The Tor Browser: security/sandbox/chromium/base/time/time

security/sandbox/chromium/base/time/time_win.cc@6474c204b198 (annotated)

security/sandbox/chromium/base/time/time_win.cc

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 // 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
 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));
 }

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security/sandbox/chromium/base/time/time_win.cc@6474c204b198 (annotated)

security/sandbox/chromium/base/time/time_win.cc