Split out Members, Persistents and SelfKeepAlive in separate headers.

third_party/WebKit/Source/platform/heap/Member.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 Member_h
+#define Member_h
+
+#include "wtf/Allocator.h"
+#include "wtf/HashFunctions.h"
+
+namespace blink {
+
+template<typename T> class Persistent;
+
+// Members are used in classes to contain strong pointers to other oilpan heap
+// allocated objects.
+// All Member fields of a class must be traced in the class' trace method.
+// During the mark phase of the GC all live objects are marked as live and
+// all Member fields of a live object will be traced marked as live as well.
+template<typename T>
+class Member {
+    DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
+public:
+    Member() : m_raw(nullptr)
+    {
+    }
+
+    Member(std::nullptr_t) : m_raw(nullptr)
+    {
+    }
+
+    Member(T* raw) : m_raw(raw)
+    {
+        checkPointer();
+    }
+
+    explicit Member(T& raw) : m_raw(&raw)
+    {
+        checkPointer();
+    }
+
+    Member(WTF::HashTableDeletedValueType) : m_raw(reinterpret_cast<T*>(-1))
+    {
+    }
+
+    bool isHashTableDeletedValue() const { return m_raw == reinterpret_cast<T*>(-1); }
+
+    Member(const Member& other) : m_raw(other)
+    {
+        checkPointer();
+    }
+
+    template<typename U>
+    Member(const Persistent<U>& other)
+    {
+        m_raw = other;
+        checkPointer();
+    }
+
+    template<typename U>
+    Member(const Member<U>& other) : m_raw(other)
+    {
+        checkPointer();
+    }
+
+    T* release()
+    {
+        T* result = m_raw;
+        m_raw = nullptr;
+        return result;
+    }
+
+    explicit operator bool() const { return m_raw; }
+
+    operator T*() const { return m_raw; }
+
+    T* operator->() const { return m_raw; }
+    T& operator*() const { return *m_raw; }
+
+    template<typename U>
+    Member& operator=(const Persistent<U>& other)
+    {
+        m_raw = other;
+        checkPointer();
+        return *this;
+    }
+
+    template<typename U>
+    Member& operator=(const Member<U>& other)
+    {
+        m_raw = other;
+        checkPointer();
+        return *this;
+    }
+
+    template<typename U>
+    Member& operator=(U* other)
+    {
+        m_raw = other;
+        checkPointer();
+        return *this;
+    }
+
+    Member& operator=(std::nullptr_t)
+    {
+        m_raw = nullptr;
+        return *this;
+    }
+
+    void swap(Member<T>& other)
+    {
+        std::swap(m_raw, other.m_raw);
+        checkPointer();
+    }
+
+    T* get() const { return m_raw; }
+
+    void clear() { m_raw = nullptr; }
+
+
+protected:
+    void checkPointer()
+    {
+#if ENABLE(ASSERT) && defined(ADDRESS_SANITIZER)
+        if (!m_raw)
+            return;
+        // HashTable can store a special value (which is not aligned to the
+        // allocation granularity) to Member<> to represent a deleted entry.
+        // Thus we treat a pointer that is not aligned to the granularity
+        // as a valid pointer.
+        if (reinterpret_cast<intptr_t>(m_raw) % allocationGranularity)
+            return;
+
+        // TODO(haraken): What we really want to check here is that the pointer
+        // is a traceable object. In other words, the pointer is either of:
+        //
+        //   (a) a pointer to the head of an on-heap object.
+        //   (b) a pointer to the head of an on-heap mixin object.
+        //
+        // We can check it by calling ThreadHeap::isHeapObjectAlive(m_raw),
+        // but we cannot call it here because it requires to include T.h.
+        // So we currently only try to implement the check for (a), but do
+        // not insist that T's definition is in scope.
+        if (IsFullyDefined<T>::value && !IsGarbageCollectedMixin<T>::value)
+            ASSERT(HeapObjectHeader::fromPayload(m_raw)->checkHeader());
+#endif
+    }
+
+    T* m_raw;
+
+    template<bool x, WTF::WeakHandlingFlag y, WTF::ShouldWeakPointersBeMarkedStrongly z, typename U, typename V> friend struct CollectionBackingTraceTrait;
+    friend class Visitor;
+
+};
+
+// WeakMember is similar to Member in that it is used to point to other oilpan
+// heap allocated objects.
+// However instead of creating a strong pointer to the object, the WeakMember creates
+// a weak pointer, which does not keep the pointee alive. Hence if all pointers to
+// to a heap allocated object are weak the object will be garbage collected. At the
+// time of GC the weak pointers will automatically be set to null.
