Add EventHandlerRegistry

Source/core/dom/EventHandlerRegistry.cpp

Index: Source/core/dom/EventHandlerRegistry.cpp
diff --git a/Source/core/dom/EventHandlerRegistry.cpp b/Source/core/dom/EventHandlerRegistry.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..75cd9939700991ae6352b30a4454d4cab8993b6c
--- /dev/null
+++ b/Source/core/dom/EventHandlerRegistry.cpp
@@ -0,0 +1,364 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "core/dom/EventHandlerRegistry.h"
+
+#include "core/dom/Document.h"
+#include "core/events/ThreadLocalEventNames.h"
+#include "core/events/WheelEvent.h"
+#include "core/frame/FrameHost.h"
+#include "core/frame/LocalFrame.h"
+#include "core/page/Chrome.h"
+#include "core/page/ChromeClient.h"
+#include "core/page/Page.h"
+#include "core/page/scrolling/ScrollingCoordinator.h"
+
+namespace WebCore {
+
+EventHandlerRegistry::WindowObserver::WindowObserver(EventHandlerRegistry& registry, DOMWindow& window)
+    : DOMWindowLifecycleObserver(&window)
+    , m_registry(registry)
+{
+}
+
+EventHandlerRegistry::WindowObserver::~WindowObserver()
+{
+}
+
+void EventHandlerRegistry::WindowObserver::didAddEventListener(DOMWindow* window, const AtomicString& eventType)
+{
+    m_registry.didAddEventHandler(*window, eventType);
+}
+
+void EventHandlerRegistry::WindowObserver::didRemoveEventListener(DOMWindow* window, const AtomicString& eventType)
+{
+    m_registry.didRemoveEventHandler(*window, eventType);
+}
+
+void EventHandlerRegistry::WindowObserver::didRemoveAllEventListeners(DOMWindow* window)
+{
+    m_registry.didRemoveAllEventHandlers(*window);
+}
+
+EventHandlerRegistry::DocumentObserver::DocumentObserver(Document& document)
+    : DocumentLifecycleObserver(&document)
+    , ActiveDOMObject(&document)
+{
+    suspendIfNeeded();
+}
+
+EventHandlerRegistry::DocumentObserver::~DocumentObserver()
+{
+}
+
+void EventHandlerRegistry::DocumentObserver::documentWasAttached()
+{
+    Document* document = DocumentLifecycleObserver::lifecycleContext();
+    if (document->parentDocument())
+        return;
+    EventHandlerRegistry* registry = EventHandlerRegistry::from(*document);

[abarth-chromium, 2014/04/11 19:08:01]

So, we're hanging the EventHandlerRegistry off the top-level document but none
of the other documents?  Why not hang the EventHandlerRegistry off the Page? 
That's generally where we put objects that exist per Page.

[Sami, 2014/04/15 18:31:52]

Sorry, this was my bug; actually EventHandlerRegistry needs to be created for
all documents that have associated event handlers. The
document->parentDocument() guard on line 59 was here to avoid sending
(ultimately redundant) notifications about handlers to ScrollingCoordinator et
al. I removed the notifications but accidentally left the guard here :\

+    DOMWindow* window = document->domWindow();
+
+    // Register any existing handlers on the window and start tracking new ones.
+    if (!registry->m_windowObserver && window) {
+        Vector<AtomicString> eventTypes = window->eventTypes();
+        for (size_t i = 0; i < eventTypes.size(); ++i) {
+            const EventListenerVector& listeners = window->getEventListeners(eventTypes[i]);
+            for (size_t count = 0; count < listeners.size(); count++) {
+                registry->didAddEventHandler(*window, eventTypes[i]);
+            }
+        }

[abarth-chromium, 2014/04/11 19:08:01]

Do you have a test that demonstrates this code being necessary?  Previously, you
had an ASSERT here.

[Sami, 2014/04/15 18:31:52]

No, but I'll try to make one based on the comment here:
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

+        registry->m_windowObserver = adoptPtr(new WindowObserver(*registry, *document->domWindow()));

[abarth-chromium, 2014/04/11 19:08:01]

Why do we only observe the top-level DOMWindow?

[Sami, 2014/04/15 18:31:52]

That's not intended -- fixed as explained under line 61.

