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;

[Siggi Cherem (dart-lang), 2013/07/22 23:06:14]

minor suggestion: consider renaming this to dirty_check?

[Jennifer Messerly, 2013/07/23 02:45:15]

Done.

+
+import 'package:logging/logging.dart';
+import 'package:observe/observe.dart' show Observable;
+
+/** The number of active observables in the system. */
+int get allObservablesCount => _allObservablesCount;
+
+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 dirtyCheckObservables() {
+  if (_delivering) return;
+  if (_allObservables == null) return;
+
+  _delivering = true;
+
+  int cycles = 0;
+  bool anyChanged = false;
+  List debugLoop = null;
+  do {
+    cycles++;
+    if (cycles == MAX_DIRTY_CHECK_CYCLES) {
+      debugLoop = [];
+    }
+
+    var toCheck = _allObservables;
+    _allObservables = <Observable>[];
+    anyChanged = false;
+
+    for (int i = 0; i < toCheck.length; i++) {
+      final observer = toCheck[i];
+      if (observer.hasObservers) {
+        if (observer.deliverChanges()) {
+          anyChanged = true;
+          if (debugLoop != null) debugLoop.add([i, observer]);
+        }
+        _allObservables.add(observer);
+      }
+    }
+  } while (cycles < MAX_DIRTY_CHECK_CYCLES && anyChanged);
+
+  if (debugLoop != null && anyChanged) {
+    _logger.warning('Possible loop in Observable.dirtyCheck, stopped '
+        'checking.');
+    for (final info in debugLoop) {
+      _logger.warning('In last iteration Observable changed at index '
+          '${info[0]}, object: ${info[1]}.');
+    }
+  }
+
+  _allObservablesCount = _allObservables.length;
+  _delivering = false;
+}
+
+const MAX_DIRTY_CHECK_CYCLES = 1000;
+
+
+/**
+ * Log for messages produced at runtime by this library. Logging can be
+ * configured by accessing Logger.root from the logging library.
+ */
+final Logger _logger = new Logger('Observable.dirtyCheck');