Make StreamController be a StreamSink, not just an EventSink.

sdk/lib/async/stream_controller.dart

Index: sdk/lib/async/stream_controller.dart
diff --git a/sdk/lib/async/stream_controller.dart b/sdk/lib/async/stream_controller.dart
index 2cdbeaf240c3553337eae7f2a74a83f3f27b1f66..ea3e81cf846047b954f55b10349ed7b92de8f18a 100644
--- a/sdk/lib/async/stream_controller.dart
+++ b/sdk/lib/async/stream_controller.dart
@@ -46,7 +46,7 @@ part of dart.async;
  * the stream at all, and won't trigger callbacks. From the controller's point
  * of view, the stream is completely inert when has completed.
  */
-abstract class StreamController<T> implements EventSink<T> {
+abstract class StreamController<T> implements StreamSink<T> {
   /** The stream that this controller is controlling. */
   Stream<T> get stream;
 
@@ -75,10 +75,17 @@ abstract class StreamController<T> implements EventSink<T> {
                             void onPause(),
                             void onResume(),
                             void onCancel(),
-                            bool sync: false})
-      => sync
+                            bool sync: false}) {
+    if (onListen == null && onPause == null &&
+        onResume == null && onCancel == null) {
+      return sync
+          ? new _NoCallbackSyncStreamController<T>()
+          : new _NoCallbackAsyncStreamController<T>();
+    }
+    return sync
          ? new _SyncStreamController<T>(onListen, onPause, onResume, onCancel)
          : new _AsyncStreamController<T>(onListen, onPause, onResume, onCancel);
+  }
 
   /**
    * A controller where [stream] can be listened to more than once.
@@ -123,9 +130,9 @@ abstract class StreamController<T> implements EventSink<T> {
   }
 
   /**
-   * Returns a view of this object that only exposes the [EventSink] interface.
+   * Returns a view of this object that only exposes the [StreamSink] interface.
    */
-  EventSink<T> get sink;
+  StreamSink<T> get sink;
 
   /**
    * Whether the stream is closed for adding more events.
@@ -162,7 +169,10 @@ abstract class StreamController<T> implements EventSink<T> {
 
 
 abstract class _StreamControllerLifecycle<T> {
-  void _recordListen(StreamSubscription<T> subscription) {}
+  StreamSubscription<T> _subscribe(void onData(T data),
+                                   void onError(Object error),
+                                   void onDone(),
+                                   bool cancelOnError);
   void _recordPause(StreamSubscription<T> subscription) {}
   void _recordResume(StreamSubscription<T> subscription) {}
   void _recordCancel(StreamSubscription<T> subscription) {}
@@ -175,81 +185,205 @@ abstract class _StreamControllerLifecycle<T> {
  */
 abstract class _StreamController<T> implements StreamController<T>,
                                                _StreamControllerLifecycle<T>,
+                                               _EventSink<T>,
                                                _EventDispatch<T> {
-  static const int _STATE_OPEN = 0;
-  static const int _STATE_CANCELLED = 1;
-  static const int _STATE_CLOSED = 2;
+  // The states are bit-flags. More than one can be set at a time.
+  //
+  // The "subscription state" goes through the states:
+  //   initial -> subscribed -> canceled.
+  // These are mutually exclusive.
+  // The "closed" state records whether the [close] method has been called
+  // on the controller. This can be done at any time. If done before
+  // subscription, the done event is queued. If done after cancel, the done
+  // event is ignored (just as any other event after a cancel).
+
+  /** The controller is in its initial state with no subscription. */
+  static const int _STATE_INITIAL = 0;
+  /** The controller has a subscription, but hasn't been closed or canceled. */
+  static const int _STATE_SUBSCRIBED = 1;
+  /** The subscription is canceled. */
+  static const int _STATE_CANCELED = 2;
+  /** Mask for the subscription state. */
+  static const int _STATE_SUBSCRIPTION_MASK = 3;
+
+  // The following state relate to the controller, not the subscription.
+  // If closed, adding more events is not allowed.
+  // If executing an [addStream], new events are not allowed either, but will
+  // be added by the stream.
 