+    }
+}
+
+void EventHandlerRegistry::DocumentObserver::stop()
+{
+    Document* document = DocumentLifecycleObserver::lifecycleContext();
+
+    // The detached document should no longer track handlers on its window.
+    EventHandlerRegistry* registry = EventHandlerRegistry::from(*document);

[abarth-chromium, 2014/04/11 19:08:01]

On line 59, we skip creating the EventHandlerRegistry for everything except the
top-level Document, but here you're accessing the EventHandlerRegistry on all
the documents in the tree.  Wouldn't this mean this code is needlessly creating
the EventHandlerRegistry on all the child documents only to ignore them?

[Sami, 2014/04/15 18:31:52]

In fact we do need an EventHandlerRegistry on all documents that have associated
event handlers. The presence or absence of handlers is communicated up the
hierarchy to the root registry.

It's possible we create unnecessary registries for documents that have handlers
of types other than those we are interested in (scroll, wheel and touch), but my
gut feeling is that the number of such documents is not high enough to warrant
adding code to guard against it.

+    if (document->domWindow())
+        registry->didRemoveAllEventHandlers(*document->domWindow());
+    registry->m_windowObserver.clear();
+
+    // Unregister our Document node from the parent for all event classes that
+    // have handlers.
+    Document* parentDocument = document->parentDocument();
+    if (!parentDocument)
+        return;
+    EventHandlerRegistry* parentRegistry = EventHandlerRegistry::from(*parentDocument);
+    parentRegistry->didRemoveAllEventHandlers(*document);

[abarth-chromium, 2014/04/11 19:08:01]

What happens if someone adds an event handler after the Document stops?

[Sami, 2014/04/15 18:31:52]

Good point. I was assuming the document would be completely inert after it
stopped. I'll make the registry stop accepting changes unless the document is
active. Since I changed how we stop tracking windows (see below), this is
covered by iframe tests in scroll-event-handler-count.html.

+}
+
+EventHandlerRegistry::HandlerState::HandlerState()
+    : externalHandlerCount(0)
+{
+}
+
+EventHandlerRegistry::HandlerState::~HandlerState()
+{
+}
+
+EventHandlerRegistry::EventHandlerRegistry(Document& document)
+    : m_document(document)
+    , m_documentObserver(DocumentObserver(document))
+    , m_windowObserver(adoptPtr(new WindowObserver(*this, *document.domWindow())))

[abarth-chromium, 2014/04/11 19:08:01]

Why is the DocumentObserver held by value but the WindowObserver held by
pointer?

[Sami, 2014/04/15 18:31:52]

This was so that we could stop tracking handlers on the window once the document
is stopped, but now it seems making the registry stop accepting all updates when
stopped is a cleaner way to achieve the same.

