || + !SafeConvertToWord(exploded.day_of_week, &st.wDayOfWeek) || + !SafeConvertToWord(exploded.day_of_month, &st.wDay) || + !SafeConvertToWord(exploded.hour, &st.wHour) || + !SafeConvertToWord(exploded.minute, &st.wMinute) || + !SafeConvertToWord(exploded.second, &st.wSecond) || + !SafeConvertToWord(exploded.millisecond, &st.wMilliseconds)) { + *time = Time(0); + return false; + } + + FILETIME ft; + bool success = true; + // Ensure that it's in UTC. + if (is_local) { + SYSTEMTIME utc_st; + success = TzSpecificLocalTimeToSystemTime(nullptr, &st, &utc_st) && + SystemTimeToFileTime(&utc_st, &ft); + } else { + success = !!SystemTimeToFileTime(&st, &ft); + } + + if (!success) { + *time = Time(0); + return false; + } + + *time = Time(FileTimeToMicroseconds(ft)); + return true; +} + +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(nullptr, &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 (*g_tick_function)(void) = &timeGetTimeWrapper; + +// A structure holding the most significant bits of "last seen" and a +// "rollover" counter. +union LastTimeAndRolloversState { + // The state as a single 32-bit opaque value. + subtle::Atomic32 as_opaque_32; + + // The state as usable values. + struct { + // The top 8-bits of the "last" time. This is enough to check for rollovers + // and the small bit-size means fewer CompareAndSwap operations to store + // changes in state, which in turn makes for fewer retries. + uint8_t last_8; + // A count of the number of detected rollovers. Using this as bits 47-32 + // of the upper half of a 64-bit value results in a 48-bit tick counter. + // This extends the total rollover period from about 49 days to about 8800 + // years while still allowing it to be stored with last_8 in a single + // 32-bit value. + uint16_t rollovers; + } as_values; +}; +subtle::Atomic32 g_last_time_and_rollovers = 0; +static_assert( + sizeof(LastTimeAndRolloversState) <= sizeof(g_last_time_and_rollovers), + "LastTimeAndRolloversState does not fit in a single atomic word"); + +// 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 +// 48.8 days (not 49 days because only changes in the top 8 bits get noticed). +TimeTicks RolloverProtectedNow() { + LastTimeAndRolloversState state; + DWORD now; // DWORD is always unsigned 32 bits. + + while (true) { + // Fetch the "now" and "last" tick values, updating "last" with "now" and + // incrementing the "rollovers" counter if the tick-value has wrapped back + // around. Atomic operations ensure that both "last" and "rollovers" are + // always updated together. + int32_t original = subtle::Acquire_Load(&g_last_time_and_rollovers); + state.as_opaque_32 = original; + now = g_tick_function(); + uint8_t now_8 = static_cast<uint8_t>(now >> 24); + if (now_8 < state.as_values.last_8) + ++state.as_values.rollovers; + state.as_values.last_8 = now_8; + + // If the state hasn't changed, exit the loop. + if (state.as_opaque_32 == original) + break; + + // Save the changed state. If the existing value is unchanged from the + // original, exit the loop. + int32_t check = subtle::Release_CompareAndSwap( + &g_last_time_and_rollovers, original, state.as_opaque_32); + if (check == original) + break; + + // Another thread has done something in between so retry from the top. + } + + return TimeTicks() + + TimeDelta::FromMilliseconds( + now + (static_cast<uint64_t>(state.as_values.rollovers) << 32)); +} + +// Discussion of tick counter options on Windows: +// +// (1) CPU cycle counter. (Retrieved via RDTSC) +// The CPU counter provides the highest resolution time stamp and is the least +// expensive to retrieve. However, on older CPUs, two issues can affect its +// reliability: First it is maintained per processor and not synchronized +// between processors. Also, 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 (<1 microsecond) time stamp. On most hardware running today, it +// auto-detects and uses the constant-rate RDTSC counter to provide