Changeset 54798 in webkit for trunk/JavaScriptCore/runtime/Structure.h

Timestamp:

Feb 15, 2010, 2:37:43 PM (15 years ago)

Author:

[email protected]

Message:

​https://bugs.webkit.org/show_bug.cgi?id=33731
Many false leaks in release builds due to PtrAndFlags

Reviewed by Darin Adler.

JavaScriptCore:

StructureTransitionTable was effectively a smart pointer type,
one machine word in size and wholly contained as a member of
of Structure. It either pointed to an actual table, or could
be used to describe a single transtion entry without use of a
table.

This, however, worked by using a PtrAndFlags, which is not
compatible with the leaks tool. Since there is no clear way to
obtain another bit for 'free' here, and since there are bits
available up in Structure, merge this functionality back up into
Structure. Having this in a separate class was quite clean
from an enacapsulation perspective, but this solution doesn't
seem to bad - all table access is now intermediated through the
Structure::structureTransitionTableFoo methods, keeping the
optimization fairly well contained.

This was the last use of PtrAndFlags, so removing the file too.

• JavaScriptCore.xcodeproj/project.pbxproj:
• bytecode/CodeBlock.h:
• runtime/Structure.cpp:

(JSC::Structure::Structure):
(JSC::Structure::~Structure):
(JSC::Structure::addPropertyTransitionToExistingStructure):
(JSC::Structure::addPropertyTransition):
(JSC::Structure::hasTransition):

• runtime/Structure.h:

(JSC::Structure::):
(JSC::Structure::structureTransitionTableContains):
(JSC::Structure::structureTransitionTableGet):
(JSC::Structure::structureTransitionTableHasTransition):
(JSC::Structure::structureTransitionTableRemove):
(JSC::Structure::structureTransitionTableAdd):
(JSC::Structure::structureTransitionTable):
(JSC::Structure::setStructureTransitionTable):
(JSC::Structure::singleTransition):
(JSC::Structure::setSingleTransition):

• runtime/StructureTransitionTable.h:
• wtf/PtrAndFlags.h: Removed.

WebCore:

PtrAndFlags has now been removed; remove forwarding header.

• ForwardingHeaders/wtf/PtrAndFlags.h: Removed.

File:

• trunk/JavaScriptCore/runtime/Structure.h (modified) (4 diffs)

trunk/JavaScriptCore/runtime/Structure.h

@@ -180 +180 @@
             return m_offset == noOffset ? 0 : m_offset + 1;
         }
+
+        typedef std::pair<Structure*, Structure*> Transition;
+        typedef HashMap<StructureTransitionTableHash::Key, Transition, StructureTransitionTableHash, StructureTransitionTableHashTraits> TransitionTable;
+
+        inline bool transitionTableContains(const StructureTransitionTableHash::Key& key, JSCell* specificValue);
+        inline void transitionTableRemove(const StructureTransitionTableHash::Key& key, JSCell* specificValue);
+        inline void transitionTableAdd(const StructureTransitionTableHash::Key& key, Structure* structure, JSCell* specificValue);
+        inline bool transitionTableHasTransition(const StructureTransitionTableHash::Key& key) const;
+        inline Structure* transitionTableGet(const StructureTransitionTableHash::Key& key, JSCell* specificValue) const;
+
+        TransitionTable* transitionTable() const { ASSERT(!m_isUsingSingleSlot); return m_transitions.m_table; }
+        inline void setTransitionTable(TransitionTable* table);
+        Structure* singleTransition() const { ASSERT(m_isUsingSingleSlot); return m_transitions.m_singleTransition; }
+        void setSingleTransition(Structure* structure) { ASSERT(m_isUsingSingleSlot); m_transitions.m_singleTransition = structure; }
         
         bool isValid(ExecState*, StructureChain* cachedPrototypeChain) const;
@@ -200 +214 @@
         JSCell* m_specificValueInPrevious;
 
-        StructureTransitionTable table;
+        // 'm_isUsingSingleSlot' indicates whether we are using the single transition optimisation.
+        union {
+            TransitionTable* m_table;
+            Structure* m_singleTransition;
+        } m_transitions;
 
         WeakGCPtr<JSPropertyNameIterator> m_enumerationCache;
@@ -225 +243 @@
         unsigned m_specificFunctionThrashCount : 2;
         unsigned m_anonymousSlotCount : 5;
-        // 5 free bits
+        unsigned m_isUsingSingleSlot : 1;
+        // 4 free bits
     };
 
@@ -272 +291 @@
         }
     }
-    
-    bool StructureTransitionTable::contains(const StructureTransitionTableHash::Key& key, JSCell* specificValue)
-    {
-        if (usingSingleTransitionSlot()) {
-            Structure* existingTransition = singleTransition();
-            return existingTransition && existingTransition->m_nameInPrevious.get() == key.first
-                   && existingTransition->m_attributesInPrevious == key.second
-                   && (existingTransition->m_specificValueInPrevious == specificValue || existingTransition->m_specificValueInPrevious == 0);
-        }
-        TransitionTable::iterator find = table()->find(key);
-        if (find == table()->end())
-            return false;
-
-        return find->second.first || find->second.second->transitionedFor(specificValue);
-    }
-
-    Structure* StructureTransitionTable::get(const StructureTransitionTableHash::Key& key, JSCell* specificValue) const
-    {
-        if (usingSingleTransitionSlot()) {
-            Structure* existingTransition = singleTransition();
-            if (existingTransition && existingTransition->m_nameInPrevious.get() == key.first
-                && existingTransition->m_attributesInPrevious == key.second
-                && (existingTransition->m_specificValueInPrevious == specificValue || existingTransition->m_specificValueInPrevious == 0))
-                return existingTransition;
-            return 0;
-        }
-
-        Transition transition = table()->get(key);
-        if (transition.second && transition.second->transitionedFor(specificValue))
-            return transition.second;
-        return transition.first;
-    }
-
-    bool StructureTransitionTable::hasTransition(const StructureTransitionTableHash::Key& key) const
-    {
-        if (usingSingleTransitionSlot()) {
-            Structure* transition = singleTransition();
-            return transition && transition->m_nameInPrevious == key.first
-            && transition->m_attributesInPrevious == key.second;
-        }
-        return table()->contains(key);
-    }
-    
-    void StructureTransitionTable::reifySingleTransition()
-    {
-        ASSERT(usingSingleTransitionSlot());
-        Structure* existingTransition = singleTransition();
-        TransitionTable* transitionTable = new TransitionTable;
-        setTransitionTable(transitionTable);
-        if (existingTransition)
-            add(std::make_pair(existingTransition->m_nameInPrevious.get(), existingTransition->m_attributesInPrevious), existingTransition, existingTransition->m_specificValueInPrevious);
-    }
+
 } // namespace JSC