+{
+}
+
+EventHandlerRegistry::~EventHandlerRegistry()
+{
+}
+
+const char* EventHandlerRegistry::supplementName()
+{
+    return "EventHandlerRegistry";
+}
+
+EventHandlerRegistry* EventHandlerRegistry::from(Document& document)
+{
+    EventHandlerRegistry* registry = static_cast<EventHandlerRegistry*>(DocumentSupplement::from(document, supplementName()));
+    if (!registry) {
+        registry = new EventHandlerRegistry(document);
+        DocumentSupplement::provideTo(document, supplementName(), adoptPtr(registry));
+    }
+    return registry;
+}
+
+bool EventHandlerRegistry::eventTypeToClass(const AtomicString& eventType, EventHandlerClass* result)
+{
+    if (eventType == EventTypeNames::wheel || eventType == EventTypeNames::mousewheel) {
+        *result = WheelEvent;
+    } else if (eventType == EventTypeNames::scroll) {
+        *result = ScrollEvent;
+    } else if (isTouchEventType(eventType)) {
+        *result = TouchEvent;
+    } else {
+        return false;
+    }
+    return true;
+}
+
+const EventTargetSet* EventHandlerRegistry::eventHandlerTargets(EventHandlerClass handlerClass) const
+{
+    return m_eventHandlers[handlerClass].targets.get();
+}
+
+bool EventHandlerRegistry::hasEventHandlers(EventHandlerClass handlerClass) const
+{
+    EventTargetSet* targets = m_eventHandlers[handlerClass].targets.get();
+    return m_eventHandlers[handlerClass].externalHandlerCount || (targets && targets->size());
+}
+
+unsigned EventHandlerRegistry::externalEventHandlerCount(EventHandlerClass handlerClass) const
+{
+    return m_eventHandlers[handlerClass].externalHandlerCount;
+}
+
+void EventHandlerRegistry::updateExternalHandlerCount(ChangeOperation op, EventHandlerClass handlerClass)
+{
+    if (op == Add) {
+        m_eventHandlers[handlerClass].externalHandlerCount++;
+    } else {
+        ASSERT(op == Remove);
+        ASSERT(m_eventHandlers[handlerClass].externalHandlerCount > 0);
+        m_eventHandlers[handlerClass].externalHandlerCount--;
+    }
+}
+
+bool EventHandlerRegistry::updateEventHandlerTargets(ChangeOperation op, EventHandlerClass handlerClass, EventTarget* target)
+{
+    EventTargetSet* targets = m_eventHandlers[handlerClass].targets.get();
+    if (op == Add) {
+#ifndef NDEBUG
+        if (Node* node = target->toNode()) {
+            // The node should either be in the document, or be the Document node of a child
+            // of the document.
+            ASSERT(&node->document() == &m_document
+                || (node->isDocumentNode() && toDocument(node)->parentDocument() == &m_document));
+        } else if (DOMWindow* window = target->toDOMWindow()) {
+            // The window should belong to this document.
+            ASSERT(window->document() == &m_document);
+        }
+#endif // NDEBUG
+
+        if (!targets) {
+            m_eventHandlers[handlerClass].targets = adoptPtr(new EventTargetSet);
+            targets = m_eventHandlers[handlerClass].targets.get();
+        }
+
+        if (!targets->add(target).isNewEntry) {
+            // Just incremented refcount, no real change.
+            // If this is a child document node, then the count should never go above 1.
+#ifndef NDEBUG
+            if (Node* node = target->toNode())
+                ASSERT(!node->isDocumentNode() || &node->document() == &m_document);
+#endif // NDEBUG
+            return false;
+        }
+    } else {
+        // Note that we can't assert that |target| is in this document because
+        // it might be in the process of moving out of it.
+        ASSERT(op == Remove || op == RemoveAll);
+        ASSERT(op == RemoveAll || targets->contains(target));
+        if (!targets)
+            return false;
+
+        if (op == RemoveAll) {
+            if (!targets->contains(target))
+                return false;
+            targets->removeAll(target);
+        } else {
+            if (!targets->remove(target)) {
+                // Just decremented refcount, no real update.
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
+void EventHandlerRegistry::updateEventHandlerInternal(ChangeOperation op, EventHandlerClass handlerClass, EventTarget* target)
+{
+    bool hadHandlers = hasEventHandlers(handlerClass);
+    bool targetSetChanged;
+    if (target) {
+        targetSetChanged = updateEventHandlerTargets(op, handlerClass, target);
+    } else {
+        updateExternalHandlerCount(op, handlerClass);
+        targetSetChanged = true;
+    }
+    bool hasHandlers = hasEventHandlers(handlerClass);
+
+    // Notify the parent document's registry if we added the first or removed
+    // the last handler.
+    if (hadHandlers != hasHandlers) {
