IntersectionObserver: second cut.

third_party/WebKit/Source/core/dom/IntersectionObserverController.h

+// Copyright 2015 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.
+
+#ifndef IntersectionObserverController_h
+#define IntersectionObserverController_h
+
+#include "core/dom/Element.h"
+#include "core/dom/IntersectionObserver.h"
+#include "platform/Timer.h"
+#include "platform/heap/Handle.h"
+#include "wtf/HashSet.h"
+#include "wtf/RefCounted.h"
+
+namespace blink {
+
+class Document;
+template<typename T> class Timer;
+
+class IntersectionObserverController : public GarbageCollectedFinalized<IntersectionObserverController> {
+public:
+    IntersectionObserverController();
+    ~IntersectionObserverController();
+
+    void scheduleIntersectionObserverForDelivery(IntersectionObserver&);
+    void resumeSuspendedIntersectionObservers();
+    void deliverIntersectionObservations(Timer<IntersectionObserverController>*);
+    void computeTrackedIntersectionObservations();
+    void addTrackedObserver(IntersectionObserver&);
+    void removeTrackedObserversForRoot(Element&);
+    void dispose();
+
+    DECLARE_TRACE();
+
+private:
+    Timer<IntersectionObserverController> m_timer;
+    // IntersectionObservers for which this is the tracking document.

[haraken, 2015/12/22 01:13:30]

Can you add a link to the dcheng's document
(https://docs.google.com/document/d/1gmIi87dPJ0zu6XU7Jk2t8JS6b-Pig7gbkwZThxZjz...),
or add a good comment about the lifetime relationship of the
IntersectionObserver-related objects somewhere?

[szager1, 2015/12/22 07:53:41]

Added a link to the design doc, which should be the ultimate resource for all of
this stuff.

+    HeapHashSet<WeakMember<IntersectionObserver>> m_trackedIntersectionObservers;

[haraken, 2015/12/22 01:13:30]

What's the relationship between m_trackedIntersectionObservers,
m_activeIntersectionObservers and m_suspendedIntersectionObservers? If x is in
m_trackedIntersectionObservers, is it guaranteed that x is in either of
m_activeIntersectionObservers or m_suspendedIntersectionObservers?

If so, I'm wondering why m_trackedIntersectionObservers needs to be weak
members.

[esprehn, 2015/12/22 07:50:33]

Can you and Stefan VC and talk about this? I know there's a holiday that's
making this move slowly.

In general I think the lifetimes need to be figured out and you two need to come
to agreement about the right way to use Oilpan here. Going around in codereview
is difficult.

[szager1, 2015/12/22 07:53:41]

m_trackedIntersectionObservers are observers for which the owning Document is
responsible for running the intersection algorithm and generating notifications.
 That's a weak member because the Document should not keep the observer alive
(e.g., if the observer's root goes away).

m_activeIntersectionObservers are observers that have pending notifications to
be sent out.

m_suspendedIntersectionObservers are observes that have pending notifications to
be sent out, but sending notifications has been delayed because the js execution
context is suspended.  The notifications will be sent when the execution context
resumes.

+    // IntersectionObservers for which this is the execution context of the callback.
+    HeapHashSet<Member<IntersectionObserver>> m_activeIntersectionObservers;
+    HeapHashSet<Member<IntersectionObserver>> m_suspendedIntersectionObservers;
+};
+
+} // namespace blink
+
+#endif // IntersectionObservationRegistry_h