implement dirty checking for @observable objects

pkg/observe/lib/src/watcher.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.
+ *
+ * Tracks observable objects for dirty checking and testing purposes.
+ *
+ * It can collect all observed objects, which can be used to trigger predictable
+ * delivery of all pending changes in a test, including objects allocated
+ * internally to another library, such as those in `package:mdv`.
+ */
+library observe.src.watcher;
+
+import 'package:observe/observe.dart' show Observable;
+
+/** The number of active observables in the system. */
+int get allObservablesCount => _allObservablesCount;

[Jennifer Messerly, 2013/07/19 01:32:58]

this is public so tests can get at it. it's not used much, but seems good to
know objects are being correctly removed from the watchers pool when no longer
observed.

+
+int _allObservablesCount = 0;
+
+List<Observable> _allObservables = null;
+
+bool _delivering = false;
+
+void registerObservable(Observable obj) {
+  if (_allObservables == null) _allObservables = <Observable>[];
+  _allObservables.add(obj);
+  _allObservablesCount++;
+}
+
+/**
+ * Synchronously deliver all change records for known observables.
+ *
+ * This will execute [Observable.deliverChanges] on objects that inherit from
+ * [ObservableMixin].
+ */
+// Note: this is called performMicrotaskCheckpoint in change_summary.js.
+void dirtyCheck() {
+  if (_delivering) return;
+  if (_allObservables == null) return;
+
+  _delivering = true;
+
+  int cycles = 0;
+  bool anyChanged = false;
+  do {
+    cycles++;
+    var toCheck = _allObservables;
+    _allObservables = <Observable>[];
+    anyChanged = false;
+
+    for (final observer in toCheck) {
+      if (observer.hasObservers) {
+        anyChanged = anyChanged || observer.deliverChanges();
+        _allObservables.add(observer);
+      }
+    }
+  } while (cycles < _MAX_DIRTY_CHECK_CYCLES && anyChanged);
+
+  // TODO(jmesserly): warn if limit is reached?
+
+  _allObservablesCount = _allObservables.length;
+  _delivering = false;
+}
+
+var _MAX_DIRTY_CHECK_CYCLES = 1000;