third_party/WebKit/Source/wtf/HashTraits.h

   1 /*
   2  * Copyright (C) 2005, 2006, 2007, 2008, 2011, 2012 Apple Inc. All rights reserved.
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Library General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Library General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Library General Public License
  15  * along with this library; see the file COPYING.LIB.  If not, write to
  16  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  17  * Boston, MA 02110-1301, USA.
  18  *
  19  */
  20
  21 #ifndef WTF_HashTraits_h
  22 #define WTF_HashTraits_h
  23
  24 #include "wtf/HashFunctions.h"
  25 #include "wtf/HashTableDeletedValueType.h"
  26 #include "wtf/StdLibExtras.h"
  27 #include "wtf/TypeTraits.h"
  28 #include <limits>
  29 #include <string.h> // For memset.
  30 #include <utility>
  31
  32 namespace WTF {
  33
  34     class String;
  35
  36     template<typename T> class OwnPtr;
  37     template<typename T> class PassOwnPtr;
  38
  39     template<typename T> struct HashTraits;
  40
  41     template<bool isInteger, typename T> struct GenericHashTraitsBase;
  42
  43     enum ShouldWeakPointersBeMarkedStrongly {
  44         WeakPointersActStrong,
  45         WeakPointersActWeak
  46     };
  47
  48     template<typename T> struct GenericHashTraitsBase<false, T> {
  49         // The emptyValueIsZero flag is used to optimize allocation of empty hash tables with zeroed memory.
  50         static const bool emptyValueIsZero = false;
  51
  52         // The hasIsEmptyValueFunction flag allows the hash table to automatically generate code to check
  53         // for the empty value when it can be done with the equality operator, but allows custom functions
  54         // for cases like String that need them.
  55         static const bool hasIsEmptyValueFunction = false;
  56
  57         // The starting table size. Can be overridden when we know beforehand that
  58         // a hash table will have at least N entries.
  59 #if defined(MEMORY_SANITIZER_INITIAL_SIZE)
  60         static const unsigned minimumTableSize = 1;
  61 #else
  62         static const unsigned minimumTableSize = 8;
  63 #endif
  64
  65         template<typename U = void>
  66         struct NeedsTracingLazily {
  67             static const bool value = NeedsTracing<T>::value;
  68         };
  69         static const WeakHandlingFlag weakHandlingFlag = IsWeak<T>::value ? WeakHandlingInCollections : NoWeakHandlingInCollections;
  70     };
  71
  72     // Default integer traits disallow both 0 and -1 as keys (max value instead of -1 for unsigned).
  73     template<typename T> struct GenericHashTraitsBase<true, T> : GenericHashTraitsBase<false, T> {
  74         static const bool emptyValueIsZero = true;
  75         static void constructDeletedValue(T& slot, bool) { slot = static_cast<T>(-1); }
  76         static bool isDeletedValue(T value) { return value == static_cast<T>(-1); }
  77     };
  78
  79     template<typename T> struct GenericHashTraits : GenericHashTraitsBase<IsInteger<T>::value, T> {
  80         typedef T TraitType;
  81         typedef T EmptyValueType;
  82
  83         static T emptyValue() { return T(); }
  84
  85         // Type for functions that do not take ownership, such as contains.
  86         typedef const T& PeekInType;
  87         typedef T* IteratorGetType;
  88         typedef const T* IteratorConstGetType;
  89         typedef T& IteratorReferenceType;
  90         typedef const T& IteratorConstReferenceType;
  91         static IteratorReferenceType getToReferenceConversion(IteratorGetType x) { return *x; }
  92         static IteratorConstReferenceType getToReferenceConstConversion(IteratorConstGetType x) { return *x; }
  93         // Type for functions that take ownership, such as add.
  94         // The store function either not be called or called once to store something passed in.
  95         // The value passed to the store function will be PassInType.
  96         typedef const T& PassInType;
  97         static void store(const T& value, T& storage) { storage = value; }
  98
  99         // Type for return value of functions that transfer ownership, such as take.
 100         typedef T PassOutType;
 101         static const T& passOut(const T& value) { return value; }
 102
 103         // Type for return value of functions that do not transfer ownership, such as get.
