Support weak WebPrivatePtr<>s.

third_party/WebKit/public/platform/WebPrivatePtr.h

 /*
  * Copyright (C) 2010 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 35 matching lines @@
 namespace blink {
 
 // By default, the destruction of a WebPrivatePtr<> must happen on the same
 // thread that created it, but can optionally be allowed to happen on
 // another thread.
 enum WebPrivatePtrDestruction {
     WebPrivatePtrDestructionSameThread,
     WebPrivatePtrDestructionCrossThread,
 };
 
+// The WebPrivatePtr<> holds by default a strong reference to its Blink object,
+// but Blink GC managed objects also support keeping a weak reference by
+// way of WebPrivatePtr<>.
+enum class WebPrivatePtrStrength {
+    Normal,
+    Weak,
+};
+
 #if INSIDE_BLINK
 enum LifetimeManagementType {
     RefCountedLifetime,
     GarbageCollectedLifetime,
     RefCountedGarbageCollectedLifetime
 };
 
 template<typename T>
 class LifetimeOf {
     static const bool isGarbageCollected = WTF::IsSubclassOfTemplate<T, GarbageCollected>::value || IsGarbageCollectedMixin<T>::value;
     static const bool isRefCountedGarbageCollected = WTF::IsSubclassOfTemplate<T, RefCountedGarbageCollected>::value;
 public:
     static const LifetimeManagementType value =
         !isGarbageCollected ? RefCountedLifetime :
         isRefCountedGarbageCollected ? RefCountedGarbageCollectedLifetime : GarbageCollectedLifetime;
 };
 
-template<typename T, WebPrivatePtrDestruction crossThreadDestruction, LifetimeManagementType lifetime>
+template<typename T, WebPrivatePtrDestruction crossThreadDestruction, WebPrivatePtrStrength strongOrWeak, LifetimeManagementType lifetime>
 class PtrStorageImpl;
 
-template<typename T, WebPrivatePtrDestruction crossThreadDestruction>
-class PtrStorageImpl<T, crossThreadDestruction, RefCountedLifetime> {
+template<typename T, WebPrivatePtrDestruction crossThreadDestruction, WebPrivatePtrStrength strongOrWeak>
+class PtrStorageImpl<T, crossThreadDestruction, strongOrWeak, RefCountedLifetime> {
 public:
     typedef PassRefPtr<T> BlinkPtrType;
 
     void assign(const BlinkPtrType& val)
     {
         static_assert(crossThreadDestruction == WebPrivatePtrDestructionSameThread || WTF::IsSubclassOfTemplate<T, WTF::ThreadSafeRefCounted>::value, "Cross thread destructible class must derive from ThreadSafeRefCounted<>");
+        static_assert(strongOrWeak == WebPrivatePtrStrength::Normal, "Ref-counted classes do not support weak WebPrivatePtr<> references");
         release();
         m_ptr = val.leakRef();
     }
 
     void assign(const PtrStorageImpl& other)
     {
         release();
         T* val = other.get();
         WTF::refIfNotNull(val);
         m_ptr = val;
@@ skipping 11 matching lines @@
     void release()
     {
         WTF::derefIfNotNull(m_ptr);
         m_ptr = 0;
     }
 
 private:
     T* m_ptr;
 };
 
-template <typename T, WebPrivatePtrDestruction>
+template <typename T, WebPrivatePtrDestruction, WebPrivatePtrStrength>
 struct WebPrivatePtrPersistentStorageType {
 public:
     using Type = Persistent<T>;
 };
 
 template <typename T>
-struct WebPrivatePtrPersistentStorageType<T, WebPrivatePtrDestructionCrossThread> {
+struct WebPrivatePtrPersistentStorageType<T, WebPrivatePtrDestructionSameThread, WebPrivatePtrStrength::Weak>  {
+public:
+    using Type = WeakPersistent<T>;
+};
+
+template <typename T>
+struct WebPrivatePtrPersistentStorageType<T, WebPrivatePtrDestructionCrossThread, WebPrivatePtrStrength::Normal> {
 public:
     using Type = CrossThreadPersistent<T>;
 };
 
-template<typename T, WebPrivatePtrDestruction crossThreadDestruction>
-class PtrStorageImpl<T, crossThreadDestruction, GarbageCollectedLifetime> {
+template <typename T>
+struct WebPrivatePtrPersistentStorageType<T, WebPrivatePtrDestructionCrossThread, WebPrivatePtrStrength::Weak> {
+public:
+    using Type = CrossThreadWeakPersistent<T>;
+};
+
+template<typename T, WebPrivatePtrDestruction crossThreadDestruction, WebPrivatePtrStrength strongOrWeak>
+    class PtrStorageImpl<T, crossThreadDestruction, strongOrWeak, GarbageCollectedLifetime> {

[hiroshige, 2016/01/27 03:55:01]

nit: no indent needed here.

