root/Source/core/dom/TreeShared.h

INCLUDED FROM

/*
 * Copyright (C) 2006, 2007, 2009, 2010, 2012 Apple Inc. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

#ifndef TreeShared_h
#define TreeShared_h

#include "public/platform/WebPrivatePtr.h"
#include "wtf/Assertions.h"
#include "wtf/MainThread.h"
#include "wtf/Noncopyable.h"

namespace WebCore {

#if SECURITY_ASSERT_ENABLED
template<typename NodeType> class TreeShared;
template<typename NodeType> void adopted(TreeShared<NodeType>*);
#endif

template<typename NodeType> class TreeShared : public NoBaseWillBeGarbageCollectedFinalized<NodeType> {
    WTF_MAKE_NONCOPYABLE(TreeShared);
protected:
    TreeShared()
        : m_refCount(1)
#if ENABLE(OILPAN)
        , m_keepAlive(adoptPtr(new Persistent<NodeType>(static_cast<NodeType*>(this))))
#endif
#if SECURITY_ASSERT_ENABLED
        , m_deletionHasBegun(false)
#if ASSERT_ENABLED
        , m_inRemovedLastRefFunction(false)
        , m_adoptionIsRequired(true)
#endif
#endif
    {
        ASSERT(isMainThread());
    }

    ~TreeShared()
    {
        ASSERT(isMainThread());
        ASSERT(!m_refCount);
#if !ENABLE(OILPAN)
        ASSERT_WITH_SECURITY_IMPLICATION(m_deletionHasBegun);
#else
        ASSERT(!m_keepAlive);
#endif
        ASSERT(!m_adoptionIsRequired);
    }

public:
    void ref()
    {
        ASSERT(isMainThread());
#if !ENABLE(OILPAN)
        ASSERT_WITH_SECURITY_IMPLICATION(!m_deletionHasBegun);
        ASSERT(!m_inRemovedLastRefFunction);
#endif
        ASSERT(!m_adoptionIsRequired);
        ++m_refCount;
#if ENABLE(OILPAN)
        if (!m_keepAlive)
            m_keepAlive = adoptPtr(new Persistent<NodeType>(static_cast<NodeType*>(this)));
#endif
    }

    void deref()
    {
        ASSERT(isMainThread());
        ASSERT(m_refCount > 0);
#if !ENABLE(OILPAN)
        ASSERT_WITH_SECURITY_IMPLICATION(!m_deletionHasBegun);
        ASSERT(!m_inRemovedLastRefFunction);
#endif
        ASSERT(!m_adoptionIsRequired);
        NodeType* thisNode = static_cast<NodeType*>(this);
        if (!--m_refCount && !thisNode->hasTreeSharedParent()) {
#if !ASSERT_DISABLED
            m_inRemovedLastRefFunction = true;
#endif
#if ENABLE(OILPAN)
            clearKeepAlive();
#endif
            thisNode->removedLastRef();
        }
    }

    int refCount() const { return m_refCount; }

#if ENABLE(OILPAN)
    void clearKeepAlive()
    {
        ASSERT(m_keepAlive);
        m_keepAlive = nullptr;
    }
#endif

private:
    int m_refCount;

#if ENABLE(OILPAN)
    // With Oilpan, a non-zero reference count will keep the TreeShared object alive
    // with a self-persistent handle. Whenever the ref count goes above zero
    // we register the TreeShared as a root for garbage collection by allocating a
    // persistent handle to the object itself. When the ref count goes to zero
    // we deallocate the persistent handle again so the object can die if there
    // are no other things keeping it alive.
    //
    // FIXME: Oilpan: Remove m_keepAlive and ref counting and use tracing instead.
    OwnPtr<Persistent<NodeType> > m_keepAlive;
#endif

#if SECURITY_ASSERT_ENABLED
public:
    bool m_deletionHasBegun;
#if ASSERT_ENABLED
    bool m_inRemovedLastRefFunction;

private:
    friend void adopted<>(TreeShared<NodeType>*);
    bool m_adoptionIsRequired;
#endif
#endif
};

#if SECURITY_ASSERT_ENABLED
template<typename NodeType> inline void adopted(TreeShared<NodeType>* object)
{
    if (!object)
        return;

    ASSERT_WITH_SECURITY_IMPLICATION(!object->m_deletionHasBegun);
#if !ASSERT_DISABLED
    ASSERT(!object->m_inRemovedLastRefFunction);
    object->m_adoptionIsRequired = false;
#endif
}
#endif

}

#endif // TreeShared.h