runtime/StructureTransitionTable.h

   1 /*
   2  * Copyright (C) 2008, 2009 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef StructureTransitionTable_h
  27 #define StructureTransitionTable_h
  28
  29 #include "UString.h"
  30 #include "WeakGCMap.h"
  31 #include <wtf/HashFunctions.h>
  32 #include <wtf/HashTraits.h>
  33 #include <wtf/OwnPtr.h>
  34 #include <wtf/RefPtr.h>
  35
  36 namespace JSC {
  37
  38 class Structure;
  39
  40 class StructureTransitionTable {
  41     static const intptr_t UsingSingleSlotFlag = 1;
  42
  43     struct Hash {
  44         typedef std::pair<RefPtr<StringImpl>, unsigned> Key;
  45         static unsigned hash(const Key& p)
  46         {
  47             return p.first->existingHash();
  48         }
  49
  50         static bool equal(const Key& a, const Key& b)
  51         {
  52             return a == b;
  53         }
  54
  55         static const bool safeToCompareToEmptyOrDeleted = true;
  56     };
  57
  58     struct HashTraits {
  59         typedef WTF::HashTraits<RefPtr<StringImpl> > FirstTraits;
  60         typedef WTF::GenericHashTraits<unsigned> SecondTraits;
  61         typedef std::pair<FirstTraits::TraitType, SecondTraits::TraitType > TraitType;
  62
  63         static const bool emptyValueIsZero = FirstTraits::emptyValueIsZero && SecondTraits::emptyValueIsZero;
  64         static TraitType emptyValue() { return std::make_pair(FirstTraits::emptyValue(), SecondTraits::emptyValue()); }
  65
  66         static const bool needsDestruction = FirstTraits::needsDestruction || SecondTraits::needsDestruction;
  67
  68         static void constructDeletedValue(TraitType& slot) { FirstTraits::constructDeletedValue(slot.first); }
  69         static bool isDeletedValue(const TraitType& value) { return FirstTraits::isDeletedValue(value.first); }
  70     };
  71
  72     struct WeakGCMapFinalizerCallback {
  73         static void* finalizerContextFor(Hash::Key)
  74         {
  75             return 0;
  76         }
  77
  78         static inline Hash::Key keyForFinalizer(void* context, Structure* structure)
  79         {
  80             return keyForWeakGCMapFinalizer(context, structure);
  81         }
  82     };
  83
  84     typedef WeakGCMap<Hash::Key, Structure, WeakGCMapFinalizerCallback, Hash, HashTraits> TransitionMap;
  85
  86     static Hash::Key keyForWeakGCMapFinalizer(void* context, Structure*);
  87
  88 public:
  89     StructureTransitionTable()
  90         : m_data(UsingSingleSlotFlag)
  91     {
  92     }
  93
  94     ~StructureTransitionTable()
  95     {
  96         if (!isUsingSingleSlot())
  97             delete map();
  98         else
  99             clearSingleTransition();
 100     }
 101
 102     inline void add(JSGlobalData&, Structure*);
 103     inline void remove(Structure*);
 104     inline bool contains(StringImpl* rep, unsigned attributes) const;
 105     inline Structure* get(StringImpl* rep, unsigned attributes) const;
 106
 107 private:
 108     bool isUsingSingleSlot() const
 109     {
 110         return m_data & UsingSingleSlotFlag;
 111     }
 112
 113     TransitionMap* map() const
 114     {
 115         ASSERT(!isUsingSingleSlot());
 116         return reinterpret_cast<TransitionMap*>(m_data);
 117     }
 118
 119     HandleSlot slot() const
 120     {
 121         ASSERT(isUsingSingleSlot());
 122         return reinterpret_cast<HandleSlot>(m_data & ~UsingSingleSlotFlag);
 123     }
 124
 125     void setMap(TransitionMap* map)
 126     {
 127         ASSERT(isUsingSingleSlot());
 128
 129         if (HandleSlot slot = this->slot())
 130             HandleHeap::heapFor(slot)->deallocate(slot);
 131
 132         // This implicitly clears the flag that indicates we're using a single transition
 133         m_data = reinterpret_cast<intptr_t>(map);
 134
 135         ASSERT(!isUsingSingleSlot());
 136     }
 137
 138     Structure* singleTransition() const
 139     {
 140         ASSERT(isUsingSingleSlot());
 141         if (HandleSlot slot = this->slot()) {
 142             if (*slot)
 143                 return reinterpret_cast<Structure*>(slot->asCell());
 144         }
 145         return 0;
 146     }
 147
 148     void clearSingleTransition()
 149     {
 150         ASSERT(isUsingSingleSlot());
 151         if (HandleSlot slot = this->slot())
 152             HandleHeap::heapFor(slot)->deallocate(slot);
 153     }
 154
 155     void setSingleTransition(JSGlobalData& globalData, Structure* structure)
 156     {
 157         ASSERT(isUsingSingleSlot());
 158         HandleSlot slot = this->slot();
 159         if (!slot) {
 160             slot = globalData.allocateGlobalHandle();
 161             HandleHeap::heapFor(slot)->makeWeak(slot, 0, 0);
 162             m_data = reinterpret_cast<intptr_t>(slot) | UsingSingleSlotFlag;
 163         }
 164         HandleHeap::heapFor(slot)->writeBarrier(slot, reinterpret_cast<JSCell*>(structure));
 165         *slot = reinterpret_cast<JSCell*>(structure);
 166     }
 167
 168     intptr_t m_data;
 169 };
 170
 171 } // namespace JSC
 172
 173 #endif // StructureTransitionTable_h