path: root/chromium/third_party/WebKit/Source/wtf/HashTable.h

/*
 * Copyright (C) 2005, 2006, 2007, 2008, 2011, 2012 Apple Inc. All rights reserved.
 * Copyright (C) 2008 David Levin <levin@chromium.org>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

#ifndef WTF_HashTable_h
#define WTF_HashTable_h

#include "wtf/Alignment.h"
#include "wtf/Assertions.h"
#include "wtf/ConditionalDestructor.h"
#include "wtf/DefaultAllocator.h"
#include "wtf/HashTraits.h"

#define DUMP_HASHTABLE_STATS 0
#define DUMP_HASHTABLE_STATS_PER_TABLE 0

#if DUMP_HASHTABLE_STATS_PER_TABLE
#include "wtf/DataLog.h"
#endif

#if DUMP_HASHTABLE_STATS
#if DUMP_HASHTABLE_STATS_PER_TABLE
#define UPDATE_PROBE_COUNTS()                            \
    ++probeCount;                                        \
    HashTableStats::recordCollisionAtCount(probeCount);  \
    ++perTableProbeCount;                                \
    m_stats->recordCollisionAtCount(perTableProbeCount)
#define UPDATE_ACCESS_COUNTS()                           \
    atomicIncrement(&HashTableStats::numAccesses);       \
    int probeCount = 0;                                  \
    ++m_stats->numAccesses;                              \
    int perTableProbeCount = 0
#else
#define UPDATE_PROBE_COUNTS()                            \
    ++probeCount;                                        \
    HashTableStats::recordCollisionAtCount(probeCount)
#define UPDATE_ACCESS_COUNTS()                           \
    atomicIncrement(&HashTableStats::numAccesses);       \
    int probeCount = 0
#endif
#else
#if DUMP_HASHTABLE_STATS_PER_TABLE
#define UPDATE_PROBE_COUNTS()                            \
    ++perTableProbeCount;                                \
    m_stats->recordCollisionAtCount(perTableProbeCount)
#define UPDATE_ACCESS_COUNTS()                           \
    ++m_stats->numAccesses;                              \
    int perTableProbeCount = 0
#else
#define UPDATE_PROBE_COUNTS() do { } while (0)
#define UPDATE_ACCESS_COUNTS() do { } while (0)
#endif
#endif

namespace WTF {

#if DUMP_HASHTABLE_STATS

struct HashTableStats {
    // The following variables are all atomically incremented when modified.
    static int numAccesses;
    static int numRehashes;
    static int numRemoves;
    static int numReinserts;

    // The following variables are only modified in the recordCollisionAtCount
    // method within a mutex.
    static int maxCollisions;
    static int numCollisions;
    static int collisionGraph[4096];

    static void recordCollisionAtCount(int count);
    static void dumpStats();
};

#endif

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
class HashTable;
template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
class HashTableIterator;
template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
class HashTableConstIterator;
template <typename Value, typename HashFunctions, typename HashTraits, typename Allocator>
class LinkedHashSet;
template <WeakHandlingFlag x, typename T, typename U, typename V, typename W, typename X, typename Y, typename Z>
struct WeakProcessingHashTableHelper;

typedef enum { HashItemKnownGood } HashItemKnownGoodTag;

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
class HashTableConstIterator {
private:
    typedef HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> HashTableType;
    typedef HashTableIterator<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> iterator;
    typedef HashTableConstIterator<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> const_iterator;
    typedef Value ValueType;
    typedef typename Traits::IteratorConstGetType GetType;
    typedef const ValueType* PointerType;

    friend class HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>;
    friend class HashTableIterator<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>;

    void skipEmptyBuckets()
    {
        while (m_position != m_endPosition && HashTableType::isEmptyOrDeletedBucket(*m_position))
            ++m_position;
    }

    HashTableConstIterator(PointerType position, PointerType endPosition, const HashTableType* container)
        : m_position(position)
        , m_endPosition(endPosition)
#if ENABLE(ASSERT)
        , m_container(container)
        , m_containerModifications(container->modifications())
#endif
    {
        skipEmptyBuckets();
    }

    HashTableConstIterator(PointerType position, PointerType endPosition, const HashTableType* container, HashItemKnownGoodTag)
        : m_position(position)
        , m_endPosition(endPosition)
#if ENABLE(ASSERT)
        , m_container(container)
        , m_containerModifications(container->modifications())
#endif
    {
        ASSERT(m_containerModifications == m_container->modifications());
    }

    void checkModifications() const
    {
        // HashTable and collections that build on it do not support
        // modifications while there is an iterator in use. The exception is
        // ListHashSet, which has its own iterators that tolerate modification
        // of the underlying set.
        ASSERT(m_containerModifications == m_container->modifications());
    }

public:
    HashTableConstIterator() {}

    GetType get() const
    {
        checkModifications();
        return m_position;
    }
    typename Traits::IteratorConstReferenceType operator*() const { return Traits::getToReferenceConstConversion(get()); }
    GetType operator->() const { return get(); }

    const_iterator& operator++()
    {
        ASSERT(m_position != m_endPosition);
        checkModifications();
        ++m_position;
        skipEmptyBuckets();
        return *this;
    }

    // postfix ++ intentionally omitted

    // Comparison.
    bool operator==(const const_iterator& other) const
    {
        return m_position == other.m_position;
    }
    bool operator!=(const const_iterator& other) const
    {
        return m_position != other.m_position;
    }
    bool operator==(const iterator& other) const
    {
        return *this == static_cast<const_iterator>(other);
    }
    bool operator!=(const iterator& other) const
    {
        return *this != static_cast<const_iterator>(other);
    }

private:
    PointerType m_position;
    PointerType m_endPosition;
#if ENABLE(ASSERT)
    const HashTableType* m_container;
    int64_t m_containerModifications;
#endif
};

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
class HashTableIterator {
private:
    typedef HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> HashTableType;
    typedef HashTableIterator<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> iterator;
    typedef HashTableConstIterator<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> const_iterator;
    typedef Value ValueType;
    typedef typename Traits::IteratorGetType GetType;
    typedef ValueType* PointerType;

    friend class HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>;

