Oilpan: DOM wrappers don't need to keep persistent handles

Source/platform/heap/Handle.h

 /*
  * Copyright (C) 2014 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 132 matching lines @@
 
 private:
     PersistentNode* m_next;
     PersistentNode* m_prev;
 
     template<typename RootsAccessor, typename Owner> friend class PersistentBase;
     friend class PersistentAnchor;
     friend class ThreadState;
 };
 
-
-const int wrapperPersistentsPerRegion = 256;
-const size_t wrapperPersistentOffsetMask = ~static_cast<size_t>(3);
-const size_t wrapperPersistentLiveBitMask = 1;
-
-class WrapperPersistentNode {
-    ALLOW_ONLY_INLINE_ALLOCATION();
-    WTF_MAKE_NONCOPYABLE(WrapperPersistentNode);
-public:
-    bool isAlive() { return m_regionOffset & wrapperPersistentLiveBitMask; }
-
-    WrapperPersistentRegion* region()
-    {
-        return reinterpret_cast<WrapperPersistentRegion*>(
-            reinterpret_cast<Address>(this) - regionOffset());
-    }
-
-    virtual void trace(Visitor* visitor) { }
-
-    static inline void destroy(const WrapperPersistentNode*);
-
-protected:
-    WrapperPersistentNode() : m_raw(0), m_regionOffset(0) { }
-    WrapperPersistentNode(void *raw, size_t regionOffset) : m_raw(raw), m_regionOffset(regionOffset) { }
-
-private:
-    size_t regionOffset() { return m_regionOffset & wrapperPersistentOffsetMask; }
-
-    WrapperPersistentNode* takeSlot()
-    {
-        // The slot should not be alive at the point where it is allocated.
-        ASSERT(!isAlive());
-        WrapperPersistentNode* nextFree = reinterpret_cast<WrapperPersistentNode*>(m_raw);
-        m_raw = 0;
-        return nextFree;
-    }
-
-    WrapperPersistentNode* freeSlot(WrapperPersistentNode* nextFree)
-    {
-        m_regionOffset &= ~wrapperPersistentLiveBitMask;
-        m_raw = nextFree;
-        return this;
-    }
-
-    // Don't allow delete being called on wrapper persistent nodes. We
-    // do use placement new to initialize the slot with the right vtable. See
-    // WrapperPersistent<T> below.
-    void operator delete(void*);
-
-protected:
-    // m_raw is used both to point to the object when the WrapperPersistentNode is used/alive
-    // and to point to the next free wrapperPersistentNode in the region when the node is
-    // unused/dead.
-    void* m_raw;
-
-    // The m_regionOffset field encodes liveness of the slot as well as being an
-    // offset from this node to the base of the containing WrapperPersistentRegion.
-    size_t m_regionOffset;
-
-    friend class WrapperPersistentRegion;
-};
-
-template<typename T>
-class WrapperPersistent final : public WrapperPersistentNode {
-    ALLOW_ONLY_INLINE_ALLOCATION();
-public:
-    static WrapperPersistent<T>* create(T* raw);
-
-    virtual void trace(Visitor* visitor) override
-    {
-        ASSERT(isAlive());
-        visitor->mark(static_cast<T*>(m_raw));
-    }
-
-private:
-    WrapperPersistent() { }
-
-    // We need to use a constructor to initialize the allocated slot since it
-    // has a vtable which must be set to the WrapperPersistent<T> type.
-    WrapperPersistent(T* raw, size_t regionOffset) : WrapperPersistentNode(raw, regionOffset) { }
-
-    // Don't allow delete being called on wrapper persistents.
-    void operator delete(void*);
-};
-
-class PLATFORM_EXPORT WrapperPersistentRegion {
-    WTF_MAKE_NONCOPYABLE(WrapperPersistentRegion);
-public:
-    WrapperPersistentRegion()
-    {
-        WrapperPersistentNode* nextFree = 0;
-        for (int i = wrapperPersistentsPerRegion - 1; i >= 0; --i) {
-            size_t regionOffset = reinterpret_cast<Address>(&m_entries[i]) - reinterpret_cast<Address>(this);
-            // Setup the free slot with an offset to the containing region's base and a pointer to the next
-            // free slot in the region.
-            ASSERT(!(regionOffset & ~wrapperPersistentOffsetMask));
-            new (&m_entries[i]) WrapperPersistentNode(nextFree, regionOffset);
-            nextFree = &m_entries[i];
