Bug 558795 - speed up nsEventTargetChainItem (de)allocation, r=jst

content/events/src/nsEventDispatcher.cpp

@@ -54,6 +54,8 @@
 #define NS_TARGET_CHAIN_WANTS_WILL_HANDLE_EVENT (1 << 1)
 #define NS_TARGET_CHAIN_MAY_HAVE_MANAGER        (1 << 2)
 
+static nsEventTargetChainItem* gCachedETCI = nsnull;
+
 // nsEventTargetChainItem represents a single item in the event target chain.
 class nsEventTargetChainItem
 {
@@ -66,7 +68,13 @@ public:
                                         nsPIDOMEventTarget* aTarget,
                                         nsEventTargetChainItem* aChild = nsnull)
   {
-    void* place = aAllocator->Alloc(sizeof(nsEventTargetChainItem));
+    void* place = nsnull;
+    if (gCachedETCI) {
+      place = gCachedETCI;
+      gCachedETCI = gCachedETCI->mNext;
+    } else {
+      place = aAllocator->Alloc(sizeof(nsEventTargetChainItem));
+    }
     return place
       ? ::new (place) nsEventTargetChainItem(aTarget, aChild)
       : nsnull;
@@ -84,7 +92,8 @@ public:
     while (item) {
       nsEventTargetChainItem* parent = item->mParent;
       item->~nsEventTargetChainItem();
-      aAllocator->Free(item, sizeof(nsEventTargetChainItem));
+      item->mNext = gCachedETCI;
+      gCachedETCI = item;
       --sCurrentEtciCount;
       item = parent;
     }
@@ -220,7 +229,11 @@ public:
 
   nsCOMPtr<nsPIDOMEventTarget>      mTarget;
   nsEventTargetChainItem*           mChild;
+  union {
     nsEventTargetChainItem*         mParent;
+     // This is used only when caching ETCI objects.
+    nsEventTargetChainItem*         mNext;
+  };
   PRUint16                          mFlags;
   PRUint16                          mItemFlags;
   nsCOMPtr<nsISupports>             mItemData;
@@ -414,6 +427,7 @@ public:
     }
     if (!sEtciPoolUsers) {
       if (nsEventTargetChainItem::MaxEtciCount() > NS_CHAIN_POOL_SIZE) {
+        gCachedETCI = nsnull;
         delete sEtciPool;
         sEtciPool = nsnull;
         nsEventTargetChainItem::ResetMaxEtciCount();
@@ -424,6 +438,7 @@ public:
   static void Shutdown()
   {
     if (!sEtciPoolUsers) {
+      gCachedETCI = nsnull;
       delete sEtciPool;
       sEtciPool = nsnull;
       nsEventTargetChainItem::ResetMaxEtciCount();