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.Exchange;
020 import org.apache.camel.Processor;
021 import org.apache.camel.impl.LoggingExceptionHandler;
022 import org.apache.camel.impl.ServiceSupport;
023 import org.apache.camel.processor.resequencer.ResequencerEngine;
024 import org.apache.camel.processor.resequencer.SequenceElementComparator;
025 import org.apache.camel.processor.resequencer.SequenceSender;
026 import org.apache.camel.spi.ExceptionHandler;
027 import org.apache.camel.util.ServiceHelper;
028
029 /**
030 * A resequencer that re-orders a (continuous) stream of {@link Exchange}s. The
031 * algorithm implemented by {@link ResequencerEngine} is based on the detection
032 * of gaps in a message stream rather than on a fixed batch size. Gap detection
033 * in combination with timeouts removes the constraint of having to know the
034 * number of messages of a sequence (i.e. the batch size) in advance.
035 * <p>
036 * Messages must contain a unique sequence number for which a predecessor and a
037 * successor is known. For example a message with the sequence number 3 has a
038 * predecessor message with the sequence number 2 and a successor message with
039 * the sequence number 4. The message sequence 2,3,5 has a gap because the
040 * sucessor of 3 is missing. The resequencer therefore has to retain message 5
041 * until message 4 arrives (or a timeout occurs).
042 * <p>
043 * Instances of this class poll for {@link Exchange}s from a given
044 * <code>endpoint</code>. Resequencing work and the delivery of messages to
045 * the next <code>processor</code> is done within the single polling thread.
046 *
047 * @author Martin Krasser
048 *
049 * @version $Revision: 724629 $
050 *
051 * @see ResequencerEngine
052 */
053 public class StreamResequencer extends ServiceSupport implements SequenceSender<Exchange>, Processor {
054
055 private static final long DELIVERY_ATTEMPT_INTERVAL = 1000L;
056
057 private ExceptionHandler exceptionHandler;
058 private ResequencerEngine<Exchange> engine;
059 private Processor processor;
060 private Delivery delivery;
061 private int capacity;
062
063 /**
064 * Creates a new {@link StreamResequencer} instance.
065 *
066 * @param endpoint
067 * endpoint to poll exchanges from.
068 * @param processor
069 * next processor that processes re-ordered exchanges.
070 * @param comparator
071 * a sequence element comparator for exchanges.
072 */
073 public StreamResequencer(Processor processor, SequenceElementComparator<Exchange> comparator) {
074 this.exceptionHandler = new LoggingExceptionHandler(getClass());
075 this.engine = new ResequencerEngine<Exchange>(comparator);
076 this.engine.setSequenceSender(this);
077 this.processor = processor;
078 }
079
080 /**
081 * Returns this resequencer's exception handler.
082 *
083 * @return this resequencer's exception handler.
084 */
085 public ExceptionHandler getExceptionHandler() {
086 return exceptionHandler;
087 }
088
089 /**
090 * Returns the next processor.
091 *
092 * @return the next processor.
093 */
094 public Processor getProcessor() {
095 return processor;
096 }
097
098 /**
099 * Returns this resequencer's capacity. The capacity is the maximum number
100 * of exchanges that can be managed by this resequencer at a given point in
101 * time. If the capacity if reached, polling from the endpoint will be
102 * skipped for <code>timeout</code> milliseconds giving exchanges the
103 * possibility to time out and to be delivered after the waiting period.
104 *
105 * @return this resequencer's capacity.
106 */
107 public int getCapacity() {
108 return capacity;
109 }
110
111 /**
112 * Returns this resequencer's timeout. This sets the resequencer engine's
113 * timeout via {@link ResequencerEngine#setTimeout(long)}. This value is
114 * also used to define the polling timeout from the endpoint.
115 *
116 * @return this resequencer's timeout.
117 * (Processor)
118 * @see ResequencerEngine#setTimeout(long)
119 */
120 public long getTimeout() {
121 return engine.getTimeout();
122 }
123
124 public void setCapacity(int capacity) {
125 this.capacity = capacity;
126 }
127
128 public void setTimeout(long timeout) {
129 engine.setTimeout(timeout);
130 }
131
132 @Override
133 public String toString() {
134 return "StreamResequencer[to: " + processor + "]";
135 }
136
137 @Override
138 protected void doStart() throws Exception {
139 ServiceHelper.startServices(processor);
140 delivery = new Delivery();
141 engine.start();
142 delivery.start();
143 }
144
145 @Override
146 protected void doStop() throws Exception {
147 // let's stop everything in the reverse order
148 // no need to stop the worker thread -- it will stop automatically when this service is stopped
149 engine.stop();
150 ServiceHelper.stopServices(processor);
151 }
152
153 /**
154 * Sends the <code>exchange</code> to the next <code>processor</code>.
155 *
156 * @param o
157 * exchange to send.
158 */
159 public void sendElement(Exchange o) throws Exception {
160 processor.process(o);
161 }
162
163 public void process(Exchange exchange) throws Exception {
164 while (engine.size() >= capacity) {
165 Thread.sleep(getTimeout());
166 }
167 engine.insert(exchange);
168 delivery.request();
169 }
170
171 private class Delivery extends Thread {
172
173 private volatile boolean cancelRequested;
174
175 public Delivery() {
176 super("Delivery Thread");
177 }
178
179 @Override
180 public void run() {
181 while (true) {
182 try {
183 Thread.sleep(DELIVERY_ATTEMPT_INTERVAL);
184 } catch (InterruptedException e) {
185 if (cancelRequested) {
186 return;
187 }
188 }
189 try {
190 engine.deliver();
191 } catch (Exception e) {
192 exceptionHandler.handleException(e);
193 }
194 }
195 }
196
197 public void cancel() {
198 cancelRequested = true;
199 interrupt();
200 }
201
202 public void request() {
203 interrupt();
204 }
205
206 }
207
208 }