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 <wtf/HashFunctions.h>
  31 #include <wtf/HashMap.h>
  32 #include <wtf/HashTraits.h>
  33 #include <wtf/RefPtr.h>
  34
  35 namespace JSC {
  36
  37     class Structure;
  38
  39     struct StructureTransitionTableHash {
  40         typedef std::pair<RefPtr<UString::Rep>, unsigned> Key;
  41         static unsigned hash(const Key& p)
  42         {
  43             return p.first->computedHash();
  44         }
  45
  46         static bool equal(const Key& a, const Key& b)
  47         {
  48             return a == b;
  49         }
  50
  51         static const bool safeToCompareToEmptyOrDeleted = true;
  52     };
  53
  54     struct StructureTransitionTableHashTraits {
  55         typedef WTF::HashTraits<RefPtr<UString::Rep> > FirstTraits;
  56         typedef WTF::GenericHashTraits<unsigned> SecondTraits;
  57         typedef std::pair<FirstTraits::TraitType, SecondTraits::TraitType > TraitType;
  58
  59         static const bool emptyValueIsZero = FirstTraits::emptyValueIsZero && SecondTraits::emptyValueIsZero;
  60         static TraitType emptyValue() { return std::make_pair(FirstTraits::emptyValue(), SecondTraits::emptyValue()); }
  61
  62         static const bool needsDestruction = FirstTraits::needsDestruction || SecondTraits::needsDestruction;
  63
  64         static void constructDeletedValue(TraitType& slot) { FirstTraits::constructDeletedValue(slot.first); }
  65         static bool isDeletedValue(const TraitType& value) { return FirstTraits::isDeletedValue(value.first); }
  66     };
  67
  68     class StructureTransitionTable {
  69         typedef std::pair<Structure*, Structure*> Transition;
  70         typedef HashMap<StructureTransitionTableHash::Key, Transition, StructureTransitionTableHash, StructureTransitionTableHashTraits> TransitionTable;
  71     public:
  72         // The contains and get methods accept imprecise matches, so if an unspecialised transition exists
  73         // for the given key they will consider that transition to be a match.  If a specialised transition
  74         // exists and it matches the provided specificValue, get will return the specific transition.
  75         inline bool contains(const StructureTransitionTableHash::Key&, JSCell* specificValue);
  76         inline Structure* get(const StructureTransitionTableHash::Key&, JSCell* specificValue) const;
  77         bool hasTransition(const StructureTransitionTableHash::Key& key)
  78         {
  79             return m_table.contains(key);
  80         }
  81         void remove(const StructureTransitionTableHash::Key& key, JSCell* specificValue)
  82         {
  83             TransitionTable::iterator find = m_table.find(key);
  84             if (!specificValue)
  85                 find->second.first = 0;
  86             else
  87                 find->second.second = 0;
  88             if (!find->second.first && !find->second.second)
  89                 m_table.remove(find);
  90         }
  91         void add(const StructureTransitionTableHash::Key& key, Structure* structure, JSCell* specificValue)
  92         {
  93             if (!specificValue) {
  94                 TransitionTable::iterator find = m_table.find(key);
  95                 if (find == m_table.end())
  96                     m_table.add(key, Transition(structure, 0));
  97                 else
  98                     find->second.first = structure;
  99             } else {
 100                 // If we're adding a transition to a specific value, then there cannot be
 101                 // an existing transition
 102                 ASSERT(!m_table.contains(key));
 103                 m_table.add(key, Transition(0, structure));
 104             }
 105
 106         }
 107     private:
 108         TransitionTable m_table;
 109     };
 110
 111 } // namespace JSC
 112
 113 #endif // StructureTransitionTable_h