Make StreamController be a StreamSink, not just an EventSink.

sdk/lib/async/broadcast_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;
+
+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) =>
+    _controller._subscribe(onData, onError, onDone, cancelOnError);
+}
+
+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;
+  // TODO(lrn): Use the _state field on _ControllerSubscription to
+  // also store this state. Requires that the subscription implementation
+  // does not assume that it's use of the state integer is the only use.
+  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) {

[floitsch, 2013/06/27 15:15:19]

=> ?

[Lasse Reichstein Nielsen, 2013/06/28 12:57:38]

Will do. 
Probably added the block to be able to do more during debugging.

+    return (_eventState & _STATE_EVENT_ID) == eventId;
+  }
+
+  void _toggleEventId() {

[floitsch, 2013/06/27 15:15:19]

=> ?

[Lasse Reichstein Nielsen, 2013/06/28 12:57:38]

doesn't return a value.

+    _eventState ^= _STATE_EVENT_ID;
+  }
+
+  bool get _isFiring => (_eventState & _STATE_FIRING) != 0;
+
+  bool _setRemoveAfterFiring() {
+    assert(_isFiring);
+    _eventState |= _STATE_REMOVE_AFTER_FIRING;
+  }
+
+  bool get _removeAfterFiring =>

[floitsch, 2013/06/27 15:15:19]

_shouldRemoveAfterFiring

[Lasse Reichstein Nielsen, 2013/06/28 12:57:38]

This is an imperative. It must be removed after firing. And it WILL be removed
after firing. There is no "should" about it.

+      (_eventState & _STATE_REMOVE_AFTER_FIRING) != 0;
+
+  void _onPause() { }
+
+  void _onResume() { }
+}

[floitsch, 2013/06/27 15:15:19]

missing _onCancel() from the _ControllerSubscription.

[Lasse Reichstein Nielsen, 2013/06/28 12:57:38]

It's inherited. We overwrite _onPause and _onResume because we know they will do
nothing, so there is no need to call the controller's _recordPause/Resume to do
nothing there.

Added comments.

+
+
+abstract class _BroadcastStreamController<T>
+    implements StreamController<T>,
+               _StreamControllerLifecycle<T>,
+               _BroadcastSubscriptionLink,
+               _EventSink<T>,
+               _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;
+  static const int _STATE_ADDSTREAM = 8;
+
+  final _NotificationHandler _onListen;
+  final _NotificationHandler _onCancel;
+
+  // State of the controller.
+  int _state;
+
+  // Double-linked list of active listeners.
+  _BroadcastSubscriptionLink _next;
+  _BroadcastSubscriptionLink _previous;
+
+  // Extra state used during an [addStream] call.
+  _AddStreamState<T> _addStreamState;
+
+  /**
+   * Future returned by [close] and [done].
+   *
+   * The future is completed whenever the done event has been sent to all
+   * relevant listeners.
+   * This means when all listeners at the time when the done event was

[floitsch, 2013/06/27 15:15:19]

bad English sentence.

[Lasse Reichstein Nielsen, 2013/06/28 12:57:38]

Reworded.

+   * scheduled have been canceled (sending the done event makes them cancel,
+   * but they can also be canceled before sending the event).
+   *
+   * To make this easier to handle, all listeners added after calling "close"
+   * will never receive any events, so we don't remember them. That means that
+   * this future can be completed whenever the controller [isClosed] and
+   * [hasListener] is false. This is checked in [close] and [_callOnCancel].
+   */
+  _FutureImpl _doneFuture;
+
+  _BroadcastStreamController(this._onListen, this._onCancel)
+      : _state = _STATE_INITIAL {
+    _next = _previous = this;
+  }
+
+  // StreamController interface.
+
+  Stream<T> get stream => new _BroadcastStream<T>(this);
+
+  StreamSink<T> get sink => new _StreamSinkWrapper<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 one or more subscribers. */
+  bool get hasListener => !_isEmpty;
+
+  /** Whether an event is being fired (sent to some, but not all, listeners). */
+  bool get _isFiring => (_state & _STATE_FIRING) != 0;
+
+  bool get _isAddingStream => (_state & _STATE_ADDSTREAM) != 0;
+
+  bool get _mayAddEvent => (_state < _STATE_CLOSED);
+
+  _FutureImpl _ensureDoneFuture() {
+    if (_doneFuture != null) return _doneFuture;
+    return _doneFuture = new _FutureImpl();
+  }
+
+  // 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;

[floitsch, 2013/06/27 15:15:19]

needs comments.
Either explain that you want to accept cyclic lists, or don't do magic things
with subscription._previous.