 104         // FIXME: We could change this type to const T& for better performance if we figured out
 105         // a way to handle the return value from emptyValue, which is a temporary.
 106         typedef T PeekOutType;
 107         static const T& peek(const T& value) { return value; }
 108     };
 109
 110     template<typename T> struct HashTraits : GenericHashTraits<T> { };
 111
 112     template<typename T> struct FloatHashTraits : GenericHashTraits<T> {
 113         static T emptyValue() { return std::numeric_limits<T>::infinity(); }
 114         static void constructDeletedValue(T& slot, bool) { slot = -std::numeric_limits<T>::infinity(); }
 115         static bool isDeletedValue(T value) { return value == -std::numeric_limits<T>::infinity(); }
 116     };
 117
 118     template<> struct HashTraits<float> : FloatHashTraits<float> { };
 119     template<> struct HashTraits<double> : FloatHashTraits<double> { };
 120
 121     // Default unsigned traits disallow both 0 and max as keys -- use these traits to allow zero and disallow max - 1.
 122     template<typename T> struct UnsignedWithZeroKeyHashTraits : GenericHashTraits<T> {
 123         static const bool emptyValueIsZero = false;
 124         static T emptyValue() { return std::numeric_limits<T>::max(); }
 125         static void constructDeletedValue(T& slot, bool) { slot = std::numeric_limits<T>::max() - 1; }
 126         static bool isDeletedValue(T value) { return value == std::numeric_limits<T>::max() - 1; }
 127     };
 128
 129     template<typename P> struct HashTraits<P*> : GenericHashTraits<P*> {
 130         static const bool emptyValueIsZero = true;
 131         static void constructDeletedValue(P*& slot, bool) { slot = reinterpret_cast<P*>(-1); }
 132         static bool isDeletedValue(P* value) { return value == reinterpret_cast<P*>(-1); }
 133     };
 134
 135     template<typename T> struct SimpleClassHashTraits : GenericHashTraits<T> {
 136         static const bool emptyValueIsZero = true;
 137         static void constructDeletedValue(T& slot, bool) { new (NotNull, &slot) T(HashTableDeletedValue); }
 138         static bool isDeletedValue(const T& value) { return value.isHashTableDeletedValue(); }
 139     };
 140
 141     template<typename P> struct HashTraits<OwnPtr<P>> : SimpleClassHashTraits<OwnPtr<P>> {
 142         typedef std::nullptr_t EmptyValueType;
 143
 144         static EmptyValueType emptyValue() { return nullptr; }
 145
 146         static const bool hasIsEmptyValueFunction = true;
 147         static bool isEmptyValue(const OwnPtr<P>& value) { return !value; }
 148
 149         typedef typename OwnPtr<P>::PtrType PeekInType;
 150
 151         typedef PassOwnPtr<P> PassInType;
 152         static void store(PassOwnPtr<P> value, OwnPtr<P>& storage) { storage = value; }
 153
 154         typedef PassOwnPtr<P> PassOutType;
 155         static PassOwnPtr<P> passOut(OwnPtr<P>& value) { return value.release(); }
 156         static PassOwnPtr<P> passOut(std::nullptr_t) { return nullptr; }
 157
 158         typedef typename OwnPtr<P>::PtrType PeekOutType;
 159         static PeekOutType peek(const OwnPtr<P>& value) { return value.get(); }
 160         static PeekOutType peek(std::nullptr_t) { return 0; }
 161     };
 162
 163     template<typename P> struct HashTraits<RefPtr<P>> : SimpleClassHashTraits<RefPtr<P>> {
 164         typedef std::nullptr_t EmptyValueType;
 165         static EmptyValueType emptyValue() { return nullptr; }
 166
 167         static const bool hasIsEmptyValueFunction = true;
 168         static bool isEmptyValue(const RefPtr<P>& value) { return !value; }
 169
 170         typedef RefPtrValuePeeker<P> PeekInType;
 171         typedef RefPtr<P>* IteratorGetType;
 172         typedef const RefPtr<P>* IteratorConstGetType;
