/*

 * Copyright (C) 2009 Apple 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:

 * 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.

 *

 * THIS SOFTWARE IS PROVIDED BY APPLE INC. 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 INC. 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.

 */

#ifndef WeakGCMap_h

#define WeakGCMap_h

#include "Collector.h"

#include <wtf/HashMap.h>

namespace JSC {

class JSCell;

// A HashMap whose get() function returns emptyValue() for cells awaiting destruction.

template<typename KeyType, typename MappedType>

class WeakGCMap : public FastAllocBase {

    /*

    Invariants:

        * A value enters the WeakGCMap marked. (Guaranteed by set().)

        * A value that becomes unmarked leaves the WeakGCMap before being recycled. (Guaranteed by the value's destructor removing it from the WeakGCMap.)

        * A value that becomes unmarked leaves the WeakGCMap before becoming marked again. (Guaranteed by all destructors running before the mark phase begins.)

        * During the mark phase, all values in the WeakGCMap are valid. (Guaranteed by all destructors running before the mark phase begins.)

    */

public:

    typedef typename HashMap<KeyType, MappedType>::iterator iterator;

    typedef typename HashMap<KeyType, MappedType>::const_iterator const_iterator;

    bool isEmpty() { return m_map.isEmpty(); }

    MappedType get(const KeyType& key) const;

    pair<iterator, bool> set(const KeyType&, const MappedType&); 

    MappedType take(const KeyType& key);

    // These unchecked functions provide access to a value even if the value's

    // mark bit is not set. This is used, among other things, to retrieve values

    // during the GC mark phase, which begins by clearing all mark bits.

    MappedType uncheckedGet(const KeyType& key) const { return m_map.get(key); }

    bool uncheckedRemove(const KeyType&, const MappedType&);

    iterator uncheckedBegin() { return m_map.begin(); }

    iterator uncheckedEnd() { return m_map.end(); }

    const_iterator uncheckedBegin() const { return m_map.begin(); }

    const_iterator uncheckedEnd() const { return m_map.end(); }

private:

    HashMap<KeyType, MappedType> m_map;

};

template<typename KeyType, typename MappedType>

inline MappedType WeakGCMap<KeyType, MappedType>::get(const KeyType& key) const

{

    MappedType result = m_map.get(key);

    if (result == HashTraits<MappedType>::emptyValue())

        return result;

    if (!Heap::isCellMarked(result))

        return HashTraits<MappedType>::emptyValue();

    return result;

}

template<typename KeyType, typename MappedType>

MappedType WeakGCMap<KeyType, MappedType>::take(const KeyType& key)

{

    MappedType result = m_map.take(key);

    if (result == HashTraits<MappedType>::emptyValue())

        return result;

    if (!Heap::isCellMarked(result))

        return HashTraits<MappedType>::emptyValue();

    return result;

}

template<typename KeyType, typename MappedType>

pair<typename HashMap<KeyType, MappedType>::iterator, bool> WeakGCMap<KeyType, MappedType>::set(const KeyType& key, const MappedType& value)

{

    Heap::markCell(value); // If value is newly allocated, it's not marked, so mark it now.

    pair<iterator, bool> result = m_map.add(key, value);

    if (!result.second) { // pre-existing entry

        result.second = !Heap::isCellMarked(result.first->second);

        result.first->second = value;

    }

    return result;

}

template<typename KeyType, typename MappedType>

bool WeakGCMap<KeyType, MappedType>::uncheckedRemove(const KeyType& key, const MappedType& value)

{

    iterator it = m_map.find(key);

    if (it == m_map.end())

        return false;

    if (it->second != value)

        return false;

    m_map.remove(it);

    return true;

}

} // namespace JSC

#endif // WeakGCMap_h