Make StreamSubscription be the active part of a stream.

sdk/lib/async/stream_controller.dart

 // Copyright (c) 2012, 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.
 
 part of dart.async;
 
 // -------------------------------------------------------------------
 // Controller for creating and adding events to a stream.
 // -------------------------------------------------------------------
 
@@ skipping 29 matching lines @@
  * a stream action, for example firing an event. If the state changes multiple
  * times during the action, and then ends up in the same state as before, no
  * callback is performed.
  *
  * If listeners are added after the stream has completed (sent a "done" event),
  * the listeners will be sent a "done" event eventually, but they won't affect
  * the stream at all, and won't trigger callbacks. From the controller's point
  * of view, the stream is completely inert when has completed.
  */
 class StreamController<T> extends EventSink<T> {
-  final _StreamImpl<T> stream;
+  static const int _STATE_OPEN = 0;
+  static const int _STATE_CANCELLED = 1;
+  static const int _STATE_CLOSED = 2;
+
+  final _NotificationHandler _onListen;
+  final _NotificationHandler _onPause;
+  final _NotificationHandler _onResume;
+  final _NotificationHandler _onCancel;
+  _StreamImpl<T> _stream;
+
+  // An active subscription on the stream, or null if no subscripton is active.
+  _ControllerSubscription<T> _subscription;
+
+  // Whether we have sent a "done" event.
+  int _state = _STATE_OPEN;
+
+  // Events added to the stream before it has an active subscription.
+  _PendingEvents _pendingEvents = null;
 
   /**
    * A controller with a [stream] that supports only one single subscriber.
    *
    * The controller will buffer all incoming events until the subscriber is
    * registered.
    *
    * The [onPause] function is called when the stream becomes
    * paused. [onResume] is called when the stream resumed.
    *
    * The [onListen] callback is called when the stream
-   * receives its listener. [onCancel] when the listener cancels
+   * receives its listener and [onCancel] when the listener ends
    * its subscription.
    *
    * If the stream is canceled before the controller needs new data the
    * [onResume] call might not be executed.
    */
   StreamController({void onListen(),
                     void onPause(),
                     void onResume(),
                     void onCancel()})
-      : stream = new _SingleControllerStream<T>(
-            onListen, onPause, onResume, onCancel);
+      : _onListen = onListen,
+        _onPause = onPause,
+        _onResume = onResume,
+        _onCancel = onCancel {
+    _stream = new _ControllerStream<T>(this);
+  }
+
+  Stream<T> get stream => _stream;
 
   /**
    * Returns a view of this object that only exposes the [EventSink] interface.
    */
   EventSink<T> get sink => new _EventSinkView<T>(this);
 
   /**
+   * Whether a listener has existed and been cancelled.
+   *
+   * After this, adding more events will be ignored.
+   */
+  bool get _isCancelled => (_state & _STATE_CANCELLED) != 0;
+
+  /**
    * Whether the stream is closed for adding more events.
    *
    * If true, the "done" event might not have fired yet, but it has been
    * scheduled, and it is too late to add more events.
    */
-  bool get isClosed => stream._isClosed;
+  bool get isClosed => (_state & _STATE_CLOSED) != 0;
 
-  /** Whether one or more active subscribers have requested a pause. */
-  bool get isPaused => stream._isInputPaused;
+  /** Whether the subscription is active and paused. */
+  bool get isPaused => _subscription != null && _subscription._isInputPaused;
 
-  /** Whether there are currently any subscribers on this [Stream]. */
-  bool get hasListener => stream._hasListener;
+  /** Whether there are currently a subscriber on the [Stream]. */
+  bool get hasListener => _subscription != null;
 
   /**
    * Send or queue a data event.
    */
-  void add(T value) => stream._add(value);
+  void add(T value) {
+    if (isClosed) throw new StateError("Adding event after close");
+    if (_subscription != null) {
+      _subscription._add(value);
+    } else if (!_isCancelled) {
+      _addPendingEvent(new _DelayedData<T>(value));
+    }
+  }
 
   /**
    * Send or enqueue an error event.
-   *
-   * If a subscription has requested to be unsubscribed on errors,
-   * it will be unsubscribed after receiving this event.
    */
   void addError(Object error, [Object stackTrace]) {
+    if (isClosed) throw new StateError("Adding event after close");
     if (stackTrace != null) {
       // Force stack trace overwrite. Even if the error already contained
       // a stack trace.
       _attachStackTrace(error, stackTrace);
     }
-    stream._addError(error);
+    if (_subscription != null) {
+      _subscription._addError(error);
+    } else if (!_isCancelled) {
+      _addPendingEvent(new _DelayedError(error));
+    }
   }
 
