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	1	/*
	2	* Copyright (C) 2009 Apple Inc. All rights reserved.
	3	*
	4	* Redistribution and use in source and binary forms, with or without
	5	* modification, are permitted provided that the following conditions
	6	* are met:
	7	* 1. Redistributions of source code must retain the above copyright
	8	* notice, this list of conditions and the following disclaimer.
	9	* 2. Redistributions in binary form must reproduce the above copyright
	10	* notice, this list of conditions and the following disclaimer in the
	11	* documentation and/or other materials provided with the distribution.
	12	*
	13	* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
	14	* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
	15	* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
	16	* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
	17	* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
	18	* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
	19	* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
	20	* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
	21	* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	22	* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
	23	* THE POSSIBILITY OF SUCH DAMAGE.
	24	*/
	25
	26	#ifndef WeakGCMap_h
	27	#define WeakGCMap_h
	28
	29	#include "Collector.h"
	30	#include <wtf/HashMap.h>
	31
	32	namespace JSC {
	33
	34	class JSCell;
	35
	36	// A HashMap whose get() function returns emptyValue() for cells awaiting destruction.
	37	template<typename KeyType, typename MappedType>
	38	class WeakGCMap : public FastAllocBase {
	39	/*
	40	Invariants:
	41	* A value enters the WeakGCMap marked. (Guaranteed by set().)
	42	* A value that becomes unmarked leaves the WeakGCMap before being recycled. (Guaranteed by the value's destructor removing it from the WeakGCMap.)
	43	* A value that becomes unmarked leaves the WeakGCMap before becoming marked again. (Guaranteed by all destructors running before the mark phase begins.)
	44	* During the mark phase, all values in the WeakGCMap are valid. (Guaranteed by all destructors running before the mark phase begins.)
	45	*/
	46
	47	public:
	48	typedef typename HashMap<KeyType, MappedType>::iterator iterator;
	49	typedef typename HashMap<KeyType, MappedType>::const_iterator const_iterator;
	50
	51	bool isEmpty() { return m_map.isEmpty(); }
	52
	53	MappedType get(const KeyType& key) const;
	54	pair<iterator, bool> set(const KeyType&, const MappedType&);
	55	MappedType take(const KeyType& key);
	56
	57	// These unchecked functions provide access to a value even if the value's
	58	// mark bit is not set. This is used, among other things, to retrieve values
	59	// during the GC mark phase, which begins by clearing all mark bits.
	60
	61	MappedType uncheckedGet(const KeyType& key) const { return m_map.get(key); }
	62	bool uncheckedRemove(const KeyType&, const MappedType&);
	63
	64	iterator uncheckedBegin() { return m_map.begin(); }
	65	iterator uncheckedEnd() { return m_map.end(); }
	66
	67	const_iterator uncheckedBegin() const { return m_map.begin(); }
	68	const_iterator uncheckedEnd() const { return m_map.end(); }
	69
	70	private:
	71	HashMap<KeyType, MappedType> m_map;
	72	};
	73
	74	template<typename KeyType, typename MappedType>
	75	inline MappedType WeakGCMap<KeyType, MappedType>::get(const KeyType& key) const
	76	{
	77	MappedType result = m_map.get(key);
	78	if (result == HashTraits<MappedType>::emptyValue())
	79	return result;
	80	if (!Heap::isCellMarked(result))
	81	return HashTraits<MappedType>::emptyValue();
	82	return result;
	83	}
	84
	85	template<typename KeyType, typename MappedType>
	86	MappedType WeakGCMap<KeyType, MappedType>::take(const KeyType& key)
	87	{
	88	MappedType result = m_map.take(key);
	89	if (result == HashTraits<MappedType>::emptyValue())
	90	return result;
	91	if (!Heap::isCellMarked(result))
	92	return HashTraits<MappedType>::emptyValue();
	93	return result;
	94	}
	95
	96	template<typename KeyType, typename MappedType>
	97	pair<typename HashMap<KeyType, MappedType>::iterator, bool> WeakGCMap<KeyType, MappedType>::set(const KeyType& key, const MappedType& value)
	98	{
	99	Heap::markCell(value); // If value is newly allocated, it's not marked, so mark it now.
	100	pair<iterator, bool> result = m_map.add(key, value);
	101	if (!result.second) { // pre-existing entry
	102	result.second = !Heap::isCellMarked(result.first->second);
	103	result.first->second = value;
	104	}
	105	return result;
	106	}
	107
	108	template<typename KeyType, typename MappedType>
	109	bool WeakGCMap<KeyType, MappedType>::uncheckedRemove(const KeyType& key, const MappedType& value)
	110	{
	111	iterator it = m_map.find(key);
	112	if (it == m_map.end())
	113	return false;
	114	if (it->second != value)
	115	return false;
	116	m_map.remove(it);
	117	return true;
	118	}
	119
	120	} // namespace JSC
	121
	122	#endif // WeakGCMap_h