Big merge from experimental to bleeding edge.

sdk/lib/async/merge_stream.dart

Index: sdk/lib/async/merge_stream.dart
diff --git a/sdk/lib/async/merge_stream.dart b/sdk/lib/async/merge_stream.dart
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+++ b/sdk/lib/async/merge_stream.dart
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+// 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 _SupercedeEntry<T> {
+  final SupercedeStream stream;
+  Stream<T> source;
+  StreamSubscription subscription = null;
+  _SupercedeEntry next;
+
+  _SupercedeEntry(this.stream, this.source, this.next);
+
+  // Whether the source stream is complete.
+  bool get isDone => source == null;
+
+  void onData(T data) {
+    // Stop all lower-priority sources.
+    stream._setData(this, data);
+  }
+
+  void onError(AsyncError error) {
+    stream._signalError(error);
+  }
+
+  void onDone() {
+    subscription = null;
+    source = null;
+    stream._setDone(this);
+  }
+
+  void start() {
+    assert(subscription == null);
+    if (!isDone) {
+      subscription =
+          source.listen(onData, onError: onError, onDone: onDone);
+    }
+  }
+
+  void stop() {
+    if (!isDone) {
+      subscription.cancel();
+      subscription = null;
+    }
+  }
+
+  void pause() {
+    if (!isDone) subscription.pause();
+  }
+
+  void resume() {
+    if (!isDone) subscription.resume();
+  }
+}
+
+/**
+ * [Stream] that forwards data from its active source with greatest priority.
+ *
+ * The [SupercedeStream] gets data from some source [Stream]s which
+ * are ordered in order of increasing priority.
+ * When a higher priority stream provides data, all lower priority streams
+ * are dropped.
+ *
+ * Errors from all (undropped) streams are forwarded.
+ */
+class SupercedeStream<T> extends _MultiStreamImpl<T> {
+  _SupercedeEntry _entries = null;
+
+  /**
+   * Create [SupercedeStream] from the given [sources].
+   *
+   * The [sources] are iterated in order of increasing priority.
+   */
+  SupercedeStream(Iterable<Stream<T>> sources) {
+    // Set up linked list of sources in decreasing priority order.
+    // The order allows us to drop all lower priority streams when a higher
+    // priority stream provides a value.
+    for (Stream<T> stream in sources) {
+      _entries = new _SupercedeEntry(this, stream, _entries);
+    }
+  }
+
+  void _onSubscriptionStateChange() {
+    if (_hasSubscribers) {
+      for (_SupercedeEntry entry = _entries;
+           entry != null;
+           entry = entry.next) {
+        entry.start();
+      }
+    } else {
+      for (_SupercedeEntry entry = _entries;
+           entry != null;
+           entry = entry.next) {
+        entry.stop();
+      }
+    }
+  }
+
+  void _onPauseStateChange() {
+    if (_isPaused) {
+      for (_SupercedeEntry entry = _entries;
+           entry != null;
+           entry = entry.next) {
+        entry.pause();
+      }
+    } else {
+      for (_SupercedeEntry entry = _entries;
+           entry != null;
+           entry = entry.next) {
+        entry.resume();
+      }
+    }
+  }
+
+  void _setData(_SupercedeEntry entry, T data) {
+    while (entry.next != null)  {
+      _SupercedeEntry nextEntry = entry.next;
+      entry.next = null;
+      nextEntry.stop();
+      entry = nextEntry;
+    }
+    _add(data);
+  }
+
+  void _setDone(_SupercedeEntry entry) {
+    if (identical(_entries, entry)) {
+      // Remove the leading completed streams. These are streams
+      // the completed without ever providing data.
+      while (_entries.isDone) {
+        _entries = _entries.next;
+        if (_entries == null) {
+          _close();
+          return;
+        }
+      }
+    }
+    // Otherwise we leave the completed entry in the list and
+    // remove it when a higher priority stream provides data or
+    // all higher priority streams have completed.
+  }
+}
+
+/**
+ * Helper class for [CyclicScheduleStream].
