From b73c1c58f3ee906351086bbd8e53a43e6ed4e477 Mon Sep 17 00:00:00 2001
From: Botond Ballo <botond@mozilla.com>
Date: Fri, 16 Oct 2015 19:00:15 -0400
Subject: [PATCH] Bug 1213273 - Use a chromium Task instead of an nsITimer for
 the timeout in TaskThrottler. r=mstange

--HG--
extra : rebase_source : 2ddc7714fff1d62aa394332fdafd8c2e5c97b065
extra : source : 00f7757e184487dc77e1be0e07ef7c4e9360e6c3
---
 gfx/layers/apz/src/TaskThrottler.cpp | 52 ++++++++++++++++------------
 gfx/layers/apz/src/TaskThrottler.h   |  7 ++--
 2 files changed, 34 insertions(+), 25 deletions(-)

diff --git a/gfx/layers/apz/src/TaskThrottler.cpp b/gfx/layers/apz/src/TaskThrottler.cpp
index afa098d829d6..399b4e4ecf7e 100644
--- a/gfx/layers/apz/src/TaskThrottler.cpp
+++ b/gfx/layers/apz/src/TaskThrottler.cpp
@@ -6,9 +6,7 @@
 
 #include "TaskThrottler.h"
 
-#include "mozilla/layers/APZThreadUtils.h"  // for NewTimerCallback
-#include "nsComponentManagerUtils.h"        // for do_CreateInstance
-#include "nsITimer.h"
+#include "base/message_loop.h"
 
 #define TASK_LOG(...)
 // #define TASK_LOG(...) printf_stderr("TASK: " __VA_ARGS__)
@@ -23,17 +21,14 @@ TaskThrottler::TaskThrottler(const TimeStamp& aTimeStamp, const TimeDuration& aM
   , mStartTime(aTimeStamp)
   , mMaxWait(aMaxWait)
   , mMean(1)
-  , mTimer(do_CreateInstance(NS_TIMER_CONTRACTID))
+  , mTimeoutTask(nullptr)
 {
-  // The TaskThrottler must be created on the main thread (or some nsITimer-
-  // compatible thread) for the nsITimer to work properly. In particular,
-  // creating it on the Compositor thread doesn't work.
-  MOZ_ASSERT(NS_IsMainThread());
 }
 
 TaskThrottler::~TaskThrottler()
 {
-  mTimer->Cancel();
+  // The timeout task holds a strong reference to the TaskThrottler, so if the
+  // TaskThrottler is being destroyed, there's no need to cancel the task.
 }
 
 void
@@ -53,17 +48,9 @@ TaskThrottler::PostTask(const tracked_objects::Location& aLocation,
       // Make sure the queued task is sent after mMaxWait time elapses,
       // even if we don't get a TaskComplete() until then.
       TimeDuration timeout = mMaxWait - TimeSinceLastRequest(aTimeStamp, lock);
-      TimeStamp timeoutTime = mStartTime + mMaxWait;
-      RefPtr<TaskThrottler> refPtrThis = this;
-      mTimer->InitWithCallback(NewTimerCallback(
-          [refPtrThis, timeoutTime]()
-          {
-            MonitorAutoLock lock(refPtrThis->mMonitor);
-            if (refPtrThis->mQueuedTask) {
-              refPtrThis->RunQueuedTask(timeoutTime, lock);
-            }
-          }),
-          timeout.ToMilliseconds(), nsITimer::TYPE_ONE_SHOT);
+      mTimeoutTask = NewRunnableMethod(this, &TaskThrottler::OnTimeout);
+      MessageLoop::current()->PostDelayedTask(FROM_HERE, mTimeoutTask,
+          timeout.ToMilliseconds());
       return;
     }
     // we've been waiting for more than the max-wait limit, so just fall through
@@ -75,6 +62,18 @@ TaskThrottler::PostTask(const tracked_objects::Location& aLocation,
   mOutstanding = true;
 }
 
+void
+TaskThrottler::OnTimeout()
+{
+  MonitorAutoLock lock(mMonitor);
+  if (mQueuedTask) {
+    RunQueuedTask(TimeStamp::Now(), lock);
+  }
+  // The message loop will delete the posted timeout task. Make sure we don't
+  // keep a dangling pointer to it.
+  mTimeoutTask = nullptr;
+}
+
 void
 TaskThrottler::TaskComplete(const TimeStamp& aTimeStamp)
 {
@@ -88,7 +87,7 @@ TaskThrottler::TaskComplete(const TimeStamp& aTimeStamp)
 
   if (mQueuedTask) {
     RunQueuedTask(aTimeStamp, lock);
-    mTimer->Cancel();
+    CancelTimeoutTask(lock);
   } else {
     mOutstanding = false;
   }
@@ -126,7 +125,16 @@ TaskThrottler::CancelPendingTask(const MonitorAutoLock& aProofOfLock)
     TASK_LOG("%p cancelling task %p\n", this, mQueuedTask.get());
     mQueuedTask->Cancel();
     mQueuedTask = nullptr;
-    mTimer->Cancel();
+    CancelTimeoutTask(aProofOfLock);
+  }
+}
+
+void
+TaskThrottler::CancelTimeoutTask(const MonitorAutoLock& aProofOfLock)
+{
+  if (mTimeoutTask) {
+    mTimeoutTask->Cancel();
+    mTimeoutTask = nullptr;  // the MessageLoop will destroy it
   }
 }
 
diff --git a/gfx/layers/apz/src/TaskThrottler.h b/gfx/layers/apz/src/TaskThrottler.h
index f86f1956965c..50a799bb6ab2 100644
--- a/gfx/layers/apz/src/TaskThrottler.h
+++ b/gfx/layers/apz/src/TaskThrottler.h
@@ -18,8 +18,6 @@
 #include "nsISupportsImpl.h"            // for NS_INLINE_DECL_THREADSAFE_REFCOUNTING
 #include "nsTArray.h"                   // for nsTArray
 
-class nsITimer;
-
 namespace tracked_objects {
 class Location;
 } // namespace tracked_objects
@@ -102,7 +100,8 @@ private:
   TimeStamp mStartTime;
   TimeDuration mMaxWait;
   RollingMean<TimeDuration, TimeDuration> mMean;
-  nsCOMPtr<nsITimer> mTimer;
+  CancelableTask* mTimeoutTask;  // not owned because it's posted to a MessageLoop
+                                 // which deletes it
 
   ~TaskThrottler();
   void RunQueuedTask(const TimeStamp& aTimeStamp,
@@ -110,6 +109,8 @@ private:
   void CancelPendingTask(const MonitorAutoLock& aProofOfLock);
   TimeDuration TimeSinceLastRequest(const TimeStamp& aTimeStamp,
                                     const MonitorAutoLock& aProofOfLock);
+  void OnTimeout();
+  void CancelTimeoutTask(const MonitorAutoLock& aProofOfLock);
 };
 
 } // namespace layers