From cff471d7a8b03b1b02dfdebe732060df348fbf37 Mon Sep 17 00:00:00 2001
From: JW Wang <jwwang@mozilla.com>
Date: Mon, 1 Aug 2016 14:39:39 +0800
Subject: [PATCH] Bug 1283724 - throttle notifications from stochastic network
 activity to save computation of buffer ranges. r=jya

MozReview-Commit-ID: BRBv2Flqu3u

--HG--
extra : rebase_source : fe28566c79f2f31a5054e4cda35d96c938985299
---
 dom/media/MediaDecoder.cpp | 24 ++++++++++++++++++++++--
 dom/media/MediaDecoder.h   |  8 ++++++++
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/dom/media/MediaDecoder.cpp b/dom/media/MediaDecoder.cpp
index 4ff04bf8c366..0e04afa4b35a 100644
--- a/dom/media/MediaDecoder.cpp
+++ b/dom/media/MediaDecoder.cpp
@@ -145,6 +145,7 @@ MediaDecoder::ResourceCallback::Connect(MediaDecoder* aDecoder)
 {
   MOZ_ASSERT(NS_IsMainThread());
   mDecoder = aDecoder;
+  mTimer = do_CreateInstance("@mozilla.org/timer;1");
 }
 
 void
@@ -152,6 +153,8 @@ MediaDecoder::ResourceCallback::Disconnect()
 {
   MOZ_ASSERT(NS_IsMainThread());
   mDecoder = nullptr;
+  mTimer->Cancel();
+  mTimer = nullptr;
 }
 
 MediaDecoderOwner*
@@ -216,13 +219,30 @@ MediaDecoder::ResourceCallback::NotifyDecodeError()
   AbstractThread::MainThread()->Dispatch(r.forget());
 }
 
+/* static */ void
+MediaDecoder::ResourceCallback::TimerCallback(nsITimer* aTimer, void* aClosure)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  ResourceCallback* thiz = static_cast<ResourceCallback*>(aClosure);
+  MOZ_ASSERT(thiz->mDecoder);
+  thiz->mDecoder->NotifyDataArrived();
+  thiz->mTimerArmed = false;
+}
+
 void
 MediaDecoder::ResourceCallback::NotifyDataArrived()
 {
   MOZ_ASSERT(NS_IsMainThread());
-  if (mDecoder) {
-    mDecoder->NotifyDataArrived();
+  if (!mDecoder || mTimerArmed) {
+    return;
   }
+  // In situations where these notifications come from stochastic network
+  // activity, we can save significant computation by throttling the
+  // calls to MediaDecoder::NotifyDataArrived() which will update the buffer
+  // ranges of the reader.
+  mTimerArmed = true;
+  mTimer->InitWithFuncCallback(
+    TimerCallback, this, sDelay, nsITimer::TYPE_ONE_SHOT);
 }
 
 void
diff --git a/dom/media/MediaDecoder.h b/dom/media/MediaDecoder.h
index cc1c1d5ed91a..9e5d1fe2b57d 100644
--- a/dom/media/MediaDecoder.h
+++ b/dom/media/MediaDecoder.h
@@ -70,6 +70,10 @@ public:
   // Used to register with MediaResource to receive notifications which will
   // be forwarded to MediaDecoder.
   class ResourceCallback : public MediaResourceCallback {
+    // Throttle calls to MediaDecoder::NotifyDataArrived()
+    // to be at most once per 500ms.
+    static const uint32_t sDelay = 500;
+
   public:
     // Start to receive notifications from ResourceCallback.
     void Connect(MediaDecoder* aDecoder);
@@ -92,8 +96,12 @@ public:
     void NotifySuspendedStatusChanged() override;
     void NotifyBytesConsumed(int64_t aBytes, int64_t aOffset) override;
 
+    static void TimerCallback(nsITimer* aTimer, void* aClosure);
+
     // The decoder to send notifications. Main-thread only.
     MediaDecoder* mDecoder = nullptr;
+    nsCOMPtr<nsITimer> mTimer;
+    bool mTimerArmed = false;
   };
 
   typedef MozPromise<SeekResolveValue, bool /* aIgnored */, /* IsExclusive = */ true> SeekPromise;