[WIP]Oilpan: checking for nearly-dead observers.

Source/platform/LifecycleNotifier.h

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2013 Google Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 20 matching lines @@
 #include "wtf/HashSet.h"
 #include "wtf/TemporaryChange.h"
 
 namespace blink {
 
 template<typename T, typename Observer>
 class LifecycleNotifier {
 public:
     virtual ~LifecycleNotifier();
 
-    void addObserver(Observer*);
-    void removeObserver(Observer*);
+    void addObserver(Observer*, bool);
+    void removeObserver(Observer*, bool);
 
     // notifyContextDestroyed() should be explicitly dispatched from an
     // observed context to notify observers that contextDestroyed().
     //
     // When contextDestroyed() is called, the observer's lifecycleContext()
     // is still valid and safe to use during the notification.
     virtual void notifyContextDestroyed();
 
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
@@ skipping 20 matching lines @@
 
 protected:
     using ObserverSet = WillBeHeapHashSet<RawPtrWillBeWeakMember<Observer>>;
 
     // FIXME: Oilpan: make LifecycleNotifier<> a GC mixin, somehow. ExecutionContext
     // is the problematic case, as it would then be a class with two GC mixin
     // bases, but cannot itself derive from a GC base class also.
     GC_PLUGIN_IGNORE("467502")
     ObserverSet m_observers;
 
+#if !ENABLE(OILPAN)
+    bool isObserverAlive(Observer*&) const;
+#endif
+
 #if ENABLE(ASSERT)
     T* context() { return static_cast<T*>(this); }
 #endif
 
 private:
     bool m_didCallContextDestroyed;
 };
 
+#if !ENABLE(OILPAN)
+template<typename T, typename Observer>
+bool LifecycleNotifier<T, Observer>::isObserverAlive(Observer*& observer) const
+{
+    if (reinterpret_cast<uintptr_t>(observer) & 0x1) {
+        observer = reinterpret_cast<Observer*>(reinterpret_cast<uintptr_t>(observer) & ~0x1);
+        if (Heap::willObjectBeLazilySwept(observer))
+            return false;
+    }
+    return true;
+}
+#endif
+
 template<typename T, typename Observer>
 inline LifecycleNotifier<T, Observer>::~LifecycleNotifier()
 {
     // FIXME: Enable the following ASSERT. Also see a FIXME in Document::detach().
     // ASSERT(!m_observers.size() || m_didCallContextDestroyed);
 
 #if !ENABLE(OILPAN)
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverAll);
     for (Observer* observer : m_observers) {
+        if (!isObserverAlive(observer))
+            continue;
         ASSERT(observer->lifecycleContext() == context());
         observer->clearLifecycleContext();
     }
 #endif
 }
 
 template<typename T, typename Observer>
 inline void LifecycleNotifier<T, Observer>::notifyContextDestroyed()
 {
     // Don't notify contextDestroyed() twice.
     if (m_didCallContextDestroyed)
         return;
 
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverAll);
     Vector<Observer*> snapshotOfObservers;
     copyToVector(m_observers, snapshotOfObservers);
     for (Observer* observer : snapshotOfObservers) {
+#if !ENABLE(OILPAN)
+        if (!isObserverAlive(observer))
+            continue;
+#endif
         // FIXME: Oilpan: At the moment, it's possible that the Observer is
         // destructed during the iteration. Once we enable Oilpan by default
         // for Observers, we can remove the hack by making m_observers
         // a HeapHashSet<WeakMember<Observers>>. (i.e., we can just iterate
         // m_observers without taking a snapshot).
         if (m_observers.contains(observer)) {
             ASSERT(observer->lifecycleContext() == context());
             observer->contextDestroyed();
         }
     }
     m_didCallContextDestroyed = true;
 }
 
 template<typename T, typename Observer>
-inline void LifecycleNotifier<T, Observer>::addObserver(Observer* observer)
+inline void LifecycleNotifier<T, Observer>::addObserver(Observer* observer, bool isGarbageCollected)
 {
     RELEASE_ASSERT(m_iterating != IteratingOverAll);
+#if !ENABLE(OILPAN)
+    if (isGarbageCollected)
+        observer = reinterpret_cast<Observer*>(reinterpret_cast<uintptr_t>(observer) | 1);
+#else
+    (void)isGarbageCollected;
+#endif
     m_observers.add(observer);
 }
 
 template<typename T, typename Observer>
-inline void LifecycleNotifier<T, Observer>::removeObserver(Observer* observer)
+inline void LifecycleNotifier<T, Observer>::removeObserver(Observer* observer, bool isGarbageCollected)
 {
+#if !ENABLE(OILPAN)
+    if (isGarbageCollected)
+        observer = reinterpret_cast<Observer*>(reinterpret_cast<uintptr_t>(observer) | 1);
+#else
+    (void)isGarbageCollected;
+#endif
     m_observers.remove(observer);
 }
 
 } // namespace blink
 
 #endif // LifecycleNotifier_h