flutter_flutter/sky/engine/wtf/HashTraits.h

/*
 * Copyright (C) 2005, 2006, 2007, 2008, 2011, 2012 Apple Inc.
 * All rights reserved.
 *
 * 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 SKY_ENGINE_WTF_HASHTRAITS_H_
#define SKY_ENGINE_WTF_HASHTRAITS_H_

#include <string.h>  // For memset.
#include <limits>
#include <utility>
#include "flutter/sky/engine/wtf/HashFunctions.h"
#include "flutter/sky/engine/wtf/HashTableDeletedValueType.h"
#include "flutter/sky/engine/wtf/StdLibExtras.h"
#include "flutter/sky/engine/wtf/TypeTraits.h"

namespace WTF {

class String;

template <typename T>
class OwnPtr;
template <typename T>
class PassOwnPtr;

template <typename T>
struct HashTraits;

template <bool isInteger, typename T>
struct GenericHashTraitsBase;

enum ShouldWeakPointersBeMarkedStrongly {
  WeakPointersActStrong,
  WeakPointersActWeak
};

template <typename T>
struct GenericHashTraitsBase<false, T> {
  // The emptyValueIsZero flag is used to optimize allocation of empty hash
  // tables with zeroed memory.
  static const bool emptyValueIsZero = false;

  // The hasIsEmptyValueFunction flag allows the hash table to automatically
  // generate code to check for the empty value when it can be done with the
  // equality operator, but allows custom functions for cases like String that
  // need them.
  static const bool hasIsEmptyValueFunction = false;

  // The needsDestruction flag is used to optimize destruction and rehashing.
  static const bool needsDestruction = true;

  // The starting table size. Can be overridden when we know beforehand that
  // a hash table will have at least N entries.
#if defined(MEMORY_SANITIZER_INITIAL_SIZE)
  static const unsigned minimumTableSize = 1;
#else
  static const unsigned minimumTableSize = 8;
#endif
  static const WeakHandlingFlag weakHandlingFlag =
      IsWeak<T>::value ? WeakHandlingInCollections
                       : NoWeakHandlingInCollections;
};

// Default integer traits disallow both 0 and -1 as keys (max value instead of
// -1 for unsigned).
template <typename T>
struct GenericHashTraitsBase<true, T> : GenericHashTraitsBase<false, T> {
  static const bool emptyValueIsZero = true;
  static const bool needsDestruction = false;
  static void constructDeletedValue(T& slot, bool) {
    slot = static_cast<T>(-1);
  }
  static bool isDeletedValue(T value) { return value == static_cast<T>(-1); }
};

template <typename T>
struct GenericHashTraits : GenericHashTraitsBase<IsInteger<T>::value, T> {
  typedef T TraitType;
  typedef T EmptyValueType;

  static T emptyValue() { return T(); }

  // Type for functions that do not take ownership, such as contains.
  typedef const T& PeekInType;
  typedef T* IteratorGetType;
  typedef const T* IteratorConstGetType;
  typedef T& IteratorReferenceType;
  typedef const T& IteratorConstReferenceType;
  static IteratorReferenceType getToReferenceConversion(IteratorGetType x) {
    return *x;
  }
  static IteratorConstReferenceType getToReferenceConstConversion(
      IteratorConstGetType x) {
    return *x;
  }
  // Type for functions that take ownership, such as add.
  // The store function either not be called or called once to store something
  // passed in. The value passed to the store function will be PassInType.
  typedef const T& PassInType;
  static void store(const T& value, T& storage) { storage = value; }

  // Type for return value of functions that transfer ownership, such as take.
  typedef T PassOutType;
  static const T& passOut(const T& value) { return value; }

  // Type for return value of functions that do not transfer ownership, such as
  // get.
  // FIXME: We could change this type to const T& for better performance if we
  // figured out a way to handle the return value from emptyValue, which is a
  // temporary.
  typedef T PeekOutType;
  static const T& peek(const T& value) { return value; }
};

template <typename T>
struct HashTraits : GenericHashTraits<T> {};

template <typename T>
struct FloatHashTraits : GenericHashTraits<T> {
  static const bool needsDestruction = false;
  static T emptyValue() { return std::numeric_limits<T>::infinity(); }
  static void constructDeletedValue(T& slot, bool) {
    slot = -std::numeric_limits<T>::infinity();
  }
  static bool isDeletedValue(T value) {
    return value == -std::numeric_limits<T>::infinity();
  }
};

template <>
struct HashTraits<float> : FloatHashTraits<float> {};
template <>
struct HashTraits<double> : FloatHashTraits<double> {};