+template<typename T>
+class WeakMember : public Member<T> {
+public:
+    WeakMember() : Member<T>() { }
+
+    WeakMember(std::nullptr_t) : Member<T>(nullptr) { }
+
+    WeakMember(T* raw) : Member<T>(raw) { }
+
+    WeakMember(WTF::HashTableDeletedValueType x) : Member<T>(x) { }
+
+    template<typename U>
+    WeakMember(const Persistent<U>& other) : Member<T>(other) { }
+
+    template<typename U>
+    WeakMember(const Member<U>& other) : Member<T>(other) { }
+
+    template<typename U>
+    WeakMember& operator=(const Persistent<U>& other)
+    {
+        this->m_raw = other;
+        this->checkPointer();
+        return *this;
+    }
+
+    template<typename U>
+    WeakMember& operator=(const Member<U>& other)
+    {
+        this->m_raw = other;
+        this->checkPointer();
+        return *this;
+    }
+
+    template<typename U>
+    WeakMember& operator=(U* other)
+    {
+        this->m_raw = other;
+        this->checkPointer();
+        return *this;
+    }
+
+    WeakMember& operator=(std::nullptr_t)
+    {
+        this->m_raw = nullptr;
+        return *this;
+    }
+
+private:
+    T** cell() const { return const_cast<T**>(&this->m_raw); }
+
+    template<typename Derived> friend class VisitorHelper;
+};
+
+// UntracedMember is a pointer to an on-heap object that is not traced for some
+// reason. Please don't use this unless you understand what you're doing.
+// Basically, all pointers to on-heap objects must be stored in either of
+// Persistent, Member or WeakMember. It is not allowed to leave raw pointers to
+// on-heap objects. However, there can be scenarios where you have to use raw
+// pointers for some reason, and in that case you can use UntracedMember. Of
+// course, it must be guaranteed that the pointing on-heap object is kept alive
+// while the raw pointer is pointing to the object.
+template<typename T>
+class UntracedMember final : public Member<T> {
+public:
+    UntracedMember() : Member<T>() { }
+
+    UntracedMember(std::nullptr_t) : Member<T>(nullptr) { }
+
+    UntracedMember(T* raw) : Member<T>(raw) { }
+
+    template<typename U>
+    UntracedMember(const Persistent<U>& other) : Member<T>(other) { }
+
+    template<typename U>
+    UntracedMember(const Member<U>& other) : Member<T>(other) { }
+
+    UntracedMember(WTF::HashTableDeletedValueType x) : Member<T>(x) { }
+
+    template<typename U>
+    UntracedMember& operator=(const Persistent<U>& other)
+    {
+        this->m_raw = other;
+        this->checkPointer();
+        return *this;
+    }
+
+    template<typename U>
+    UntracedMember& operator=(const Member<U>& other)
+    {
+        this->m_raw = other;
+        this->checkPointer();
+        return *this;
+    }
+
+    template<typename U>
+    UntracedMember& operator=(U* other)
+    {
+        this->m_raw = other;
+        this->checkPointer();
+        return *this;
+    }
+
+    UntracedMember& operator=(std::nullptr_t)
+    {
+        this->m_raw = nullptr;
+        return *this;
+    }
+};
+
+} // namespace blink
+
+namespace WTF {
+
+template <typename T>
+struct MemberHash : PtrHash<T> {
+    STATIC_ONLY(MemberHash);
+    template <typename U>
+    static unsigned hash(const U& key) { return PtrHash<T>::hash(key); }
+    template <typename U, typename V>
+    static bool equal(const U& a, const V& b) { return a == b; }
+};
+
+template <typename T>
+struct WeakMemberHash : MemberHash<T> {
+    STATIC_ONLY(WeakMemberHash);
+};
+
+template <typename T>
+struct UntracedMemberHash : MemberHash<T> {
+    STATIC_ONLY(UntracedMemberHash);
+};
+
+// PtrHash is the default hash for hash tables with members.
+template <typename T>
+struct DefaultHash<blink::Member<T>> {
+    STATIC_ONLY(DefaultHash);
+    using Hash = MemberHash<T>;
+};
+
+template <typename T>
+struct DefaultHash<blink::WeakMember<T>> {
+    STATIC_ONLY(DefaultHash);
+    using Hash = WeakMemberHash<T>;
+};
+
+template <typename T>
+struct DefaultHash<blink::UntracedMember<T>> {
+    STATIC_ONLY(DefaultHash);
+    using Hash = UntracedMemberHash<T>;
+};
+
+template<typename T>
+struct NeedsTracing<blink::Member<T>> {
+    STATIC_ONLY(NeedsTracing);
+    static const bool value = true;
+};
+
+template<typename T>
+struct IsWeak<blink::WeakMember<T>> {
+    STATIC_ONLY(IsWeak);
+    static const bool value = true;
+};
+
+} // namespace WTF
+
+#endif // Member_h
+