-        }
-        m_prev = 0;
-        m_next = 0;
-        m_freeHead = nextFree;
-        m_count = 0;
-    }
-
-    Address allocate()
-    {
-        if (!m_freeHead) {
-            ASSERT(m_count == wrapperPersistentsPerRegion);
-            return 0;
-        }
-        // We have a free persistent slot in this region.
-        WrapperPersistentNode* freeSlot = m_freeHead;
-        // Take the slot and advance m_freeHead to the next free slot.
-        m_freeHead = freeSlot->takeSlot();
-        ASSERT(m_count < wrapperPersistentsPerRegion);
-        m_count++;
-        return reinterpret_cast<Address>(freeSlot);
-    }
-
-    void free(WrapperPersistentNode* object)
-    {
-        ASSERT(object);
-        m_freeHead = object->freeSlot(m_freeHead);
-        ASSERT(m_count > 0);
-        m_count--;
-        if (!m_count)
-            ThreadState::current()->freeWrapperPersistentRegion(this);
-    }
-
-    bool removeIfNotLast(WrapperPersistentRegion** headPtr);
-    static void insertHead(WrapperPersistentRegion** headPtr, WrapperPersistentRegion* newHead);
-    static WrapperPersistentRegion* removeHead(WrapperPersistentRegion** headPtr);
-    static Address outOfLineAllocate(ThreadState*, WrapperPersistentRegion**);
-    static void trace(WrapperPersistentRegion* head, Visitor* visitor)
-    {
-        for (WrapperPersistentRegion* current = head; current; current = current->m_next)
-            current->traceRegion(visitor);
-    }
-
-private:
-    void traceRegion(Visitor* visitor)
-    {
-        size_t live = 0;
-
-#ifdef NDEBUG
-        for (int i = 0; i < wrapperPersistentsPerRegion && live < m_count; ++i) {
-#else
-        // In DEBUG mode we scan all entries to validate we only have m_count
-        // live entries.
-        for (int i = 0; i < wrapperPersistentsPerRegion; ++i) {
-#endif
-            if (m_entries[i].isAlive()) {
-                m_entries[i].trace(visitor);
-                live++;
-            }
-        }
-        ASSERT(live == m_count);
-    }
-
-    WrapperPersistentRegion* m_prev;
-    WrapperPersistentRegion* m_next;
-    WrapperPersistentNode* m_freeHead;
-    size_t m_count;
-    WrapperPersistentNode m_entries[wrapperPersistentsPerRegion];
-};
-
-template<typename T>
-WrapperPersistent<T>* WrapperPersistent<T>::create(T* raw)
-{
-    ThreadState* state = ThreadState::current();
-    WrapperPersistentRegion* region = state->wrapperRoots();
-    ASSERT(region);
-    Address persistentSlot = region->allocate();
-    if (!persistentSlot)
-        persistentSlot = WrapperPersistentRegion::outOfLineAllocate(state, &region);
-    ASSERT(persistentSlot);
-    ASSERT(!reinterpret_cast<WrapperPersistentNode*>(persistentSlot)->isAlive());
-
-    size_t regionOffset = persistentSlot - reinterpret_cast<Address>(region);
-    regionOffset |= wrapperPersistentLiveBitMask;
-
-    // We use placement new to call the constructor to ensure that we setup the
-    // vtable correctly.
-    return new (persistentSlot) WrapperPersistent<T>(raw, regionOffset);
-}
-
-void WrapperPersistentNode::destroy(const WrapperPersistentNode* node)
-{
-    WrapperPersistentNode* persistent = const_cast<WrapperPersistentNode*>(node);
-    persistent->region()->free(persistent);
-}
-
 // RootsAccessor for Persistent that provides access to thread-local list
 // of persistent handles. Can only be used to create handles that
 // are constructed and destructed on the same thread.
 template<ThreadAffinity Affinity>
 class ThreadLocalPersistents {
 public:
     static PersistentNode* roots() { return state()->roots(); }
 
     // No locking required. Just check that we are at the right thread.
     class Lock {
@@ skipping 993 matching lines @@
 struct ParamStorageTraits<T*> : public PointerParamStorageTraits<T*, blink::IsGarbageCollectedType<T>::value> {
 };
 
 template<typename T>
 struct ParamStorageTraits<RawPtr<T> > : public PointerParamStorageTraits<T*, blink::IsGarbageCollectedType<T>::value> {
 };
 
 } // namespace WTF
 
 #endif