Bug 1588745 - part 4: Make TextControlState reuse its instance by itself r=Ehsan

Currently, only `HTMLInputElement` reuses `TextControlState` instance since
`HTMLTextAreaElement` had the instance as a member rather than allocate it.

Now, all instances are allocated in the heap independently for guaranteeing
their lifetime.  So, the reuse mechanism should be managed by
`TextControlState` itself.

Depends on D51393

Differential Revision: https://phabricator.services.mozilla.com/D51394

dom/base/nsContentUtils.cpp

@@ -1802,7 +1802,7 @@ void nsContentUtils::Shutdown() {
     NS_RELEASE(sUserInteractionObserver);
   }
 
-  HTMLInputElement::Shutdown();
+  TextControlState::Shutdown();
   nsMappedAttributes::Shutdown();
 }
 

dom/html/HTMLInputElement.cpp

@@ -937,28 +937,6 @@ static nsresult FireEventForAccessibility(HTMLInputElement* aTarget,
                                           EventMessage aEventMessage);
 #endif
 
-TextControlState* HTMLInputElement::sCachedTextControlState = nullptr;
-bool HTMLInputElement::sShutdown = false;
-
-/* static */
-void HTMLInputElement::ReleaseTextControlState(TextControlState* aState) {
-  if (!sShutdown && !sCachedTextControlState && !aState->IsBusy()) {
-    aState->PrepareForReuse();
-    sCachedTextControlState = aState;
-  } else {
-    aState->Destroy();
-  }
-}
-
-/* static */
-void HTMLInputElement::Shutdown() {
-  sShutdown = true;
-  if (sCachedTextControlState) {
-    sCachedTextControlState->Destroy();
-    sCachedTextControlState = nullptr;
-  }
-}
-
 //
 // construction, destruction
 //
@@ -1001,8 +979,7 @@ HTMLInputElement::HTMLInputElement(
                 "performance regression!");
 
   // We are in a type=text so we now we currenty need a TextControlState.
-  mInputData.mState =
-      TextControlState::Construct(this, &sCachedTextControlState);
+  mInputData.mState = TextControlState::Construct(this);
 
   void* memory = mInputTypeMem;
   mInputType = InputType::Create(this, mType, memory);
@@ -1033,7 +1010,7 @@ void HTMLInputElement::FreeData() {
     mInputData.mValue = nullptr;
   } else {
     UnbindFromFrame(nullptr);
-    ReleaseTextControlState(mInputData.mState);
+    mInputData.mState->Destroy();
     mInputData.mState = nullptr;
   }
 
@@ -4515,8 +4492,7 @@ void HTMLInputElement::HandleTypeChange(uint8_t aNewType, bool aNotify) {
   mInputType = InputType::Create(this, mType, memory);
 
   if (IsSingleLineTextControl()) {
-    mInputData.mState =
-        TextControlState::Construct(this, &sCachedTextControlState);
+    mInputData.mState = TextControlState::Construct(this);
     if (!sp.IsDefault()) {
       mInputData.mState->SetSelectionProperties(sp);
     }

dom/html/HTMLInputElement.h

@@ -846,8 +846,6 @@ class HTMLInputElement final : public nsGenericHTMLFormElementWithState,
   void UpdateEntries(
       const nsTArray<OwningFileOrDirectory>& aFilesOrDirectories);
 
-  static void Shutdown();
-
   /**
    * Returns if the required attribute applies for the current type.
    */
@@ -1660,11 +1658,6 @@ class HTMLInputElement final : public nsGenericHTMLFormElementWithState,
     nsCOMPtr<nsIFilePicker> mFilePicker;
     RefPtr<HTMLInputElement> mInput;
   };
-
-  static void ReleaseTextControlState(TextControlState* aState);
-
-  static TextControlState* sCachedTextControlState;
-  static bool sShutdown;
 };
 
 }  // namespace dom

dom/html/TextControlState.cpp

@@ -1127,7 +1127,7 @@ class MOZ_STACK_CLASS AutoTextControlHandlingState {
   ~AutoTextControlHandlingState() {
     mTextControlState.mHandlingState = mParent;
     if (!mParent && mTextControlStateDestroyed) {
-      mTextControlState.Destroy();
+      mTextControlState.DeleteOrCacheForReuse();
     }
   }
 
@@ -1180,6 +1180,9 @@ class MOZ_STACK_CLASS AutoTextControlHandlingState {
  * mozilla::TextControlState
  *****************************************************************************/
 