    HashTableIterator(PointerType pos, PointerType end, const HashTableType* container) : m_iterator(pos, end, container) {}
    HashTableIterator(PointerType pos, PointerType end, const HashTableType* container, HashItemKnownGoodTag tag) : m_iterator(pos, end, container, tag) {}

public:
    HashTableIterator() {}

    // default copy, assignment and destructor are OK

    GetType get() const { return const_cast<GetType>(m_iterator.get()); }
    typename Traits::IteratorReferenceType operator*() const { return Traits::getToReferenceConversion(get()); }
    GetType operator->() const { return get(); }

    iterator& operator++() { ++m_iterator; return *this; }

    // postfix ++ intentionally omitted

    // Comparison.
    bool operator==(const iterator& other) const { return m_iterator == other.m_iterator; }
    bool operator!=(const iterator& other) const { return m_iterator != other.m_iterator; }
    bool operator==(const const_iterator& other) const { return m_iterator == other; }
    bool operator!=(const const_iterator& other) const { return m_iterator != other; }

    operator const_iterator() const { return m_iterator; }

private:
    const_iterator m_iterator;
};

using std::swap;

// Work around MSVC's standard library, whose swap for pairs does not swap by component.
template <typename T> inline void hashTableSwap(T& a, T& b)
{
    swap(a, b);
}

template <typename T, typename U> inline void hashTableSwap(KeyValuePair<T, U>& a, KeyValuePair<T, U>& b)
{
    swap(a.key, b.key);
    swap(a.value, b.value);
}

template <typename T, typename Allocator, bool useSwap = !IsTriviallyDestructible<T>::value>
struct Mover;
template <typename T, typename Allocator> struct Mover<T, Allocator, true> {
    static void move(T& from, T& to)
    {
        // The key and value cannot be swapped atomically, and it would be wrong
        // to have a GC when only one was swapped and the other still contained
        // garbage (eg. from a previous use of the same slot).  Therefore we
        // forbid a GC until both the key and the value are swapped.
        Allocator::enterGCForbiddenScope();
        hashTableSwap(from, to);
        Allocator::leaveGCForbiddenScope();
    }
};

template <typename T, typename Allocator> struct Mover<T, Allocator, false> {
    static void move(T& from, T& to) { to = from; }
};

template <typename HashFunctions> class IdentityHashTranslator {
public:
    template <typename T> static unsigned hash(const T& key) { return HashFunctions::hash(key); }
    template <typename T, typename U> static bool equal(const T& a, const U& b) { return HashFunctions::equal(a, b); }
    template <typename T, typename U, typename V> static void translate(T& location, const U&, const V& value) { location = value; }
};

template <typename HashTableType, typename ValueType> struct HashTableAddResult {
    HashTableAddResult(const HashTableType* container, ValueType* storedValue, bool isNewEntry)
        : storedValue(storedValue)
        , isNewEntry(isNewEntry)
#if ENABLE(SECURITY_ASSERT)
        , m_container(container)
        , m_containerModifications(container->modifications())
#endif
    {
        ASSERT_UNUSED(container, container);
    }

    ValueType* storedValue;
    bool isNewEntry;

#if ENABLE(SECURITY_ASSERT)
    ~HashTableAddResult()
    {
        // If rehash happened before accessing storedValue, it's
        // use-after-free. Any modification may cause a rehash, so we check for
        // modifications here.

        // Rehash after accessing storedValue is harmless but will assert if the
        // AddResult destructor takes place after a modification. You may need
        // to limit the scope of the AddResult.
        ASSERT_WITH_SECURITY_IMPLICATION(m_containerModifications == m_container->modifications());
    }

private:
    const HashTableType* m_container;
    const int64_t m_containerModifications;
#endif
};

template <typename Value, typename Extractor, typename KeyTraits>
struct HashTableHelper {
    static bool isEmptyBucket(const Value& value) { return isHashTraitsEmptyValue<KeyTraits>(Extractor::extract(value)); }
    static bool isDeletedBucket(const Value& value) { return KeyTraits::isDeletedValue(Extractor::extract(value)); }
    static bool isEmptyOrDeletedBucket(const Value& value) { return isEmptyBucket(value) || isDeletedBucket(value); }
};

template <typename HashTranslator, typename KeyTraits, bool safeToCompareToEmptyOrDeleted>
struct HashTableKeyChecker {
    // There's no simple generic way to make this check if
    // safeToCompareToEmptyOrDeleted is false, so the check always passes.
    template <typename T>
    static bool checkKey(const T&) { return true; }
};

template <typename HashTranslator, typename KeyTraits>
struct HashTableKeyChecker<HashTranslator, KeyTraits, true> {
    template <typename T>
    static bool checkKey(const T& key)
    {
        // FIXME : Check also equality to the deleted value.
        return !HashTranslator::equal(KeyTraits::emptyValue(), key);
    }
};

// Note: empty or deleted key values are not allowed, using them may lead to
// undefined behavior.  For pointer keys this means that null pointers are not
// allowed unless you supply custom key traits.
template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
class HashTable : public ConditionalDestructor<HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>, Allocator::isGarbageCollected> {
public:
    typedef HashTableIterator<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> iterator;
    typedef HashTableConstIterator<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> const_iterator;
    typedef Traits ValueTraits;
    typedef Key KeyType;
    typedef typename KeyTraits::PeekInType KeyPeekInType;
    typedef typename KeyTraits::PassInType KeyPassInType;
    typedef Value ValueType;
    typedef Extractor ExtractorType;
    typedef KeyTraits KeyTraitsType;
    typedef typename Traits::PassInType ValuePassInType;
    typedef IdentityHashTranslator<HashFunctions> IdentityTranslatorType;
    typedef HashTableAddResult<HashTable, ValueType> AddResult;

#if DUMP_HASHTABLE_STATS_PER_TABLE
    struct Stats {
        Stats()
            : numAccesses(0)
            , numRehashes(0)
            , numRemoves(0)
            , numReinserts(0)
            , maxCollisions(0)
            , numCollisions(0)
            , collisionGraph()
        {
        }

        int numAccesses;
        int numRehashes;
        int numRemoves;
        int numReinserts;

        int maxCollisions;
        int numCollisions;
        int collisionGraph[4096];

        void recordCollisionAtCount(int count)
        {
            if (count > maxCollisions)
                maxCollisions = count;
            numCollisions++;
            collisionGraph[count]++;
        }

        void dumpStats()
        {
            dataLogF("\nWTF::HashTable::Stats dump\n\n");
            dataLogF("%d accesses\n", numAccesses);
            dataLogF("%d total collisions, average %.2f probes per access\n", numCollisions, 1.0 * (numAccesses + numCollisions) / numAccesses);
            dataLogF("longest collision chain: %d\n", maxCollisions);
            for (int i = 1; i <= maxCollisions; i++) {
                dataLogF("  %d lookups with exactly %d collisions (%.2f%% , %.2f%% with this many or more)\n", collisionGraph[i], i, 100.0 * (collisionGraph[i] - collisionGraph[i+1]) / numAccesses, 100.0 * collisionGraph[i] / numAccesses);
            }
            dataLogF("%d rehashes\n", numRehashes);
            dataLogF("%d reinserts\n", numReinserts);
        }
    };
#endif

