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      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
    174