Specialize base::IsWeakReceiver for Blink weak pointers to support base::Bind (1/5)

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

 // Copyright 2016 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 Persistent_h
 #define Persistent_h
 
 #include "platform/heap/Member.h"
 #include "platform/heap/PersistentNode.h"
 #include "wtf/Allocator.h"
@@ skipping 622 matching lines @@
 public:
     PersistentHeapDeque() { }
 
     template<size_t otherCapacity>
     PersistentHeapDeque(const HeapDeque<T, otherCapacity>& other)
         : PersistentHeapCollectionBase<HeapDeque<T, inlineCapacity>>(other)
     {
     }
 };
 
-// Only a very reduced form of weak heap object references can currently be held
-// by WTF::Closure<>s. i.e., bound as a 'this' pointer only.
-//
-// TODO(sof): once wtf/Functional.h is able to work over platform/heap/ types
-// (like CrossThreadWeakPersistent<>), drop the restriction on weak persistent
-// use by function closures (and rename this ad-hoc type.)
-template<typename T>
-class WeakPersistentThisPointer {
-    STACK_ALLOCATED();
-public:
-    explicit WeakPersistentThisPointer(T* value) : m_value(value) { }
-    WeakPersistent<T> value() const { return m_value; }
-private:
-    WeakPersistent<T> m_value;
-};
-
-template<typename T>
-class CrossThreadWeakPersistentThisPointer {
-    STACK_ALLOCATED();
-public:
-    explicit CrossThreadWeakPersistentThisPointer(T* value) : m_value(value) { }
-    CrossThreadWeakPersistent<T> value() const { return m_value; }
-private:
-    CrossThreadWeakPersistent<T> m_value;
-};
-
 template <typename T>
 Persistent<T> wrapPersistent(T* value)
 {
     return Persistent<T>(value);
 }
 
 template <typename T>
+WeakPersistent<T> wrapWeakPersistent(T* value)
+{
+    return WeakPersistent<T>(value);
+}
+
+template <typename T>
 CrossThreadPersistent<T> wrapCrossThreadPersistent(T* value)
 {
     return CrossThreadPersistent<T>(value);
 }
 
+template <typename T>
+CrossThreadWeakPersistent<T> wrapCrossThreadWeakPersistent(T* value)
+{
+    return CrossThreadWeakPersistent<T>(value);
+}
+
 // Comparison operators between (Weak)Members, Persistents, and UntracedMembers.
 template<typename T, typename U> inline bool operator==(const Member<T>& a, const Member<U>& b) { return a.get() == b.get(); }
 template<typename T, typename U> inline bool operator!=(const Member<T>& a, const Member<U>& b) { return a.get() != b.get(); }
 template<typename T, typename U> inline bool operator==(const Persistent<T>& a, const Persistent<U>& b) { return a.get() == b.get(); }
 template<typename T, typename U> inline bool operator!=(const Persistent<T>& a, const Persistent<U>& b) { return a.get() != b.get(); }
 
 template<typename T, typename U> inline bool operator==(const Member<T>& a, const Persistent<U>& b) { return a.get() == b.get(); }
 template<typename T, typename U> inline bool operator!=(const Member<T>& a, const Persistent<U>& b) { return a.get() != b.get(); }
 template<typename T, typename U> inline bool operator==(const Persistent<T>& a, const Member<U>& b) { return a.get() == b.get(); }
 template<typename T, typename U> inline bool operator!=(const Persistent<T>& a, const Member<U>& b) { return a.get() != b.get(); }
@@ skipping 19 matching lines @@
     STATIC_ONLY(DefaultHash);
     using Hash = MemberHash<T>;
 };
 
 template <typename T>
 struct DefaultHash<blink::CrossThreadWeakPersistent<T>> {
     STATIC_ONLY(DefaultHash);
     using Hash = MemberHash<T>;
 };
 
-template<typename T>
-struct ParamStorageTraits<blink::WeakPersistentThisPointer<T>> {
-    STATIC_ONLY(ParamStorageTraits);
-    static_assert(sizeof(T), "T must be fully defined");
-    using StorageType = blink::WeakPersistent<T>;
-
-    static StorageType wrap(const blink::WeakPersistentThisPointer<T>& value) { return value.value(); }
-
-    // WTF::FunctionWrapper<> handles WeakPtr<>, so recast this weak persistent
-    // into it.
-    //
-    // TODO(sof): remove this hack once wtf/Functional.h can also work with a type like
-    // WeakPersistent<>.
-    static WeakPtr<T> unwrap(const StorageType& value) { return WeakPtr<T>(WeakReference<T>::create(value.get())); }
-};
-
-template<typename T>
-struct ParamStorageTraits<blink::CrossThreadWeakPersistentThisPointer<T>> {
-    STATIC_ONLY(ParamStorageTraits);
-    static_assert(sizeof(T), "T must be fully defined");
-    using StorageType = blink::CrossThreadWeakPersistent<T>;
-
-    static StorageType wrap(const blink::CrossThreadWeakPersistentThisPointer<T>& value) { return value.value(); }
-
-    // WTF::FunctionWrapper<> handles WeakPtr<>, so recast this weak persistent
-    // into it.
-    //
-    // TODO(sof): remove this hack once wtf/Functional.h can also work with a type like
-    // CrossThreadWeakPersistent<>.
-    static WeakPtr<T> unwrap(const StorageType& value) { return WeakPtr<T>(WeakReference<T>::create(value.get())); }
-};
-
 } // namespace WTF
 
+namespace base {
+
+template <typename T>
+struct IsWeakReceiver<blink::WeakPersistent<T>> : std::true_type {};

[sof, 2016/06/24 08:56:02]

It would be good to have (HeapTest) unit tests for this.

[tzik, 2016/06/24 09:41:41]

Done.

+
+template <typename T>
+struct IsWeakReceiver<blink::CrossThreadWeakPersistent<T>> : std::true_type {};
+
+}
+
+
 #endif // Persistent_h