Fix regression where high resolution timers could be activated even under...

base/time_win.cc

 // Copyright (c) 2009 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
 //
@@ skipping 81 matching lines @@
 // 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.
   //
@@ skipping 43 matching lines @@
   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 activate) {
-  if (!high_resolution_timer_enabled_)
+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 (activate)
+  if (activating) {
     result = timeBeginPeriod(kMinTimerIntervalMs);
-  else
+    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;
@@ skipping 208 matching lines @@
 
 // static
 int64 TimeTicks::GetQPCDriftMicroseconds() {
   return Singleton<HighResNowSingleton>::get()->GetQPCDriftMicroseconds();
 }
 
 // static
 bool TimeTicks::IsHighResClockWorking() {
   return Singleton<HighResNowSingleton>::get()->IsUsingHighResClock();
 }