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Diffstat (limited to 'JavaScriptCore/runtime/WeakGCMap.h')
-rw-r--r-- | JavaScriptCore/runtime/WeakGCMap.h | 122 |
1 files changed, 122 insertions, 0 deletions
diff --git a/JavaScriptCore/runtime/WeakGCMap.h b/JavaScriptCore/runtime/WeakGCMap.h new file mode 100644 index 0000000..39a91c5 --- /dev/null +++ b/JavaScriptCore/runtime/WeakGCMap.h @@ -0,0 +1,122 @@ +/* + * 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 |