Implement Microtask Delivery Queue

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 45 matching lines @@
 // implementation of (1) and (2) have "optimized" states which represent
 // common cases which can be handled more efficiently.
 
 var observationState = %GetObservationState();
 if (IS_UNDEFINED(observationState.callbackInfoMap)) {
   observationState.callbackInfoMap = %ObservationWeakMapCreate();
   observationState.objectInfoMap = %ObservationWeakMapCreate();
   observationState.notifierObjectInfoMap = %ObservationWeakMapCreate();
   observationState.pendingObservers = null;
   observationState.nextCallbackPriority = 0;
+  observationState.microtaskScheduled = false;
 }
 
 function ObservationWeakMap(map) {
   this.map_ = map;
 }
 
 ObservationWeakMap.prototype = {
   get: function(key) {
     key = %UnwrapGlobalProxy(key);
     if (!IS_SPEC_OBJECT(key)) return UNDEFINED;
@@ skipping 311 matching lines @@
        !%IsAccessAllowedForObserver(
            callback, changeRecord.object, changeRecord.name))) {
     return;
   }
 
   var callbackInfo = CallbackInfoNormalize(callback);
   if (!observationState.pendingObservers)
     observationState.pendingObservers = nullProtoObject();
   observationState.pendingObservers[callbackInfo.priority] = callback;
   callbackInfo.push(changeRecord);
-  %SetMicrotaskPending(true);
+  EnqueueObserveMicrotask();
 }
 
 function ObjectInfoEnqueueExternalChangeRecord(objectInfo, changeRecord, type) {
   if (!ObjectInfoHasActiveObservers(objectInfo))
     return;
 
   var hasType = !IS_UNDEFINED(type);
   var newRecord = hasType ?
       { object: ObjectInfoGetObject(objectInfo), type: type } :
       { object: ObjectInfoGetObject(objectInfo) };
@@ skipping 160 matching lines @@
 }
 
 function ObjectDeliverChangeRecords(callback) {
   if (!IS_SPEC_FUNCTION(callback))
     throw MakeTypeError("observe_non_function", ["deliverChangeRecords"]);
 
   while (CallbackDeliverPending(callback)) {}
 }
 
 function ObserveMicrotaskRunner() {
+  observationState.microtaskScheduled = false;
   var pendingObservers = observationState.pendingObservers;
   if (pendingObservers) {
     observationState.pendingObservers = null;
     for (var i in pendingObservers) {
       CallbackDeliverPending(pendingObservers[i]);
     }
   }
 }
-RunMicrotasks.runners.push(ObserveMicrotaskRunner);
+
+function EnqueueObserveMicrotask() {
+  if (observationState.microtaskScheduled)
+    return;
+
+  RunMicrotasks.queue.push(ObserveMicrotaskRunner);
+  %SetMicrotaskPending(true);
+  observationState.microtaskScheduled = true;
+}
 
 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();