 173         typedef RefPtr<P>& IteratorReferenceType;
 174         typedef const RefPtr<P>& IteratorConstReferenceType;
 175         static IteratorReferenceType getToReferenceConversion(IteratorGetType x) { return *x; }
 176         static IteratorConstReferenceType getToReferenceConstConversion(IteratorConstGetType x) { return *x; }
 177
 178         typedef PassRefPtr<P> PassInType;
 179         static void store(PassRefPtr<P> value, RefPtr<P>& storage) { storage = value; }
 180
 181         typedef PassRefPtr<P> PassOutType;
 182         static PassOutType passOut(RefPtr<P>& value) { return value.release(); }
 183         static PassOutType passOut(std::nullptr_t) { return nullptr; }
 184
 185         typedef P* PeekOutType;
 186         static PeekOutType peek(const RefPtr<P>& value) { return value.get(); }
 187         static PeekOutType peek(std::nullptr_t) { return 0; }
 188     };
 189
 190     template<typename T> struct HashTraits<RawPtr<T>> : HashTraits<T*> { };
 191
 192     template<> struct HashTraits<String> : SimpleClassHashTraits<String> {
 193         static const bool hasIsEmptyValueFunction = true;
 194         static bool isEmptyValue(const String&);
 195     };
 196
 197     // This struct template is an implementation detail of the isHashTraitsEmptyValue function,
 198     // which selects either the emptyValue function or the isEmptyValue function to check for empty values.
 199     template<typename Traits, bool hasEmptyValueFunction> struct HashTraitsEmptyValueChecker;
 200     template<typename Traits> struct HashTraitsEmptyValueChecker<Traits, true> {
 201         template<typename T> static bool isEmptyValue(const T& value) { return Traits::isEmptyValue(value); }
 202     };
 203     template<typename Traits> struct HashTraitsEmptyValueChecker<Traits, false> {
 204         template<typename T> static bool isEmptyValue(const T& value) { return value == Traits::emptyValue(); }
 205     };
 206     template<typename Traits, typename T> inline bool isHashTraitsEmptyValue(const T& value)
 207     {
 208         return HashTraitsEmptyValueChecker<Traits, Traits::hasIsEmptyValueFunction>::isEmptyValue(value);
 209     }
 210
 211     template<typename FirstTraitsArg, typename SecondTraitsArg>
 212     struct PairHashTraits : GenericHashTraits<std::pair<typename FirstTraitsArg::TraitType, typename SecondTraitsArg::TraitType>> {
 213         typedef FirstTraitsArg FirstTraits;
 214         typedef SecondTraitsArg SecondTraits;
 215         typedef std::pair<typename FirstTraits::TraitType, typename SecondTraits::TraitType> TraitType;
 216         typedef std::pair<typename FirstTraits::EmptyValueType, typename SecondTraits::EmptyValueType> EmptyValueType;
 217
 218         static const bool emptyValueIsZero = FirstTraits::emptyValueIsZero && SecondTraits::emptyValueIsZero;
 219         static EmptyValueType emptyValue() { return std::make_pair(FirstTraits::emptyValue(), SecondTraits::emptyValue()); }
 220
 221         static const unsigned minimumTableSize = FirstTraits::minimumTableSize;
 222
 223         static void constructDeletedValue(TraitType& slot, bool zeroValue)
 224         {
 225             FirstTraits::constructDeletedValue(slot.first, zeroValue);
 226             // For GC collections the memory for the backing is zeroed when it
 227             // is allocated, and the constructors may take advantage of that,
 228             // especially if a GC occurs during insertion of an entry into the
 229             // table. This slot is being marked deleted, but If the slot is
 230             // reused at a later point, the same assumptions around memory
 231             // zeroing must hold as they did at the initial allocation.
 232             // Therefore we zero the value part of the slot here for GC
 233             // collections.
