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.util.List; 020 021import org.apache.activemq.broker.region.MessageReference; 022import org.apache.activemq.broker.region.Subscription; 023import org.apache.activemq.filter.MessageEvaluationContext; 024 025/** 026 * Abstraction to allow different dispatching policies to be plugged 027 * into the region implementations. This is used by a queue to deliver 028 * messages to the matching subscriptions. 029 * 030 * 031 */ 032public interface DispatchPolicy { 033 034 /** 035 * Decides how to dispatch a selected message to a collection of consumers. A safe 036 * approach is to dispatch to every subscription that matches. Queue Subscriptions that 037 * have not exceeded their pre-fetch limit will attempt to lock the message before 038 * dispatching to the client. First subscription to lock the message wins. 039 * 040 * Order of dispatching to the subscriptions matters since a subscription with a 041 * large pre-fetch may take all the messages if he is always dispatched to first. 042 * Once a message has been locked, it does not need to be dispatched to any 043 * further subscriptions. 044 * 045 * The list will be safe to iterate over when this method is called 046 * 047 * @return true if at least one consumer was dispatched or false if there are no active subscriptions that could be dispatched 048 */ 049 boolean dispatch(MessageReference node, MessageEvaluationContext msgContext, List<Subscription> consumers) throws Exception; 050 051}