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 java.util.ArrayList;
020    import java.util.List;
021    import java.util.concurrent.TimeUnit;
022    import java.util.concurrent.locks.Condition;
023    import java.util.concurrent.locks.Lock;
024    import java.util.concurrent.locks.ReentrantLock;
025    
026    import org.apache.camel.Exchange;
027    import org.apache.camel.Navigate;
028    import org.apache.camel.Processor;
029    import org.apache.camel.impl.LoggingExceptionHandler;
030    import org.apache.camel.impl.ServiceSupport;
031    import org.apache.camel.processor.resequencer.ResequencerEngine;
032    import org.apache.camel.processor.resequencer.SequenceElementComparator;
033    import org.apache.camel.processor.resequencer.SequenceSender;
034    import org.apache.camel.spi.ExceptionHandler;
035    import org.apache.camel.util.ServiceHelper;
036    
037    /**
038     * A resequencer that re-orders a (continuous) stream of {@link Exchange}s. The
039     * algorithm implemented by {@link ResequencerEngine} is based on the detection
040     * of gaps in a message stream rather than on a fixed batch size. Gap detection
041     * in combination with timeouts removes the constraint of having to know the
042     * number of messages of a sequence (i.e. the batch size) in advance.
043     * <p>
044     * Messages must contain a unique sequence number for which a predecessor and a
045     * successor is known. For example a message with the sequence number 3 has a
046     * predecessor message with the sequence number 2 and a successor message with
047     * the sequence number 4. The message sequence 2,3,5 has a gap because the
048     * sucessor of 3 is missing. The resequencer therefore has to retain message 5
049     * until message 4 arrives (or a timeout occurs).
050     * <p>
051     * Instances of this class poll for {@link Exchange}s from a given
052     * <code>endpoint</code>. Resequencing work and the delivery of messages to
053     * the next <code>processor</code> is done within the single polling thread.
054     * 
055     * @version $Revision: 792319 $
056     * 
057     * @see ResequencerEngine
058     */
059    public class StreamResequencer extends ServiceSupport implements SequenceSender<Exchange>, Processor, Navigate<Processor>, Traceable {
060    
061        private static final long DELIVERY_ATTEMPT_INTERVAL = 1000L;
062        
063        private final ExceptionHandler exceptionHandler;
064        private final ResequencerEngine<Exchange> engine;
065        private final Processor processor;
066        private Delivery delivery;
067        private int capacity;
068        
069        /**
070         * Creates a new {@link StreamResequencer} instance.
071         * 
072         * @param processor next processor that processes re-ordered exchanges.
073         * @param comparator a sequence element comparator for exchanges.
074         */
075        public StreamResequencer(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.processor = processor;
080        }
081    
082        /**
083         * Returns this resequencer's exception handler.
084         */
085        public ExceptionHandler getExceptionHandler() {
086            return exceptionHandler;
087        }
088    
089        /**
090         * Returns the next processor.
091         */
092        public Processor getProcessor() {
093            return processor;
094        }
095    
096        /**
097         * Returns this resequencer's capacity. The capacity is the maximum number
098         * of exchanges that can be managed by this resequencer at a given point in
099         * time. If the capacity if reached, polling from the endpoint will be
100         * skipped for <code>timeout</code> milliseconds giving exchanges the
101         * possibility to time out and to be delivered after the waiting period.
102         * 
103         * @return this resequencer's capacity.
104         */
105        public int getCapacity() {
106            return capacity;
107        }
108    
109        /**
110         * Returns this resequencer's timeout. This sets the resequencer engine's
111         * timeout via {@link ResequencerEngine#setTimeout(long)}. This value is
112         * also used to define the polling timeout from the endpoint.
113         * 
114         * @return this resequencer's timeout. (Processor)
115         * @see ResequencerEngine#setTimeout(long)
116         */
117        public long getTimeout() {
118            return engine.getTimeout();
119        }
120    
121        public void setCapacity(int capacity) {
122            this.capacity = capacity;
123        }
124    
125        public void setTimeout(long timeout) {
126            engine.setTimeout(timeout);
127        }
128    
129        @Override
130        public String toString() {
131            return "StreamResequencer[to: " + processor + "]";
132        }
133    
134        public String getTraceLabel() {
135            return "StreamResequence";
136        }
137    
138        @Override
139        protected void doStart() throws Exception {
140            ServiceHelper.startServices(processor);
141            delivery = new Delivery();
142            engine.start();
143            delivery.start();
144        }
145    
146        @Override
147        protected void doStop() throws Exception {
148            // let's stop everything in the reverse order
149            // no need to stop the worker thread -- it will stop automatically when this service is stopped
150            engine.stop();
151            ServiceHelper.stopServices(processor);
152        }
153    
154        /**
155         * Sends the <code>exchange</code> to the next <code>processor</code>.
156         * 
157         * @param exchange exchange to send.
158         */
159        public void sendElement(Exchange exchange) throws Exception {
160            processor.process(exchange);
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        public boolean hasNext() {
172            return processor != null;
173        }
174    
175        public List<Processor> next() {
176            if (!hasNext()) {
177                return null;
178            }
179            List<Processor> answer = new ArrayList<Processor>(1);
180            answer.add(processor);
181            return answer;
182        }
183    
184        private class Delivery extends Thread {
185    
186            private Lock deliveryRequestLock = new ReentrantLock();
187            private Condition deliveryRequestCondition = deliveryRequestLock.newCondition();
188            
189            public Delivery() {
190                super("Resequencer Delivery Thread");
191            }
192            
193            @Override
194            public void run() {
195                while (true) {
196                    try {
197                        deliveryRequestLock.lock();
198                        try {
199                            deliveryRequestCondition.await(DELIVERY_ATTEMPT_INTERVAL, TimeUnit.MILLISECONDS);
200                        } finally {
201                            deliveryRequestLock.unlock();
202                        }
203                    } catch (InterruptedException e) {
204                        break;
205                    }
206                    try {
207                        engine.deliver();
208                    } catch (Exception e) {
209                        exceptionHandler.handleException(e);
210                    }
211                }
212            }
213    
214            public void cancel() {
215                interrupt();
216            }
217            
218            public void request() {
219                deliveryRequestLock.lock();
220                try {
221                    deliveryRequestCondition.signal();
222                } finally {
223                    deliveryRequestLock.unlock();
224                }
225            }
226            
227        }
228        
229    }