extremely +// efficient and reliable time stamps. +// +// On older CPUs where RDTSC is unreliable, it falls back to using more +// expensive (20X to 40X more costly) alternate clocks, such as HPET or the ACPI +// PM timer, and can involve system calls; and all this 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 results on a multiprocessor computer, but for older CPUs it +// can be unreliable due bugs in BIOS or HAL. +// +// (3) System time. The system time provides a low-resolution (from ~1 to ~15.6 +// milliseconds) time stamp but is comparatively less expensive to retrieve and +// more reliable. Time::EnableHighResolutionTimer() and +// Time::ActivateHighResolutionTimer() can be called to alter the resolution of +// this timer; and also other Windows applications can alter it, affecting this +// one. + +TimeTicks InitialNowFunction(); + +// See "threading notes" in InitializeNowFunctionPointer() for details on how +// concurrent reads/writes to these globals has been made safe. +TimeTicksNowFunction g_time_ticks_now_ignoring_override_function = + &InitialNowFunction; +int64_t g_qpc_ticks_per_second = 0; + +// As of January 2015, use of <atomic> is forbidden in Chromium code. This is +// what std::atomic_thread_fence does on Windows on all Intel architectures when +// the memory_order argument is anything but std::memory_order_seq_cst: +#define ATOMIC_THREAD_FENCE(memory_order) _ReadWriteBarrier(); + +TimeDelta QPCValueToTimeDelta(LONGLONG qpc_value) { + // Ensure that the assignment to |g_qpc_ticks_per_second|, made in + // InitializeNowFunctionPointer(), has happened by this point. + ATOMIC_THREAD_FENCE(memory_order_acquire); + + DCHECK_GT(g_qpc_ticks_per_second, 0); + + // If the QPC Value is below the overflow threshold, we proceed with + // simple multiply and divide. + if (qpc_value < Time::kQPCOverflowThreshold) { + return TimeDelta::FromMicroseconds( + qpc_value * Time::kMicrosecondsPerSecond / g_qpc_ticks_per_second); + } + // Otherwise, calculate microseconds in a round about manner to avoid + // overflow and precision issues. + int64_t whole_seconds = qpc_value / g_qpc_ticks_per_second; + int64_t leftover_ticks = qpc_value - (whole_seconds * g_qpc_ticks_per_second); + return TimeDelta::FromMicroseconds( + (whole_seconds * Time::kMicrosecondsPerSecond) + + ((leftover_ticks * Time::kMicrosecondsPerSecond) / + g_qpc_ticks_per_second)); +} + +TimeTicks QPCNow() { + return TimeTicks() + QPCValueToTimeDelta(QPCNowRaw()); +} + +void InitializeNowFunctionPointer() { + LARGE_INTEGER ticks_per_sec = {}; + if (!QueryPerformanceFrequency(&ticks_per_sec)) + ticks_per_sec.QuadPart = 0; + + // If Windows cannot provide a QPC implementation, TimeTicks::Now() must use + // the low-resolution clock. + // + // If the QPC implementation is expensive and/or unreliable, TimeTicks::Now() + // will still use the low-resolution clock. A CPU lacking a non-stop time + // counter will cause Windows to provide an alternate QPC implementation that + // works, but is expensive to use. + // + // Otherwise, Now uses the high-resolution QPC clock. As of 21 August 2015, + // ~72% of users fall within this category. + TimeTicksNowFunction now_function; + CPU cpu; + if (ticks_per_sec.QuadPart <= 0 || !cpu.has_non_stop_time_stamp_counter()) { + now_function = &RolloverProtectedNow; + } else { + now_function = &QPCNow; + } + + // Threading note 1: In an unlikely race condition, it's possible for two or + // more threads to enter InitializeNowFunctionPointer() in parallel. This is + // not a problem since all threads should end up writing out the same values + // to the global variables. + // + // Threading note 2: A release fence is placed here to ensure, from the + // perspective of other threads using the function pointers, that the + // assignment to |g_qpc_ticks_per_second| happens before the function pointers + // are changed. + g_qpc_ticks_per_second = ticks_per_sec.QuadPart; + ATOMIC_THREAD_FENCE(memory_order_release); + // Also set g_time_ticks_now_function to avoid the additional indirection via + // TimeTicksNowIgnoringOverride() for future calls to TimeTicks::Now(). But + // g_time_ticks_now_function may have already be overridden. + if (internal::g_time_ticks_now_function == + &subtle::TimeTicksNowIgnoringOverride) { + internal::g_time_ticks_now_function = now_function; + } + g_time_ticks_now_ignoring_override_function = now_function; +} + +TimeTicks InitialNowFunction() { + InitializeNowFunctionPointer(); + return g_time_ticks_now_ignoring_override_function(); +} + +} // namespace + +// static +TimeTicks::TickFunctionType TimeTicks::SetMockTickFunction( + TickFunctionType ticker) { + TickFunctionType old = g_tick_function; + g_tick_function = ticker; + subtle::NoBarrier_Store(&g_last_time_and_rollovers, 0); + return old; +} + +namespace subtle { +TimeTicks TimeTicksNowIgnoringOverride() { + return g_time_ticks_now_ignoring_override_function(); +} +} // namespace subtle + +// static +bool TimeTicks::IsHighResolution() { + if (g_time_ticks_now_ignoring_override_function == &InitialNowFunction) + InitializeNowFunctionPointer(); + return g_time_ticks_now_ignoring_override_function == &QPCNow; +} + +// static +bool TimeTicks::IsConsistentAcrossProcesses() { + // According to Windows documentation [1] QPC is consistent post-Windows + // Vista. So if we are using QPC then we are consistent which is the same as + // being high resolution. + // + // [1] https://msdn.microsoft.com/en-us/library/windows/desktop/dn553408(v=vs.85).aspx + // + // "In general, the performance counter results are consistent across all + // processors in multi-core and multi-processor systems, even when measured on + // different threads or processes. Here are some exceptions to this rule: + // - Pre-Windows Vista operating systems that run on certain processors might + // violate this consistency because of one of these reasons: + // 1. The hardware processors have a non-invariant TSC and the BIOS + // doesn't indicate this condition correctly. + // 2. The TSC synchronization algorithm that was used wasn't suitable for + // systems with large numbers of processors." + return IsHighResolution(); +} + +// static +TimeTicks::Clock TimeTicks::GetClock() { + return IsHighResolution() ? + Clock::WIN_QPC : Clock::WIN_ROLLOVER_PROTECTED_TIME_GET_TIME; +} + +// ThreadTicks ---------------------------------------------------------------- + +namespace subtle { +ThreadTicks ThreadTicksNowIgnoringOverride() { + return ThreadTicks::GetForThread(PlatformThread::CurrentHandle()); +} +} // namespace subtle + +// static +ThreadTicks ThreadTicks::GetForThread( + const PlatformThreadHandle& thread_handle) { + DCHECK(IsSupported()); + +#if defined(ARCH_CPU_ARM64) + // QueryThreadCycleTime versus TSCTicksPerSecond doesn't have much relation to + // actual elapsed time on Windows on Arm, because QueryThreadCycleTime is + // backed by the actual number of CPU cycles executed, rather than a + // constant-rate timer like Intel. To work around this, use GetThreadTimes + // (which isn't as accurate but is meaningful as a measure of elapsed + // per-thread time). + FILETIME creation_time, exit_time, kernel_time, user_time; + ::GetThreadTimes(thread_handle.platform_handle(), &creation_time, &exit_time, + &kernel_time, &user_time); + + int64_t us = FileTimeToMicroseconds(user_time); + return ThreadTicks(us); +#else + // Get the number of TSC ticks used by the current thread. + ULONG64 thread_cycle_time = 0; + ::QueryThreadCycleTime(thread_handle.platform_handle(), &thread_cycle_time); + + // Get the frequency of the TSC. + double tsc_ticks_per_second = TSCTicksPerSecond(); + if (tsc_ticks_per_second == 0) + return ThreadTicks(); + + // Return the CPU time of the current thread. + double thread_time_seconds = thread_cycle_time / tsc_ticks_per_second; + return ThreadTicks( + static_cast<int64_t>(thread_time_seconds * Time::kMicrosecondsPerSecond)); +#endif +} + +// static +bool ThreadTicks::IsSupportedWin() { + static bool is_supported = CPU().has_non_stop_time_stamp_counter(); + return is_supported; +} + +// static +void ThreadTicks::WaitUntilInitializedWin() { +#if !defined(ARCH_CPU_ARM64) + while (TSCTicksPerSecond() == 0) + ::Sleep(10); +#endif +} + +#if !defined(ARCH_CPU_ARM64) +double ThreadTicks::TSCTicksPerSecond() { + DCHECK(IsSupported()); + // The value returned by QueryPerformanceFrequency() cannot be used as the TSC + // frequency, because there is no guarantee that the TSC frequency is equal to + // the performance counter frequency. + // The TSC frequency is cached in a static variable because it takes some time + // to compute it. + static double tsc_ticks_per_second = 0; + if (tsc_ticks_per_second != 0) + return tsc_ticks_per_second; + + // Increase the thread priority to reduces the chances of having a context + // switch during a reading of the TSC and the performance counter. + int previous_priority = ::GetThreadPriority(::GetCurrentThread()); + ::SetThreadPriority(::GetCurrentThread(), THREAD_PRIORITY_HIGHEST); + + // The first time that this function is called, make an initial reading of the + // TSC and the performance counter. + + static const uint64_t tsc_initial = __rdtsc(); + static const uint64_t perf_counter_initial = QPCNowRaw(); + + // Make a another reading of the TSC and the performance counter every time + // that this function is called. + uint64_t tsc_now = __rdtsc(); + uint64_t perf_counter_now = QPCNowRaw(); + + // Reset the thread priority. + ::SetThreadPriority(::GetCurrentThread(), previous_priority); + + // Make sure that at least 50 ms elapsed between the 2 readings. The first + // time that this function is called, we don't expect this to be the case. + // Note: The longer the elapsed time between the 2 readings is, the more + // accurate the computed TSC frequency will be. The 50 ms value was + // chosen because local benchmarks show that it allows us to get a + // stddev of less than 1 tick/us between multiple runs. + // Note: According to the MSDN documentation for QueryPerformanceFrequency(), + // this will never fail on systems that run XP or later. + // https://msdn.microsoft.com/library/windows/desktop/ms644905.aspx + LARGE_INTEGER perf_counter_frequency = {}; + ::QueryPerformanceFrequency(&perf_counter_frequency); + DCHECK_GE(perf_counter_now, perf_counter_initial); + uint64_t perf_counter_ticks = perf_counter_now - perf_counter_initial; + double elapsed_time_seconds = + perf_counter_ticks / static_cast<double>(perf_counter_frequency.QuadPart); + + static constexpr double kMinimumEvaluationPeriodSeconds = 0.05; + if (elapsed_time_seconds < kMinimumEvaluationPeriodSeconds) + return 0; + + // Compute the frequency of the TSC. + DCHECK_GE(tsc_now, tsc_initial); + uint64_t tsc_ticks = tsc_now - tsc_initial; + tsc_ticks_per_second = tsc_ticks / elapsed_time_seconds; + + return tsc_ticks_per_second; +} +#endif // defined(ARCH_CPU_ARM64) + +// static +TimeTicks TimeTicks::FromQPCValue(LONGLONG qpc_value) { + return TimeTicks() + QPCValueToTimeDelta(qpc_value); +} + +// TimeDelta ------------------------------------------------------------------ + +// static +TimeDelta TimeDelta::FromQPCValue(LONGLONG qpc_value) { + return QPCValueToTimeDelta(qpc_value); +} + +// static +TimeDelta TimeDelta::FromFileTime(FILETIME ft) { + return TimeDelta::FromMicroseconds(FileTimeToMicroseconds(ft)); +} + +// static +TimeDelta TimeDelta::FromWinrtDateTime(ABI::Windows::Foundation::DateTime dt) { + // UniversalTime is 100 ns intervals since January 1, 1601 (UTC) + return TimeDelta::FromMicroseconds(dt.UniversalTime / 10); +} + +ABI::Windows::Foundation::DateTime TimeDelta::ToWinrtDateTime() const { + ABI::Windows::Foundation::DateTime date_time; + date_time.UniversalTime = InMicroseconds() * 10; + return date_time; +} + +} // namespace base |