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

Source/platform/LifecycleNotifier.h

Index: Source/platform/LifecycleNotifier.h
diff --git a/Source/platform/LifecycleNotifier.h b/Source/platform/LifecycleNotifier.h
index b11ad9b50835020d9650eabb9649551c0d084384..9106a799c3e62951f579bae007b43b3b4f5e3278 100644
--- a/Source/platform/LifecycleNotifier.h
+++ b/Source/platform/LifecycleNotifier.h
@@ -38,8 +38,8 @@ 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().
@@ -80,6 +80,10 @@ protected:
     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
@@ -88,6 +92,19 @@ 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()
 {
@@ -97,6 +114,8 @@ inline LifecycleNotifier<T, Observer>::~LifecycleNotifier()
 #if !ENABLE(OILPAN)
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverAll);
     for (Observer* observer : m_observers) {
+        if (!isObserverAlive(observer))
+            continue;
         ASSERT(observer->lifecycleContext() == context());
         observer->clearLifecycleContext();
     }
@@ -114,6 +133,10 @@ inline void LifecycleNotifier<T, Observer>::notifyContextDestroyed()
     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
@@ -128,15 +151,27 @@ inline void LifecycleNotifier<T, Observer>::notifyContextDestroyed()
 }
 
 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);
 }