   /**
-   * Send or enqueue a "done" message.
+   * Closes this controller.
    *
-   * The "done" message should be sent at most once by a stream, and it
-   * should be the last message sent.
+   * After closing, no further events may be added using [add] or [addError].
+   *
+   * You are allowed to close the controller more than once, but only the first
+   * call has any effect.
+   *
+   * The first time a controller is closed, a "done" event is sent to its
+   * stream.
    */
-  void close() { stream._close(); }
+  void close() {
+    if (isClosed) return;
+    _state |= _STATE_CLOSED;
+    if (_subscription != null) {
+      _subscription._close();
+    } else if (!_isCancelled) {
+      _addPendingEvent(const _DelayedDone());
+    }
+  }
+
+  void _addPendingEvent(_DelayedEvent event) {
+    if (_isCancelled) return;
+    _StreamImplEvents events = _pendingEvents;
+    if (events == null) {
+      events = _pendingEvents = new _StreamImplEvents();
+    }
+    events.add(event);
+  }
+
+  void _recordListen(_BufferingStreamSubscription subscription) {

[floitsch, 2013/05/24 15:53:17]

add function comment.

+    assert(_subscription == null);
+    _subscription = subscription;
+    subscription._setPendingEvents(_pendingEvents);
+    _pendingEvents = null;
+    subscription._guardCallback(() {

[floitsch, 2013/05/24 15:53:17]

Explain why you don't call _runGuarded directly.

+      _runGuarded(_onListen);
+    });
+  }
+
+  void _recordCancel() {
+    _subscription = null;
+    _state |= _STATE_CANCELLED;
+    _runGuarded(_onCancel);
+  }
+
+  void _recordPause() {
+    _runGuarded(_onPause);
+  }
+
+  void _recordResume() {
+    _runGuarded(_onResume);
+  }
 }
 
 typedef void _NotificationHandler();
 
-class _SingleControllerStream<T> extends _SingleStreamImpl<T> {
-  _NotificationHandler _onListen;
-  _NotificationHandler _onPause;
-  _NotificationHandler _onResume;
-  _NotificationHandler _onCancel;
+void _runGuarded(_NotificationHandler notificationHandler) {
+  if (notificationHandler == null) return;
+  try {
+    notificationHandler();
+  } catch (e, s) {
+    _throwDelayed(e, s);
+  }
+}
 
-  // TODO(floitsch): share this code with _MultiControllerStream.
-  _runGuarded(_NotificationHandler notificationHandler) {
-    if (notificationHandler == null) return;
-    try {
-      notificationHandler();
-    } catch (e, s) {
-      _throwDelayed(e, s);
+class _ControllerStream<T> extends _StreamImpl<T> {
+  StreamController _controller;
+  bool _hasListener = false;
+
+  _ControllerStream(this._controller);
+
+  StreamSubscription<T> _createSubscription(
+      void onData(T data),
+      void onError(Object error),
+      void onDone(),
+      bool cancelOnError) {
+    if (_hasListener) {
+      throw new StateError("The stream has already been listened to.");
     }
+    _hasListener = true;
+    return new _ControllerSubscription<T>(
+        _controller, onData, onError, onDone, cancelOnError);
   }
 
-  _SingleControllerStream(this._onListen,
-                          this._onPause,
-                          this._onResume,
-                          this._onCancel);
+  void _onListen(_BufferingStreamSubscription subscription) {
+    _controller._recordListen(subscription);
+  }
+}
 
-  void _onSubscriptionStateChange() {
-    _runGuarded(_hasListener ? _onListen : _onCancel);
+class _ControllerSubscription<T> extends _BufferingStreamSubscription<T> {
+  final StreamController _controller;
+
+  _ControllerSubscription(StreamController controller,
+                          void onData(T data),
+                          void onError(Object error),
+                          void onDone(),
+                          bool cancelOnError)
+      : _controller = controller,
+        super(onData, onError, onDone, cancelOnError);
+
+  void _onCancel() {
+    _controller._recordCancel();
   }
 
-  void _onPauseStateChange() {
-    _runGuarded(_isPaused ? _onPause : _onResume);
+  void _onPause() {
+    _controller._recordPause();
+  }
+
+  void _onResume() {
+    _controller._recordResume();
   }
 }