Optimize the message queue for many active ports with few messages.

runtime/lib/isolate_patch.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.
 
 patch class ReceivePort {
   /* patch */ factory ReceivePort() {
     return new _ReceivePortImpl();
   }
 }
 
@@ skipping 17 matching lines @@
   // Called from the VM to create a new ReceivePort instance.
   static _ReceivePortImpl _get_or_create(int id) {
     if (_portMap != null) {
       _ReceivePortImpl port = _portMap[id];
       if (port != null) {
         return port;
       }
     }
     return new _ReceivePortImpl._internal(id);
   }
+
   _ReceivePortImpl._internal(int id) : _id = id {
     if (_portMap == null) {
       _portMap = new Map();
     }
     _portMap[id] = this;
   }
 
+  // Called from the VM to retrieve the ReceivePort for a message.
+  static _ReceivePortImpl _lookupReceivePort(int id) {
+    assert(_portMap != null);
+    return _portMap[id];
+  }
+
   // Called from the VM to dispatch to the handler.
-  static void _handleMessage(int id, int replyId, var message) {
-    assert(_portMap != null);
-    ReceivePort port = _portMap[id];
+  static void _handleMessage(_ReceivePortImpl port, int replyId, var message) {
+    assert(port != null);
     SendPort replyTo = (replyId == 0) ? null : new _SendPortImpl(replyId);
     (port._onMessage)(message, replyTo);
   }
 
   // Call into the VM to close the VM maintained mappings.
   static _closeInternal(int id) native "ReceivePortImpl_closeInternal";
 
   final int _id;
   var _onMessage;
 
@@ skipping 97 matching lines @@
 
 class _TimerFactory {
   static _TimerFactoryClosure _factory;
 }
 
 // TODO(ahe): Warning: this is NOT called by Dartium. Instead, it sets
 // [_TimerFactory._factory] directly.
 void _setTimerFactoryClosure(_TimerFactoryClosure closure) {
   _TimerFactory._factory = closure;
 }