Roll Observatory packages and add a roll script

watcher/lib/src/resubscribable.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.
-
-library watcher.resubscribable;
-
-import 'dart:async';
-
-import '../watcher.dart';
-import 'watch_event.dart';
-
-typedef ManuallyClosedWatcher WatcherFactory();
-
-/// A wrapper for [ManuallyClosedWatcher] that encapsulates support for closing
-/// the watcher when it has no subscribers and re-opening it when it's
-/// re-subscribed.
-///
-/// It's simpler to implement watchers without worrying about this behavior.
-/// This class wraps a watcher class which can be written with the simplifying
-/// assumption that it can continue emitting events until an explicit `close`
-/// method is called, at which point it will cease emitting events entirely. The
-/// [ManuallyClosedWatcher] interface is used for these watchers.
-///
-/// This would be more cleanly implemented as a function that takes a class and
-/// emits a new class, but Dart doesn't support that sort of thing. Instead it
-/// takes a factory function that produces instances of the inner class.
-abstract class ResubscribableWatcher implements Watcher {
-  /// The factory function that produces instances of the inner class.
-  final WatcherFactory _factory;
-
-  final String path;
-
-  Stream<WatchEvent> get events => _eventsController.stream;
-  StreamController<WatchEvent> _eventsController;
-
-  bool get isReady => _readyCompleter.isCompleted;
-
-  Future get ready => _readyCompleter.future;
-  var _readyCompleter = new Completer();
-
-  /// Creates a new [ResubscribableWatcher] wrapping the watchers
-  /// emitted by [_factory].
-  ResubscribableWatcher(this.path, this._factory) {
-    var watcher;
-    var subscription;
-
-    _eventsController = new StreamController<WatchEvent>.broadcast(
-        onListen: () {
-      watcher = _factory();
-      subscription = watcher.events.listen(_eventsController.add,
-          onError: _eventsController.addError,
-          onDone: _eventsController.close);
-
-      // It's important that we complete the value of [_readyCompleter] at the
-      // time [onListen] is called, as opposed to the value when [watcher.ready]
-      // fires. A new completer may be created by that time.
-      watcher.ready.then(_readyCompleter.complete);
-    }, onCancel: () {
-      // Cancel the subscription before closing the watcher so that the
-      // watcher's `onDone` event doesn't close [events].
-      subscription.cancel();
-      watcher.close();
-      _readyCompleter = new Completer();
-    }, sync: true);
-  }
-}
-
-/// An interface for watchers with an explicit, manual [close] method.
-///
-/// See [ResubscribableWatcher].
-abstract class ManuallyClosedWatcher implements Watcher {
-  /// Closes the watcher.
-  ///
-  /// Subclasses should close their [events] stream and release any internal
-  /// resources.
-  void close();
-}