Changeset 38407 in webkit for trunk/JavaScriptCore/runtime/JSObject.h

Timestamp:

Nov 14, 2008, 3:36:06 PM (17 years ago)

Author:

[email protected]

Message:

2008-11-13 Sam Weinig <​[email protected]>

Reviewed by Darin Adler

Fix for ​https://bugs.webkit.org/show_bug.cgi?id=22269
Reduce PropertyMap usage

From observation of StructureID statistics, it became clear that many
StructureID's were not being used as StructureIDs themselves, but rather
only being necessary as links in the transition chain. Acknowledging this
and that PropertyMaps stored in StructureIDs can be treated as caches, that
is that they can be reconstructed on demand, it became clear that we could
reduce the memory consumption of StructureIDs by only keeping PropertyMaps
for the StructureIDs that need them the most.

The specific strategy used to reduce the number of StructureIDs with
PropertyMaps is to take the previous StructureIDs PropertyMap when initially
transitioning (addPropertyTransition) from it and clearing out the pointer
in the process. The next time we need to do the same transition, for instance
repeated calls to the same constructor, we use the new addPropertyTransitionToExistingStructure
first, which allows us not to need the PropertyMap to determine if the property
exists already, since a transition to that property would require it not already
be present in the StructureID. Should there be no transition, the PropertyMap
can be constructed on demand (via materializePropertyMap) to determine if the put is a
replace or a transition to a new StructureID.

Reduces memory use on Membuster head test (30 pages open) by ~15MB.

• JavaScriptCore.exp:
• runtime/JSObject.h: (JSC::JSObject::putDirect): First use addPropertyTransitionToExistingStructure so that we can avoid building the PropertyMap on subsequent similar object creations.
• runtime/PropertyMapHashTable.h: (JSC::PropertyMapEntry::PropertyMapEntry): Add version of constructor which takes all values to be used when lazily building the PropertyMap.
• runtime/StructureID.cpp: (JSC::StructureID::dumpStatistics): Add statistics on the number of StructureIDs with PropertyMaps. (JSC::StructureID::StructureID): Rename m_cachedTransistionOffset to m_offset (JSC::isPowerOf2): (JSC::nextPowerOf2): (JSC::sizeForKeyCount): Returns the expected size of a PropertyMap for a key count. (JSC::StructureID::materializePropertyMap): Builds the PropertyMap out of its previous pointer chain. (JSC::StructureID::addPropertyTransitionToExistingStructure): Only transitions if there is a an existing transition. (JSC::StructureID::addPropertyTransition): Instead of always copying the ProperyMap, try and take it from it previous pointer. (JSC::StructureID::removePropertyTransition): Simplify by calling toDictionaryTransition() to do transition work. (JSC::StructureID::changePrototypeTransition): Build the PropertyMap if necessary before transitioning because once you have transitioned, you will not be able to reconstruct it afterwards as there is no previous pointer, pinning the ProperyMap as well. (JSC::StructureID::getterSetterTransition): Ditto. (JSC::StructureID::toDictionaryTransition): Pin the PropertyMap so that it is not destroyed on further transitions. (JSC::StructureID::fromDictionaryTransition): We can only transition back from a dictionary transition if there are no deleted offsets. (JSC::StructureID::addPropertyWithoutTransition): Build PropertyMap on demands and pin. (JSC::StructureID::removePropertyWithoutTransition): Ditto. (JSC::StructureID::get): Build on demand. (JSC::StructureID::createPropertyMapHashTable): Add version of create that takes a size for on demand building. (JSC::StructureID::expandPropertyMapHashTable): (JSC::StructureID::rehashPropertyMapHashTable): (JSC::StructureID::getEnumerablePropertyNamesInternal): Build PropertyMap on demand.
• runtime/StructureID.h: (JSC::StructureID::propertyStorageSize): Account for StructureIDs without PropertyMaps. (JSC::StructureID::isEmpty): Ditto. (JSC::StructureID::materializePropertyMapIfNecessary): (JSC::StructureID::get): Build PropertyMap on demand

File:

• trunk/JavaScriptCore/runtime/JSObject.h (modified) (2 diffs)

trunk/JavaScriptCore/runtime/JSObject.h

@@ -410 +410 @@
     }
 
+    size_t offset;
+    size_t currentCapacity = m_structureID->propertyStorageCapacity();
+    if (RefPtr<StructureID> structureID = StructureID::addPropertyTransitionToExistingStructure(m_structureID, propertyName, attributes, offset)) {
+        if (currentCapacity != structureID->propertyStorageCapacity())
+            allocatePropertyStorage(currentCapacity, structureID->propertyStorageCapacity());
+
+        ASSERT(offset < structureID->propertyStorageCapacity());
+        m_propertyStorage[offset] = value;
+        slot.setNewProperty(this, offset);
+        slot.setWasTransition(true);
+        setStructureID(structureID.release());
+        return;
+    }
+
     unsigned currentAttributes;
-    size_t offset = m_structureID->get(propertyName, currentAttributes);
+    offset = m_structureID->get(propertyName, currentAttributes);
     if (offset != WTF::notFound) {
         if (checkReadOnly && currentAttributes & ReadOnly)
@@ -420 +434 @@
     }
 
-    size_t currentCapacity = m_structureID->propertyStorageCapacity();
     RefPtr<StructureID> structureID = StructureID::addPropertyTransition(m_structureID, propertyName, attributes, offset);
     if (currentCapacity != structureID->propertyStorageCapacity())