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/OwnPtr.h>
  33 #include <wtf/RefPtr.h>
  34
  35 namespace JSC {
  36
  37 class JSCell;
  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 WeakGCMapFinalizerCallback {
  59         static void* finalizerContextFor(Hash::Key)
  60         {
  61             return 0;
  62         }
  63
  64         static inline Hash::Key keyForFinalizer(void* context, Structure* structure)
  65         {
  66             return keyForWeakGCMapFinalizer(context, structure);
  67         }
  68     };
  69
  70     typedef WeakGCMap<Hash::Key, Structure, WeakGCMapFinalizerCallback, Hash> TransitionMap;
  71
  72     static Hash::Key keyForWeakGCMapFinalizer(void* context, Structure*);
  73
  74 public:
  75     StructureTransitionTable()
  76         : m_data(UsingSingleSlotFlag)
  77     {
  78     }
  79
  80     ~StructureTransitionTable()
  81     {
  82         if (!isUsingSingleSlot()) {
  83             delete map();
  84             return;
  85         }
  86
  87         WeakImpl* impl = this->weakImpl();
  88         if (!impl)
  89             return;
  90         WeakSet::deallocate(impl);
  91     }
  92
  93     inline void add(JSGlobalData&, Structure*);
  94     inline bool contains(StringImpl* rep, unsigned attributes) const;
  95     inline Structure* get(StringImpl* rep, unsigned attributes) const;
  96
  97 private:
  98     bool isUsingSingleSlot() const
  99     {
 100         return m_data & UsingSingleSlotFlag;
 101     }
 102
 103     TransitionMap* map() const
 104     {
 105         ASSERT(!isUsingSingleSlot());
 106         return reinterpret_cast<TransitionMap*>(m_data);
 107     }
 108
 109     WeakImpl* weakImpl() const
 110     {
 111         ASSERT(isUsingSingleSlot());
 112         return reinterpret_cast<WeakImpl*>(m_data & ~UsingSingleSlotFlag);
 113     }
 114
 115     void setMap(TransitionMap* map)
 116     {
 117         ASSERT(isUsingSingleSlot());
 118
 119         if (WeakImpl* impl = this->weakImpl())
 120             WeakSet::deallocate(impl);
 121
 122         // This implicitly clears the flag that indicates we're using a single transition
 123         m_data = reinterpret_cast<intptr_t>(map);
 124
 125         ASSERT(!isUsingSingleSlot());
 126     }
 127
 128     Structure* singleTransition() const
 129     {
 130         ASSERT(isUsingSingleSlot());
 131         if (WeakImpl* impl = this->weakImpl()) {
 132             if (impl->state() == WeakImpl::Live)
 133                 return reinterpret_cast<Structure*>(impl->jsValue().asCell());
 134         }
 135         return 0;
 136     }
 137
 138     void setSingleTransition(JSGlobalData&, Structure* structure)
 139     {
 140         ASSERT(isUsingSingleSlot());
 141         if (WeakImpl* impl = this->weakImpl())
 142             WeakSet::deallocate(impl);
 143         WeakImpl* impl = WeakSet::allocate(reinterpret_cast<JSCell*>(structure));
 144         m_data = reinterpret_cast<intptr_t>(impl) | UsingSingleSlotFlag;
 145     }
 146
 147     intptr_t m_data;
 148 };
 149
 150 } // namespace JSC
 151
 152 #endif // StructureTransitionTable_h