    HashTable();
    void finalize()
    {
        ASSERT(!Allocator::isGarbageCollected);
        if (LIKELY(!m_table))
            return;
        deleteAllBucketsAndDeallocate(m_table, m_tableSize);
        m_table = nullptr;
    }

    HashTable(const HashTable&);
    void swap(HashTable&);
    HashTable& operator=(const HashTable&);

    // When the hash table is empty, just return the same iterator for end as
    // for begin.  This is more efficient because we don't have to skip all the
    // empty and deleted buckets, and iterating an empty table is a common case
    // that's worth optimizing.
    iterator begin() { return isEmpty() ? end() : makeIterator(m_table); }
    iterator end() { return makeKnownGoodIterator(m_table + m_tableSize); }
    const_iterator begin() const { return isEmpty() ? end() : makeConstIterator(m_table); }
    const_iterator end() const { return makeKnownGoodConstIterator(m_table + m_tableSize); }

    unsigned size() const { return m_keyCount; }
    unsigned capacity() const { return m_tableSize; }
    bool isEmpty() const { return !m_keyCount; }

    void reserveCapacityForSize(unsigned size);

    AddResult add(ValuePassInType value)
    {
        return add<IdentityTranslatorType>(Extractor::extract(value), value);
    }

    // A special version of add() that finds the object by hashing and comparing
    // with some other type, to avoid the cost of type conversion if the object
    // is already in the table.
    template <typename HashTranslator, typename T, typename Extra> AddResult add(const T& key, const Extra&);
    template <typename HashTranslator, typename T, typename Extra> AddResult addPassingHashCode(const T& key, const Extra&);

    iterator find(KeyPeekInType key) { return find<IdentityTranslatorType>(key); }
    const_iterator find(KeyPeekInType key) const { return find<IdentityTranslatorType>(key); }
    bool contains(KeyPeekInType key) const { return contains<IdentityTranslatorType>(key); }

    template <typename HashTranslator, typename T> iterator find(const T&);
    template <typename HashTranslator, typename T> const_iterator find(const T&) const;
    template <typename HashTranslator, typename T> bool contains(const T&) const;

    void remove(KeyPeekInType);
    void remove(iterator);
    void remove(const_iterator);
    void clear();

    static bool isEmptyBucket(const ValueType& value) { return isHashTraitsEmptyValue<KeyTraits>(Extractor::extract(value)); }
    static bool isDeletedBucket(const ValueType& value) { return KeyTraits::isDeletedValue(Extractor::extract(value)); }
    static bool isEmptyOrDeletedBucket(const ValueType& value) { return HashTableHelper<ValueType, Extractor, KeyTraits>:: isEmptyOrDeletedBucket(value); }

    ValueType* lookup(KeyPeekInType key) { return lookup<IdentityTranslatorType, KeyPeekInType>(key); }
    template <typename HashTranslator, typename T> ValueType* lookup(T);
    template <typename HashTranslator, typename T> const ValueType* lookup(T) const;

    template <typename VisitorDispatcher> void trace(VisitorDispatcher);

#if ENABLE(ASSERT)
    int64_t modifications() const { return m_modifications; }
    void registerModification() { m_modifications++; }
    // HashTable and collections that build on it do not support modifications
    // while there is an iterator in use. The exception is ListHashSet, which
    // has its own iterators that tolerate modification of the underlying set.
    void checkModifications(int64_t mods) const { ASSERT(mods == m_modifications); }
#else
    int64_t modifications() const { return 0; }
    void registerModification() {}
    void checkModifications(int64_t mods) const {}
#endif

private:
    static ValueType* allocateTable(unsigned size);
    static void deleteAllBucketsAndDeallocate(ValueType* table, unsigned size);

    typedef std::pair<ValueType*, bool> LookupType;
    typedef std::pair<LookupType, unsigned> FullLookupType;

    LookupType lookupForWriting(const Key& key) { return lookupForWriting<IdentityTranslatorType>(key); }
    template <typename HashTranslator, typename T> FullLookupType fullLookupForWriting(const T&);
    template <typename HashTranslator, typename T> LookupType lookupForWriting(const T&);

    void remove(ValueType*);

    bool shouldExpand() const { return (m_keyCount + m_deletedCount) * m_maxLoad >= m_tableSize; }
    bool mustRehashInPlace() const { return m_keyCount * m_minLoad < m_tableSize * 2; }
    bool shouldShrink() const
    {
        // isAllocationAllowed check should be at the last because it's
        // expensive.
        return m_keyCount * m_minLoad < m_tableSize
            && m_tableSize > KeyTraits::minimumTableSize
            && Allocator::isAllocationAllowed();
    }
    ValueType* expand(ValueType* entry = 0);
    void shrink() { rehash(m_tableSize / 2, 0); }

    ValueType* expandBuffer(unsigned newTableSize, ValueType* entry, bool&);
    ValueType* rehashTo(ValueType* newTable, unsigned newTableSize, ValueType* entry);
    ValueType* rehash(unsigned newTableSize, ValueType* entry);
    ValueType* reinsert(ValueType&);

    static void initializeBucket(ValueType& bucket);
    static void deleteBucket(ValueType& bucket) { bucket.~ValueType(); Traits::constructDeletedValue(bucket, Allocator::isGarbageCollected); }

