JavaScriptCore-1218.35.tar.gz

[apple/javascriptcore.git] / runtime / WeakGCMap.h

/*
 * Copyright (C) 2009 Apple Inc. All rights reserved.
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 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
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#ifndef WeakGCMap_h
#define WeakGCMap_h

#include <heap/Weak.h>
#include <heap/WeakInlines.h>
#include <wtf/HashMap.h>

namespace JSC {

// A HashMap with Weak<JSCell> values, which automatically removes values once they're garbage collected.

template<typename KeyArg, typename RawMappedArg, typename HashArg = typename DefaultHash<KeyArg>::Hash,
    typename KeyTraitsArg = HashTraits<KeyArg> >
class WeakGCMap : public HashMap<KeyArg, Weak<RawMappedArg>, HashArg, KeyTraitsArg> {
    typedef Weak<RawMappedArg> MappedType;
    typedef HashMap<KeyArg, MappedType, HashArg, KeyTraitsArg> Base;
    typedef WeakGCMap<KeyArg, RawMappedArg, HashArg, KeyTraitsArg> Self;
    typedef HashTraits<MappedType> MappedTraits;
    typedef typename MappedTraits::PassInType MappedPassInType;

public:
    typedef typename Base::KeyType KeyType;
    typedef typename Base::AddResult AddResult;
    typedef typename Base::iterator iterator;
    typedef typename Base::const_iterator const_iterator;
    using Base::begin;
    using Base::end;
    using Base::size;
    using Base::remove;

    WeakGCMap()
        : m_gcThreshold(minGCThreshold)
    {
    }

    AddResult set(const KeyType& key, MappedPassInType value)
    {
        gcMapIfNeeded();
        return Base::set(key, value);
    }

    AddResult add(const KeyType& key, MappedPassInType value)
    {
        gcMapIfNeeded();
        AddResult addResult = Base::add(key, nullptr);
        if (!addResult.iterator->value) { // New value or found a zombie value.
            addResult.isNewEntry = true;
            addResult.iterator->value = value;
        }
        return addResult;
    }

    iterator find(const KeyType& key)
    {
        iterator it = Base::find(key);
        iterator end = Base::end();
        if (it != end && !it->value) // Found a zombie value.
            return end;
        return it;
    }

    const_iterator find(const KeyType& key) const
    {
        return const_cast<Self*>(this)->find(key);
    }

    bool contains(const KeyType& key) const
    {
        return find(key) != end();
    }

private:
    static const int minGCThreshold = 3;

    void gcMap()
    {
        Vector<KeyType, 4> zombies;
        iterator end = this->end();
        for (iterator it = begin(); it != end; ++it) {
            if (!it->value)
                zombies.append(it->key);
        }
        for (size_t i = 0; i < zombies.size(); ++i)
            remove(zombies[i]);
    }

    void gcMapIfNeeded()
    {
        if (size() < m_gcThreshold)
            return;

        gcMap();
        m_gcThreshold = std::max(minGCThreshold, size() * 2 - 1);
    }

    int m_gcThreshold;
};

template<typename KeyArg, typename RawMappedArg, typename HashArg, typename KeyTraitsArg>
const int WeakGCMap<KeyArg, RawMappedArg, HashArg, KeyTraitsArg>::minGCThreshold;

} // namespace JSC

#endif // WeakGCMap_h