Bug 1519861 - Improve mozilla::GetTabSizes - r=smaug

Introduces a generation number in dom::base::Document as well
as a cached version of TabSizes we can Get and Set.
When the document is changed, the cache is invalidated.

This change improves about:performance speed by avoiding
a heavy recursive call on big DOM trees via GetTabSizes() calls.
If the page does not change, the cached values are returned.

Differential Revision: https://phabricator.services.mozilla.com/D20526

--HG--
extra : moz-landing-system : lando

dom/base/Document.cpp

@@ -1341,7 +1341,9 @@ Document::Document(const char* aContentType)
       mIgnoreOpensDuringUnloadCounter(0),
       mDocLWTheme(Doc_Theme_Uninitialized),
       mSavedResolution(1.0f),
-      mPendingInitialTranslation(false) {
+      mPendingInitialTranslation(false),
+      mGeneration(0),
+      mCachedTabSizeGeneration(0) {
   MOZ_LOG(gDocumentLeakPRLog, LogLevel::Debug, ("DOCUMENT %p created", this));
 
   SetIsInDocument();
@@ -12549,6 +12551,24 @@ bool Document::StorageAccessSandboxed() const {
          (GetSandboxFlags() & SANDBOXED_STORAGE_ACCESS) != 0;
 }
 
+bool Document::GetCachedSizes(nsTabSizes* aSizes) {
+  if (mCachedTabSizeGeneration == 0 ||
+      GetGeneration() != mCachedTabSizeGeneration) {
+    return false;
+  }
+  aSizes->mDom += mCachedTabSizes.mDom;
+  aSizes->mStyle += mCachedTabSizes.mStyle;
+  aSizes->mOther += mCachedTabSizes.mOther;
+  return true;
+}
+
+void Document::SetCachedSizes(nsTabSizes* aSizes) {
+  mCachedTabSizes.mDom = aSizes->mDom;
+  mCachedTabSizes.mStyle = aSizes->mStyle;
+  mCachedTabSizes.mOther = aSizes->mOther;
+  mCachedTabSizeGeneration = GetGeneration();
+}
+
 already_AddRefed<nsAtom> Document::GetContentLanguageAsAtomForStyle() const {
   nsAutoString contentLang;
   GetContentLanguage(contentLang);

dom/base/Document.h

@@ -1490,6 +1490,21 @@ class Document : public nsINode,
   // flag.
   bool StorageAccessSandboxed() const;
 
+  // Increments the document generation.
+  inline void Changed() { ++mGeneration; }
+
+  // Returns the current generation.
+  inline int32_t GetGeneration() const { return mGeneration; }
+
+  // Adds cached sizes values to aSizes if there's any
+  // cached value and if the document generation hasn't
+  // changed since the cache was created.
+  // Returns true if sizes were added.
+  bool GetCachedSizes(nsTabSizes* aSizes);
+
+  // Sets the cache sizes for the current generation.
+  void SetCachedSizes(nsTabSizes* aSizes);
+
  protected:
   friend class nsUnblockOnloadEvent;
 
@@ -4641,6 +4656,13 @@ class Document : public nsINode,
 
   bool mPendingInitialTranslation;
 
+  // Document generation. Gets incremented everytime it changes.
+  int32_t mGeneration;
+
+  // Cached TabSizes values for the document.
+  int32_t mCachedTabSizeGeneration;
+  nsTabSizes mCachedTabSizes;
+
  public:
   // Needs to be public because the bindings code pokes at it.
   js::ExpandoAndGeneration mExpandoAndGeneration;