    FullLookupType makeLookupResult(ValueType* position, bool found, unsigned hash)
        { return FullLookupType(LookupType(position, found), hash); }

    iterator makeIterator(ValueType* pos) { return iterator(pos, m_table + m_tableSize, this); }
    const_iterator makeConstIterator(ValueType* pos) const { return const_iterator(pos, m_table + m_tableSize, this); }
    iterator makeKnownGoodIterator(ValueType* pos) { return iterator(pos, m_table + m_tableSize, this, HashItemKnownGood); }
    const_iterator makeKnownGoodConstIterator(ValueType* pos) const { return const_iterator(pos, m_table + m_tableSize, this, HashItemKnownGood); }

    static const unsigned m_maxLoad = 2;
    static const unsigned m_minLoad = 6;

    unsigned tableSizeMask() const
    {
        size_t mask = m_tableSize - 1;
        ASSERT((mask & m_tableSize) == 0);
        return mask;
    }

    void setEnqueued() { m_queueFlag = true; }
    void clearEnqueued() { m_queueFlag = false; }
    bool enqueued() { return m_queueFlag; }

    ValueType* m_table;
    unsigned m_tableSize;
    unsigned m_keyCount;
    unsigned m_deletedCount:31;
    unsigned m_queueFlag:1;
#if ENABLE(ASSERT)
    unsigned m_modifications;
#endif

#if DUMP_HASHTABLE_STATS_PER_TABLE
public:
    mutable OwnPtr<Stats> m_stats;
#endif

    template <WeakHandlingFlag x, typename T, typename U, typename V, typename W, typename X, typename Y, typename Z> friend struct WeakProcessingHashTableHelper;
    template <typename T, typename U, typename V, typename W> friend class LinkedHashSet;
};

// Set all the bits to one after the most significant bit:
// 00110101010 -> 00111111111.
template <unsigned size> struct OneifyLowBits;
template <>
struct OneifyLowBits<0> {
    static const unsigned value = 0;
};
template <unsigned number>
struct OneifyLowBits {
    static const unsigned value = number | OneifyLowBits<(number >> 1)>::value;
};
// Compute the first power of two integer that is an upper bound of the
// parameter 'number'.
template <unsigned number>
struct UpperPowerOfTwoBound {
    static const unsigned value = (OneifyLowBits<number - 1>::value + 1) * 2;
};

// Because power of two numbers are the limit of maxLoad, their capacity is
// twice the UpperPowerOfTwoBound, or 4 times their values.
template <unsigned size, bool isPowerOfTwo> struct HashTableCapacityForSizeSplitter;
template <unsigned size>
struct HashTableCapacityForSizeSplitter<size, true> {
    static const unsigned value = size * 4;
};
template <unsigned size>
struct HashTableCapacityForSizeSplitter<size, false> {
    static const unsigned value = UpperPowerOfTwoBound<size>::value;
};

// HashTableCapacityForSize computes the upper power of two capacity to hold the
// size parameter.  This is done at compile time to initialize the HashTraits.
template <unsigned size>
struct HashTableCapacityForSize {
    static const unsigned value = HashTableCapacityForSizeSplitter<size, !(size & (size - 1))>::value;
    static_assert(size > 0, "HashTable minimum capacity should be > 0");
    static_assert(!static_cast<int>(value >> 31), "HashTable capacity should not overflow 32bit int");
    static_assert(value > (2 * size), "HashTable capacity should be able to hold content size");
};

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
inline HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::HashTable()
    : m_table(nullptr)
    , m_tableSize(0)
    , m_keyCount(0)
    , m_deletedCount(0)
    , m_queueFlag(false)
#if ENABLE(ASSERT)
    , m_modifications(0)
#endif
#if DUMP_HASHTABLE_STATS_PER_TABLE
    , m_stats(adoptPtr(new Stats))
#endif
{
}

inline unsigned doubleHash(unsigned key)
{
    key = ~key + (key >> 23);
    key ^= (key << 12);
    key ^= (key >> 7);
    key ^= (key << 2);
    key ^= (key >> 20);
    return key;
}

inline unsigned calculateCapacity(unsigned size)
{
    for (unsigned mask = size; mask; mask >>= 1)
        size |= mask; // 00110101010 -> 00111111111
    return (size + 1) * 2; // 00111111111 -> 10000000000
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::reserveCapacityForSize(unsigned newSize)
{
    unsigned newCapacity = calculateCapacity(newSize);
    if (newCapacity < KeyTraits::minimumTableSize)
        newCapacity = KeyTraits::minimumTableSize;

    if (newCapacity > capacity()) {
        RELEASE_ASSERT(!static_cast<int>(newCapacity >> 31)); // HashTable capacity should not overflow 32bit int.
        rehash(newCapacity, 0);
    }
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
template <typename HashTranslator, typename T>
inline Value* HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::lookup(T key)
{
    return const_cast<Value*>(const_cast<const HashTable*>(this)->lookup<HashTranslator, T>(key));
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
template <typename HashTranslator, typename T>
inline const Value* HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::lookup(T key) const
{
    ASSERT((HashTableKeyChecker<HashTranslator, KeyTraits, HashFunctions::safeToCompareToEmptyOrDeleted>::checkKey(key)));
    const ValueType* table = m_table;
    if (!table)
        return nullptr;

    size_t k = 0;
    size_t sizeMask = tableSizeMask();
    unsigned h = HashTranslator::hash(key);
    size_t i = h & sizeMask;

    UPDATE_ACCESS_COUNTS();

    while (1) {
        const ValueType* entry = table + i;

        if (HashFunctions::safeToCompareToEmptyOrDeleted) {
            if (HashTranslator::equal(Extractor::extract(*entry), key))
                return entry;

            if (isEmptyBucket(*entry))
                return nullptr;
        } else {
            if (isEmptyBucket(*entry))
                return nullptr;

            if (!isDeletedBucket(*entry) && HashTranslator::equal(Extractor::extract(*entry), key))
                return entry;
        }
        UPDATE_PROBE_COUNTS();
        if (!k)
            k = 1 | doubleHash(h);
        i = (i + k) & sizeMask;
    }
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
template <typename HashTranslator, typename T>
inline typename HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::LookupType HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::lookupForWriting(const T& key)
{
    ASSERT(m_table);
    registerModification();

    ValueType* table = m_table;
    size_t k = 0;
    size_t sizeMask = tableSizeMask();
    unsigned h = HashTranslator::hash(key);
    size_t i = h & sizeMask;

    UPDATE_ACCESS_COUNTS();

