Re-enable freezing of Object.observe changeRecords now that freezing is faster.

src/object-observe.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 290 matching lines @@
 
   var changeRecord = {
     type: 'splice',
     object: array,
     index: index,
     removed: removed,
     addedCount: addedCount
   };
 
   changeRecord.removed.length = deleteCount;
-  // TODO(rafaelw): This breaks spec-compliance. Re-enable when freezing isn't
-  // slow.
-  // ObjectFreeze(changeRecord);
-  // ObjectFreeze(changeRecord.removed);
+  ObjectFreeze(changeRecord);
+  ObjectFreeze(changeRecord.removed);

[adamk, 2013/05/23 21:12:39]

I'd leave this out for now, as it basically doubles the cost of creating a
splice record (create the removed array, then create a dictionary backing store
and copy everything over).

[rafaelw, 2013/05/23 22:53:18]

I went back and tried as hard as I could to create a case where freezing the
removed array impacted the over-all time noticeably -- and failed to produce
anything that was obviously not in the noise.

I think it's fine to leave this in.

On 2013/05/23 21:12:39, adamk wrote:

[adamk, 2013/05/23 22:55:49]

Sounds good to me, thanks for doing the footwork to verify this.

   EnqueueChangeRecord(changeRecord, objectInfo.changeObservers);
 }
 
 function NotifyChange(type, object, name, oldValue) {
   var objectInfo = objectInfoMap.get(object);
   if (objectInfo.changeObservers.length === 0)
     return;
 
   var changeRecord = (arguments.length < 4) ?
       { type: type, object: object, name: name } :
       { type: type, object: object, name: name, oldValue: oldValue };
-  // TODO(rafaelw): This breaks spec-compliance. Re-enable when freezing isn't
-  // slow.
-  // ObjectFreeze(changeRecord);
+  ObjectFreeze(changeRecord);
   EnqueueChangeRecord(changeRecord, objectInfo.changeObservers);
 }
 
 var notifierPrototype = {};
 
 function ObjectNotifierNotify(changeRecord) {
   if (!IS_SPEC_OBJECT(this))
     throw MakeTypeError("called_on_non_object", ["notify"]);
 
   var target = notifierTargetMap.get(this);
   if (IS_UNDEFINED(target))
     throw MakeTypeError("observe_notify_non_notifier");
   if (!IS_STRING(changeRecord.type))
     throw MakeTypeError("observe_type_non_string");
 
   var objectInfo = objectInfoMap.get(target);
   if (IS_UNDEFINED(objectInfo) || objectInfo.changeObservers.length === 0)
     return;
 
   var newRecord = { object: target };
   for (var prop in changeRecord) {
     if (prop === 'object') continue;
     %DefineOrRedefineDataProperty(newRecord, prop, changeRecord[prop],
         READ_ONLY + DONT_DELETE);
   }
-  // TODO(rafaelw): This breaks spec-compliance. Re-enable when freezing isn't
-  // slow.
-  // ObjectFreeze(newRecord);
+  ObjectFreeze(newRecord);
 
   EnqueueChangeRecord(newRecord, objectInfo.changeObservers);
 }
 
 function ObjectNotifierPerformChange(changeType, changeFn, receiver) {
   if (!IS_SPEC_OBJECT(this))
     throw MakeTypeError("called_on_non_object", ["performChange"]);
 
   var target = notifierTargetMap.get(this);
   if (IS_UNDEFINED(target))
@@ skipping 86 matching lines @@
     "observe", ArrayObserve,
     "unobserve", ArrayUnobserve
   ));
   InstallFunctions(notifierPrototype, DONT_ENUM, $Array(
     "notify", ObjectNotifierNotify,
     "performChange", ObjectNotifierPerformChange
   ));
 }
 
 SetupObjectObserve();