sdk/lib/async/timer.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;

abstract class Timer {
  // Internal list used to group Timer.run callbacks.
  static List _runCallbacks = [];

  /**
   * Creates a new timer.
   *
   * The [callback] callback is invoked after the given [duration].
   * A negative duration is treated similar to a duration of 0.
   *
   * If the [duration] is statically known to be 0, consider using [run].
   *
   * Frequently the [duration] is either a constant or computed as in the
   * following example (taking advantage of the multiplication operator of
   * the Duration class):
   *
   *     const TIMEOUT = const Duration(seconds: 3);
   *     const ms = const Duration(milliseconds: 1);
   *
   *     startTimeout([int milliseconds]) {
   *       var duration = milliseconds == null ? TIMEOUT : ms * milliseconds;
   *       return new Timer(duration, handleTimeout);
   *     }
   */
  external factory Timer(Duration duration, void callback());

  /**
   * Creates a new repeating timer.
   *
   * The [callback] is invoked repeatedly with [duration] intervals until
   * canceled. A negative duration is treated similar to a duration of 0.
   */
  external factory Timer.periodic(Duration duration,
                                  void callback(Timer timer));

  /**
   * Runs the given [callback] asynchronously as soon as possible.
   */
  static void run(void callback()) {
    // Optimizing a group of Timer.run callbacks to be executed in the
    // same Timer callback.
    _runCallbacks.add(callback);
    if (_runCallbacks.length == 1) {
      new Timer(const Duration(milliseconds: 0), () {
        List runCallbacks = _runCallbacks;
        // Create new list to make sure we don't call newly added callbacks in
        // this event.
        _runCallbacks = [];
        for (int i = 0; i < runCallbacks.length; i++) {
          Function callback = runCallbacks[i];
          try {
            callback();
          } catch (e) {
            List newCallbacks = _runCallbacks;
            _runCallbacks = [];
            i++;  // Skip the current;
            _runCallbacks.addAll(
                runCallbacks.sublist(i));
            _runCallbacks.addAll(newCallbacks);
            throw;
          }
        }
      });
    }
  }

  /**
   * Cancels the timer.
   */
  void cancel();
}