    ValueType* deletedEntry = nullptr;

    while (1) {
        ValueType* entry = table + i;

        if (isEmptyBucket(*entry))
            return LookupType(deletedEntry ? deletedEntry : entry, false);

        if (HashFunctions::safeToCompareToEmptyOrDeleted) {
            if (HashTranslator::equal(Extractor::extract(*entry), key))
                return LookupType(entry, true);

            if (isDeletedBucket(*entry))
                deletedEntry = entry;
        } else {
            if (isDeletedBucket(*entry))
                deletedEntry = entry;
            else if (HashTranslator::equal(Extractor::extract(*entry), key))
                return LookupType(entry, true);
        }
        UPDATE_PROBE_COUNTS();
        if (!k)
            k = 1 | doubleHash(h);
        i = (i + k) & sizeMask;
    }
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
template <typename HashTranslator, typename T>
inline typename HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::FullLookupType HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::fullLookupForWriting(const T& key)
{
    ASSERT(m_table);
    registerModification();

    ValueType* table = m_table;
    size_t k = 0;
    size_t sizeMask = tableSizeMask();
    unsigned h = HashTranslator::hash(key);
    size_t i = h & sizeMask;

    UPDATE_ACCESS_COUNTS();

    ValueType* deletedEntry = nullptr;

    while (1) {
        ValueType* entry = table + i;

        if (isEmptyBucket(*entry))
            return makeLookupResult(deletedEntry ? deletedEntry : entry, false, h);

        if (HashFunctions::safeToCompareToEmptyOrDeleted) {
            if (HashTranslator::equal(Extractor::extract(*entry), key))
                return makeLookupResult(entry, true, h);

            if (isDeletedBucket(*entry))
                deletedEntry = entry;
        } else {
            if (isDeletedBucket(*entry))
                deletedEntry = entry;
            else if (HashTranslator::equal(Extractor::extract(*entry), key))
                return makeLookupResult(entry, true, h);
        }
        UPDATE_PROBE_COUNTS();
        if (!k)
            k = 1 | doubleHash(h);
        i = (i + k) & sizeMask;
    }
}

template <bool emptyValueIsZero> struct HashTableBucketInitializer;

template <> struct HashTableBucketInitializer<false> {
    template <typename Traits, typename Value> static void initialize(Value& bucket)
    {
        new (NotNull, &bucket) Value(Traits::emptyValue());
    }
};

template <> struct HashTableBucketInitializer<true> {
    template <typename Traits, typename Value> static void initialize(Value& bucket)
    {
        // This initializes the bucket without copying the empty value.  That
        // makes it possible to use this with types that don't support copying.
        // The memset to 0 looks like a slow operation but is optimized by the
        // compilers.
        memset(&bucket, 0, sizeof(bucket));
    }
};

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
inline void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::initializeBucket(ValueType& bucket)
{
    HashTableBucketInitializer<Traits::emptyValueIsZero>::template initialize<Traits>(bucket);
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
template <typename HashTranslator, typename T, typename Extra>
typename HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::AddResult HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::add(const T& key, const Extra& extra)
{
    ASSERT(Allocator::isAllocationAllowed());
    if (!m_table)
        expand();

    ASSERT(m_table);

    ValueType* table = m_table;
    size_t k = 0;
    size_t sizeMask = tableSizeMask();
    unsigned h = HashTranslator::hash(key);
    size_t i = h & sizeMask;

    UPDATE_ACCESS_COUNTS();

    ValueType* deletedEntry = nullptr;
    ValueType* entry;
    while (1) {
        entry = table + i;

        if (isEmptyBucket(*entry))
            break;

        if (HashFunctions::safeToCompareToEmptyOrDeleted) {
            if (HashTranslator::equal(Extractor::extract(*entry), key))
                return AddResult(this, entry, false);

            if (isDeletedBucket(*entry))
                deletedEntry = entry;
        } else {
            if (isDeletedBucket(*entry))
                deletedEntry = entry;
            else if (HashTranslator::equal(Extractor::extract(*entry), key))
                return AddResult(this, entry, false);
        }
        UPDATE_PROBE_COUNTS();
        if (!k)
            k = 1 | doubleHash(h);
        i = (i + k) & sizeMask;
    }

    registerModification();

    if (deletedEntry) {
        // Overwrite any data left over from last use, using placement new or
        // memset.
        initializeBucket(*deletedEntry);
        entry = deletedEntry;
        --m_deletedCount;
    }

    HashTranslator::translate(*entry, key, extra);
    ASSERT(!isEmptyOrDeletedBucket(*entry));

    ++m_keyCount;

    if (shouldExpand())
        entry = expand(entry);

    return AddResult(this, entry, true);
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
template <typename HashTranslator, typename T, typename Extra>
typename HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::AddResult HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::addPassingHashCode(const T& key, const Extra& extra)
{
    ASSERT(Allocator::isAllocationAllowed());
    if (!m_table)
        expand();

    FullLookupType lookupResult = fullLookupForWriting<HashTranslator>(key);

    ValueType* entry = lookupResult.first.first;
    bool found = lookupResult.first.second;
    unsigned h = lookupResult.second;

    if (found)
        return AddResult(this, entry, false);

    registerModification();

    if (isDeletedBucket(*entry)) {
        initializeBucket(*entry);
        --m_deletedCount;
    }

    HashTranslator::translate(*entry, key, extra, h);
    ASSERT(!isEmptyOrDeletedBucket(*entry));

    ++m_keyCount;
    if (shouldExpand())
        entry = expand(entry);

    return AddResult(this, entry, true);
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
Value* HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::reinsert(ValueType& entry)
{
    ASSERT(m_table);
    registerModification();
    ASSERT(!lookupForWriting(Extractor::extract(entry)).second);
    ASSERT(!isDeletedBucket(*(lookupForWriting(Extractor::extract(entry)).first)));
#if DUMP_HASHTABLE_STATS
    atomicIncrement(&HashTableStats::numReinserts);
#endif
#if DUMP_HASHTABLE_STATS_PER_TABLE
    ++m_stats->numReinserts;
#endif
    Value* newEntry = lookupForWriting(Extractor::extract(entry)).first;
    Mover<ValueType, Allocator>::move(entry, *newEntry);

    return newEntry;
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
template <typename HashTranslator, typename T>
inline typename HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::iterator HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::find(const T& key)
{
    ValueType* entry = lookup<HashTranslator>(key);
    if (!entry)
        return end();

    return makeKnownGoodIterator(entry);
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
template <typename HashTranslator, typename T>
inline typename HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::const_iterator HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::find(const T& key) const
{
    ValueType* entry = const_cast<HashTable*>(this)->lookup<HashTranslator>(key);
    if (!entry)
        return end();