dom/base/nsNodeUtils.cpp

@@ -136,6 +136,7 @@ void nsNodeUtils::CharacterDataWillChange(
 void nsNodeUtils::CharacterDataChanged(nsIContent* aContent,
                                        const CharacterDataChangeInfo& aInfo) {
   Document* doc = aContent->OwnerDoc();
+  doc->Changed();
   IMPL_MUTATION_NOTIFICATION(CharacterDataChanged, aContent, (aContent, aInfo),
                              IsRemoveNotification::No);
 }
@@ -152,6 +153,7 @@ void nsNodeUtils::AttributeChanged(Element* aElement, int32_t aNameSpaceID,
                                    nsAtom* aAttribute, int32_t aModType,
                                    const nsAttrValue* aOldValue) {
   Document* doc = aElement->OwnerDoc();
+  doc->Changed();
   IMPL_MUTATION_NOTIFICATION(
       AttributeChanged, aElement,
       (aElement, aNameSpaceID, aAttribute, aModType, aOldValue),
@@ -170,7 +172,7 @@ void nsNodeUtils::AttributeSetToCurrentValue(Element* aElement,
 void nsNodeUtils::ContentAppended(nsIContent* aContainer,
                                   nsIContent* aFirstNewContent) {
   Document* doc = aContainer->OwnerDoc();
-
+  doc->Changed();
   IMPL_MUTATION_NOTIFICATION(ContentAppended, aContainer, (aFirstNewContent),
                              IsRemoveNotification::No);
 }
@@ -188,6 +190,7 @@ void nsNodeUtils::ContentInserted(nsINode* aContainer, nsIContent* aChild) {
   MOZ_ASSERT(aContainer->IsContent() || aContainer->IsDocument(),
              "container must be an nsIContent or an Document");
   Document* doc = aContainer->OwnerDoc();
+  doc->Changed();
   IMPL_MUTATION_NOTIFICATION(ContentInserted, aContainer, (aChild),
                              IsRemoveNotification::No);
 }
@@ -197,6 +200,7 @@ void nsNodeUtils::ContentRemoved(nsINode* aContainer, nsIContent* aChild,
   MOZ_ASSERT(aContainer->IsContent() || aContainer->IsDocument(),
              "container must be an nsIContent or an Document");
   Document* doc = aContainer->OwnerDoc();
+  doc->Changed();
   MOZ_ASSERT(aChild->GetParentNode() == aContainer,
              "We expect the parent link to be still around at this point");
   IMPL_MUTATION_NOTIFICATION(ContentRemoved, aContainer,

toolkit/components/perfmonitoring/PerformanceUtils.cpp

@@ -60,22 +60,41 @@ nsTArray<RefPtr<PerformanceInfoPromise>> CollectPerformanceInfo() {
   return promises;
 }
 
-nsresult GetTabSizes(nsGlobalWindowOuter* aWindow, nsTabSizes* aSizes) {
+void AddWindowTabSizes(nsGlobalWindowOuter* aWindow, nsTabSizes* aSizes) {
+  Document* document = aWindow->GetDocument();
+  if (document && document->GetCachedSizes(aSizes)) {
+    // We got a cached version
+    return;
+  }
+  // We measure the sizes on a fresh nsTabSizes instance
+  // because we want to cache the value and aSizes might
+  // already have some values from other windows.
+  nsTabSizes sizes;
+
   // Measure the window.
   SizeOfState state(moz_malloc_size_of);
   nsWindowSizes windowSizes(state);
   aWindow->AddSizeOfIncludingThis(windowSizes);
-
   // Measure the inner window, if there is one.
   nsGlobalWindowInner* inner = aWindow->GetCurrentInnerWindowInternal();
   if (inner != nullptr) {
     inner->AddSizeOfIncludingThis(windowSizes);
   }
+  windowSizes.addToTabSizes(&sizes);
+  if (document) {
+    document->SetCachedSizes(&sizes);
+  }
+  aSizes->mDom += sizes.mDom;
+  aSizes->mStyle += sizes.mStyle;
+  aSizes->mOther += sizes.mOther;
+}
+
+nsresult GetTabSizes(nsGlobalWindowOuter* aWindow, nsTabSizes* aSizes) {
+  // Add the window (and inner window) sizes. Might be cached.
+  AddWindowTabSizes(aWindow, aSizes);
 
-  windowSizes.addToTabSizes(aSizes);
   nsDOMWindowList* frames = aWindow->GetFrames();
   uint32_t length = frames->GetLength();
-
   // Measure this window's descendents.
   for (uint32_t i = 0; i < length; i++) {
     nsCOMPtr<nsPIDOMWindowOuter> child = frames->IndexedGetter(i);