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      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