Bug 1311425 - Add pref for how far into the timer queue, r=smaug,f=froydnj

--HG--
extra : rebase_source : 170404bed646efffa71f1e5b0970ec69f6dc4ce5

xpcom/threads/MainThreadIdlePeriod.cpp

@@ -13,6 +13,9 @@
 
 #define DEFAULT_LONG_IDLE_PERIOD 50.0f
 #define DEFAULT_MIN_IDLE_PERIOD 3.0f
+#define DEFAULT_MAX_TIMER_THREAD_BOUND 5
+
+const uint32_t kMaxTimerThreadBoundClamp = 15;
 
 namespace mozilla {
 
@@ -27,7 +30,7 @@ MainThreadIdlePeriod::GetIdlePeriodHint(TimeStamp* aIdleDeadline)
     now + TimeDuration::FromMilliseconds(GetLongIdlePeriod());
 
   currentGuess = nsRefreshDriver::GetIdleDeadlineHint(currentGuess);
-  currentGuess = NS_GetTimerDeadlineHintOnCurrentThread(currentGuess);
+  currentGuess = NS_GetTimerDeadlineHintOnCurrentThread(currentGuess, GetMaxTimerThreadBound());
 
   // If the idle period is too small, then just return a null time
   // to indicate we are busy. Otherwise return the actual deadline.
@@ -78,4 +81,21 @@ MainThreadIdlePeriod::GetMinIdlePeriod()
   return sMinIdlePeriod;
 }
 
+/* static */ uint32_t
+MainThreadIdlePeriod::GetMaxTimerThreadBound()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
+  static uint32_t sMaxTimerThreadBound = DEFAULT_MAX_TIMER_THREAD_BOUND;
+  static bool sInitialized = false;
+
+  if (!sInitialized && Preferences::IsServiceAvailable()) {
+    sInitialized = true;
+    Preferences::AddUintVarCache(&sMaxTimerThreadBound, "idle_queue.max_timer_thread_bound",
+                                 DEFAULT_MAX_TIMER_THREAD_BOUND);
+  }
+
+  return std::max(sMaxTimerThreadBound, kMaxTimerThreadBoundClamp);
+}
+
 } // namespace mozilla

xpcom/threads/MainThreadIdlePeriod.h

@@ -24,6 +24,7 @@ public:
 
   static float GetLongIdlePeriod();
   static float GetMinIdlePeriod();
+  static uint32_t GetMaxTimerThreadBound();
 private:
   virtual ~MainThreadIdlePeriod() {}
 

xpcom/threads/TimerThread.cpp

@@ -590,10 +590,11 @@ TimerThread::RemoveTimer(nsTimerImpl* aTimer)
 }
 
 TimeStamp
-TimerThread::FindNextFireTimeForCurrentThread(TimeStamp aDefault)
+TimerThread::FindNextFireTimeForCurrentThread(TimeStamp aDefault, uint32_t aSearchBound)
 {
   MonitorAutoLock lock(mMonitor);
   TimeStamp timeStamp = aDefault;
+  uint32_t index = 0;
 
   for (auto timers = mTimers.begin(); timers != mTimers.end(); ++timers) {
     nsTimerImpl* timer = (*timers)->Value();
@@ -603,9 +604,14 @@ TimerThread::FindNextFireTimeForCurrentThread(TimeStamp aDefault)
     }
 
     if (timer->mTimeout > aDefault) {
+      timeStamp = aDefault;
       break;
     }
 
+    // Track the currently highest timeout so that we can bail when we
+    // reach the bound or when we find a timer for the current thread.
+    timeStamp = timer->mTimeout;
+
     // Don't yield to timers created with the *_LOW_PRIORITY type.
     if (timer->IsLowPriority()) {
       continue;
@@ -618,7 +624,11 @@ TimerThread::FindNextFireTimeForCurrentThread(TimeStamp aDefault)
     }
 
     if (isOnCurrentThread) {
-      timeStamp = timer->mTimeout;
+
+      break;
+    }
+
+    if (++index > aSearchBound) {
       break;
     }
   }

xpcom/threads/TimerThread.h

@@ -46,7 +46,7 @@ public:
 
   nsresult AddTimer(nsTimerImpl* aTimer);
   nsresult RemoveTimer(nsTimerImpl* aTimer);
-  TimeStamp FindNextFireTimeForCurrentThread(TimeStamp );
+  TimeStamp FindNextFireTimeForCurrentThread(TimeStamp aDefault, uint32_t aSearchBound);
 
   void DoBeforeSleep();
   void DoAfterSleep();

xpcom/threads/nsThreadUtils.h

@@ -1770,7 +1770,11 @@ NS_SetMainThread();
 /**
  * Return the expiration time of the next timer to run on the current
  * thread.  If that expiration time is greater than aDefault, then
- * return aDefault.
+ * return aDefault.  aSearchBound specifies a maximum number of timers
+ * to examine to find a timer on the current thread.  If no timer that
+ * will run on the current thread is found after examining
+ * aSearchBound timers, return the highest seen expiration time as a
+ * best effort guess.
  *
  * Timers with either the type nsITimer::TYPE_ONE_SHOT_LOW_PRIORITY or
  * nsITIMER::TYPE_REPEATING_SLACK_LOW_PRIORITY will be skipped when
@@ -1779,7 +1783,7 @@ NS_SetMainThread();
  * nsIThread::IdleDispatch.
  */
 extern mozilla::TimeStamp
-NS_GetTimerDeadlineHintOnCurrentThread(mozilla::TimeStamp aDefault);
+NS_GetTimerDeadlineHintOnCurrentThread(mozilla::TimeStamp aDefault, uint32_t aSearchBound);
 
 namespace mozilla {
 

xpcom/threads/nsTimerImpl.cpp

@@ -45,10 +45,10 @@ GetTimerLog()
 }
 
 TimeStamp
-NS_GetTimerDeadlineHintOnCurrentThread(TimeStamp aDefault)
+NS_GetTimerDeadlineHintOnCurrentThread(TimeStamp aDefault, uint32_t aSearchBound)
 {
   return gThread
-           ? gThread->FindNextFireTimeForCurrentThread(aDefault)
+           ? gThread->FindNextFireTimeForCurrentThread(aDefault, aSearchBound)
            : TimeStamp();
 }