-  final _NotificationHandler _onListen;
-  final _NotificationHandler _onPause;
-  final _NotificationHandler _onResume;
-  final _NotificationHandler _onCancel;
-  _StreamImpl<T> _stream;
+  /**
+   * The controller is closed due to calling [close].
+   *
+   * When the stream is closed, you can neither add new events nor add new
+   * listeners.
+   */
+  static const int _STATE_CLOSED = 4;
+  /**
+   * The controller is in the middle of an [addStream] operation.
+   *
+   * While adding events from a stream, no new events can be added directly
+   * on the controller.
+   */
+  static const int _STATE_ADDSTREAM = 8;
+
+  /**
+   * Field containing different data depending on the current subscription
+   * state.
+   *
+   * If [_state] is [_STATE_INITIAL], the field may contain a [_PendingEvents]
+   * for events added to the controller before a subscription.
+   *
+   * While [_state] is [_STATE_SUBSCRIBED], the field contains the subscription.
+   *
+   * When [_state] is [_STATE_CANCELED] the field is currently not used.
+   */
+  var _varData;
 
-  // An active subscription on the stream, or null if no subscripton is active.
-  _ControllerSubscription<T> _subscription;
+  /** Current state of the controller. */
+  int _state = _STATE_INITIAL;
 
-  // Whether we have sent a "done" event.
-  int _state = _STATE_OPEN;
+  /**
+   * Future completed when the stream sends its last event.
+   *
+   * This is also the future returned by [close].
+   */
+  // TODO(lrn): Could this be stored in the varData field too, if it's not
+  // accessed until the call to "close"? Then we need to special case if it's
+  // accessed earlier, or if close is called before subscribing.
+  _FutureImpl _doneFuture;
 
-  // Events added to the stream before it has an active subscription.
-  _PendingEvents _pendingEvents = null;
+  _StreamController();
 
-  _StreamController(this._onListen,
-                    this._onPause,
-                    this._onResume,
-                    this._onCancel) {
-    _stream = new _ControllerStream<T>(this);
-  }
+  _NotificationHandler get _onListen;
+  _NotificationHandler get _onPause;
+  _NotificationHandler get _onResume;
+  _NotificationHandler get _onCancel;
 
-  Stream<T> get stream => _stream;
+  // Return a new stream every time. The streams are equal, but not identical.
+  Stream<T> get stream => new _ControllerStream(this);
 
   /**
-   * Returns a view of this object that only exposes the [EventSink] interface.
+   * Returns a view of this object that only exposes the [StreamSink] interface.
    */
-  EventSink<T> get sink => new _EventSinkView<T>(this);
+  StreamSink<T> get sink => new _StreamSinkWrapper<T>(this);
 
   /**
-   * Whether a listener has existed and been cancelled.
+   * Whether a listener has existed and been canceled.
    *
    * After this, adding more events will be ignored.
    */
-  bool get _isCancelled => (_state & _STATE_CANCELLED) != 0;
+  bool get _isCanceled => (_state & _STATE_CANCELED) != 0;
+
+  /** Whether there is an active listener. */
+  bool get hasListener => (_state & _STATE_SUBSCRIBED) != 0;
+
+  /** Whether there has not been a listener yet. */
+  bool get _isInitialState =>
+      (_state & _STATE_SUBSCRIPTION_MASK) == _STATE_INITIAL;
 
   bool get isClosed => (_state & _STATE_CLOSED) != 0;
 
   bool get isPaused => hasListener ? _subscription._isInputPaused
-                                   : !_isCancelled;
+                                   : !_isCanceled;
+
+  bool get _isAddingStream => (_state & _STATE_ADDSTREAM) != 0;
+
+  /** New events may not be added after close, or during addStream. */
+  bool get _mayAddEvent => (_state < _STATE_CLOSED);
+
+  // Returns the pending events.
+  // Pending events are events added before a subscription exists.
+  // They are added to the subscription when it is created.
+  // Pending events, if any, are kept in the _varData field until the
+  // stream is listened to.
+  // While adding a stream, pending events are moved into the
+  // state object to allow the state object to use the _varData field.
+  _PendingEvents get _pendingEvents {
+    assert(_isInitialState);
+    if (!_isAddingStream) {
+      return _varData;
+    }
+    _StreamControllerAddStreamState state = _varData;
+    return state.varData;
+  }
 
