Bug 1669588 - Factor out a OneShotPostRefreshObserver utility class. r=kats

Differential Revision: https://phabricator.services.mozilla.com/D93897

gfx/layers/apz/util/APZCCallbackHelper.cpp

@@ -649,7 +649,7 @@ static bool PrepareForSetTargetAPZCNotification(
 
 static void SendLayersDependentApzcTargetConfirmation(
     PresShell* aPresShell, uint64_t aInputBlockId,
-    const nsTArray<ScrollableLayerGuid>& aTargets) {
+    nsTArray<ScrollableLayerGuid>&& aTargets) {
   LayerManager* lm = aPresShell->GetLayerManager();
   if (!lm) {
     return;
@@ -679,11 +679,13 @@ static void SendLayersDependentApzcTargetConfirmation(
 
 DisplayportSetListener::DisplayportSetListener(
     nsIWidget* aWidget, PresShell* aPresShell, const uint64_t& aInputBlockId,
-    const nsTArray<ScrollableLayerGuid>& aTargets)
-    : mWidget(aWidget),
-      mPresShell(aPresShell),
+    nsTArray<ScrollableLayerGuid>&& aTargets)
+    : OneShotPostRefreshObserver(
+          aPresShell,
+          [this](PresShell* aPresShell) { OnPostRefresh(this, aPresShell); }),
+      mWidget(aWidget),
       mInputBlockId(aInputBlockId),
-      mTargets(aTargets.Clone()) {}
+      mTargets(std::move(aTargets)) {}
 
 DisplayportSetListener::~DisplayportSetListener() = default;
 
@@ -699,29 +701,13 @@ bool DisplayportSetListener::Register() {
   return false;
 }
 
-void DisplayportSetListener::DidRefresh() {
-  if (!mPresShell) {
-    MOZ_ASSERT_UNREACHABLE(
-        "Post-refresh observer fired again after failed attempt at "
-        "unregistering it");
-    return;
-  }
-
+/* static */
+void DisplayportSetListener::OnPostRefresh(DisplayportSetListener* aListener,
+                                           PresShell* aPresShell) {
   APZCCH_LOG("Got refresh, sending target APZCs for input block %" PRIu64 "\n",
-             mInputBlockId);
-  SendLayersDependentApzcTargetConfirmation(mPresShell, mInputBlockId,
-                                            std::move(mTargets));
-
-  if (!mPresShell->RemovePostRefreshObserver(this)) {
-    MOZ_ASSERT_UNREACHABLE(
-        "Unable to unregister post-refresh observer! Leaking it instead of "
-        "leaving garbage registered");
-    // Graceful handling, just in case...
-    mPresShell = nullptr;
-    return;
-  }
-
-  delete this;
+             aListener->mInputBlockId);
+  SendLayersDependentApzcTargetConfirmation(
+      aPresShell, aListener->mInputBlockId, std::move(aListener->mTargets));
 }
 
 UniquePtr<DisplayportSetListener>

gfx/layers/apz/util/APZCCallbackHelper.h

@@ -35,20 +35,21 @@ typedef std::function<void(uint64_t, const nsTArray<TouchBehaviorFlags>&)>
     SetAllowedTouchBehaviorCallback;
 
 /* Refer to documentation on SendSetTargetAPZCNotification for this class */
-class DisplayportSetListener : public nsAPostRefreshObserver {
+class DisplayportSetListener : public OneShotPostRefreshObserver {
  public:
   DisplayportSetListener(nsIWidget* aWidget, PresShell* aPresShell,
                          const uint64_t& aInputBlockId,
-                         const nsTArray<ScrollableLayerGuid>& aTargets);
+                         nsTArray<ScrollableLayerGuid>&& aTargets);
   virtual ~DisplayportSetListener();
   bool Register();
-  void DidRefresh() override;
 
  private:
   RefPtr<nsIWidget> mWidget;
-  RefPtr<PresShell> mPresShell;
   uint64_t mInputBlockId;
   nsTArray<ScrollableLayerGuid> mTargets;
+
+  static void OnPostRefresh(DisplayportSetListener* aListener,
+                            PresShell* aPresShell);
 };
 
