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 */
017package org.apache.activemq.broker.region.policy;
018
019import java.io.IOException;
020import java.util.LinkedList;
021
022import org.apache.activemq.broker.region.MessageReference;
023
024/**
025 * A strategy for evicting messages from slow consumers.
026 * 
027 * 
028 */
029public 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}