-  bool get hasListener => _subscription != null;
+  // Returns the pending events, and creates the object if necessary.
+  _StreamImplEvents _ensurePendingEvents() {
+    assert(_isInitialState);
+    if (!_isAddingStream) {
+      if (_varData == null) _varData = new _StreamImplEvents();
+      return _varData;
+    }
+    _StreamControllerAddStreamState state = _varData;
+    if (state.varData == null) state.varData = new _StreamImplEvents();
+    return state.varData;
+  }
+
+  // Get the current subscription.
+  // If we are adding a stream, the subscription is moved into the state
+  // object to allow the state object to use the _varData field.
+  _ControllerSubscription get _subscription {
+    assert(hasListener);
+    if (_isAddingStream) {
+      _StreamControllerAddStreamState addState = _varData;
+      return addState.varData;
+    }
+    return _varData;
+  }
 
   /**
-   * Send or queue a data event.
+   * Creates an error describing why an event cannot be added.
+   *
+   * The reason, and therefore the error message, depends on the current state.
    */
-  void add(T value) {
-    if (isClosed) throw new StateError("Adding event after close");
-    if (_subscription != null) {
-      _sendData(value);
-    } else if (!_isCancelled) {
-      _addPendingEvent(new _DelayedData<T>(value));
+  Error _badEventState() {
+    if (isClosed) {
+      return new StateError("Cannot add event after closing");
+    }
+    assert(_isAddingStream);
+    return new StateError("Cannot add event while adding a stream");
+  }
+
+  // StreamSink interface.
+  Future addStream(Stream<T> source) {
+    if (!_mayAddEvent) throw _badEventState();
+    if (_isCanceled) return new _FutureImpl.immediate(null);
+    _StreamControllerAddStreamState addState =
+        new _StreamControllerAddStreamState(this, _varData, source);
+    _varData = addState;
+    _state |= _STATE_ADDSTREAM;
+    return addState.addStreamFuture;
+  }
+
+  Future get done => _ensureDoneFuture();
+
+  Future _ensureDoneFuture() {
+    if (_doneFuture == null) {
+      _doneFuture = new _FutureImpl();
+      if (_isCanceled) _doneFuture._setValue(null);
     }
+    return _doneFuture;
+  }
+
+  /**
+   * Send or enqueue a data event.
+   */
+  void add(T value) {
+    if (!_mayAddEvent) throw _badEventState();
+    _add(value);
   }
 
   /**
    * Send or enqueue an error event.
    */
   void addError(Object error, [Object stackTrace]) {
-    if (isClosed) throw new StateError("Adding event after close");
+    if (!_mayAddEvent) throw _badEventState();
     if (stackTrace != null) {
       // Force stack trace overwrite. Even if the error already contained
       // a stack trace.
       _attachStackTrace(error, stackTrace);
     }
-    if (_subscription != null) {
-      _sendError(error);
-    } else if (!_isCancelled) {
-      _addPendingEvent(new _DelayedError(error));
-    }
+    _addError(error);
   }
 
   /**
@@ -263,60 +397,111 @@ abstract class _StreamController<T> implements StreamController<T>,
    * The first time a controller is closed, a "done" event is sent to its
    * stream.
    */
-  void close() {
-    if (isClosed) return;
+  Future close() {
+    if (isClosed) {
+      assert(_doneFuture != null);  // Was set when close was first called.
+      return _doneFuture;
+    }
+    if (!_mayAddEvent) throw _badEventState();
     _state |= _STATE_CLOSED;
-    if (_subscription != null) {
+    _ensureDoneFuture();
+    if (hasListener) {
       _sendDone();
-    } else if (!_isCancelled) {
-      _addPendingEvent(const _DelayedDone());
+    } else if (_isInitialState) {
+      _ensurePendingEvents().add(const _DelayedDone());
     }
+    return _doneFuture;
   }
 
-  // EventDispatch interface
+  // EventSink interface. Used by the [addStream] events.
 
