Implicit prefinalizer registration.

Switch to implicit registration of prefinalizers along with removing
the ability to dynamically unregister a prefinalizer; the latter
being an unused feature.

The requirement to manually register a prefinalizer has proven to be
a chore and a source of bugs. Case in point: HTMLCanvasElement
currently declares a prefinalizer, but doesn't register it. Simplify
the programming model by automatically registering prefinalizers.

R=haraken
BUG=673645

Review-Url: https://codereview.chromium.org/2565983002
Cr-Commit-Position: refs/heads/master@{#438110}

third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp

@@ -146,7 +146,8 @@ HTMLCanvasElement::~HTMLCanvasElement() {
 }
 
 void HTMLCanvasElement::dispose() {
-  releasePlaceholderFrame();
+  if (placeholderFrame())
+    releasePlaceholderFrame();
 
   if (m_context) {
     m_context->detachCanvas();

third_party/WebKit/Source/platform/heap/BlinkGCAPIReference.md

@@ -178,17 +178,10 @@ with a destructor.
 
 A pre-finalizer must have the following function signature: `void preFinalizer()`. You can change the function name.
 
-A pre-finalizer must be registered in the constructor by using the following statement:
-"`ThreadState::current()->registerPreFinalizer(this);`".
-
 ```c++
 class YourClass : public GarbageCollectedFinalized<YourClass> {
     USING_PRE_FINALIZER(YourClass, dispose);
 public:
-    YourClass()
-    {
-        ThreadState::current()->registerPreFinalizer(this);
-    }
     void dispose()
     {
         m_other->dispose(); // OK; you can touch other on-heap objects in a pre-finalizer.

third_party/WebKit/Source/platform/heap/HeapTest.cpp

@@ -1160,7 +1160,6 @@ class ObservableWithPreFinalizer
   ~ObservableWithPreFinalizer() { m_wasDestructed = true; }
   DEFINE_INLINE_TRACE() {}
   void dispose() {
-    ThreadState::current()->unregisterPreFinalizer(this);
     EXPECT_FALSE(m_wasDestructed);
     s_disposeWasCalled = true;
   }
@@ -1168,7 +1167,6 @@ class ObservableWithPreFinalizer
 
  protected:
   ObservableWithPreFinalizer() : m_wasDestructed(false) {
-    ThreadState::current()->registerPreFinalizer(this);
   }
 
   bool m_wasDestructed;
@@ -1197,7 +1195,6 @@ class PreFinalizerBase : public GarbageCollectedFinalized<PreFinalizerBase> {
 
  protected:
   PreFinalizerBase() : m_wasDestructed(false) {
-    ThreadState::current()->registerPreFinalizer(this);
   }
   bool m_wasDestructed;
 };
@@ -1218,7 +1215,6 @@ class PreFinalizerMixin : public GarbageCollectedMixin {
 
  protected:
   PreFinalizerMixin() : m_wasDestructed(false) {
-    ThreadState::current()->registerPreFinalizer(this);
   }
   bool m_wasDestructed;
 };
@@ -1241,7 +1237,6 @@ class PreFinalizerSubClass : public PreFinalizerBase, public PreFinalizerMixin {
 
  protected:
   PreFinalizerSubClass() : m_wasDestructed(false) {
-    ThreadState::current()->registerPreFinalizer(this);
   }
   bool m_wasDestructed;
 };
@@ -1561,7 +1556,6 @@ class PreFinalizationAllocator
  public:
   PreFinalizationAllocator(Persistent<IntWrapper>* wrapper)
       : m_wrapper(wrapper) {
-    ThreadState::current()->registerPreFinalizer(this);
   }
 
   void dispose() {
@@ -3881,25 +3875,11 @@ TEST(HeapTest, FinalizationObserver) {
 
 TEST(HeapTest, PreFinalizer) {
   Observable::s_willFinalizeWasCalled = false;
-  {
-    Observable* foo = Observable::create(Bar::create());
-    ThreadState::current()->registerPreFinalizer(foo);
-  }
+  { Observable::create(Bar::create()); }
   preciselyCollectGarbage();
   EXPECT_TRUE(Observable::s_willFinalizeWasCalled);
 }
 
-TEST(HeapTest, PreFinalizerIsNotCalledIfUnregistered) {
-  Observable::s_willFinalizeWasCalled = false;
-  {
-    Observable* foo = Observable::create(Bar::create());
-    ThreadState::current()->registerPreFinalizer(foo);
-    ThreadState::current()->unregisterPreFinalizer(foo);
-  }
-  preciselyCollectGarbage();
-  EXPECT_FALSE(Observable::s_willFinalizeWasCalled);
-}
-
 TEST(HeapTest, PreFinalizerUnregistersItself) {
   ObservableWithPreFinalizer::s_disposeWasCalled = false;
   ObservableWithPreFinalizer::create();

third_party/WebKit/Source/platform/heap/ThreadState.h

@@ -91,11 +91,6 @@ class Visitor;
 //
 // class Foo : GarbageCollected<Foo> {
