DispatchPolicy


1   /**
2    *
3    * Licensed to the Apache Software Foundation (ASF) under one or more
4    * contributor license agreements.  See the NOTICE file distributed with
5    * this work for additional information regarding copyright ownership.
6    * The ASF licenses this file to You under the Apache License, Version 2.0
7    * (the "License"); you may not use this file except in compliance with
8    * the License.  You may obtain a copy of the License at
9    *
10   * http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  package org.apache.activemq.broker.region.policy;
19  
20  import java.util.List  ;
21  
22  import org.apache.activemq.broker.ConnectionContext;
23  import org.apache.activemq.broker.region.MessageReference;
24  import org.apache.activemq.filter.MessageEvaluationContext;
25  
26  /**
27   * Abstraction to allow different dispatching policies to be plugged
28   * into the region implementations.  This is used by a queue to deliver
29   * messages to the matching subscriptions.
30   * 
31   * @version $Revision$
32   */
33  public interface DispatchPolicy {
34      
35      /**
36       * Decides how to dispatch a selected message to a collection of consumers.  A safe
37       * approach is to dispatch to every subscription that matches.  Queue Subscriptions that 
38       * have not exceeded their pre-fetch limit will attempt to lock the message before 
39       * dispatching to the client.  First subscription to lock the message wins.  
40       * 
41       * Order of dispatching to the subscriptions matters since a subscription with a 
42       * large pre-fetch may take all the messages if he is always dispatched to first.  
43       * Once a message has been locked, it does not need to be dispatched to any 
44       * further subscriptions.
45       * 
46       * @return true if at least one consumer was dispatched or false if there are no active subscriptions that could be dispatched
47       */
48      boolean dispatch(MessageReference node, MessageEvaluationContext msgContext, List   consumers) throws Exception  ;
49  
50  }
51
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