 /* This class contains some helper methods that facilitate implementing the

layout/base/moz.build

@@ -125,6 +125,7 @@ UNIFIED_SOURCES += [
     "nsPresArena.cpp",
     "nsPresContext.cpp",
     "nsQuoteList.cpp",
+    "nsRefreshObservers.cpp",
     "nsStyleChangeList.cpp",
     "nsStyleSheetService.cpp",
     "PositionedEventTargeting.cpp",

layout/base/nsRefreshObservers.cpp

@@ -0,0 +1,41 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsRefreshObservers.h"
+#include "PresShell.h"
+
+namespace mozilla {
+
+OneShotPostRefreshObserver::OneShotPostRefreshObserver(PresShell* aPresShell,
+                                                       Action&& aAction)
+    : mPresShell(aPresShell), mAction(std::move(aAction)) {}
+
+OneShotPostRefreshObserver::~OneShotPostRefreshObserver() = default;
+
+void OneShotPostRefreshObserver::DidRefresh() {
+  if (!mPresShell) {
+    MOZ_ASSERT_UNREACHABLE(
+        "Post-refresh observer fired again after failed attempt at "
+        "unregistering it");
+    return;
+  }
+
+  mAction(mPresShell);
+
+  if (!mPresShell->RemovePostRefreshObserver(this)) {
+    MOZ_ASSERT_UNREACHABLE(
+        "Unable to unregister post-refresh observer! Leaking it instead of "
+        "leaving garbage registered");
+    // Graceful handling, just in case...
+    mPresShell = nullptr;
+    mAction = Action();
+    return;
+  }
+
+  delete this;
+}
+
+}  // namespace mozilla

layout/base/nsRefreshObservers.h

@@ -19,6 +19,7 @@
 namespace mozilla {
 class AnimationEventDispatcher;
 class PendingFullscreenEvent;
+class PresShell;
 class RefreshDriverTimer;
 namespace layout {
 class VsyncChild;
@@ -64,4 +65,28 @@ class nsAPostRefreshObserver {
   virtual void DidRefresh() = 0;
 };
 
+namespace mozilla {
+
+/**
+ * A wrapper for nsAPostRefreshObserver that's one-shot (unregisters itself
+ * after firing once) and can be used without writing a derived class by passing
+ * in the action in the form of a lambda (or other function object).
+ *
+ * Note, while the observer unregisters itself, the registering still needs to
+ * be done by the caller.
+ */
+class OneShotPostRefreshObserver : public nsAPostRefreshObserver {
+ public:
+  using Action = std::function<void(mozilla::PresShell*)>;
+  OneShotPostRefreshObserver(mozilla::PresShell* aPresShell, Action&& aAction);
+  virtual ~OneShotPostRefreshObserver();
+  void DidRefresh() override;
+
+ protected:
+  RefPtr<mozilla::PresShell> mPresShell;
+  Action mAction;
+};
+
+}  // namespace mozilla
+
 #endif

layout/xul/nsSliderFrame.cpp

@@ -894,42 +894,6 @@ nsresult nsSliderMediator::HandleEvent(dom::Event* aEvent) {
   return NS_OK;
 }
 
-class AsyncScrollbarDragStarter final : public nsAPostRefreshObserver {
- public:
-  AsyncScrollbarDragStarter(mozilla::PresShell* aPresShell, nsIWidget* aWidget,
-                            const AsyncDragMetrics& aDragMetrics)
-      : mPresShell(aPresShell), mWidget(aWidget), mDragMetrics(aDragMetrics) {}
-  virtual ~AsyncScrollbarDragStarter() = default;
-
-  void DidRefresh() override {
-    if (!mPresShell) {
-      MOZ_ASSERT_UNREACHABLE(
-          "Post-refresh observer fired again after failed attempt at "
-          "unregistering it");
-      return;
-    }
-
-    mWidget->StartAsyncScrollbarDrag(mDragMetrics);
-
-    if (!mPresShell->RemovePostRefreshObserver(this)) {
-      MOZ_ASSERT_UNREACHABLE(
-          "Unable to unregister post-refresh observer! Leaking it instead of "
-          "leaving garbage registered");
-      // Graceful handling, just in case...
-      mPresShell = nullptr;
-      mWidget = nullptr;
-      return;
-    }
-
-    delete this;
-  }
-
- private:
-  RefPtr<mozilla::PresShell> mPresShell;
-  RefPtr<nsIWidget> mWidget;
-  AsyncDragMetrics mDragMetrics;
-};
-
 static bool ScrollFrameWillBuildScrollInfoLayer(nsIFrame* aScrollFrame) {
   /*
    * Note: if changing the conditions in this function, make a corresponding
@@ -1026,8 +990,12 @@ void nsSliderFrame::StartAPZDrag(WidgetGUIEvent* aEvent) {
   bool waitForRefresh = InputAPZContext::HavePendingLayerization();
   nsIWidget* widget = this->GetNearestWidget();
   if (waitForRefresh) {
-    waitForRefresh = presShell->AddPostRefreshObserver(
-        new AsyncScrollbarDragStarter(presShell, widget, dragMetrics));
+    waitForRefresh =
+        presShell->AddPostRefreshObserver(new OneShotPostRefreshObserver(
+            presShell, [widget = RefPtr<nsIWidget>(widget),
+                        dragMetrics](mozilla::PresShell*) {
+              widget->StartAsyncScrollbarDrag(dragMetrics);
+            }));
   }
   if (!waitForRefresh) {
     widget->StartAsyncScrollbarDrag(dragMetrics);