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pkg/observe/lib/src/microtask.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * *Warning*: this library is **internal**, and APIs are subject to change.
  *
  * Wraps a callback using [wrapMicrotask] and provides the ability to pump all
  * observable objects and [runAsync] calls via [performMicrotaskCheckpoint].
  */
 library observe.src.microtask;
 
 import 'dart:async' show Completer, runZonedExperimental;
+import 'dart:collection';
 import 'package:observe/observe.dart' show Observable;
 
 // TODO(jmesserly): remove "microtask" from these names and instead import
 // the library "as microtask"?
 
 /**
  * This change pumps events relevant to observers and data-binding tests.
  * This must be used inside an [observeTest].
  *
  * Executes all pending [runAsync] calls on the event loop, as well as
  * performing [Observable.dirtyCheck], until there are no more pending events.
  * It will always dirty check at least once.
  */
 void performMicrotaskCheckpoint() {
   Observable.dirtyCheck();
 
-  while (_pending.length > 0) {
-    var pending = _pending;
-    _pending = [];
+  while (_pending.isNotEmpty) {
 
-    for (var callback in pending) {
+    for (int len = _pending.length; len > 0 && _pending.isNotEmpty; len--) {
+      final callback = _pending.removeFirst();
       try {
         callback();
       } catch (e, s) {
         new Completer().completeError(e, s);
       }
     }
 
     Observable.dirtyCheck();
   }
 }
 
-List<Function> _pending = [];
+final Queue<Function> _pending = new Queue<Function>();
 
 /**
- * Wraps the [testCase] in a zone that supports [performMicrotaskCheckpoint],
+ * Wraps the [body] in a zone that supports [performMicrotaskCheckpoint],
  * and returns the test case.
  */
-wrapMicrotask(void testCase()) {
+// TODO(jmesserly): do we want to support nested microtasks similar to nested
+// zones? Instead of a single pending list we'd need one per wrapMicrotask,
+// and [performMicrotaskCheckpoint] would only run pending callbacks
+// corresponding to the innermost wrapMicrotask body.
+wrapMicrotask(void body()) {
   return () {
     runZonedExperimental(() {
       try {
-        testCase();
+        body();
       } finally {
         performMicrotaskCheckpoint();
       }
     }, onRunAsync: (callback) => _pending.add(callback));
   };
 }