-  void _addPendingEvent(_DelayedEvent event) {
-    if (_isCancelled) return;
-    _StreamImplEvents events = _pendingEvents;
-    if (events == null) {
-      events = _pendingEvents = new _StreamImplEvents();
+  // Add data event, used both by the [addStream] events and by [add].
+  void _add(T value) {
+    if (hasListener) {
+      _sendData(value);
+    } else if (_isInitialState) {
+      _ensurePendingEvents().add(new _DelayedData<T>(value));
     }
-    events.add(event);
   }
 
-  void _recordListen(_BufferingStreamSubscription<T> subscription) {
-    assert(_subscription == null);
-    _subscription = subscription;
-    subscription._setPendingEvents(_pendingEvents);
-    _pendingEvents = null;
+  void _addError(Object error) {
+    if (hasListener) {
+      _sendError(error);
+    } else if (_isInitialState) {
+      _ensurePendingEvents().add(new _DelayedError(error));
+    }
+  }
+
+  void _close() {
+    // End of addStream stream.
+    assert(_isAddingStream);
+    _StreamControllerAddStreamState addState = _varData;
+    _varData = addState.varData;
+    _state &= ~_STATE_ADDSTREAM;
+    addState.complete();
+  }
+
+  // _StreamControllerLifeCycle interface
+
+  StreamSubscription<T> _subscribe(void onData(T data),
+                                   void onError(Object error),
+                                   void onDone(),
+                                   bool cancelOnError) {
+    if (!_isInitialState) {
+      throw new StateError("Stream has already been listened to.");
+    }
+    _ControllerSubscription subscription = new _ControllerSubscription(
+        this, onData, onError, onDone, cancelOnError);
+
+    _PendingEvents pendingEvents = _pendingEvents;
+    _state |= _STATE_SUBSCRIBED;
+    if (_isAddingStream) {
+      _StreamControllerAddStreamState addState = _varData;
+      addState.varData = subscription;
+    } else {
+      _varData = subscription;
+    }
+    subscription._setPendingEvents(pendingEvents);
     subscription._guardCallback(() {
       _runGuarded(_onListen);
     });
+
+    return subscription;
   }
 
   void _recordCancel(StreamSubscription<T> subscription) {
-    assert(identical(_subscription, subscription));
-    _subscription = null;
-    _state |= _STATE_CANCELLED;
+    if (_isAddingStream) {
+      _StreamControllerAddStreamState addState = _varData;
+      addState.cancel();
+    }
+    _varData = null;
+    _state =
+        (_state & ~(_STATE_SUBSCRIBED | _STATE_ADDSTREAM)) | _STATE_CANCELED;
     _runGuarded(_onCancel);
+    if (_doneFuture != null && _doneFuture._mayComplete) {
+      _doneFuture._asyncSetValue(null);
+    }
   }
 
   void _recordPause(StreamSubscription<T> subscription) {
+    if (_isAddingStream) {
+      _StreamControllerAddStreamState addState = _varData;
+      addState.pause();
+    }
     _runGuarded(_onPause);
   }
 
   void _recordResume(StreamSubscription<T> subscription) {
+    if (_isAddingStream) {
+      _StreamControllerAddStreamState addState = _varData;
+      addState.resume();
+    }
     _runGuarded(_onResume);
   }
 }
 
-class _SyncStreamController<T> extends _StreamController<T> {
-  _SyncStreamController(void onListen(),
-                        void onPause(),
-                        void onResume(),
-                        void onCancel())
-      : super(onListen, onPause, onResume, onCancel);
-
+abstract class _SyncStreamControllerDispatch<T>
+    implements _StreamController<T> {
   void _sendData(T data) {
     _subscription._add(data);
   }
@@ -330,13 +515,8 @@ class _SyncStreamController<T> extends _StreamController<T> {
   }
 }
 
-class _AsyncStreamController<T> extends _StreamController<T> {
-  _AsyncStreamController(void onListen(),
-                         void onPause(),
-                         void onResume(),
-                         void onCancel())
-      : super(onListen, onPause, onResume, onCancel);
-
+abstract class _AsyncStreamControllerDispatch<T>
+    implements _StreamController<T> {
   void _sendData(T data) {
     _subscription._addPending(new _DelayedData(data));
   }
@@ -350,6 +530,48 @@ class _AsyncStreamController<T> extends _StreamController<T> {
   }
 }
 