// Default unsigned traits disallow both 0 and max as keys -- use these traits
// to allow zero and disallow max - 1.
template <typename T>
struct UnsignedWithZeroKeyHashTraits : GenericHashTraits<T> {
  static const bool emptyValueIsZero = false;
  static const bool needsDestruction = false;
  static T emptyValue() { return std::numeric_limits<T>::max(); }
  static void constructDeletedValue(T& slot, bool) {
    slot = std::numeric_limits<T>::max() - 1;
  }
  static bool isDeletedValue(T value) {
    return value == std::numeric_limits<T>::max() - 1;
  }
};

template <typename P>
struct HashTraits<P*> : GenericHashTraits<P*> {
  static const bool emptyValueIsZero = true;
  static const bool needsDestruction = false;
  static void constructDeletedValue(P*& slot, bool) {
    slot = reinterpret_cast<P*>(-1);
  }
  static bool isDeletedValue(P* value) {
    return value == reinterpret_cast<P*>(-1);
  }
};

template <typename T>
struct SimpleClassHashTraits : GenericHashTraits<T> {
  static const bool emptyValueIsZero = true;
  static void constructDeletedValue(T& slot, bool) {
    new (NotNull, &slot) T(HashTableDeletedValue);
  }
  static bool isDeletedValue(const T& value) {
    return value.isHashTableDeletedValue();
  }
};

template <typename P>
struct HashTraits<OwnPtr<P>> : SimpleClassHashTraits<OwnPtr<P>> {
  typedef std::nullptr_t EmptyValueType;

  static EmptyValueType emptyValue() { return nullptr; }

  static const bool hasIsEmptyValueFunction = true;
  static bool isEmptyValue(const OwnPtr<P>& value) { return !value; }

  typedef typename OwnPtr<P>::PtrType PeekInType;

  typedef PassOwnPtr<P> PassInType;
  static void store(PassOwnPtr<P> value, OwnPtr<P>& storage) {
    storage = value;
  }

  typedef PassOwnPtr<P> PassOutType;
  static PassOwnPtr<P> passOut(OwnPtr<P>& value) { return value.release(); }
  static PassOwnPtr<P> passOut(std::nullptr_t) { return nullptr; }

  typedef typename OwnPtr<P>::PtrType PeekOutType;
  static PeekOutType peek(const OwnPtr<P>& value) { return value.get(); }
  static PeekOutType peek(std::nullptr_t) { return 0; }
};

template <typename P>
struct HashTraits<RefPtr<P>> : SimpleClassHashTraits<RefPtr<P>> {
  typedef std::nullptr_t EmptyValueType;
  static EmptyValueType emptyValue() { return nullptr; }

  static const bool hasIsEmptyValueFunction = true;
  static bool isEmptyValue(const RefPtr<P>& value) { return !value; }

  typedef RefPtrValuePeeker<P> PeekInType;
  typedef RefPtr<P>* IteratorGetType;
  typedef const RefPtr<P>* IteratorConstGetType;
  typedef RefPtr<P>& IteratorReferenceType;
  typedef const RefPtr<P>& IteratorConstReferenceType;
  static IteratorReferenceType getToReferenceConversion(IteratorGetType x) {
    return *x;
  }
  static IteratorConstReferenceType getToReferenceConstConversion(
      IteratorConstGetType x) {
    return *x;
  }

  typedef PassRefPtr<P> PassInType;
  static void store(PassRefPtr<P> value, RefPtr<P>& storage) {
    storage = value;
  }

  typedef PassRefPtr<P> PassOutType;
  static PassOutType passOut(RefPtr<P>& value) { return value.release(); }
  static PassOutType passOut(std::nullptr_t) { return nullptr; }

  typedef P* PeekOutType;
  static PeekOutType peek(const RefPtr<P>& value) { return value.get(); }
  static PeekOutType peek(std::nullptr_t) { return 0; }
};

template <typename T>
struct HashTraits<RawPtr<T>> : HashTraits<T*> {};

template <>
struct HashTraits<String> : SimpleClassHashTraits<String> {
  static const bool hasIsEmptyValueFunction = true;
  static bool isEmptyValue(const String&);
};

// This struct template is an implementation detail of the
// isHashTraitsEmptyValue function, which selects either the emptyValue function
// or the isEmptyValue function to check for empty values.
template <typename Traits, bool hasEmptyValueFunction>
struct HashTraitsEmptyValueChecker;
template <typename Traits>
struct HashTraitsEmptyValueChecker<Traits, true> {
  template <typename T>
  static bool isEmptyValue(const T& value) {
    return Traits::isEmptyValue(value);
  }
};
template <typename Traits>
struct HashTraitsEmptyValueChecker<Traits, false> {
  template <typename T>
  static bool isEmptyValue(const T& value) {
    return value == Traits::emptyValue();
  }
};
template <typename Traits, typename T>
inline bool isHashTraitsEmptyValue(const T& value) {
  return HashTraitsEmptyValueChecker<
      Traits, Traits::hasIsEmptyValueFunction>::isEmptyValue(value);
}

template <typename FirstTraitsArg, typename SecondTraitsArg>
struct PairHashTraits
    : GenericHashTraits<std::pair<typename FirstTraitsArg::TraitType,
                                  typename SecondTraitsArg::TraitType>> {
  typedef FirstTraitsArg FirstTraits;
  typedef SecondTraitsArg SecondTraits;
  typedef std::pair<typename FirstTraits::TraitType,
                    typename SecondTraits::TraitType>
      TraitType;
  typedef std::pair<typename FirstTraits::EmptyValueType,
                    typename SecondTraits::EmptyValueType>
      EmptyValueType;

