/*

 * Copyright (C) 2007, 2008, 2010 Apple Inc. All rights reserved.

 * Copyright (C) 2007 Justin Haygood (jhaygood@reaktix.com)

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * 1.  Redistributions of source code must retain the above copyright

 *     notice, this list of conditions and the following disclaimer. 

 * 2.  Redistributions in binary form must reproduce the above copyright

 *     notice, this list of conditions and the following disclaimer in the

 *     documentation and/or other materials provided with the distribution. 

 * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of

 *     its contributors may be used to endorse or promote products derived

 *     from this software without specific prior written permission. 

 *

 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY

 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

 * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY

 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES

 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;

 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND

 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 *

 *

 * Note: The implementations of InterlockedIncrement and InterlockedDecrement are based

 * on atomic_increment and atomic_exchange_and_add from the Boost C++ Library. The license

 * is virtually identical to the Apple license above but is included here for completeness.

 *

 * Boost Software License - Version 1.0 - August 17th, 2003

 * 

 * Permission is hereby granted, free of charge, to any person or organization

 * obtaining a copy of the software and accompanying documentation covered by

 * this license (the "Software") to use, reproduce, display, distribute,

 * execute, and transmit the Software, and to prepare derivative works of the

 * Software, and to permit third-parties to whom the Software is furnished to

 * do so, all subject to the following:

 * 

 * The copyright notices in the Software and this entire statement, including

 * the above license grant, this restriction and the following disclaimer,

 * must be included in all copies of the Software, in whole or in part, and

 * all derivative works of the Software, unless such copies or derivative

 * works are solely in the form of machine-executable object code generated by

 * a source language processor.

 * 

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT

 * SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE

 * FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,

 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER

 * DEALINGS IN THE SOFTWARE.

 */

#ifndef ThreadSafeShared_h

#define ThreadSafeShared_h

#include "Platform.h"

#include <wtf/Atomics.h>

#include <wtf/Noncopyable.h>

#include <wtf/ThreadingPrimitives.h>

namespace WTF {

class ThreadSafeSharedBase : public Noncopyable {

public:

    ThreadSafeSharedBase(int initialRefCount = 1)

        : m_refCount(initialRefCount)

    {

    }

    void ref()

    {

#if USE(LOCKFREE_THREADSAFESHARED)

        atomicIncrement(&m_refCount);

#else

        MutexLocker locker(m_mutex);

        ++m_refCount;

#endif

    }

    bool hasOneRef()

    {

        return refCount() == 1;

    }

    int refCount() const

    {

#if !USE(LOCKFREE_THREADSAFESHARED)

        MutexLocker locker(m_mutex);

#endif

        return static_cast<int const volatile &>(m_refCount);

    }

protected:

    // Returns whether the pointer should be freed or not.

    bool derefBase()

    {

#if USE(LOCKFREE_THREADSAFESHARED)

        if (atomicDecrement(&m_refCount) <= 0)

            return true;

#else

        int refCount;

        {

            MutexLocker locker(m_mutex);

            --m_refCount;

            refCount = m_refCount;

        }

        if (refCount <= 0)

            return true;

#endif

        return false;

    }

private:

    template<class T>

    friend class CrossThreadRefCounted;

    int m_refCount;

#if !USE(LOCKFREE_THREADSAFESHARED)

    mutable Mutex m_mutex;

#endif

};

template<class T> class ThreadSafeShared : public ThreadSafeSharedBase {

public:

    void deref()

    {

        if (derefBase())

            delete static_cast<T*>(this);

    }

protected:

    ThreadSafeShared()

    {

    }

};

} // namespace WTF

using WTF::ThreadSafeShared;

#endif // ThreadSafeShared_h