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.camel.processor;
018
019 import org.apache.camel.Endpoint;
020 import org.apache.camel.Exchange;
021 import org.apache.camel.PollingConsumer;
022 import org.apache.camel.Processor;
023 import org.apache.camel.impl.LoggingExceptionHandler;
024 import org.apache.camel.impl.ServiceSupport;
025 import org.apache.camel.processor.resequencer.ResequencerEngine;
026 import org.apache.camel.processor.resequencer.SequenceElementComparator;
027 import org.apache.camel.processor.resequencer.SequenceSender;
028 import org.apache.camel.spi.ExceptionHandler;
029 import org.apache.camel.util.ServiceHelper;
030
031 /**
032 * A resequencer that re-orders a (continuous) stream of {@link Exchange}s. The
033 * algorithm implemented by {@link ResequencerEngine} is based on the detection
034 * of gaps in a message stream rather than on a fixed batch size. Gap detection
035 * in combination with timeouts removes the constraint of having to know the
036 * number of messages of a sequence (i.e. the batch size) in advance.
037 * <p>
038 * Messages must contain a unique sequence number for which a predecessor and a
039 * successor is known. For example a message with the sequence number 3 has a
040 * predecessor message with the sequence number 2 and a successor message with
041 * the sequence number 4. The message sequence 2,3,5 has a gap because the
042 * sucessor of 3 is missing. The resequencer therefore has to retain message 5
043 * until message 4 arrives (or a timeout occurs).
044 * <p>
045 * Instances of this class poll for {@link Exchange}s from a given
046 * <code>endpoint</code>. Resequencing work and the delivery of messages to
047 * the next <code>processor</code> is done within the single polling thread.
048 *
049 * @author Martin Krasser
050 *
051 * @version $Revision: 52390 $
052 *
053 * @see ResequencerEngine
054 */
055 public class StreamResequencer extends ServiceSupport implements SequenceSender<Exchange>, Runnable, Processor {
056
057 private ExceptionHandler exceptionHandler;
058 private ResequencerEngine<Exchange> engine;
059 private PollingConsumer<? extends Exchange> consumer;
060 private Endpoint<? extends Exchange> endpoint;
061 private Processor processor;
062 private Thread worker;
063 private int capacity;
064
065 /**
066 * Creates a new {@link StreamResequencer} instance.
067 *
068 * @param endpoint
069 * endpoint to poll exchanges from.
070 * @param processor
071 * next processor that processes re-ordered exchanges.
072 * @param comparator
073 * a sequence element comparator for exchanges.
074 */
075 public StreamResequencer(Endpoint<? extends Exchange> endpoint, Processor processor, SequenceElementComparator<Exchange> comparator) {
076 this.exceptionHandler = new LoggingExceptionHandler(getClass());
077 this.engine = new ResequencerEngine<Exchange>(comparator);
078 this.engine.setSequenceSender(this);
079 this.endpoint = endpoint;
080 this.processor = processor;
081 }
082
083 /**
084 * Returns this resequencer's exception handler.
085 *
086 * @return this resequencer's exception handler.
087 */
088 public ExceptionHandler getExceptionHandler() {
089 return exceptionHandler;
090 }
091
092 /**
093 * Returns the next processor.
094 *
095 * @return the next processor.
096 */
097 public Processor getProcessor() {
098 return processor;
099 }
100
101 /**
102 * Returns this resequencer's capacity. The capacity is the maximum number
103 * of exchanges that can be managed by this resequencer at a given point in
104 * time. If the capacity if reached, polling from the endpoint will be
105 * skipped for <code>timeout</code> milliseconds giving exchanges the
106 * possibility to time out and to be delivered after the waiting period.
107 *
108 * @return this resequencer's capacity.
109 */
110 public int getCapacity() {
111 return capacity;
112 }
113
114 /**
115 * Returns this resequencer's timeout. This sets the resequencer engine's
116 * timeout via {@link ResequencerEngine#setTimeout(long)}. This value is
117 * also used to define the polling timeout from the endpoint.
118 *
119 * @return this resequencer's timeout.
120 * (Processor)
121 * @see ResequencerEngine#setTimeout(long)
122 */
123 public long getTimeout() {
124 return engine.getTimeout();
125 }
126
127 public void setCapacity(int capacity) {
128 this.capacity = capacity;
129 }
130
131 public void setTimeout(long timeout) {
132 engine.setTimeout(timeout);
133 }
134
135 @Override
136 public String toString() {
137 return "StreamResequencer[to: " + processor + "]";
138 }
139
140 @Override
141 protected void doStart() throws Exception {
142 consumer = endpoint.createPollingConsumer();
143 ServiceHelper.startServices(processor, consumer);
144 worker = new Thread(this, this + " Polling Thread");
145 engine.start();
146 worker.start();
147 }
148
149 @Override
150 protected void doStop() throws Exception {
151 // let's stop everything in the reverse order
152 // no need to stop the worker thread -- it will stop automatically when this service is stopped
153 engine.stop();
154 ServiceHelper.stopServices(consumer, processor);
155 }
156
157 /**
158 * Sends the <code>exchange</code> to the next <code>processor</code>.
159 *
160 * @param o
161 * exchange to send.
162 */
163 public void sendElement(Exchange o) throws Exception {
164 processor.process(o);
165 }
166
167 /**
168 * Loops over {@link #processExchange()}.
169 */
170 public void run() {
171 while (!isStopped() && !isStopping()) {
172 try {
173 processExchange();
174 } catch (Exception e) {
175 exceptionHandler.handleException(e);
176 }
177 }
178 }
179
180 /**
181 * Processes an exchange received from the this resequencer's
182 * <code>endpoint</code>. Received exchanges are processed via
183 * {@link ResequencerEngine#insert(Object)}.
184 * {@link ResequencerEngine#deliver()} is then called in any case regardless
185 * whether a message was received or receiving timed out.
186 *
187 * @throws Exception
188 * if exchange delivery fails.
189 */
190 protected void processExchange() throws Exception {
191 if (engine.size() >= capacity) {
192 Thread.sleep(getTimeout());
193 } else {
194 Exchange exchange = consumer.receive(getTimeout());
195 if (exchange != null) {
196 engine.insert(exchange);
197 }
198 }
199 engine.deliver();
200 }
201
202 public void process(Exchange exchange) throws Exception {
203 // empty since exchanges come from endpoint's polling consumer
204 }
205
206 }