Bug 1309147 - Part 5: Eliminate performance cliff when accessing CEReactions code.

Tag UXP Issue #1344

2 files changed, 19 insertions, 5 deletions

diff --git a/dom/base/CustomElementRegistry.cpp b/dom/base/CustomElementRegistry.cpp
index b50a1345e..c3d25465e 100644
--- a/dom/base/CustomElementRegistry.cpp
+++ b/dom/base/CustomElementRegistry.cpp
@@ -905,7 +905,11 @@ CustomElementReactionsStack::PopAndInvokeElementQueue()
              "Reaction stack shouldn't be empty");
 
   ElementQueue& elementQueue = mReactionsStack.LastElement();
-  InvokeReactions(elementQueue);
+  // Check element queue size in order to reduce function call overhead.
+  if (!elementQueue.IsEmpty()) {
+    InvokeReactions(elementQueue);
+  }
+
   DebugOnly<bool> isRemovedElement = mReactionsStack.RemoveElement(elementQueue);
   MOZ_ASSERT(isRemovedElement,
              "Reaction stack should have an element queue to remove");
@@ -954,7 +958,10 @@ CustomElementReactionsStack::Enqueue(Element* aElement,
 void
 CustomElementReactionsStack::InvokeBackupQueue()
 {
-  InvokeReactions(mBackupQueue);
+  // Check backup queue size in order to reduce function call overhead.
+  if (!mBackupQueue.IsEmpty()) {
+    InvokeReactions(mBackupQueue);
+  }
 }
 
 void
diff --git a/dom/base/CustomElementRegistry.h b/dom/base/CustomElementRegistry.h
index 5fc2eb2fd..24d501d73 100644
--- a/dom/base/CustomElementRegistry.h
+++ b/dom/base/CustomElementRegistry.h
@@ -179,7 +179,8 @@ public:
   // nsWeakPtr is a weak pointer of Element
   // The element reaction queues are stored in ElementReactionQueueMap.
   // We need to lookup ElementReactionQueueMap again to get relevant reaction queue.
-  typedef nsTArray<nsWeakPtr> ElementQueue;
+  // The choice of 1 for the auto size here is based on gut feeling.
+  typedef AutoTArray<nsWeakPtr, 1> ElementQueue;
 
   /**
    * Enqueue a custom element upgrade reaction
@@ -201,13 +202,19 @@ public:
 private:
   ~CustomElementReactionsStack() {};
 
-  typedef nsTArray<nsAutoPtr<CustomElementReaction>> ReactionQueue;
+  // There is 1 reaction in reaction queue, when 1) it becomes disconnected,
+  // 2) it’s adopted into a new document, 3) its attributes are changed,
+  // appended, removed, or replaced.
+  // There are 3 reactions in reaction queue when doing upgrade operation,
+  // e.g., create an element, insert a node.
+  typedef AutoTArray<nsAutoPtr<CustomElementReaction>, 3> ReactionQueue;
   typedef nsClassHashtable<nsISupportsHashKey, ReactionQueue>
     ElementReactionQueueMap;
 
   ElementReactionQueueMap mElementReactionQueueMap;
 
-  nsTArray<ElementQueue> mReactionsStack;
+  // The choice of 8 for the auto size here is based on gut feeling.
+  AutoTArray<ElementQueue, 8> mReactionsStack;
   ElementQueue mBackupQueue;
   // https://html.spec.whatwg.org/#enqueue-an-element-on-the-appropriate-element-queue
   bool mIsBackupQueueProcessing;