[Lasse Reichstein Nielsen, 2013/06/28 12:57:38]

Done.

+    _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;

[floitsch, 2013/06/27 15:15:19]

please make this nicer to read:
var prev = sub.prev;
var next = sub.next;
prev.next = next;
next.prev = prev;
sub.next = sub.prev = sub;

[Lasse Reichstein Nielsen, 2013/06/28 12:57:38]

Done.

+    subscription._next._previous = subscription._previous;
+    subscription._next = subscription._previous = subscription;
+  }
+
+  // _StreamControllerLifecycle interface.
+
+  StreamSubscription<T> _subscribe(void onData(T data),
+                                   void onError(Object error),
+                                   void onDone(),
+                                   bool cancelOnError) {
+    if (isClosed) {
+      // No events will ever reach the new subscription, so we don't attach
+      // it to anything.
+      return new _DoneSubscription<T>();

[floitsch, 2013/06/27 15:15:19]

Let's throw instead.

[Lasse Reichstein Nielsen, 2013/06/28 12:57:38]

Done.

+    }
+    StreamSubscription subscription = new _BroadcastSubscription<T>(
+        this, onData, onError, onDone, cancelOnError);
+    _addListener(subscription);
+    if (identical(_next, _previous)) {
+      // Only one listener, so it must be the first listener.
+      _runGuarded(_onListen);
+    }
+    return subscription;
+  }
+
+  void _recordCancel(_BroadcastSubscription<T> subscription) {
+    // If already removed by the stream, don't remove it again.
+    if (identical(subscription._next, subscription)) return;
+    assert(!identical(subscription._next, subscription));
+    if (subscription._isFiring) {
+      subscription._setRemoveAfterFiring();
+    } else {
+      assert(!identical(subscription._next, subscription));
+      _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) {

[floitsch, 2013/06/27 15:15:19]

if (!_isFiring && _isEmpty)

[Lasse Reichstein Nielsen, 2013/06/28 12:57:38]

Done.

+        _callOnCancel();
+      }
+    }
+  }
+
+  void _recordPause(StreamSubscription<T> subscription) {}
+  void _recordResume(StreamSubscription<T> subscription) {}
+
+  // EventSink interface.
+
+  Error _addEventError() {
+    if (isClosed) {
+      return new StateError("Cannot add new events after calling close");
+    }
+    assert(_isAddingStream);
+    return new StateError("Cannot add new events while doing an addStream");
+  }
+
+  void add(T data) {
+    if (!_mayAddEvent) throw _addEventError();
+    _sendData(data);
+  }
+
+  void addError(Object error, [Object stackTrace]) {
+    if (!_mayAddEvent) throw _addEventError();
+    if (stackTrace != null) _attachStackTrace(error, stackTrace);
+    _sendError(error);
+  }
+
+  Future close() {
+    if (isClosed) {
+      assert(_doneFuture != null);
+      return _doneFuture;
+    }
+    if (!_mayAddEvent) throw _addEventError();
+    _state |= _STATE_CLOSED;
+    Future doneFuture = _ensureDoneFuture();
+    _sendDone();
+    return doneFuture;
+  }
+
+  Future get done => _ensureDoneFuture();
+
+  Future addStream(Stream<T> stream) {
+    if (!_mayAddEvent) throw _addEventError();
+    _state |= _STATE_ADDSTREAM;
+    _addStreamState = new _AddStreamState(this, stream);
+    return _addStreamState.addStreamFuture;
+  }
+
+  // _EventSink interface, called from AddStramState.

[floitsch, 2013/06/27 15:15:19]

AddStreamState

[Lasse Reichstein Nielsen, 2013/06/28 12:57:38]

Done.