    return makeKnownGoodConstIterator(entry);
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
template <typename HashTranslator, typename T>
bool HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::contains(const T& key) const
{
    return const_cast<HashTable*>(this)->lookup<HashTranslator>(key);
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::remove(ValueType* pos)
{
    registerModification();
#if DUMP_HASHTABLE_STATS
    atomicIncrement(&HashTableStats::numRemoves);
#endif
#if DUMP_HASHTABLE_STATS_PER_TABLE
    ++m_stats->numRemoves;
#endif

    deleteBucket(*pos);
    ++m_deletedCount;
    --m_keyCount;

    if (shouldShrink())
        shrink();
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
inline void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::remove(iterator it)
{
    if (it == end())
        return;
    remove(const_cast<ValueType*>(it.m_iterator.m_position));
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
inline void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::remove(const_iterator it)
{
    if (it == end())
        return;
    remove(const_cast<ValueType*>(it.m_position));
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
inline void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::remove(KeyPeekInType key)
{
    remove(find(key));
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
Value* HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::allocateTable(unsigned size)
{
    size_t allocSize = size * sizeof(ValueType);
    ValueType* result;
    // Assert that we will not use memset on things with a vtable entry.  The
    // compiler will also check this on some platforms. We would like to check
    // this on the whole value (key-value pair), but IsPolymorphic will return
    // false for a pair of two types, even if one of the components is
    // polymorphic.
    static_assert(!Traits::emptyValueIsZero || !IsPolymorphic<KeyType>::value, "empty value cannot be zero for things with a vtable");

#if ENABLE(OILPAN)
    static_assert(Allocator::isGarbageCollected
        || ((!IsAllowOnlyInlineAllocation<KeyType>::value || !NeedsTracing<KeyType>::value)
        && (!IsAllowOnlyInlineAllocation<ValueType>::value || !NeedsTracing<ValueType>::value))
        , "Cannot put ALLOW_ONLY_INLINE_ALLOCATION objects that have trace methods into an off-heap HashTable");
#endif
    if (Traits::emptyValueIsZero) {
        result = Allocator::template allocateZeroedHashTableBacking<ValueType, HashTable>(allocSize);
    } else {
        result = Allocator::template allocateHashTableBacking<ValueType, HashTable>(allocSize);
        for (unsigned i = 0; i < size; i++)
            initializeBucket(result[i]);
    }
    return result;
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::deleteAllBucketsAndDeallocate(ValueType* table, unsigned size)
{
    if (!IsTriviallyDestructible<ValueType>::value) {
        for (unsigned i = 0; i < size; ++i) {
            // This code is called when the hash table is cleared or resized. We
            // have allocated a new backing store and we need to run the
            // destructors on the old backing store, as it is being freed. If we
            // are GCing we need to both call the destructor and mark the bucket
            // as deleted, otherwise the destructor gets called again when the
            // GC finds the backing store. With the default allocator it's
            // enough to call the destructor, since we will free the memory
            // explicitly and we won't see the memory with the bucket again.
            if (Allocator::isGarbageCollected) {
                if (!isEmptyOrDeletedBucket(table[i]))
                    deleteBucket(table[i]);
            } else {
                if (!isDeletedBucket(table[i]))
                    table[i].~ValueType();
            }
        }
    }
    Allocator::freeHashTableBacking(table);
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
Value* HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::expand(Value* entry)
{
    unsigned newSize;
    if (!m_tableSize) {
        newSize = KeyTraits::minimumTableSize;
    } else if (mustRehashInPlace()) {
        newSize = m_tableSize;
    } else {
        newSize = m_tableSize * 2;
        RELEASE_ASSERT(newSize > m_tableSize);
    }

    return rehash(newSize, entry);
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
Value* HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::expandBuffer(unsigned newTableSize, Value* entry, bool& success)
{
    success = false;
    ASSERT(m_tableSize < newTableSize);
    if (!Allocator::expandHashTableBacking(m_table, newTableSize * sizeof(ValueType)))
        return nullptr;

    success = true;

    Value* newEntry = nullptr;
    unsigned oldTableSize = m_tableSize;
    ValueType* originalTable = m_table;

    ValueType* temporaryTable = allocateTable(oldTableSize);
    for (unsigned i = 0; i < oldTableSize; i++) {
        if (&m_table[i] == entry)
            newEntry = &temporaryTable[i];
        if (isEmptyOrDeletedBucket(m_table[i])) {
            ASSERT(&m_table[i] != entry);
            if (Traits::emptyValueIsZero) {
                memset(&temporaryTable[i], 0, sizeof(ValueType));
            } else {
                initializeBucket(temporaryTable[i]);
            }
        } else {
            Mover<ValueType, Allocator>::move(m_table[i], temporaryTable[i]);
        }
    }
    m_table = temporaryTable;

    if (Traits::emptyValueIsZero) {
        memset(originalTable, 0, newTableSize * sizeof(ValueType));
    } else {
        for (unsigned i = 0; i < newTableSize; i++)
            initializeBucket(originalTable[i]);
    }
    newEntry = rehashTo(originalTable, newTableSize, newEntry);
    deleteAllBucketsAndDeallocate(temporaryTable, oldTableSize);

    return newEntry;
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
Value* HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::rehashTo(ValueType* newTable, unsigned newTableSize, Value* entry)
{
    unsigned oldTableSize = m_tableSize;
    ValueType* oldTable = m_table;

#if DUMP_HASHTABLE_STATS
    if (oldTableSize != 0)
        atomicIncrement(&HashTableStats::numRehashes);
#endif

#if DUMP_HASHTABLE_STATS_PER_TABLE
    if (oldTableSize != 0)
        ++m_stats->numRehashes;
#endif

    m_table = newTable;
    m_tableSize = newTableSize;

    Value* newEntry = nullptr;
    for (unsigned i = 0; i != oldTableSize; ++i) {
        if (isEmptyOrDeletedBucket(oldTable[i])) {
            ASSERT(&oldTable[i] != entry);
            continue;
        }
        Value* reinsertedEntry = reinsert(oldTable[i]);
        if (&oldTable[i] == entry) {
            ASSERT(!newEntry);
            newEntry = reinsertedEntry;
        }
    }

    m_deletedCount = 0;

    return newEntry;
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
Value* HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::rehash(unsigned newTableSize, Value* entry)
{
    unsigned oldTableSize = m_tableSize;
    ValueType* oldTable = m_table;