 //     USING_PRE_FINALIZER(Foo, dispose);
-// public:
-//     Foo()
-//     {
-//         ThreadState::current()->registerPreFinalizer(this);
-//     }
 // private:
 //     void dispose()
 //     {
@@ -103,15 +98,18 @@ class Visitor;
 //     }
 //     Member<Bar> m_bar;
 // };
-#define USING_PRE_FINALIZER(Class, preFinalizer)    \
- public:                                            \
-  static bool invokePreFinalizer(void* object) {    \
-    Class* self = reinterpret_cast<Class*>(object); \
-    if (ThreadHeap::isHeapObjectAlive(self))        \
-      return false;                                 \
-    self->Class::preFinalizer();                    \
-    return true;                                    \
-  }                                                 \
+#define USING_PRE_FINALIZER(Class, preFinalizer)                           \
+ public:                                                                   \
+  static bool invokePreFinalizer(void* object) {                           \
+    Class* self = reinterpret_cast<Class*>(object);                        \
+    if (ThreadHeap::isHeapObjectAlive(self))                               \
+      return false;                                                        \
+    self->Class::preFinalizer();                                           \
+    return true;                                                           \
+  }                                                                        \
+                                                                           \
+ private:                                                                  \
+  ThreadState::PrefinalizerRegistration<Class> m_prefinalizerDummy = this; \
   using UsingPreFinalizerMacroNeedsTrailingSemiColon = char
 
 class PLATFORM_EXPORT ThreadState {
@@ -415,32 +413,9 @@ class PLATFORM_EXPORT ThreadState {
 
   size_t objectPayloadSizeForTesting();
 
-  // Register the pre-finalizer for the |self| object. This method is normally
-  // called in the constructor of the |self| object. The class T must have
-  // USING_PRE_FINALIZER().
+  // TODO: no longer needed, remove all uses.
   template <typename T>
   void registerPreFinalizer(T* self) {
-    static_assert(sizeof(&T::invokePreFinalizer) > 0,
-                  "USING_PRE_FINALIZER(T) must be defined.");
-    ASSERT(checkThread());
-    ASSERT(!sweepForbidden());
-    ASSERT(!m_orderedPreFinalizers.contains(
-        PreFinalizer(self, T::invokePreFinalizer)));
-    m_orderedPreFinalizers.add(PreFinalizer(self, T::invokePreFinalizer));
-  }
-
-  // Unregister the pre-finalizer for the |self| object.
-  template <typename T>
-  void unregisterPreFinalizer(T* self) {
-    static_assert(sizeof(&T::invokePreFinalizer) > 0,
-                  "USING_PRE_FINALIZER(T) must be defined.");
-    ASSERT(checkThread());
-    // Ignore pre-finalizers called during pre-finalizers or destructors.
-    if (sweepForbidden())
-      return;
-    ASSERT(m_orderedPreFinalizers.contains(
-        PreFinalizer(self, T::invokePreFinalizer)));
-    m_orderedPreFinalizers.remove(PreFinalizer(self, &T::invokePreFinalizer));
   }
 
   void shouldFlushHeapDoesNotContainCache() {
@@ -565,7 +540,29 @@ class PLATFORM_EXPORT ThreadState {
   void collectGarbageForTerminatingThread();
   void collectAllGarbage();
 
+  // Register the pre-finalizer for the |self| object. The class T must have
+  // USING_PRE_FINALIZER().
+  template <typename T>
+  class PrefinalizerRegistration final {
+   public:
+    PrefinalizerRegistration(T* self) {
+      static_assert(sizeof(&T::invokePreFinalizer) > 0,
+                    "USING_PRE_FINALIZER(T) must be defined.");
+      ThreadState* state = ThreadState::current();
+#if ENABLE(ASSERT)
+      DCHECK(state->checkThread());
+#endif
+      DCHECK(!state->sweepForbidden());
+      DCHECK(!state->m_orderedPreFinalizers.contains(
+          PreFinalizer(self, T::invokePreFinalizer)));
+      state->m_orderedPreFinalizers.add(
+          PreFinalizer(self, T::invokePreFinalizer));
+    }
+  };
+
  private:
+  template <typename T>
+  friend class PrefinalizerRegistration;
   enum SnapshotType { HeapSnapshot, FreelistSnapshot };
 
   explicit ThreadState(BlinkGC::ThreadHeapMode);