+// TODO(lrn): Use common superclass for callback-controllers when VM supports
+// constructors in mixin superclasses.
+
+class _AsyncStreamController<T> extends _StreamController<T>
+                                   with _AsyncStreamControllerDispatch<T> {
+  final _NotificationHandler _onListen;
+  final _NotificationHandler _onPause;
+  final _NotificationHandler _onResume;
+  final _NotificationHandler _onCancel;
+
+  _AsyncStreamController(void this._onListen(),
+                         void this._onPause(),
+                         void this._onResume(),
+                         void this._onCancel());
+}
+
+class _SyncStreamController<T> extends _StreamController<T>
+                                  with _SyncStreamControllerDispatch<T> {
+  final _NotificationHandler _onListen;
+  final _NotificationHandler _onPause;
+  final _NotificationHandler _onResume;
+  final _NotificationHandler _onCancel;
+
+  _SyncStreamController(void this._onListen(),
+                        void this._onPause(),
+                        void this._onResume(),
+                        void this._onCancel());
+}
+
+abstract class _NoCallbacks {
+  _NotificationHandler get _onListen => null;
+  _NotificationHandler get _onPause => null;
+  _NotificationHandler get _onResume => null;
+  _NotificationHandler get _onCancel => null;
+}
+
+typedef _NoCallbackAsyncStreamController<T> = _StreamController<T>
+       with _AsyncStreamControllerDispatch/*<T>*/, _NoCallbacks;
+
+typedef _NoCallbackSyncStreamController<T> = _StreamController<T>
+       with _SyncStreamControllerDispatch/*<T>*/, _NoCallbacks;
+
 typedef void _NotificationHandler();
 
 void _runGuarded(_NotificationHandler notificationHandler) {
@@ -363,7 +585,6 @@ void _runGuarded(_NotificationHandler notificationHandler) {
 
 class _ControllerStream<T> extends _StreamImpl<T> {
   _StreamControllerLifecycle<T> _controller;
-  bool _hasListener = false;
 
   _ControllerStream(this._controller);
 
@@ -371,17 +592,19 @@ class _ControllerStream<T> extends _StreamImpl<T> {
       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);
-  }
+      bool cancelOnError) =>
+    _controller._subscribe(onData, onError, onDone, cancelOnError);
 
-  void _onListen(_BufferingStreamSubscription subscription) {
-    _controller._recordListen(subscription);
+  // Override == and hashCode so that new streams returned by the same
+  // controller are considered equal. The controller returns a new stream
+  // each time it's queried, but doesn't have to cache the result.
+
+  int get hashCode => _controller.hashCode ^ 0x35323532;
+
+  bool operator==(Object other) {
+    if (other is! _ControllerStream) return false;
+    _ControllerStream otherStream = other;
+    return identical(otherStream._controller, this);
   }
 }
 
@@ -408,367 +631,64 @@ class _ControllerSubscription<T> extends _BufferingStreamSubscription<T> {
   }
 }
 