[sof, 2016/01/29 09:12:23]

oops, thanks for catching that.

 public:
     void assign(const RawPtr<T>& val)
     {
         if (!val) {
             release();
             return;
         }
 
         if (!m_handle)
-            m_handle = new (typename WebPrivatePtrPersistentStorageType<T, crossThreadDestruction>::Type)();
+            m_handle = new (typename WebPrivatePtrPersistentStorageType<T, crossThreadDestruction, strongOrWeak>::Type)();
 
         (*m_handle) = val;
     }
 
     void assign(T* ptr) { assign(RawPtr<T>(ptr)); }
     template<typename U> void assign(const RawPtr<U>& val) { assign(RawPtr<T>(val)); }
 
     void assign(const PtrStorageImpl& other) { assign(other.get()); }
 
     void moveFrom(PtrStorageImpl& other)
     {
         release();
         m_handle = other.m_handle;
         other.m_handle = 0;
     }
 
     T* get() const { return m_handle ? m_handle->get() : 0; }
 
     void release()
     {
         delete m_handle;
         m_handle = 0;
     }
 
 private:
-    typename WebPrivatePtrPersistentStorageType<T, crossThreadDestruction>::Type* m_handle;
+    typename WebPrivatePtrPersistentStorageType<T, crossThreadDestruction, strongOrWeak>::Type* m_handle;
 };
 
-template<typename T, WebPrivatePtrDestruction crossThreadDestruction>
-class PtrStorageImpl<T, crossThreadDestruction, RefCountedGarbageCollectedLifetime> : public PtrStorageImpl<T, crossThreadDestruction, GarbageCollectedLifetime> {
+template<typename T, WebPrivatePtrDestruction crossThreadDestruction, WebPrivatePtrStrength strongOrWeak>
+class PtrStorageImpl<T, crossThreadDestruction, strongOrWeak, RefCountedGarbageCollectedLifetime> : public PtrStorageImpl<T, crossThreadDestruction, strongOrWeak, GarbageCollectedLifetime> {
 public:
-    void assign(const PassRefPtrWillBeRawPtr<T>& val) { PtrStorageImpl<T, crossThreadDestruction, GarbageCollectedLifetime>::assign(val.get()); }
+    void assign(const PassRefPtrWillBeRawPtr<T>& val) { PtrStorageImpl<T, crossThreadDestruction, strongOrWeak, GarbageCollectedLifetime>::assign(val.get()); }
 
-    void assign(const PtrStorageImpl& other) { PtrStorageImpl<T, crossThreadDestruction, GarbageCollectedLifetime>::assign(other.get()); }
+    void assign(const PtrStorageImpl& other) { PtrStorageImpl<T, crossThreadDestruction, strongOrWeak, GarbageCollectedLifetime>::assign(other.get()); }
 };
 
-template<typename T, WebPrivatePtrDestruction crossThreadDestruction>
-class PtrStorage : public PtrStorageImpl<T, crossThreadDestruction, LifetimeOf<T>::value> {
+template<typename T, WebPrivatePtrDestruction crossThreadDestruction, WebPrivatePtrStrength strongOrWeak>
+class PtrStorage : public PtrStorageImpl<T, crossThreadDestruction, strongOrWeak, LifetimeOf<T>::value> {
 public:
     static PtrStorage& fromSlot(void** slot)
     {
         static_assert(sizeof(PtrStorage) == sizeof(void*), "PtrStorage must be the size of a pointer");
         return *reinterpret_cast<PtrStorage*>(slot);
     }
 
     static const PtrStorage& fromSlot(void* const* slot)
     {
         static_assert(sizeof(PtrStorage) == sizeof(void*), "PtrStorage must be the size of a pointer");
@@ skipping 36 matching lines @@
 //    #endif
 //
 //    private:
 //        WebPrivatePtr<Foo> m_private;
 //    };
 //
 //    // WebFoo.cpp
 //    WebFoo::~WebFoo() { m_private.reset(); }
 //    void WebFoo::assign(const WebFoo& other) { ... }
 //
-template <typename T, WebPrivatePtrDestruction crossThreadDestruction = WebPrivatePtrDestructionSameThread>
+template <typename T, WebPrivatePtrDestruction crossThreadDestruction = WebPrivatePtrDestructionSameThread, WebPrivatePtrStrength strongOrWeak = WebPrivatePtrStrength::Normal>
 class WebPrivatePtr {
 public:
     WebPrivatePtr() : m_storage(0) { }
     ~WebPrivatePtr()
     {
         // We don't destruct the object pointed by m_ptr here because we don't
         // want to expose destructors of core classes to embedders. We should
         // call reset() manually in destructors of classes with WebPrivatePtr
         // members.
         BLINK_ASSERT(!m_storage);
@@ skipping 40 matching lines @@
 
     T* operator->() const
     {
         ASSERT(m_storage);
         return get();
     }
 #endif
 
 private:
 #if INSIDE_BLINK
-    PtrStorage<T, crossThreadDestruction>& storage() { return PtrStorage<T, crossThreadDestruction>::fromSlot(&m_storage); }
-    const PtrStorage<T, crossThreadDestruction>& storage() const { return PtrStorage<T, crossThreadDestruction>::fromSlot(&m_storage); }
+    PtrStorage<T, crossThreadDestruction, strongOrWeak>& storage() { return PtrStorage<T, crossThreadDestruction, strongOrWeak>::fromSlot(&m_storage); }
+    const PtrStorage<T, crossThreadDestruction, strongOrWeak>& storage() const { return PtrStorage<T, crossThreadDestruction, strongOrWeak>::fromSlot(&m_storage); }
 #endif
 
 #if !INSIDE_BLINK
     // Disable the assignment operator; we define it above for when
     // INSIDE_BLINK is set, but we need to make sure that it is not
     // used outside there; the compiler-provided version won't handle reference
     // counting properly.
     WebPrivatePtr& operator=(const WebPrivatePtr& other);
 #endif
     // Disable the copy constructor; classes that contain a WebPrivatePtr
     // should implement their copy constructor using assign().
     WebPrivatePtr(const WebPrivatePtr&);
 
     void* m_storage;
 };
 
 } // namespace blink
 
-#endif
+#endif // WebPrivatePtr_h