  static const bool emptyValueIsZero =
      FirstTraits::emptyValueIsZero && SecondTraits::emptyValueIsZero;
  static EmptyValueType emptyValue() {
    return std::make_pair(FirstTraits::emptyValue(),
                          SecondTraits::emptyValue());
  }

  static const bool needsDestruction =
      FirstTraits::needsDestruction || SecondTraits::needsDestruction;

  static const unsigned minimumTableSize = FirstTraits::minimumTableSize;

  static void constructDeletedValue(TraitType& slot, bool zeroValue) {
    FirstTraits::constructDeletedValue(slot.first, zeroValue);
    // For GC collections the memory for the backing is zeroed when it
    // is allocated, and the constructors may take advantage of that,
    // especially if a GC occurs during insertion of an entry into the
    // table. This slot is being marked deleted, but If the slot is
    // reused at a later point, the same assumptions around memory
    // zeroing must hold as they did at the initial allocation.
    // Therefore we zero the value part of the slot here for GC
    // collections.
    if (zeroValue)
      memset(reinterpret_cast<void*>(&slot.second), 0, sizeof(slot.second));
  }
  static bool isDeletedValue(const TraitType& value) {
    return FirstTraits::isDeletedValue(value.first);
  }
};

template <typename First, typename Second>
struct HashTraits<std::pair<First, Second>>
    : public PairHashTraits<HashTraits<First>, HashTraits<Second>> {};

template <typename KeyTypeArg, typename ValueTypeArg>
struct KeyValuePair {
  typedef KeyTypeArg KeyType;

  KeyValuePair() {}

  KeyValuePair(const KeyTypeArg& _key, const ValueTypeArg& _value)
      : key(_key), value(_value) {}

  template <typename OtherKeyType, typename OtherValueType>
  KeyValuePair(const KeyValuePair<OtherKeyType, OtherValueType>& other)
      : key(other.key), value(other.value) {}

  KeyTypeArg key;
  ValueTypeArg value;
};

template <typename KeyTraitsArg, typename ValueTraitsArg>
struct KeyValuePairHashTraits
    : GenericHashTraits<KeyValuePair<typename KeyTraitsArg::TraitType,
                                     typename ValueTraitsArg::TraitType>> {
  typedef KeyTraitsArg KeyTraits;
  typedef ValueTraitsArg ValueTraits;
  typedef KeyValuePair<typename KeyTraits::TraitType,
                       typename ValueTraits::TraitType>
      TraitType;
  typedef KeyValuePair<typename KeyTraits::EmptyValueType,
                       typename ValueTraits::EmptyValueType>
      EmptyValueType;

  static const bool emptyValueIsZero =
      KeyTraits::emptyValueIsZero && ValueTraits::emptyValueIsZero;
  static EmptyValueType emptyValue() {
    return KeyValuePair<typename KeyTraits::EmptyValueType,
                        typename ValueTraits::EmptyValueType>(
        KeyTraits::emptyValue(), ValueTraits::emptyValue());
  }

  static const bool needsDestruction =
      KeyTraits::needsDestruction || ValueTraits::needsDestruction;
  static const WeakHandlingFlag weakHandlingFlag =
      (KeyTraits::weakHandlingFlag == WeakHandlingInCollections ||
       ValueTraits::weakHandlingFlag == WeakHandlingInCollections)
          ? WeakHandlingInCollections
          : NoWeakHandlingInCollections;

  static const unsigned minimumTableSize = KeyTraits::minimumTableSize;

  static void constructDeletedValue(TraitType& slot, bool zeroValue) {
    KeyTraits::constructDeletedValue(slot.key, zeroValue);
    // See similar code in this file for why we need to do this.
    if (zeroValue)
      memset(reinterpret_cast<void*>(&slot.value), 0, sizeof(slot.value));
  }
  static bool isDeletedValue(const TraitType& value) {
    return KeyTraits::isDeletedValue(value.key);
  }
};

template <typename Key, typename Value>
struct HashTraits<KeyValuePair<Key, Value>>
    : public KeyValuePairHashTraits<HashTraits<Key>, HashTraits<Value>> {};

template <typename T>
struct NullableHashTraits : public HashTraits<T> {
  static const bool emptyValueIsZero = false;
  static T emptyValue() { return reinterpret_cast<T>(1); }
};

// This is for tracing inside collections that have special support for weak
// pointers. The trait has a trace method which returns true if there are weak
// pointers to things that have not (yet) been marked live. Returning true
// indicates that the entry in the collection may yet be removed by weak
// handling. Default implementation for non-weak types is to use the regular
// non-weak TraceTrait. Default implementation for types with weakness is to
// call traceInCollection on the type's trait.
template <WeakHandlingFlag weakHandlingFlag,
          ShouldWeakPointersBeMarkedStrongly strongify,
          typename T,
          typename Traits>
struct TraceInCollectionTrait;

}  // namespace WTF

using WTF::HashTraits;
using WTF::NullableHashTraits;
using WTF::PairHashTraits;
using WTF::SimpleClassHashTraits;

#endif  // SKY_ENGINE_WTF_HASHTRAITS_H_