-class _BroadcastStream<T> extends _StreamImpl<T> {
-  _BroadcastStreamController _controller;
-
-  _BroadcastStream(this._controller);
-
-  bool get isBroadcast => true;
-
-  StreamSubscription<T> _createSubscription(
-      void onData(T data),
-      void onError(Object error),
-      void onDone(),
-      bool cancelOnError) {
-    return new _BroadcastSubscription<T>(
-        _controller, onData, onError, onDone, cancelOnError);
-  }
-
-  void _onListen(_BufferingStreamSubscription subscription) {
-    _controller._recordListen(subscription);
-  }
-}
-
-abstract class _BroadcastSubscriptionLink {
-  _BroadcastSubscriptionLink _next;
-  _BroadcastSubscriptionLink _previous;
-}
-
-class _BroadcastSubscription<T> extends _ControllerSubscription<T>
-                                implements _BroadcastSubscriptionLink {
-  static const int _STATE_EVENT_ID = 1;
-  static const int _STATE_FIRING = 2;
-  static const int _STATE_REMOVE_AFTER_FIRING = 4;
-  int _eventState;
-
-  _BroadcastSubscriptionLink _next;
-  _BroadcastSubscriptionLink _previous;
-
-  _BroadcastSubscription(_StreamControllerLifecycle controller,
-                         void onData(T data),
-                         void onError(Object error),
-                         void onDone(),
-                         bool cancelOnError)
-      : super(controller, onData, onError, onDone, cancelOnError) {
-    _next = _previous = this;
-  }
-
-  _BroadcastStreamController get _controller => super._controller;
-
-  bool _expectsEvent(int eventId) {
-    return (_eventState & _STATE_EVENT_ID) == eventId;
-  }
-
-  void _toggleEventId() {
-    _eventState ^= _STATE_EVENT_ID;
-  }
-
-  bool get _isFiring => (_eventState & _STATE_FIRING) != 0;
-
-  bool _setRemoveAfterFiring() {
-    assert(_isFiring);
-    _eventState |= _STATE_REMOVE_AFTER_FIRING;
-  }
-
-  bool get _removeAfterFiring =>
-      (_eventState & _STATE_REMOVE_AFTER_FIRING) != 0;
-}
-
-
-abstract class _BroadcastStreamController<T>
-    implements StreamController<T>,
-               _StreamControllerLifecycle<T>,
-               _BroadcastSubscriptionLink,
-               _EventDispatch<T> {
-  static const int _STATE_INITIAL = 0;
-  static const int _STATE_EVENT_ID = 1;
-  static const int _STATE_FIRING = 2;
-  static const int _STATE_CLOSED = 4;
-
-  final _NotificationHandler _onListen;
-  final _NotificationHandler _onCancel;
-
-  // State of the controller.
-  int _state;
-
-  // Double-linked list of active listeners.
-  _BroadcastSubscriptionLink _next;
-  _BroadcastSubscriptionLink _previous;
-
-  _BroadcastStreamController(this._onListen, this._onCancel)
-      : _state = _STATE_INITIAL {
-    _next = _previous = this;
-  }
-
-  // StreamController interface.
-
-  Stream<T> get stream => new _BroadcastStream<T>(this);
-
-  EventSink<T> get sink => new _EventSinkView<T>(this);
-
-  bool get isClosed => (_state & _STATE_CLOSED) != 0;
-
-  /**
-   * A broadcast controller is never paused.
-   *
-   * Each receiving stream may be paused individually, and they handle their
-   * own buffering.
-   */
-  bool get isPaused => false;
-
-  /** Whether there are currently a subscriber on the [Stream]. */
-  bool get hasListener => !_isEmpty;
-
-  /** Whether an event is being fired (sent to some, but not all, listeners). */
-  bool get _isFiring => (_state & _STATE_FIRING) != 0;
-
-  // Linked list helpers
-
-  bool get _isEmpty => identical(_next, this);
-
-  /** Adds subscription to linked list of active listeners. */
-  void _addListener(_BroadcastSubscription<T> subscription) {
-    _BroadcastSubscriptionLink previous = _previous;
-    previous._next = subscription;
-    _previous = subscription._previous;
-    subscription._previous._next = this;
-    subscription._previous = previous;
-    subscription._eventState = (_state & _STATE_EVENT_ID);
-  }
-
-  void _removeListener(_BroadcastSubscription<T> subscription) {
-    assert(identical(subscription._controller, this));
-    assert(!identical(subscription._next, subscription));
-    subscription._previous._next = subscription._next;
-    subscription._next._previous = subscription._previous;
-    subscription._next = subscription._previous = subscription;
-  }
-
-  // _StreamControllerLifecycle interface.
-
-  void _recordListen(_BroadcastSubscription<T> subscription) {
-    _addListener(subscription);
-    if (identical(_next, _previous)) {
-      // Only one listener, so it must be the first listener.
-      _runGuarded(_onListen);
-    }
-  }
-
-  void _recordCancel(_BroadcastSubscription<T> subscription) {
-    if (subscription._isFiring) {
-      subscription._setRemoveAfterFiring();
-    } else {
-      _removeListener(subscription);
-      // If we are currently firing an event, the empty-check is performed at
-      // the end of the listener loop instead of here.
-      if ((_state & _STATE_FIRING) == 0 && _isEmpty) {
-        _callOnCancel();
-      }
-    }
-  }
-
-  void _recordPause(StreamSubscription<T> subscription) {}
-  void _recordResume(StreamSubscription<T> subscription) {}
-
-  // EventSink interface.
 