 234             if (zeroValue)
 235                 memset(reinterpret_cast<void*>(&slot.second), 0, sizeof(slot.second));
 236         }
 237         static bool isDeletedValue(const TraitType& value) { return FirstTraits::isDeletedValue(value.first); }
 238     };
 239
 240     template<typename First, typename Second>
 241     struct HashTraits<std::pair<First, Second>> : public PairHashTraits<HashTraits<First>, HashTraits<Second>> { };
 242
 243     template<typename KeyTypeArg, typename ValueTypeArg>
 244     struct KeyValuePair {
 245         typedef KeyTypeArg KeyType;
 246
 247         KeyValuePair(const KeyTypeArg& _key, const ValueTypeArg& _value)
 248             : key(_key)
 249             , value(_value)
 250         {
 251         }
 252
 253         template <typename OtherKeyType, typename OtherValueType>
 254         KeyValuePair(const KeyValuePair<OtherKeyType, OtherValueType>& other)
 255             : key(other.key)
 256             , value(other.value)
 257         {
 258         }
 259
 260         KeyTypeArg key;
 261         ValueTypeArg value;
 262     };
 263
 264     template<typename KeyTraitsArg, typename ValueTraitsArg>
 265     struct KeyValuePairHashTraits : GenericHashTraits<KeyValuePair<typename KeyTraitsArg::TraitType, typename ValueTraitsArg::TraitType>> {
 266         typedef KeyTraitsArg KeyTraits;
 267         typedef ValueTraitsArg ValueTraits;
 268         typedef KeyValuePair<typename KeyTraits::TraitType, typename ValueTraits::TraitType> TraitType;
 269         typedef KeyValuePair<typename KeyTraits::EmptyValueType, typename ValueTraits::EmptyValueType> EmptyValueType;
 270
 271         static const bool emptyValueIsZero = KeyTraits::emptyValueIsZero && ValueTraits::emptyValueIsZero;
 272         static EmptyValueType emptyValue() { return KeyValuePair<typename KeyTraits::EmptyValueType, typename ValueTraits::EmptyValueType>(KeyTraits::emptyValue(), ValueTraits::emptyValue()); }
 273
 274         template<typename U = void>
 275         struct NeedsTracingLazily {
 276             static const bool value = ShouldBeTraced<KeyTraits>::value || ShouldBeTraced<ValueTraits>::value;
 277         };
 278         static const WeakHandlingFlag weakHandlingFlag = (KeyTraits::weakHandlingFlag == WeakHandlingInCollections || ValueTraits::weakHandlingFlag == WeakHandlingInCollections) ? WeakHandlingInCollections : NoWeakHandlingInCollections;
 279
 280         static const unsigned minimumTableSize = KeyTraits::minimumTableSize;
 281
 282         static void constructDeletedValue(TraitType& slot, bool zeroValue)
 283         {
 284             KeyTraits::constructDeletedValue(slot.key, zeroValue);
 285             // See similar code in this file for why we need to do this.
 286             if (zeroValue)
 287                 memset(reinterpret_cast<void*>(&slot.value), 0, sizeof(slot.value));
 288         }
 289         static bool isDeletedValue(const TraitType& value) { return KeyTraits::isDeletedValue(value.key); }
 290     };
 291
 292     template<typename Key, typename Value>
 293     struct HashTraits<KeyValuePair<Key, Value>> : public KeyValuePairHashTraits<HashTraits<Key>, HashTraits<Value>> { };
 294
 295     template<typename T>
 296     struct NullableHashTraits : public HashTraits<T> {
 297         static const bool emptyValueIsZero = false;
 298         static T emptyValue() { return reinterpret_cast<T>(1); }
 299     };
 300
 301     // This is for tracing inside collections that have special support for weak
 302     // pointers. The trait has a trace method which returns true if there are weak
 303     // pointers to things that have not (yet) been marked live. Returning true
 304     // indicates that the entry in the collection may yet be removed by weak
 305     // handling. Default implementation for non-weak types is to use the regular
 306     // non-weak TraceTrait. Default implementation for types with weakness is to
 307     // call traceInCollection on the type's trait.
 308     template<WeakHandlingFlag weakHandlingFlag, ShouldWeakPointersBeMarkedStrongly strongify, typename T, typename Traits>
 309     struct TraceInCollectionTrait;
 310
 311 } // namespace WTF
 312
 313 using WTF::HashTraits;
 314 using WTF::PairHashTraits;
 315 using WTF::NullableHashTraits;
 316 using WTF::SimpleClassHashTraits;
 317
 318 #endif // WTF_HashTraits_h