Introduce optimized Timer.run queue for immediate runs.

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 [Duration]) has passed. 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
@@ skipping 22 matching lines @@
    * canceled. A negative duration is treated similar to a duration of 0.
    *
    * *Deprecation warning*: this constructor used to take an [int] (the time
    * in milliseconds). This has changed to a [Duration].
    */
   external factory Timer.repeating(var duration,
                                    void callback(Timer timer));
 
   /**
    * Runs the given [callback] asynchronously as soon as possible.
-   *
-   * Returns a [Timer] that can be cancelled if the callback is not necessary
-   * anymore.
    */
-  static Timer run(void callback()) {
-    return new Timer(const Duration(), callback);
+  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 = [];
+            _runCallbacks.addAll(runCallbacks.skip(i + 1));
+            _runCallbacks.addAll(newCallbacks);
+            throw;
+          }
+        }
+      });
+    }
   }
 
   /**
    * Cancels the timer.
    */
   void cancel();
 }