#if DUMP_HASHTABLE_STATS
    if (oldTableSize != 0)
        atomicIncrement(&HashTableStats::numRehashes);
#endif

#if DUMP_HASHTABLE_STATS_PER_TABLE
    if (oldTableSize != 0)
        ++m_stats->numRehashes;
#endif

    // The Allocator::isGarbageCollected check is not needed.  The check is just
    // a static hint for a compiler to indicate that Base::expandBuffer returns
    // false if Allocator is a DefaultAllocator.
    if (Allocator::isGarbageCollected && newTableSize > oldTableSize) {
        bool success;
        Value* newEntry = expandBuffer(newTableSize, entry, success);
        if (success)
            return newEntry;
    }

    ValueType* newTable = allocateTable(newTableSize);
    Value* newEntry = rehashTo(newTable, newTableSize, entry);
    deleteAllBucketsAndDeallocate(oldTable, oldTableSize);

    return newEntry;
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::clear()
{
    registerModification();
    if (!m_table)
        return;

    deleteAllBucketsAndDeallocate(m_table, m_tableSize);
    m_table = nullptr;
    m_tableSize = 0;
    m_keyCount = 0;
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::HashTable(const HashTable& other)
    : m_table(nullptr)
    , m_tableSize(0)
    , m_keyCount(0)
    , m_deletedCount(0)
    , m_queueFlag(false)
#if ENABLE(ASSERT)
    , m_modifications(0)
#endif
#if DUMP_HASHTABLE_STATS_PER_TABLE
    , m_stats(adoptPtr(new Stats(*other.m_stats)))
#endif
{
    // Copy the hash table the dumb way, by adding each element to the new
    // table.  It might be more efficient to copy the table slots, but it's not
    // clear that efficiency is needed.
    const_iterator end = other.end();
    for (const_iterator it = other.begin(); it != end; ++it)
        add(*it);
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::swap(HashTable& other)
{
    std::swap(m_table, other.m_table);
    std::swap(m_tableSize, other.m_tableSize);
    std::swap(m_keyCount, other.m_keyCount);
    // std::swap does not work for bit fields.
    unsigned deleted = m_deletedCount;
    m_deletedCount = other.m_deletedCount;
    other.m_deletedCount = deleted;
    ASSERT(!m_queueFlag);
    ASSERT(!other.m_queueFlag);

#if ENABLE(ASSERT)
    std::swap(m_modifications, other.m_modifications);
#endif

#if DUMP_HASHTABLE_STATS_PER_TABLE
    m_stats.swap(other.m_stats);
#endif
}

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>& HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::operator=(const HashTable& other)
{
    HashTable tmp(other);
    swap(tmp);
    return *this;
}

template <WeakHandlingFlag weakHandlingFlag, typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
struct WeakProcessingHashTableHelper;

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
struct WeakProcessingHashTableHelper<NoWeakHandlingInCollections, Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> {
    static void process(typename Allocator::Visitor* visitor, void* closure) {}
    static void ephemeronIteration(typename Allocator::Visitor* visitor, void* closure) {}
    static void ephemeronIterationDone(typename Allocator::Visitor* visitor, void* closure) {}
};

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
struct WeakProcessingHashTableHelper<WeakHandlingInCollections, Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> {
    // Used for purely weak and for weak-and-strong tables (ephemerons).
    static void process(typename Allocator::Visitor* visitor, void* closure)
    {
        typedef HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> HashTableType;
        HashTableType* table = reinterpret_cast<HashTableType*>(closure);
        ASSERT(table->m_table);
        // Now perform weak processing (this is a no-op if the backing was
        // accessible through an iterator and was already marked strongly).
        typedef typename HashTableType::ValueType ValueType;
        for (ValueType* element = table->m_table + table->m_tableSize - 1; element >= table->m_table; element--) {
            if (!HashTableType::isEmptyOrDeletedBucket(*element)) {
                // At this stage calling trace can make no difference
                // (everything is already traced), but we use the return value
                // to remove things from the collection.

                // FIXME: This should be rewritten so that this can check if the
                // element is dead without calling trace, which is semantically
                // not correct to be called in weak processing stage.
                if (TraceInCollectionTrait<WeakHandlingInCollections, WeakPointersActWeak, ValueType, Traits>::trace(visitor, *element)) {
                    table->registerModification();
                    HashTableType::deleteBucket(*element); // Also calls the destructor.
                    table->m_deletedCount++;
                    table->m_keyCount--;
                    // We don't rehash the backing until the next add or delete,
                    // because that would cause allocation during GC.
                }
            }
        }
    }

    // Called repeatedly for tables that have both weak and strong pointers.
    static void ephemeronIteration(typename Allocator::Visitor* visitor, void* closure)
    {
        typedef HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> HashTableType;
        HashTableType* table = reinterpret_cast<HashTableType*>(closure);
        ASSERT(table->m_table);
        // Check the hash table for elements that we now know will not be
        // removed by weak processing. Those elements need to have their strong
        // pointers traced.
        typedef typename HashTableType::ValueType ValueType;
        for (ValueType* element = table->m_table + table->m_tableSize - 1; element >= table->m_table; element--) {
            if (!HashTableType::isEmptyOrDeletedBucket(*element))
                TraceInCollectionTrait<WeakHandlingInCollections, WeakPointersActWeak, ValueType, Traits>::trace(visitor, *element);
        }
    }

    // Called when the ephemeron iteration is done and before running the per
    // thread weak processing. It is guaranteed to be called before any thread
    // is resumed.
    static void ephemeronIterationDone(typename Allocator::Visitor* visitor, void* closure)
    {
        typedef HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator> HashTableType;
        HashTableType* table = reinterpret_cast<HashTableType*>(closure);
        ASSERT(Allocator::weakTableRegistered(visitor, table));
        table->clearEnqueued();
    }
};