+ *
+ * Used to maintain a list of source streams which are activated in cyclic
+ * order.
+ *
+ * The stream is either unsubscribed, paused or active. Only one stream
+ * will be active at a time. A source is not subscribed until it's first
+ * activated.
+ *
+ * If the source completes, the entry is removed from [stream].
+ */
+class _CycleEntry<T> {
+  final CyclicScheduleStream stream;
+  /** A single source stream for the [CyclicScheduleStream]. */
+  Stream source;
+  /** The active subscription, if any. */
+  StreamSubscription subscription = null;
+  /** Next entry in a linked list of entries. */
+  _CycleEntry next;
+
+  _CycleEntry(this.stream, this.source);
+
+  void cancel() {
+    // This method may be called event if this entry has never been activated.
+    if (subscription != null) {
+      subscription.cancel();
+      subscription = null;
+    }
+  }
+
+  void pause() {
+    ensureSubscribed();
+    if (!subscription.isPaused) {
+      subscription.pause();
+    }
+  }
+
+  void activate() {
+    ensureSubscribed();
+    if (subscription.isPaused) {
+      subscription.resume();
+    }
+  }
+
+  void ensureSubscribed() {
+    if (subscription == null) {
+      subscription =
+          source.listen(stream._onData,
+                        onError: stream._signalError,
+                        onDone: stream._onDone);
+    }
+  }
+}
+
+/**
+ * [Stream] that schedules events from multiple sources in cyclic order.
+ *
+ * The source streams are activated and paused so that only one data event
+ * is generated at a time, and those data events are output on this stream.
+ *
+ * Error events from the currently active stream are forwarded without
+ * changing the schedule. When a source stream ends, it is removed from
+ * the schedule.
+ */
+class CyclicScheduleStream<T> extends _MultiStreamImpl<T> {
+  _CycleEntry _currentEntry = null;
+  _CycleEntry _lastEntry = null;
+
+  /**
+   * Create a [Stream] that provides data from [sources] one event at a time.
+   *
+   * The data are provided as one event from each stream in the order they are
+   * given by the [Iterable], and then cycling as long as there are data.
+   */
+  CyclicScheduleStream(Iterable<Stream<T>> sources) {
+    _CycleEntry entry = null;
+    for (Stream<T> source in sources) {
+      _CycleEntry newEntry = new _CycleEntry(this, source);
+      if (_lastEntry == null) {
+        _currentEntry = _lastEntry = newEntry;
+      } else {
+        _lastEntry = _lastEntry.next = newEntry;
+      }
+    }
+    if (_currentEntry == null) {
+      _close();
+    }
+  }
+
+  void _onSubscriptionStateChange() {
+    if (_hasSubscribers) {
+      _currentEntry.activate();
+      for (_CycleEntry entry = _currentEntry.next;
+           entry != null;
+           entry = entry.next) {
+        entry.pause();
+      }
+      return;
+    }
+    for (_CycleEntry entry = _currentEntry; entry != null; entry = entry.next) {
+      entry.cancel();
+    }
+  }
+
+  void _onPauseStateChange() {
+    if (_isPaused) {
+      _currentEntry.pause();
+    } else {
+      _currentEntry.activate();
+    }
+  }
+
+  void _onData(T data) {
+    if (_currentEntry.next != null) {
+      _currentEntry.pause();
+      _add(data);
+      // Move the current entry to the end of the list.
+      _lastEntry = _lastEntry.next = _currentEntry;
+      _currentEntry = _currentEntry.next;
+      _lastEntry.next = null;
+      _currentEntry.activate();
+    } else {
+      // No pausing with only one entry left.
+      _add(data);
+    }
+  }
+
+  void _onDone() {
+    if (_currentEntry.next == null) {
+      _close();
+      _currentEntry = _lastEntry = null;
+    } else {
+      // Remove the current entry from the list now that it's complete.
+      _currentEntry = _currentEntry.next;
+      _currentEntry.activate();
+    }
+  }
+}