+TextControlState* TextControlState::sReleasedInstance = nullptr;
+bool TextControlState::sHasShutDown = false;
+
 TextControlState::TextControlState(nsITextControlElement* aOwningElement)
     : mTextCtrlElement(aOwningElement),
       mBoundFrame(nullptr),
@@ -1199,11 +1202,11 @@ TextControlState::TextControlState(nsITextControlElement* aOwningElement)
 }
 
 TextControlState* TextControlState::Construct(
-    nsITextControlElement* aOwningElement, TextControlState** aReusedState) {
-  if (aReusedState && *aReusedState) {
-    TextControlState* state = *aReusedState;
-    MOZ_ASSERT(!state->IsBusy());
-    *aReusedState = nullptr;
+    nsITextControlElement* aOwningElement) {
+  if (sReleasedInstance) {
+    MOZ_ASSERT(!sReleasedInstance->IsBusy());
+    TextControlState* state = sReleasedInstance;
+    sReleasedInstance = nullptr;
     state->mTextCtrlElement = aOwningElement;
     state->mBoundFrame = nullptr;
     state->mSelectionProperties = SelectionProperties();
@@ -1228,12 +1231,32 @@ TextControlState::~TextControlState() {
   Clear();
 }
 
+void TextControlState::Shutdown() {
+  sHasShutDown = true;
+  if (sReleasedInstance) {
+    sReleasedInstance->DeleteOrCacheForReuse();
+    sReleasedInstance = nullptr;
+  }
+}
+
 void TextControlState::Destroy() {
   // If we're handling something, we should be deleted later.
   if (mHandlingState) {
     mHandlingState->OnDestroyTextControlState();
     return;
   }
+  DeleteOrCacheForReuse();
+}
+
+void TextControlState::DeleteOrCacheForReuse() {
+  MOZ_ASSERT(!IsBusy());
+
+  // If we can cache this instance, we should do it instead of deleting it.
+  if (!sHasShutDown && !sReleasedInstance) {
+    sReleasedInstance = this;
+    sReleasedInstance->PrepareForReuse();
+    return;
+  }
   delete this;
 }
 

dom/html/TextControlState.h

@@ -141,8 +141,9 @@ class TextControlState final : public SupportsWeakPtr<TextControlState> {
 
   MOZ_DECLARE_WEAKREFERENCE_TYPENAME(TextControlState)
 
-  static TextControlState* Construct(nsITextControlElement* aOwningElement,
-                                     TextControlState** aReusedState = nullptr);
+  static TextControlState* Construct(nsITextControlElement* aOwningElement);
+
+  static void Shutdown();
 
   /**
    * Destroy() deletes the instance immediately or later.
@@ -161,13 +162,6 @@ class TextControlState final : public SupportsWeakPtr<TextControlState> {
 
   bool IsBusy() const { return !!mHandlingState || mValueTransferInProgress; }
 
-  void PrepareForReuse() {
-    MOZ_ASSERT(!IsBusy());
-    Unlink();
-    mValue.reset();
-    mTextCtrlElement = nullptr;
-  }
-
   TextEditor* GetTextEditor();
   TextEditor* GetTextEditorWithoutCreation();
   nsISelectionController* GetSelectionController() const;
@@ -386,6 +380,18 @@ class TextControlState final : public SupportsWeakPtr<TextControlState> {
   explicit TextControlState(nsITextControlElement* aOwningElement);
   MOZ_CAN_RUN_SCRIPT_BOUNDARY ~TextControlState();
 
+  /**
+   * Delete the instance or cache to reuse it if possible.
+   */
+  void DeleteOrCacheForReuse();
+
+  void PrepareForReuse() {
+    MOZ_ASSERT(!IsBusy());
+    Unlink();
+    mValue.reset();
+    mTextCtrlElement = nullptr;
+  }
+
   void ValueWasChanged(bool aNotify);
 
   MOZ_CAN_RUN_SCRIPT void DestroyEditor();
@@ -425,6 +431,16 @@ class TextControlState final : public SupportsWeakPtr<TextControlState> {
   bool mPlaceholderVisibility;
   bool mPreviewVisibility;
 
+  /**
+   * For avoiding allocation cost of the instance, we should reuse instances
+   * as far as possible.
+   * TODO: Maybe, we should cache more instances with array.  Then, it must
+   *       be faster to load pages which have a lot of `<input type="text">`
+   *       elements.
+   */
+  static TextControlState* sReleasedInstance;
+  static bool sHasShutDown;
+
   friend class AutoTextControlHandlingState;
   friend class PrepareEditorEvent;
   friend class RestoreSelectionState;