template <typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
template <typename VisitorDispatcher>
void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::trace(VisitorDispatcher visitor)
{
    // If someone else already marked the backing and queued up the trace and/or
    // weak callback then we are done. This optimization does not happen for
    // ListHashSet since its iterator does not point at the backing.
    if (!m_table || Allocator::isHeapObjectAlive(m_table))
        return;
    // Normally, we mark the backing store without performing trace. This means
    // it is marked live, but the pointers inside it are not marked.  Instead we
    // will mark the pointers below. However, for backing stores that contain
    // weak pointers the handling is rather different.  We don't mark the
    // backing store here, so the marking GC will leave the backing unmarked. If
    // the backing is found in any other way than through its HashTable (ie from
    // an iterator) then the mark bit will be set and the pointers will be
    // marked strongly, avoiding problems with iterating over things that
    // disappear due to weak processing while we are iterating over them. We
    // register the backing store pointer for delayed marking which will take
    // place after we know if the backing is reachable from elsewhere. We also
    // register a weakProcessing callback which will perform weak processing if
    // needed.
    if (Traits::weakHandlingFlag == NoWeakHandlingInCollections) {
        Allocator::markNoTracing(visitor, m_table);
    } else {
        Allocator::registerDelayedMarkNoTracing(visitor, m_table);
        // Since we're delaying marking this HashTable, it is possible that the
        // registerWeakMembers is called multiple times (in rare
        // cases). However, it shouldn't cause any issue.
        Allocator::registerWeakMembers(visitor, this, m_table, WeakProcessingHashTableHelper<Traits::weakHandlingFlag, Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::process);
    }
    if (ShouldBeTraced<Traits>::value) {
        if (Traits::weakHandlingFlag == WeakHandlingInCollections) {
            // If we have both strong and weak pointers in the collection then
            // we queue up the collection for fixed point iteration a la
            // Ephemerons:
            // http://dl.acm.org/citation.cfm?doid=263698.263733 - see also
            // http://www.jucs.org/jucs_14_21/eliminating_cycles_in_weak
            ASSERT(!enqueued() || Allocator::weakTableRegistered(visitor, this));
            if (!enqueued()) {
                Allocator::registerWeakTable(visitor, this,
                    WeakProcessingHashTableHelper<Traits::weakHandlingFlag, Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::ephemeronIteration,
                    WeakProcessingHashTableHelper<Traits::weakHandlingFlag, Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::ephemeronIterationDone);
                setEnqueued();
            }
            // We don't need to trace the elements here, since registering as a
            // weak table above will cause them to be traced (perhaps several
            // times). It's better to wait until everything else is traced
            // before tracing the elements for the first time; this may reduce
            // (by one) the number of iterations needed to get to a fixed point.
            return;
        }
        for (ValueType* element = m_table + m_tableSize - 1; element >= m_table; element--) {
            if (!isEmptyOrDeletedBucket(*element))
                Allocator::template trace<VisitorDispatcher, ValueType, Traits>(visitor, *element);
        }
    }
}

// iterator adapters

template <typename HashTableType, typename Traits> struct HashTableConstIteratorAdapter {
    HashTableConstIteratorAdapter() {}
    HashTableConstIteratorAdapter(const typename HashTableType::const_iterator& impl) : m_impl(impl) {}
    typedef typename Traits::IteratorConstGetType GetType;
    typedef typename HashTableType::ValueTraits::IteratorConstGetType SourceGetType;

    GetType get() const { return const_cast<GetType>(SourceGetType(m_impl.get())); }
    typename Traits::IteratorConstReferenceType operator*() const { return Traits::getToReferenceConstConversion(get()); }
    GetType operator->() const { return get(); }

    HashTableConstIteratorAdapter& operator++() { ++m_impl; return *this; }
    // postfix ++ intentionally omitted

    typename HashTableType::const_iterator m_impl;
};

template <typename HashTableType, typename Traits> struct HashTableIteratorAdapter {
    typedef typename Traits::IteratorGetType GetType;
    typedef typename HashTableType::ValueTraits::IteratorGetType SourceGetType;

    HashTableIteratorAdapter() {}
    HashTableIteratorAdapter(const typename HashTableType::iterator& impl) : m_impl(impl) {}

    GetType get() const { return const_cast<GetType>(SourceGetType(m_impl.get())); }
    typename Traits::IteratorReferenceType operator*() const { return Traits::getToReferenceConversion(get()); }
    GetType operator->() const { return get(); }

    HashTableIteratorAdapter& operator++() { ++m_impl; return *this; }
    // postfix ++ intentionally omitted

    operator HashTableConstIteratorAdapter<HashTableType, Traits>()
    {
        typename HashTableType::const_iterator i = m_impl;
        return i;
    }

    typename HashTableType::iterator m_impl;
};

template <typename T, typename U>
inline bool operator==(const HashTableConstIteratorAdapter<T, U>& a, const HashTableConstIteratorAdapter<T, U>& b)
{
    return a.m_impl == b.m_impl;
}

template <typename T, typename U>
inline bool operator!=(const HashTableConstIteratorAdapter<T, U>& a, const HashTableConstIteratorAdapter<T, U>& b)
{
    return a.m_impl != b.m_impl;
}

template <typename T, typename U>
inline bool operator==(const HashTableIteratorAdapter<T, U>& a, const HashTableIteratorAdapter<T, U>& b)
{
    return a.m_impl == b.m_impl;
}

template <typename T, typename U>
inline bool operator!=(const HashTableIteratorAdapter<T, U>& a, const HashTableIteratorAdapter<T, U>& b)
{
    return a.m_impl != b.m_impl;
}

// All 4 combinations of ==, != and Const,non const.
template <typename T, typename U>
inline bool operator==(const HashTableConstIteratorAdapter<T, U>& a, const HashTableIteratorAdapter<T, U>& b)
{
    return a.m_impl == b.m_impl;
}

template <typename T, typename U>
inline bool operator!=(const HashTableConstIteratorAdapter<T, U>& a, const HashTableIteratorAdapter<T, U>& b)
{
    return a.m_impl != b.m_impl;
}

template <typename T, typename U>
inline bool operator==(const HashTableIteratorAdapter<T, U>& a, const HashTableConstIteratorAdapter<T, U>& b)
{
    return a.m_impl == b.m_impl;
}

template <typename T, typename U>
inline bool operator!=(const HashTableIteratorAdapter<T, U>& a, const HashTableConstIteratorAdapter<T, U>& b)
{
    return a.m_impl != b.m_impl;
}

template <typename Collection1, typename Collection2>
inline void removeAll(Collection1& collection, const Collection2& toBeRemoved)
{
    if (collection.isEmpty() || toBeRemoved.isEmpty())
        return;
    typedef typename Collection2::const_iterator CollectionIterator;
    CollectionIterator end(toBeRemoved.end());
    for (CollectionIterator it(toBeRemoved.begin()); it != end; ++it)
        collection.remove(*it);
}

} // namespace WTF

#include "wtf/HashIterators.h"

#endif // WTF_HashTable_h