001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.activemq.broker.region.policy;
018    
019    import java.io.IOException;
020    import java.util.LinkedList;
021    
022    import org.apache.activemq.broker.region.MessageReference;
023    
024    /**
025     * A strategy for evicting messages from slow consumers.
026     * 
027     * 
028     */
029    public interface MessageEvictionStrategy {
030    
031        /**
032         * Find the message reference in the given list with oldest messages at the front and newer messages at the end
033         * 
034         * @return the message that has been evicted.
035         * @throws IOException if an exception occurs such as reading a message content (but should not ever happen
036         * as usually all the messages will be in RAM when this method is called).
037         */
038        MessageReference[] evictMessages(LinkedList messages) throws IOException;
039    
040        /**
041         * REturns the high water mark on which we will eagerly evict expired messages from RAM
042         */
043        int getEvictExpiredMessagesHighWatermark();
044    
045    }