+  void _add(T data) {
+    _sendData(data);
+  }
+
+  void _addError(Object error) {
+    assert(_isAddingStream);

[floitsch, 2013/06/27 15:15:19]

Why is an error fatal? Isn't it just passed through?

[Lasse Reichstein Nielsen, 2013/06/28 12:57:38]

Let's pass it through, the controller can handle it.

+    _AddStreamState addState = _addStreamState;
+    _addStreamState = null;
+    _state &= ~_STATE_ADDSTREAM;
+    addState.completeWithError(error);
+  }
+
+  void _close() {
+    assert(_isAddingStream);
+    _AddStreamState addState = _addStreamState;
+    _addStreamState = null;
+    _state &= ~_STATE_ADDSTREAM;
+    addState.complete();
+  }
+
+  // Event handling.
+  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() {
+    assert(_isEmpty);
+    if (isClosed && _doneFuture._mayComplete) {
+      // When closed, _doneFuture is not null.
+      _doneFuture._asyncSetValue(null);
+    }
+    _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) {
+      _forEachListener((_BroadcastSubscription<T> subscription) {
+        subscription._close();
+      });
+    } else {
+      assert(_doneFuture != null);
+      assert(_doneFuture._mayComplete);
+      _doneFuture._asyncSetValue(null);
+    }
+  }
+}
+
+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() {
+    if (!_isEmpty) {
+      for (_BroadcastSubscriptionLink link = _next;
+           !identical(link, this);
+           link = link._next) {
+        _BroadcastSubscription<T> subscription = link;
+        subscription._addPending(const _DelayedDone());
+      }
+    } else {
+      assert(_doneFuture != null);
+      assert(_doneFuture._mayComplete);
+      _doneFuture._asyncSetValue(null);
+    }
+  }
+}
+
+/**
+ * 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.
+ */
+class _AsBroadcastStreamController<T>
+    extends _SyncBroadcastStreamController<T>
+    implements _EventDispatch<T> {
+  _StreamImplEvents _pending;
+
+  _AsBroadcastStreamController(void onListen(), void onCancel())
+      : super(onListen, onCancel);
+
+  bool get _hasPending => _pending != null && ! _pending.isEmpty;
+
+  void _addPendingEvent(_DelayedEvent event) {
+    if (_pending == null) {
+      _pending = new _StreamImplEvents();
+    }
+    _pending.add(event);
+  }
+
+  void add(T data) {
+    if (!isClosed && _isFiring) {
+      _addPendingEvent(new _DelayedData<T>(data));
+      return;
+    }
+    super.add(data);
+    while (_hasPending) {
+      _pending.handleNext(this);
+    }
+  }
+
+  void addError(Object error, [StackTrace stackTrace]) {
+    if (!isClosed && _isFiring) {
+      _addPendingEvent(new _DelayedError(error));
+      return;
+    }
+    super.addError(error, stackTrace);
+    while (_hasPending) {
+      _pending.handleNext(this);
+    }
+  }
+
+  void close() {
+    if (!isClosed && _isFiring) {
+      _addPendingEvent(const _DelayedDone());
+      _state |= _STATE_CLOSED;
+      return;
+    }
+    super.close();
+    assert(!_hasPending);
+  }
+
+  void _callOnCancel() {
+    if (_hasPending) {
+      _pending.clear();
+      _pending = null;
+    }
+    super._callOnCancel();
+  }
+}
+
+// A subscription that never receives any events.
+// It can simulate pauses, but otherwise does nothing.
+class _DoneSubscription<T> implements StreamSubscription<T> {
+  int _pauseCount = 0;
+  void onData(void handleData(T data)) {}
+  void onError(void handleErrr(Object error)) {}
+  void onDone(void handleDone()) {}
+  void pause([Future resumeSignal]) {
+    if (resumeSignal != null) resumeSignal.then(_resume);
+    _pauseCount++;
+  }
+  void resume() { _resume(null); }
+  void _resume(_) {
+    if (_pauseCount > 0) _pauseCount--;
+  }
+  void cancel() {}
+  bool get isPaused => _pauseCount > 0;
+  Future asFuture(Object value) => new _FutureImpl();
+}