MessageEvictionStrategy


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 org.apache.activemq.broker.region.MessageReference;
21  
22  import java.io.IOException  ;
23  import java.util.LinkedList  ;
24  
25  /**
26   * A strategy for evicting messages from slow consumers.
27   * 
28   * @version $Revision: 430023 $
29   */
30  public interface MessageEvictionStrategy {
31  
32      /**
33       * Find the message reference in the given list with oldest messages at the front and newer messages at the end
34       * 
35       * @return the message that has been evicted.
36       * @throws IOException if an exception occurs such as reading a message content (but should not ever happen
37       * as usually all the messages will be in RAM when this method is called).
38       */
39      MessageReference[] evictMessages(LinkedList   messages) throws IOException  ;
40  
41      /**
42       * REturns the high water mark on which we will eagerly evict expired messages from RAM
43       */
44      int getEvictExpiredMessagesHighWatermark();
45  
46  }
47

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