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 needsDestruction flag is used to optimize destruction and rehashing. 58 static const bool needsDestruction = true; 59 60 // The starting table size. Can be overridden when we know beforehand that 61 // a hash table will have at least N entries. 62 #if defined(MEMORY_SANITIZER_INITIAL_SIZE) 63 static const unsigned minimumTableSize = 1; 64 #else 65 static const unsigned minimumTableSize = 8; 66 #endif 67 68 template<typename U = void> 69 struct NeedsTracingLazily { 70 static const bool value = NeedsTracing<T>::value; 71 }; 72 static const WeakHandlingFlag weakHandlingFlag = IsWeak<T>::value ? WeakHandlingInCollections : NoWeakHandlingInCollections; 73 }; 74 75 // Default integer traits disallow both 0 and -1 as keys (max value instead of -1 for unsigned). 76 template<typename T> struct GenericHashTraitsBase<true, T> : GenericHashTraitsBase<false, T> { 77 static const bool emptyValueIsZero = true; 78 static const bool needsDestruction = false; 79 static void constructDeletedValue(T& slot, bool) { slot = static_cast<T>(-1); } 80 static bool isDeletedValue(T value) { return value == static_cast<T>(-1); } 81 }; 82 83 template<typename T> struct GenericHashTraits : GenericHashTraitsBase<IsInteger<T>::value, T> { 84 typedef T TraitType; 85 typedef T EmptyValueType; 86 87 static T emptyValue() { return T(); } 88 89 // Type for functions that do not take ownership, such as contains. 90 typedef const T& PeekInType; 91 typedef T* IteratorGetType; 92 typedef const T* IteratorConstGetType; 93 typedef T& IteratorReferenceType; 94 typedef const T& IteratorConstReferenceType; 95 static IteratorReferenceType getToReferenceConversion(IteratorGetType x) { return *x; } 96 static IteratorConstReferenceType getToReferenceConstConversion(IteratorConstGetType x) { return *x; } 97 // Type for functions that take ownership, such as add. 98 // The store function either not be called or called once to store something passed in. 99 // The value passed to the store function will be PassInType. 100 typedef const T& PassInType; 101 static void store(const T& value, T& storage) { storage = value; } 102 103 // Type for return value of functions that transfer ownership, such as take. 104 typedef T PassOutType; 105 static const T& passOut(const T& value) { return value; } 106 107 // Type for return value of functions that do not transfer ownership, such as get. 108 // FIXME: We could change this type to const T& for better performance if we figured out 109 // a way to handle the return value from emptyValue, which is a temporary. 110 typedef T PeekOutType; 111 static const T& peek(const T& value) { return value; } 112 }; 113 114 template<typename T> struct HashTraits : GenericHashTraits<T> { }; 115 116 template<typename T> struct FloatHashTraits : GenericHashTraits<T> { 117 static const bool needsDestruction = false; 118 static T emptyValue() { return std::numeric_limits<T>::infinity(); } 119 static void constructDeletedValue(T& slot, bool) { slot = -std::numeric_limits<T>::infinity(); } 120 static bool isDeletedValue(T value) { return value == -std::numeric_limits<T>::infinity(); } 121 }; 122 123 template<> struct HashTraits<float> : FloatHashTraits<float> { }; 124 template<> struct HashTraits<double> : FloatHashTraits<double> { }; 125 126 // Default unsigned traits disallow both 0 and max as keys -- use these traits to allow zero and disallow max - 1. 127 template<typename T> struct UnsignedWithZeroKeyHashTraits : GenericHashTraits<T> { 128 static const bool emptyValueIsZero = false; 129 static const bool needsDestruction = false; 130 static T emptyValue() { return std::numeric_limits<T>::max(); } 131 static void constructDeletedValue(T& slot, bool) { slot = std::numeric_limits<T>::max() - 1; } 132 static bool isDeletedValue(T value) { return value == std::numeric_limits<T>::max() - 1; } 133 }; 134 135 template<typename P> struct HashTraits<P*> : GenericHashTraits<P*> { 136 static const bool emptyValueIsZero = true; 137 static const bool needsDestruction = false; 138 static void constructDeletedValue(P*& slot, bool) { slot = reinterpret_cast<P*>(-1); } 139 static bool isDeletedValue(P* value) { return value == reinterpret_cast<P*>(-1); } 140 }; 141 142 template<typename T> struct SimpleClassHashTraits : GenericHashTraits<T> { 143 static const bool emptyValueIsZero = true; 144 static void constructDeletedValue(T& slot, bool) { new (NotNull, &slot) T(HashTableDeletedValue); } 