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    1   /**
    2    * Licensed to the Apache Software Foundation (ASF) under one or more
    3    * contributor license agreements.  See the NOTICE file distributed with
    4    * this work for additional information regarding copyright ownership.
    5    * The ASF licenses this file to You under the Apache License, Version 2.0
    6    * (the "License"); you may not use this file except in compliance with
    7    * the License.  You may obtain a copy of the License at
    8    *
    9    *      http://www.apache.org/licenses/LICENSE-2.0
   10    *
   11    * Unless required by applicable law or agreed to in writing, software
   12    * distributed under the License is distributed on an "AS IS" BASIS,
   13    * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   14    * See the License for the specific language governing permissions and
   15    * limitations under the License.
   16    */
   17   package org.apache.activemq.broker.region.policy;
   18   
   19   import java.io.IOException;
   20   import java.util.LinkedList;
   21   
   22   import org.apache.activemq.broker.region.MessageReference;
   23   
   24   /**
   25    * A strategy for evicting messages from slow consumers.
   26    * 
   27    * @version $Revision: 564057 $
   28    */
   29   public interface MessageEvictionStrategy {
   30   
   31       /**
   32        * Find the message reference in the given list with oldest messages at the front and newer messages at the end
   33        * 
   34        * @return the message that has been evicted.
   35        * @throws IOException if an exception occurs such as reading a message content (but should not ever happen
   36        * as usually all the messages will be in RAM when this method is called).
   37        */
   38       MessageReference[] evictMessages(LinkedList messages) throws IOException;
   39   
   40       /**
   41        * REturns the high water mark on which we will eagerly evict expired messages from RAM
   42        */
   43       int getEvictExpiredMessagesHighWatermark();
   44   
   45   }

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