[PageLifecycle] Ensure that the show_plc/hide_plc callbacks are invoked after the visibilityChange events are dispatched.

Author: magomez

Source/WebCore/dom/Document.cpp

@@ -1854,10 +1854,15 @@ void Document::unregisterForVisibilityStateChangedCallbacks(VisibilityChangeClie
     m_visibilityStateCallbackClients.remove(client);
 }
 
-void Document::visibilityStateChanged()
+void Document::visibilityStateChanged(CompletionHandler<void(Document&)>&& completionHandler)
 {
     // https://w3c.github.io/page-visibility/#reacting-to-visibilitychange-changes
-    queueTaskToDispatchEvent(TaskSource::UserInteraction, Event::create(eventNames().visibilitychangeEvent, Event::CanBubble::Yes, Event::IsCancelable::No));
+    eventLoop().queueTask(TaskSource::UserInteraction, [document = Ref { *this }, completionHandler = WTFMove(completionHandler)] () mutable {
+        document->dispatchEvent(Event::create(eventNames().visibilitychangeEvent, Event::CanBubble::Yes, Event::IsCancelable::No));
+        if (completionHandler)
+            completionHandler(document);
+    });
+
     for (auto& client : m_visibilityStateCallbackClients)
         client.visibilityStateChanged();
 

Source/WebCore/dom/Document.h

@@ -493,7 +493,7 @@ class Document
     WEBCORE_EXPORT void setDocumentURI(const String&);
 
     WEBCORE_EXPORT VisibilityState visibilityState() const;
-    void visibilityStateChanged();
+    void visibilityStateChanged(CompletionHandler<void(Document&)>&&);
     WEBCORE_EXPORT bool hidden() const;
 
     void setTimerThrottlingEnabled(bool);

Source/WebCore/page/Page.cpp

@@ -2544,6 +2544,24 @@ void Page::setIsVisible(bool isVisible)
     setActivityState(state);
 }
 
+class VisibilityChangeEventNotifier : public RefCounted<VisibilityChangeEventNotifier> {
+public:
+    VisibilityChangeEventNotifier() = default;
+    virtual ~VisibilityChangeEventNotifier() = default;
+
+    void setCompletionHandler(CompletionHandler<void()>&& completionHandler) { m_completionHandler = WTFMove(completionHandler); };
+    void addDocument(Ref<Document> document) { m_documents.add(document); };
+    void removeDocument(Ref<Document> document) {
+        m_documents.remove(document);
+        if (m_documents.isEmpty())
+            m_completionHandler();
+    }
+
+private:
+    CompletionHandler<void()> m_completionHandler;
+    HashSet<Ref<Document>> m_documents;
+};
+
 void Page::setIsVisibleInternal(bool isVisible)
 {
     // FIXME: The visibility state should be stored on the top-level document.
@@ -2608,9 +2626,21 @@ void Page::setIsVisibleInternal(bool isVisible)
             view->hide();
     }
 
-    forEachDocument([] (Document& document) {
-        document.visibilityStateChanged();
-    });
+    if (m_visibilityChangeCompletionHandler) {
+        Ref<VisibilityChangeEventNotifier> notifier = adoptRef(*new VisibilityChangeEventNotifier());
+        notifier->setCompletionHandler(std::exchange(m_visibilityChangeCompletionHandler, { }));
+
+        forEachDocument([notifier] (Document& document) {
+            notifier->addDocument(document);
+            document.visibilityStateChanged([protectedNotifier = Ref { notifier }] (Document& document) {
+                protectedNotifier->removeDocument(document);
+            });
+        });
+    } else {
+        forEachDocument([] (Document& document) {
+            document.visibilityStateChanged({ });
+        });
+    }
 }
 
 void Page::setIsPrerender()

Source/WebCore/page/Page.h

@@ -53,6 +53,7 @@
 #include <memory>
 #include <pal/SessionID.h>
 #include <wtf/Assertions.h>
+#include <wtf/CompletionHandler.h>
 #include <wtf/Forward.h>
 #include <wtf/Function.h>
 #include <wtf/HashSet.h>
@@ -980,6 +981,7 @@ class Page : public Supplementable<Page>, public CanMakeWeakPtr<Page> {
 #if ENABLE(IMAGE_ANALYSIS)
     WEBCORE_EXPORT void analyzeImagesForFindInPage();
 #endif
+    void setVisibilityChangeCompletionHandler(CompletionHandler<void()>&& completionHandler) { m_visibilityChangeCompletionHandler = WTFMove(completionHandler); }
 private:
     struct Navigation {
         RegistrableDomain domain;
@@ -1342,6 +1344,8 @@ class Page : public Supplementable<Page>, public CanMakeWeakPtr<Page> {
 #endif
 
     ContentSecurityPolicyModeForExtension m_contentSecurityPolicyModeForExtension { ContentSecurityPolicyModeForExtension::None };
+
+    CompletionHandler<void()> m_visibilityChangeCompletionHandler;
 };
 
 inline PageGroup& Page::group()

Source/WebKit/WebProcess/WebPage/CoordinatedGraphics/DrawingAreaCoordinatedGraphics.cpp

@@ -429,7 +429,8 @@ void DrawingAreaCoordinatedGraphics::activityStateDidChange(OptionSet<ActivitySt
         }
     }
 
-    completionHandler();
+    if (completionHandler)
+        completionHandler();
 }
 
 void DrawingAreaCoordinatedGraphics::attachViewOverlayGraphicsLayer(GraphicsLayer* viewOverlayRootLayer)

Source/WebKit/WebProcess/WebPage/WebPage.cpp

@@ -3634,6 +3634,15 @@ void WebPage::setActivityState(OptionSet<ActivityState::Flag> activityState, Act
 
     ASSERT_WITH_MESSAGE(m_page, "setActivityState called on %" PRIu64 " but WebCore page was null", identifier().toUInt64());
     if (m_page) {
+        if (changed & ActivityState::IsVisible) {
+            // VisibilityChange events are queued, not emitted directly. Due to that, in order to ensure that the
+            // UIProcess will be notified after the event was dispatched and not before, we need to execute the callback
+            // after the event is dispatched to the page and the different documents, and not just after the drawingArea is
+            // done, which is the usual case.
+            // So, in this case, pass an empty callback to the drawingArea and pass the real callback to the page.
+            m_page->setVisibilityChangeCompletionHandler(std::exchange(callback, { }));
+        }
+
         SetForScope currentlyChangingActivityState { m_lastActivityStateChanges, changed };
         m_page->setActivityState(activityState);
     }