[Object.observe] Lazily allocate callbackInfo structure

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 10 matching lines @@
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 "use strict";
 
 var observationState = %GetObservationState();
-if (IS_UNDEFINED(observationState.observerInfoMap)) {
-  observationState.observerInfoMap = %ObservationWeakMapCreate();
+if (IS_UNDEFINED(observationState.callbackInfoMap)) {
+  observationState.callbackInfoMap = %ObservationWeakMapCreate();
   observationState.objectInfoMap = %ObservationWeakMapCreate();
   observationState.notifierTargetMap = %ObservationWeakMapCreate();
   observationState.pendingObservers = new InternalArray;
-  observationState.observerPriority = 0;
+  observationState.nextCallbackPriority = 0;
 }
 
 function ObservationWeakMap(map) {
   this.map_ = map;
 }
 
 ObservationWeakMap.prototype = {
   get: function(key) {
     key = %UnwrapGlobalProxy(key);
     if (!IS_SPEC_OBJECT(key)) return void 0;
     return %WeakMapGet(this.map_, key);
   },
   set: function(key, value) {
     key = %UnwrapGlobalProxy(key);
     if (!IS_SPEC_OBJECT(key)) return void 0;
     %WeakMapSet(this.map_, key, value);
   },
   has: function(key) {
     return !IS_UNDEFINED(this.get(key));
   }
 };
 
-var observerInfoMap =
-    new ObservationWeakMap(observationState.observerInfoMap);
+var callbackInfoMap =
+    new ObservationWeakMap(observationState.callbackInfoMap);
 var objectInfoMap = new ObservationWeakMap(observationState.objectInfoMap);
 var notifierTargetMap =
     new ObservationWeakMap(observationState.notifierTargetMap);
 
 function CreateObjectInfo(object) {
   var info = {
     changeObservers: new InternalArray,
     notifier: null,
     inactiveObservers: new InternalArray,
     performing: { __proto__: null },
@@ skipping 120 matching lines @@
     return false;
 
   var length = arg.length;
   for (var i = 0; i < length; i++) {
     if (!IS_STRING(arg[i]))
       return false;
   }
   return true;
 }
 
+function EnsureCallbackPriority(callback) {
+  if (!callbackInfoMap.has(callback))
+    callbackInfoMap.set(callback, observationState.nextCallbackPriority++);
+}
+
+function NormalizeCallbackInfo(callback) {
+  var callbackInfo = callbackInfoMap.get(callback);
+  if (IS_NUMBER(callbackInfo)) {
+    var priority = callbackInfo;
+    callbackInfo = new InternalArray;
+    callbackInfo.priority = priority;
+    callbackInfoMap.set(callback, callbackInfo);
+  }
+  return callbackInfo;
+}
+
 function ObjectObserve(object, callback, accept) {
   if (!IS_SPEC_OBJECT(object))
     throw MakeTypeError("observe_non_object", ["observe"]);
   if (!IS_SPEC_FUNCTION(callback))
     throw MakeTypeError("observe_non_function", ["observe"]);
   if (ObjectIsFrozen(callback))
     throw MakeTypeError("observe_callback_frozen");
   if (!AcceptArgIsValid(accept))
     throw MakeTypeError("observe_accept_invalid");
 
-  if (!observerInfoMap.has(callback)) {
-    observerInfoMap.set(callback, {
-      pendingChangeRecords: null,
-      priority: observationState.observerPriority++,
-    });
-  }
+  EnsureCallbackPriority(callback);
 
   var objectInfo = objectInfoMap.get(object);
   if (IS_UNDEFINED(objectInfo)) {
     objectInfo = CreateObjectInfo(object);
     %SetIsObserved(object);
   }
 
   EnsureObserverRemoved(objectInfo, callback);
 
   var observer = CreateObserver(callback, accept);
@@ skipping 23 matching lines @@
   return ObjectObserve(object, callback, ['new',
                                           'updated',
                                           'deleted',
                                           'splice']);
 }
 
 function ArrayUnobserve(object, callback) {
   return ObjectUnobserve(object, callback);
 }
 