-  void add(T data) {
-    if (isClosed) {
-      throw new StateError("Cannot add new events after calling close()");
-    }
-    _sendData(data);
-  }
-
-  void addError(Object error, [Object stackTrace]) {
-    if (isClosed) {
-      throw new StateError("Cannot add new events after calling close()");
-    }
-    if (stackTrace != null) _attachStackTrace(error, stackTrace);
-    _sendError(error);
-  }
-
-  void close() {
-    if (isClosed) {
-      throw new StateError("Cannot add new events after calling close()");
-    }
-    _state |= _STATE_CLOSED;
-    _sendDone();
-  }
-
-  void _forEachListener(
-      void action(_BufferingStreamSubscription<T> subscription)) {
-    if (_isFiring) {
-      throw new StateError(
-          "Cannot fire new event. Controller is already firing an event");
-    }
-    if (_isEmpty) return;
-
-    // Get event id of this event.
-    int id = (_state & _STATE_EVENT_ID);
-    // Start firing (set the _STATE_FIRING bit). We don't do [_onCancel]
-    // callbacks while firing, and we prevent reentrancy of this function.
-    //
-    // Set [_state]'s event id to the next event's id.
-    // Any listeners added while firing this event will expect the next event,
-    // not this one, and won't get notified.
-    _state ^= _STATE_EVENT_ID | _STATE_FIRING;
-    _BroadcastSubscriptionLink link = _next;
-    while (!identical(link, this)) {
-      _BroadcastSubscription<T> subscription = link;
-      if (subscription._expectsEvent(id)) {
-        subscription._eventState |= _BroadcastSubscription._STATE_FIRING;
-        action(subscription);
-        subscription._toggleEventId();
-        link = subscription._next;
-        if (subscription._removeAfterFiring) {
-          _removeListener(subscription);
-        }
-        subscription._eventState &= ~_BroadcastSubscription._STATE_FIRING;
-      } else {
-        link = subscription._next;
-      }
-    }
-    _state &= ~_STATE_FIRING;
-
-    if (_isEmpty) {
-      _callOnCancel();
-    }
-  }
-
-  void _callOnCancel() {
-    _runGuarded(_onCancel);
-  }
-}
-
-class _SyncBroadcastStreamController<T> extends _BroadcastStreamController<T> {
-  _SyncBroadcastStreamController(void onListen(), void onCancel())
-      : super(onListen, onCancel);
-
-  // EventDispatch interface.
-
-  void _sendData(T data) {
-    if (_isEmpty) return;
-    _forEachListener((_BufferingStreamSubscription<T> subscription) {
-      subscription._add(data);
-    });
-  }
-
-  void _sendError(Object error) {
-    if (_isEmpty) return;
-    _forEachListener((_BufferingStreamSubscription<T> subscription) {
-      subscription._addError(error);
-    });
-  }
-
-  void _sendDone() {
-    if (_isEmpty) return;
-    _forEachListener((_BroadcastSubscription<T> subscription) {
-      subscription._close();
-      subscription._eventState |=
-          _BroadcastSubscription._STATE_REMOVE_AFTER_FIRING;
-    });
-  }
-}
-
-class _AsyncBroadcastStreamController<T> extends _BroadcastStreamController<T> {
-  _AsyncBroadcastStreamController(void onListen(), void onCancel())
-      : super(onListen, onCancel);
-
-  // EventDispatch interface.
-
-  void _sendData(T data) {
-    for (_BroadcastSubscriptionLink link = _next;
-         !identical(link, this);
-         link = link._next) {
-      _BroadcastSubscription<T> subscription = link;
-      subscription._addPending(new _DelayedData(data));
-    }
-  }
-
-  void _sendError(Object error) {
-    for (_BroadcastSubscriptionLink link = _next;
-         !identical(link, this);
-         link = link._next) {
-      _BroadcastSubscription<T> subscription = link;
-      subscription._addPending(new _DelayedError(error));
-    }
-  }
-
-  void _sendDone() {
-    for (_BroadcastSubscriptionLink link = _next;
-         !identical(link, this);
-         link = link._next) {
-      _BroadcastSubscription<T> subscription = link;
-      subscription._addPending(const _DelayedDone());
-    }
-  }
+/** A class that exposes only the [StreamSink] interface of an object. */
+class _StreamSinkWrapper<T> implements StreamSink<T> {
+  final StreamSink _target;
+  _StreamSinkWrapper(this._target);
+  void add(T data) { _target.add(data); }
+  void addError(Object error) { _target.addError(error); }
+  Future close() => _target.close();
+  Future addStream(Stream<T> source) => _target.addStream(source);
+  Future get done => _target.done;
 }
 