+        if (Document* parent = m_document.parentDocument()) {
+            // Report change to parent with our Document as the target.
+            EventHandlerRegistry::from(*parent)->updateEventHandlerInternal(op, handlerClass, &m_document);
+        } else {
+            // This is the root registry; notify clients accordingly.
+            notifyHasHandlersChanged(handlerClass, hasHandlers);
+        }
+    }
+
+    // Only notify the client when something actually changed, and then only if
+    // this wasn't a notification that was sent by a sub-registry.
+    if (!targetSetChanged)
+        return;
+    Node* node = target ? target->toNode() : 0;
+    if (!node || !node->isDocumentNode() || node == &m_document)
+        notifyDidAddOrRemoveEventHandlerTarget(handlerClass);
+}
+
+void EventHandlerRegistry::updateEventHandlerOfType(ChangeOperation op, const AtomicString& eventType, EventTarget* target)
+{
+    EventHandlerClass handlerClass;
+    if (!eventTypeToClass(eventType, &handlerClass))
+        return;
+    updateEventHandlerInternal(op, handlerClass, target);
+}
+
+void EventHandlerRegistry::didAddExternalEventHandler(const AtomicString& eventType)
+{
+    updateEventHandlerOfType(Add, eventType, 0);
+}
+
+void EventHandlerRegistry::didRemoveExternalEventHandler(const AtomicString& eventType)
+{
+    updateEventHandlerOfType(Remove, eventType, 0);
+}
+
+void EventHandlerRegistry::didAddEventHandler(EventTarget& target, const AtomicString& eventType)
+{
+    updateEventHandlerOfType(Add, eventType, &target);
+}
+
+void EventHandlerRegistry::didRemoveEventHandler(EventTarget& target, const AtomicString& eventType)
+{
+    updateEventHandlerOfType(Remove, eventType, &target);
+}
+
+void EventHandlerRegistry::didAddEventHandler(EventTarget& target, EventHandlerClass handlerClass)
+{
+    updateEventHandlerInternal(Add, handlerClass, &target);
+}
+
+void EventHandlerRegistry::didRemoveEventHandler(EventTarget& target, EventHandlerClass handlerClass)
+{
+    updateEventHandlerInternal(Remove, handlerClass, &target);
+}
+
+void EventHandlerRegistry::didMoveFromOtherDocument(EventTarget& target, Document& oldDocument)
+{
+    EventHandlerRegistry* oldRegistry = EventHandlerRegistry::from(oldDocument);
+    for (size_t i = 0; i < EventHandlerClassCount; ++i) {
+        EventHandlerClass handlerClass = static_cast<EventHandlerClass>(i);
+        const EventTargetSet* targets = oldRegistry->eventHandlerTargets(handlerClass);
+        if (!targets)
+            continue;
+        for (unsigned count = targets->count(&target); count > 0; --count) {
+            oldRegistry->updateEventHandlerInternal(Remove, handlerClass, &target);
+            updateEventHandlerInternal(Add, handlerClass, &target);
+        }
+    }
+}
+
+void EventHandlerRegistry::didRemoveAllEventHandlers(EventTarget& target)
+{
+    for (size_t i = 0; i < EventHandlerClassCount; ++i) {
+        EventHandlerClass handlerClass = static_cast<EventHandlerClass>(i);
+        const EventTargetSet* targets = eventHandlerTargets(handlerClass);
+        if (!targets)
+            continue;
+        updateEventHandlerInternal(RemoveAll, handlerClass, &target);
+    }
+}
+
+void EventHandlerRegistry::notifyHasHandlersChanged(EventHandlerClass handlerClass, bool hasActiveHandlers)
+{
+    Page* page = m_document.page();
+    LocalFrame* mainFrame = page ? page->mainFrame() : 0;
+    ScrollingCoordinator* scrollingCoordinator = page ? page->scrollingCoordinator() : 0;
+
+    switch (handlerClass) {
+    case WheelEvent:
+        if (mainFrame) {
+            // TODO(skyostil): This notification is wired up to a black hole, so remove it.
+            mainFrame->notifyChromeClientWheelEventHandlerCountChanged();
+        }
+        if (scrollingCoordinator)
+            scrollingCoordinator->haveWheelEventHandlersChangedForPage();
+        break;
+    case ScrollEvent:
+        if (scrollingCoordinator)
+            scrollingCoordinator->haveScrollEventHandlersChangedForPage();
+        break;
+    case TouchEvent:
+        if (FrameHost* frameHost = m_document.frameHost())
+            frameHost->chrome().client().needTouchEvents(hasActiveHandlers);
+        break;
+    default:
+        ASSERT_NOT_REACHED();
+        break;
+    }
+}
+
+void EventHandlerRegistry::notifyDidAddOrRemoveEventHandlerTarget(EventHandlerClass handlerClass)
+{
+    Page* page = m_document.page();
+    if (!page)
+        return;
+
+    ScrollingCoordinator* scrollingCoordinator = page->scrollingCoordinator();
+    if (!scrollingCoordinator)
+        return;
+
+    if (handlerClass == TouchEvent)
+        scrollingCoordinator->touchEventTargetRectsDidChange();
+}
+
+} // namespace WebCore