+function EnqueueToCallback(callback, changeRecord) {
+  var callbackInfo = NormalizeCallbackInfo(callback);
+  observationState.pendingObservers[callbackInfo.priority] = callback;
+  callbackInfo.push(changeRecord);
+  %SetObserverDeliveryPending();
+}
+
 function EnqueueChangeRecord(changeRecord, observers) {
   // TODO(rossberg): adjust once there is a story for symbols vs proxies.
   if (IS_SYMBOL(changeRecord.name)) return;
 
   for (var i = 0; i < observers.length; i++) {
     var observer = observers[i];
     if (IS_UNDEFINED(observer.accept[changeRecord.type]))
       continue;
 
-    var callback = observer.callback;
-    var observerInfo = observerInfoMap.get(callback);
-    observationState.pendingObservers[observerInfo.priority] = callback;
-    %SetObserverDeliveryPending();
-    if (IS_NULL(observerInfo.pendingChangeRecords)) {
-      observerInfo.pendingChangeRecords = new InternalArray(changeRecord);
-    } else {
-      observerInfo.pendingChangeRecords.push(changeRecord);
-    }
+    EnqueueToCallback(observer.callback, changeRecord);
   }
 }
 
 function BeginPerformSplice(array) {
   var objectInfo = objectInfoMap.get(array);
   if (!IS_UNDEFINED(objectInfo))
     BeginPerformChange(objectInfo, 'splice');
 }
 
 function EndPerformSplice(array) {
@@ skipping 99 matching lines @@
   if (IS_UNDEFINED(objectInfo)) objectInfo = CreateObjectInfo(object);
 
   if (IS_NULL(objectInfo.notifier)) {
     objectInfo.notifier = { __proto__: notifierPrototype };
     notifierTargetMap.set(objectInfo.notifier, object);
   }
 
   return objectInfo.notifier;
 }
 
-function DeliverChangeRecordsForObserver(observer) {
-  var observerInfo = observerInfoMap.get(observer);
-  if (IS_UNDEFINED(observerInfo))
+function CallbackDeliverPending(callback) {
+  var callbackInfo = callbackInfoMap.get(callback);
+  if (IS_UNDEFINED(callbackInfo) || IS_NUMBER(callbackInfo))
     return false;
 
-  var pendingChangeRecords = observerInfo.pendingChangeRecords;
-  if (IS_NULL(pendingChangeRecords))
-    return false;
+  // Clear the pending change records from callback and return it to its
+  // "optimized" state.
+  var priority = callbackInfo.priority;
+  callbackInfoMap.set(callback, priority);
 
-  observerInfo.pendingChangeRecords = null;
-  delete observationState.pendingObservers[observerInfo.priority];
+  delete observationState.pendingObservers[priority];
   var delivered = [];
-  %MoveArrayContents(pendingChangeRecords, delivered);
+  %MoveArrayContents(callbackInfo, delivered);
+
   try {
-    %Call(void 0, delivered, observer);
+    %Call(void 0, delivered, callback);
   } catch (ex) {}
   return true;
 }
 
 function ObjectDeliverChangeRecords(callback) {
   if (!IS_SPEC_FUNCTION(callback))
     throw MakeTypeError("observe_non_function", ["deliverChangeRecords"]);
 
-  while (DeliverChangeRecordsForObserver(callback)) {}
+  while (CallbackDeliverPending(callback)) {}
 }
 
 function DeliverChangeRecords() {
   while (observationState.pendingObservers.length) {
     var pendingObservers = observationState.pendingObservers;
     observationState.pendingObservers = new InternalArray;
     for (var i in pendingObservers) {
-      DeliverChangeRecordsForObserver(pendingObservers[i]);
+      CallbackDeliverPending(pendingObservers[i]);
     }
   }
 }
 
 function SetupObjectObserve() {
   %CheckIsBootstrapping();
   InstallFunctions($Object, DONT_ENUM, $Array(
     "deliverChangeRecords", ObjectDeliverChangeRecords,
     "getNotifier", ObjectGetNotifier,
     "observe", ObjectObserve,
     "unobserve", ObjectUnobserve
   ));
   InstallFunctions($Array, DONT_ENUM, $Array(
     "observe", ArrayObserve,
     "unobserve", ArrayUnobserve
   ));
   InstallFunctions(notifierPrototype, DONT_ENUM, $Array(
     "notify", ObjectNotifierNotify,
     "performChange", ObjectNotifierPerformChange
   ));
 }
 
 SetupObjectObserve();