145 static bool isDeletedValue(const T& value) { return value.isHashTableDeletedValue(); } 146 }; 147 148 template<typename P> struct HashTraits<OwnPtr<P> > : SimpleClassHashTraits<OwnPtr<P> > { 149 typedef std::nullptr_t EmptyValueType; 150 151 static EmptyValueType emptyValue() { return nullptr; } 152 153 static const bool hasIsEmptyValueFunction = true; 154 static bool isEmptyValue(const OwnPtr<P>& value) { return !value; } 155 156 typedef typename OwnPtr<P>::PtrType PeekInType; 157 158 typedef PassOwnPtr<P> PassInType; 159 static void store(PassOwnPtr<P> value, OwnPtr<P>& storage) { storage = value; } 160 161 typedef PassOwnPtr<P> PassOutType; 162 static PassOwnPtr<P> passOut(OwnPtr<P>& value) { return value.release(); } 163 static PassOwnPtr<P> passOut(std::nullptr_t) { return nullptr; } 164 165 typedef typename OwnPtr<P>::PtrType PeekOutType; 166 static PeekOutType peek(const OwnPtr<P>& value) { return value.get(); } 167 static PeekOutType peek(std::nullptr_t) { return 0; } 168 }; 169 170 template<typename P> struct HashTraits<RefPtr<P> > : SimpleClassHashTraits<RefPtr<P> > { 171 typedef std::nullptr_t EmptyValueType; 172 static EmptyValueType emptyValue() { return nullptr; } 173 174 static const bool hasIsEmptyValueFunction = true; 175 static bool isEmptyValue(const RefPtr<P>& value) { return !value; } 176 177 typedef RefPtrValuePeeker<P> PeekInType; 178 typedef RefPtr<P>* IteratorGetType; 179 typedef const RefPtr<P>* IteratorConstGetType; 180 typedef RefPtr<P>& IteratorReferenceType; 181 typedef const RefPtr<P>& IteratorConstReferenceType; 182 static IteratorReferenceType getToReferenceConversion(IteratorGetType x) { return *x; } 183 static IteratorConstReferenceType getToReferenceConstConversion(IteratorConstGetType x) { return *x; } 184 185 typedef PassRefPtr<P> PassInType; 186 static void store(PassRefPtr<P> value, RefPtr<P>& storage) { storage = value; } 187 188 typedef PassRefPtr<P> PassOutType; 189 static PassOutType passOut(RefPtr<P>& value) { return value.release(); } 190 static PassOutType passOut(std::nullptr_t) { return nullptr; } 191 192 typedef P* PeekOutType; 193 static PeekOutType peek(const RefPtr<P>& value) { return value.get(); } 194 static PeekOutType peek(std::nullptr_t) { return 0; } 195 }; 196 197 template<typename T> struct HashTraits<RawPtr<T> > : HashTraits<T*> { }; 198 199 template<> struct HashTraits<String> : SimpleClassHashTraits<String> { 200 static const bool hasIsEmptyValueFunction = true; 201 static bool isEmptyValue(const String&); 202 }; 203 204 // This struct template is an implementation detail of the isHashTraitsEmptyValue function, 205 // which selects either the emptyValue function or the isEmptyValue function to check for empty values. 206 template<typename Traits, bool hasEmptyValueFunction> struct HashTraitsEmptyValueChecker; 207 template<typename Traits> struct HashTraitsEmptyValueChecker<Traits, true> { 208 template<typename T> static bool isEmptyValue(const T& value) { return Traits::isEmptyValue(value); } 209 }; 210 template<typename Traits> struct HashTraitsEmptyValueChecker<Traits, false> { 211 template<typename T> static bool isEmptyValue(const T& value) { return value == Traits::emptyValue(); } 212 }; 213 template<typename Traits, typename T> inline bool isHashTraitsEmptyValue(const T& value) 214 { 215 return HashTraitsEmptyValueChecker<Traits, Traits::hasIsEmptyValueFunction>::isEmptyValue(value); 216 } 217 218 template<typename FirstTraitsArg, typename SecondTraitsArg> 219 struct PairHashTraits : GenericHashTraits<std::pair<typename FirstTraitsArg::TraitType, typename SecondTraitsArg::TraitType> > { 220 typedef FirstTraitsArg FirstTraits; 221 typedef SecondTraitsArg SecondTraits; 222 typedef std::pair<typename FirstTraits::TraitType, typename SecondTraits::TraitType> TraitType; 223 typedef std::pair<typename FirstTraits::EmptyValueType, typename SecondTraits::EmptyValueType> EmptyValueType; 224 225 static const bool emptyValueIsZero = FirstTraits::emptyValueIsZero && SecondTraits::emptyValueIsZero; 226 static EmptyValueType emptyValue() { return std::make_pair(FirstTraits::emptyValue(), SecondTraits::emptyValue()); } 227 228 static const bool needsDestruction = FirstTraits::needsDestruction || SecondTraits::needsDestruction; 229 230 static const unsigned minimumTableSize = FirstTraits::minimumTableSize; 231 232 static void constructDeletedValue(TraitType& slot, bool zeroValue) 233 { 234 FirstTraits::constructDeletedValue(slot.first, zeroValue); 235 // For GC collections the memory for the backing is zeroed when it 236 // is allocated, and the constructors may take advantage of that, 237 // especially if a GC occurs during insertion of an entry into the 238 // table. This slot is being marked deleted, but If the slot is 239 // reused at a later point, the same assumptions around memory 240 // zeroing must hold as they did at the initial allocation. 