Bug 1291045 (Part 1) - Use a different IDecodingTask for animated images. r=dholbert,edwin

image/DecoderFactory.cpp

@@ -187,7 +187,7 @@ DecoderFactory::CreateAnimationDecoder(DecoderType aType,
     return nullptr;
   }
 
-  RefPtr<IDecodingTask> task = new DecodingTask(WrapNotNull(decoder));
+  RefPtr<IDecodingTask> task = new AnimationDecodingTask(WrapNotNull(decoder));
   return task.forget();
 }
 

image/IDecodingTask.cpp

@@ -92,6 +92,8 @@ DecodingTask::DecodingTask(NotNull<Decoder*> aDecoder)
 {
   MOZ_ASSERT(!mDecoder->IsMetadataDecode(),
              "Use MetadataDecodingTask for metadata decodes");
+  MOZ_ASSERT(mDecoder->IsFirstFrameDecode(),
+             "Use AnimationDecodingTask for animation decodes");
 }
 
 void
@@ -131,6 +133,56 @@ DecodingTask::ShouldPreferSyncRun() const
 }
 
 
+///////////////////////////////////////////////////////////////////////////////
+// AnimationDecodingTask implementation.
+///////////////////////////////////////////////////////////////////////////////
+
+AnimationDecodingTask::AnimationDecodingTask(NotNull<Decoder*> aDecoder)
+  : mDecoder(aDecoder)
+{
+  MOZ_ASSERT(!mDecoder->IsMetadataDecode(),
+             "Use MetadataDecodingTask for metadata decodes");
+  MOZ_ASSERT(!mDecoder->IsFirstFrameDecode(),
+             "Use DecodingTask for single-frame image decodes");
+}
+
+void
+AnimationDecodingTask::Run()
+{
+  while (true) {
+    LexerResult result = mDecoder->Decode(WrapNotNull(this));
+
+    if (result.is<TerminalState>()) {
+      NotifyDecodeComplete(mDecoder);
+      return;  // We're done.
+    }
+
+    MOZ_ASSERT(result.is<Yield>());
+
+    // Notify for the progress we've made so far.
+    if (mDecoder->HasProgress()) {
+      NotifyProgress(mDecoder);
+    }
+
+    if (result == LexerResult(Yield::NEED_MORE_DATA)) {
+      // We can't make any more progress right now. The decoder itself will
+      // ensure that we get reenqueued when more data is available; just return
+      // for now.
+      return;
+    }
+
+    // Right now we don't do anything special for other kinds of yields, so just
+    // keep working.
+  }
+}
+
+bool
+AnimationDecodingTask::ShouldPreferSyncRun() const
+{
+  return mDecoder->ShouldSyncDecode(gfxPrefs::ImageMemDecodeBytesAtATime());
+}
+
+
 ///////////////////////////////////////////////////////////////////////////////
 // MetadataDecodingTask implementation.
 ///////////////////////////////////////////////////////////////////////////////

image/IDecodingTask.h

@@ -56,7 +56,7 @@ protected:
 
 
 /**
- * An IDecodingTask implementation for full decodes of images.
+ * An IDecodingTask implementation for full decodes of single frame images.
  */
 class DecodingTask final : public IDecodingTask
 {
@@ -81,6 +81,32 @@ private:
 };
 
 
+/**
+ * An IDecodingTask implementation for full decodes of animated images.
+ */
+class AnimationDecodingTask final : public IDecodingTask
+{
+public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(AnimationDecodingTask, override)
+
+  explicit AnimationDecodingTask(NotNull<Decoder*> aDecoder);
+
+  void Run() override;
+  bool ShouldPreferSyncRun() const override;
+
+  // Full decodes are low priority compared to metadata decodes because they
+  // don't block layout or page load.
+  TaskPriority Priority() const override { return TaskPriority::eLow; }
+
+  NotNull<Decoder*> GetDecoder() const override { return mDecoder; }
+
+private:
+  virtual ~AnimationDecodingTask() { }
+
+  NotNull<RefPtr<Decoder>> mDecoder;
+};
+
+
 /**
  * An IDecodingTask implementation for metadata decodes of images.
  */