Source/wtf/RefCounted.h

/*
 * Copyright (C) 2006, 2007, 2008, 2009, 2010 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 RefCounted_h
#define RefCounted_h

#include <wtf/Assertions.h>
#include <wtf/FastAllocBase.h>
#include <wtf/Noncopyable.h>
#include <wtf/OwnPtr.h>
#include <wtf/ThreadRestrictionVerifier.h>
#include <wtf/UnusedParam.h>

namespace WTF {

#ifdef NDEBUG
#define CHECK_REF_COUNTED_LIFECYCLE 0
#else
#define CHECK_REF_COUNTED_LIFECYCLE 1
#endif

// This base class holds the non-template methods and attributes.
// The RefCounted class inherits from it reducing the template bloat
// generated by the compiler (technique called template hoisting).
class RefCountedBase {
public:
    void ref()
    {
#if CHECK_REF_COUNTED_LIFECYCLE
        // Start thread verification as soon as the ref count gets to 2. This
        // heuristic reflects the fact that items are often created on one thread
        // and then given to another thread to be used.
        // FIXME: Make this restriction tigher. Especially as we move to more
        // common methods for sharing items across threads like CrossThreadCopier.h
        // We should be able to add a "detachFromThread" method to make this explicit.
        if (m_refCount == 1)
            m_verifier.setShared(true);
        // If this assert fires, it either indicates a thread safety issue or
        // that the verification needs to change. See ThreadRestrictionVerifier for
        // the different modes.
        ASSERT(m_verifier.isSafeToUse());
        ASSERT(!m_deletionHasBegun);
        ASSERT(!m_adoptionIsRequired);
#endif
        ++m_refCount;
    }

    bool hasOneRef() const
    {
#if CHECK_REF_COUNTED_LIFECYCLE
        ASSERT(m_verifier.isSafeToUse());
        ASSERT(!m_deletionHasBegun);
#endif
        return m_refCount == 1;
    }

    int refCount() const
    {
#if CHECK_REF_COUNTED_LIFECYCLE
        ASSERT(m_verifier.isSafeToUse());
#endif
        return m_refCount;
    }

    void relaxAdoptionRequirement()
    {
#if CHECK_REF_COUNTED_LIFECYCLE
        ASSERT(!m_deletionHasBegun);
        ASSERT(m_adoptionIsRequired);
        m_adoptionIsRequired = false;
#endif
    }

protected:
    RefCountedBase()
        : m_refCount(1)
#if CHECK_REF_COUNTED_LIFECYCLE
        , m_deletionHasBegun(false)
        , m_adoptionIsRequired(true)
#endif
    {
    }

    ~RefCountedBase()
    {
#if CHECK_REF_COUNTED_LIFECYCLE
        ASSERT(m_deletionHasBegun);
        ASSERT(!m_adoptionIsRequired);
#endif
    }

    // Returns whether the pointer should be freed or not.
    bool derefBase()
    {
#if CHECK_REF_COUNTED_LIFECYCLE
        ASSERT(m_verifier.isSafeToUse());
        ASSERT(!m_deletionHasBegun);
        ASSERT(!m_adoptionIsRequired);
#endif

        ASSERT(m_refCount > 0);
        if (m_refCount == 1) {
#if CHECK_REF_COUNTED_LIFECYCLE
            m_deletionHasBegun = true;
#endif
            return true;
        }

        --m_refCount;
#if CHECK_REF_COUNTED_LIFECYCLE
        // Stop thread verification when the ref goes to 1 because it
        // is safe to be passed to another thread at this point.
        if (m_refCount == 1)
            m_verifier.setShared(false);
#endif
        return false;
    }

#if CHECK_REF_COUNTED_LIFECYCLE
    bool deletionHasBegun() const
    {
        return m_deletionHasBegun;
    }
#endif

private:

#if CHECK_REF_COUNTED_LIFECYCLE
    friend void adopted(RefCountedBase*);
#endif

    int m_refCount;
#if CHECK_REF_COUNTED_LIFECYCLE
    bool m_deletionHasBegun;
    bool m_adoptionIsRequired;
    ThreadRestrictionVerifier m_verifier;
#endif
};

#if CHECK_REF_COUNTED_LIFECYCLE
inline void adopted(RefCountedBase* object)
{
    if (!object)
        return;
    ASSERT(!object->m_deletionHasBegun);
    object->m_adoptionIsRequired = false;
}
#endif

template<typename T> class RefCounted : public RefCountedBase {
    WTF_MAKE_NONCOPYABLE(RefCounted); WTF_MAKE_FAST_ALLOCATED;
public:
    void deref()
    {
        if (derefBase())
            delete static_cast<T*>(this);
    }

protected:
    RefCounted() { }
    ~RefCounted()
    {
    }
};

template<typename T> class RefCountedCustomAllocated : public RefCountedBase {
    WTF_MAKE_NONCOPYABLE(RefCountedCustomAllocated);

public:
    void deref()
    {
        if (derefBase())
            delete static_cast<T*>(this);
    }

protected:
    ~RefCountedCustomAllocated()
    {
    }
};

} // namespace WTF

using WTF::RefCounted;
using WTF::RefCountedCustomAllocated;

#endif // RefCounted_h