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26 #ifndef StructureTransitionTable_h
27 #define StructureTransitionTable_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>
40 class StructureTransitionTable {
41 static const intptr_t UsingSingleSlotFlag = 1;
44 typedef std::pair<RefPtr<StringImpl>, unsigned> Key;
45 static unsigned hash(const Key& p)
47 return p.first->existingHash();
50 static bool equal(const Key& a, const Key& b)
55 static const bool safeToCompareToEmptyOrDeleted = true;
59 typedef WTF::HashTraits<RefPtr<StringImpl> > FirstTraits;
60 typedef WTF::GenericHashTraits<unsigned> SecondTraits;
61 typedef std::pair<FirstTraits::TraitType, SecondTraits::TraitType > TraitType;
63 static const bool emptyValueIsZero = FirstTraits::emptyValueIsZero && SecondTraits::emptyValueIsZero;
64 static TraitType emptyValue() { return std::make_pair(FirstTraits::emptyValue(), SecondTraits::emptyValue()); }
66 static const bool needsDestruction = FirstTraits::needsDestruction || SecondTraits::needsDestruction;
68 static const int minimumTableSize = FirstTraits::minimumTableSize;
70 static void constructDeletedValue(TraitType& slot) { FirstTraits::constructDeletedValue(slot.first); }
71 static bool isDeletedValue(const TraitType& value) { return FirstTraits::isDeletedValue(value.first); }
74 struct WeakGCMapFinalizerCallback {
75 static void* finalizerContextFor(Hash::Key)
80 static inline Hash::Key keyForFinalizer(void* context, Structure* structure)
82 return keyForWeakGCMapFinalizer(context, structure);
86 typedef WeakGCMap<Hash::Key, Structure, WeakGCMapFinalizerCallback, Hash, HashTraits> TransitionMap;
88 static Hash::Key keyForWeakGCMapFinalizer(void* context, Structure*);
91 StructureTransitionTable()
92 : m_data(UsingSingleSlotFlag)
96 ~StructureTransitionTable()
98 if (!isUsingSingleSlot()) {
103 HandleSlot slot = this->slot();
106 HandleHeap::heapFor(slot)->deallocate(slot);
109 inline void add(JSGlobalData&, Structure*);
110 inline bool contains(StringImpl* rep, unsigned attributes) const;
111 inline Structure* get(StringImpl* rep, unsigned attributes) const;
114 bool isUsingSingleSlot() const
116 return m_data & UsingSingleSlotFlag;
119 TransitionMap* map() const
121 ASSERT(!isUsingSingleSlot());
122 return reinterpret_cast<TransitionMap*>(m_data);
125 HandleSlot slot() const
127 ASSERT(isUsingSingleSlot());
128 return reinterpret_cast<HandleSlot>(m_data & ~UsingSingleSlotFlag);
131 void setMap(TransitionMap* map)
133 ASSERT(isUsingSingleSlot());
135 if (HandleSlot slot = this->slot())
136 HandleHeap::heapFor(slot)->deallocate(slot);
138 // This implicitly clears the flag that indicates we're using a single transition
139 m_data = reinterpret_cast<intptr_t>(map);
141 ASSERT(!isUsingSingleSlot());
144 Structure* singleTransition() const
146 ASSERT(isUsingSingleSlot());
147 if (HandleSlot slot = this->slot()) {
149 return reinterpret_cast<Structure*>(slot->asCell());
154 void setSingleTransition(JSGlobalData& globalData, Structure* structure)
156 ASSERT(isUsingSingleSlot());
157 HandleSlot slot = this->slot();
159 slot = globalData.allocateGlobalHandle();
160 HandleHeap::heapFor(slot)->makeWeak(slot, 0, 0);
161 m_data = reinterpret_cast<intptr_t>(slot) | UsingSingleSlotFlag;
163 HandleHeap::heapFor(slot)->writeBarrier(slot, reinterpret_cast<JSCell*>(structure));
164 *slot = reinterpret_cast<JSCell*>(structure);
172 #endif // StructureTransitionTable_h