 /**
- * Stream controller that is used by [Stream.asBroadcastStream].
- *
- * This stream controller allows incoming events while it is firing
- * other events. This is handled by delaying the events until the
- * current event is done firing, and then fire the pending events.
- *
- * This class extends [_SyncBroadcastStreamController]. Events of
- * an "asBroadcastStream" stream are always initiated by events
- * on another stream, and it is fine to forward them synchronously.
+ * Object containing the state used to handle [StreamController.addStream].
  */
-class _AsBroadcastStreamController<T>
-    extends _SyncBroadcastStreamController<T>
-    implements _EventDispatch<T> {
-  _StreamImplEvents _pending;
+class _AddStreamState<T> {
+  // [_FutureImpl] returned by call to addStream.
+  _FutureImpl addStreamFuture;
 
-  _AsBroadcastStreamController(void onListen(), void onCancel())
-      : super(onListen, onCancel);
+  // Subscription on stream argument to addStream.
+  StreamSubscription addSubscription;
 
-  bool get _hasPending => _pending != null && ! _pending.isEmpty;
+  _AddStreamState(StreamSink controller, Stream source)
+      : addStreamFuture = new _FutureImpl(),
+        addSubscription = source.listen(controller._add,
+                                        onError: controller._addError,
+                                        onDone: controller._close,
+                                        cancelOnError: true);
 
-  void _addPendingEvent(_DelayedEvent event) {
-    if (_pending == null) {
-      _pending = new _StreamImplEvents();
-    }
-    _pending.add(event);
+  void pause() {
+    addSubscription.pause();
   }
 
-  void add(T data) {
-    if (_isFiring) {
-      _addPendingEvent(new _DelayedData<T>(data));
-      return;
-    }
-    super.add(data);
-    while (_hasPending) {
-      _pending.handleNext(this);
-    }
+  void resume() {
+    addSubscription.resume();
   }
 
-  void addError(Object error, [StackTrace stackTrace]) {
-    if (_isFiring) {
-      _addPendingEvent(new _DelayedError(error));
-      return;
-    }
-    super.addError(error, stackTrace);
-    while (_hasPending) {
-      _pending.handleNext(this);
-    }
+  void cancel() {
+    addSubscription.cancel();
+    complete();
   }
 
-  void close() {
-    if (_isFiring) {
-      _addPendingEvent(const _DelayedDone());
-      _state |= _STATE_CLOSED;
-      return;
-    }
-    super.close();
-    assert(!_hasPending);
+  void complete() {
+    addStreamFuture._asyncSetValue(null);
   }
+}
 
-  void _callOnCancel() {
-    if (_hasPending) {
-      _pending.clear();
-      _pending = null;
+class _StreamControllerAddStreamState<T> extends _AddStreamState<T> {
+  // The subscription or pending data of a _StreamController.
+  // Stored here because we reuse the `_varData` field  in the _StreamController
+  // to store this state object.
+  var varData;
+
+  _StreamControllerAddStreamState(_StreamController controller,
+                                  this.varData,
+                                  Stream source) : super(controller, source) {
+    if (controller.isPaused) {
+      addSubscription.pause();
     }
-    super._callOnCancel();
   }
 }