241 // Therefore we zero the value part of the slot here for GC 242 // collections. 243 if (zeroValue) 244 memset(reinterpret_cast<void*>(&slot.second), 0, sizeof(slot.second)); 245 } 246 static bool isDeletedValue(const TraitType& value) { return FirstTraits::isDeletedValue(value.first); } 247 }; 248 249 template<typename First, typename Second> 250 struct HashTraits<std::pair<First, Second> > : public PairHashTraits<HashTraits<First>, HashTraits<Second> > { }; 251 252 template<typename KeyTypeArg, typename ValueTypeArg> 253 struct KeyValuePair { 254 typedef KeyTypeArg KeyType; 255 256 KeyValuePair(const KeyTypeArg& _key, const ValueTypeArg& _value) 257 : key(_key) 258 , value(_value) 259 { 260 } 261 262 template <typename OtherKeyType, typename OtherValueType> 263 KeyValuePair(const KeyValuePair<OtherKeyType, OtherValueType>& other) 264 : key(other.key) 265 , value(other.value) 266 { 267 } 268 269 KeyTypeArg key; 270 ValueTypeArg value; 271 }; 272 273 template<typename KeyTraitsArg, typename ValueTraitsArg> 274 struct KeyValuePairHashTraits : GenericHashTraits<KeyValuePair<typename KeyTraitsArg::TraitType, typename ValueTraitsArg::TraitType> > { 275 typedef KeyTraitsArg KeyTraits; 276 typedef ValueTraitsArg ValueTraits; 277 typedef KeyValuePair<typename KeyTraits::TraitType, typename ValueTraits::TraitType> TraitType; 278 typedef KeyValuePair<typename KeyTraits::EmptyValueType, typename ValueTraits::EmptyValueType> EmptyValueType; 279 280 static const bool emptyValueIsZero = KeyTraits::emptyValueIsZero && ValueTraits::emptyValueIsZero; 281 static EmptyValueType emptyValue() { return KeyValuePair<typename KeyTraits::EmptyValueType, typename ValueTraits::EmptyValueType>(KeyTraits::emptyValue(), ValueTraits::emptyValue()); } 282 283 static const bool needsDestruction = KeyTraits::needsDestruction || ValueTraits::needsDestruction; 284 template<typename U = void> 285 struct NeedsTracingLazily { 286 static const bool value = ShouldBeTraced<KeyTraits>::value || ShouldBeTraced<ValueTraits>::value; 287 }; 288 static const WeakHandlingFlag weakHandlingFlag = (KeyTraits::weakHandlingFlag == WeakHandlingInCollections || ValueTraits::weakHandlingFlag == WeakHandlingInCollections) ? WeakHandlingInCollections : NoWeakHandlingInCollections; 289 290 static const unsigned minimumTableSize = KeyTraits::minimumTableSize; 291 292 static void constructDeletedValue(TraitType& slot, bool zeroValue) 293 { 294 KeyTraits::constructDeletedValue(slot.key, zeroValue); 295 // See similar code in this file for why we need to do this. 296 if (zeroValue) 297 memset(reinterpret_cast<void*>(&slot.value), 0, sizeof(slot.value)); 298 } 299 static bool isDeletedValue(const TraitType& value) { return KeyTraits::isDeletedValue(value.key); } 300 }; 301 302 template<typename Key, typename Value> 303 struct HashTraits<KeyValuePair<Key, Value> > : public KeyValuePairHashTraits<HashTraits<Key>, HashTraits<Value> > { }; 304 305 template<typename T> 306 struct NullableHashTraits : public HashTraits<T> { 307 static const bool emptyValueIsZero = false; 308 static T emptyValue() { return reinterpret_cast<T>(1); } 309 }; 310 311 // This is for tracing inside collections that have special support for weak 312 // pointers. The trait has a trace method which returns true if there are weak 313 // pointers to things that have not (yet) been marked live. Returning true 314 // indicates that the entry in the collection may yet be removed by weak 315 // handling. Default implementation for non-weak types is to use the regular 316 // non-weak TraceTrait. Default implementation for types with weakness is to 317 // call traceInCollection on the type's trait. 318 template<WeakHandlingFlag weakHandlingFlag, ShouldWeakPointersBeMarkedStrongly strongify, typename T, typename Traits> 319 struct TraceInCollectionTrait; 320 321 } // namespace WTF 322 323 using WTF::HashTraits; 324 using WTF::PairHashTraits; 325 using WTF::NullableHashTraits; 326 using WTF::SimpleClassHashTraits; 327 328 #endif // WTF_HashTraits_h 329