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quiver/lib/src/async/future_group.dart

-// Copyright 2013 Google Inc. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-part of quiver.async;
-
-/**
- * A collection of [Future]s that signals when all added Futures complete. New
- * Futures can be added to the group as long as it hasn't completed.
- *
- * FutureGroup is useful for managing a set of async tasks that may spawn new
- * async tasks as they execute.
- */
-class FutureGroup<E> {
-  static const _FINISHED = -1;
-
-  int _pending = 0;
-  Future _failedTask;
-  final Completer<List> _completer = new Completer<List>();
-  final List results = [];
-
-  /** Gets the task that failed, if any. */
-  Future get failedTask => _failedTask;
-
-  /**
-   * Wait for [task] to complete.
-   *
-   * If this group has already been marked as completed, a [StateError] will be
-   * thrown.
-   *
-   * If this group has a [failedTask], new tasks will be ignored, because the
-   * error has already been signaled.
-   */
-  void add(Future task) {
-    if (_failedTask != null) return;
-    if (_pending == _FINISHED) throw new StateError("Future already completed");
-
-    _pending++;
-    var i = results.length;
-    results.add(null);
-    task.then((res) {
-      results[i] = res;
-      if (_failedTask != null) return;
-      _pending--;
-      if (_pending == 0) {
-        _pending = _FINISHED;
-        _completer.complete(results);
-      }
-    }, onError: (e, s) {
-      if (_failedTask != null) return;
-      _failedTask = task;
-      _completer.completeError(e, s);
-    });
-  }
-
-  /**
-   * A Future that complets with a List of the values from all the added
-   * tasks, when they have all completed.
-   *
-   * If any task fails, this Future will receive the error. Only the first
-   * error will be sent to the Future.
-   */
-  Future<List<E>> get future => _completer.future;
-}