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     * @author Martin Krasser
056     * 
057     * @version $Revision: 769303 $
058     * 
059     * @see ResequencerEngine
060     */
061    public class StreamResequencer extends ServiceSupport implements SequenceSender<Exchange>, Processor, Navigate<Processor> {
062    
063        private static final long DELIVERY_ATTEMPT_INTERVAL = 1000L;
064        
065        private final ExceptionHandler exceptionHandler;
066        private final ResequencerEngine<Exchange> engine;
067        private final Processor processor;
068        private Delivery delivery;
069        private int capacity;
070        
071        /**
072         * Creates a new {@link StreamResequencer} instance.
073         * 
074         * @param processor next processor that processes re-ordered exchanges.
075         * @param comparator a sequence element comparator for exchanges.
076         */
077        public StreamResequencer(Processor processor, SequenceElementComparator<Exchange> comparator) {
078            this.exceptionHandler = new LoggingExceptionHandler(getClass());
079            this.engine = new ResequencerEngine<Exchange>(comparator);
080            this.engine.setSequenceSender(this);
081            this.processor = processor;
082        }
083    
084        /**
085         * Returns this resequencer's exception handler.
086         */
087        public ExceptionHandler getExceptionHandler() {
088            return exceptionHandler;
089        }
090    
091        /**
092         * Returns 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. (Processor)
117         * @see ResequencerEngine#setTimeout(long)
118         */
119        public long getTimeout() {
120            return engine.getTimeout();
121        }
122    
123        public void setCapacity(int capacity) {
124            this.capacity = capacity;
125        }
126    
127        public void setTimeout(long timeout) {
128            engine.setTimeout(timeout);
129        }
130    
131        @Override
132        public String toString() {
133            return "StreamResequencer[to: " + processor + "]";
134        }
135    
136        @Override
137        protected void doStart() throws Exception {
138            ServiceHelper.startServices(processor);
139            delivery = new Delivery();
140            engine.start();
141            delivery.start();
142        }
143    
144        @Override
145        protected void doStop() throws Exception {
146            // let's stop everything in the reverse order
147            // no need to stop the worker thread -- it will stop automatically when this service is stopped
148            engine.stop();
149            ServiceHelper.stopServices(processor);
150        }
151    
152        /**
153         * Sends the <code>exchange</code> to the next <code>processor</code>.
154         * 
155         * @param exchange exchange to send.
156         */
157        public void sendElement(Exchange exchange) throws Exception {
158            processor.process(exchange);
159        }
160    
161        public void process(Exchange exchange) throws Exception {
162            while (engine.size() >= capacity) {
163                Thread.sleep(getTimeout());
164            }
165            engine.insert(exchange);
166            delivery.request();
167        }
168    
169        public boolean hasNext() {
170            return processor != null;
171        }
172    
173        public List<Processor> next() {
174            if (!hasNext()) {
175                return null;
176            }
177            List<Processor> answer = new ArrayList<Processor>(1);
178            answer.add(processor);
179            return answer;
180        }
181    
182        private class Delivery extends Thread {
183    
184            private Lock deliveryRequestLock = new ReentrantLock();
185            private Condition deliveryRequestCondition = deliveryRequestLock.newCondition();
186            
187            public Delivery() {
188                super("Resequencer Delivery Thread");
189            }
190            
191            @Override
192            public void run() {
193                while (true) {
194                    try {
195                        deliveryRequestLock.lock();
196                        try {
197                            deliveryRequestCondition.await(DELIVERY_ATTEMPT_INTERVAL, TimeUnit.MILLISECONDS);
198                        } finally {
199                            deliveryRequestLock.unlock();
200                        }
201                    } catch (InterruptedException e) {
202                        break;
203                    }
204                    try {
205                        engine.deliver();
206                    } catch (Exception e) {
207                        exceptionHandler.handleException(e);
208                    }
209                }
210            }
211    
212            public void cancel() {
213                interrupt();
214            }
215            
216            public void request() {
217                deliveryRequestLock.lock();
218                try {
219                    deliveryRequestCondition.signal();
220                } finally {
221                    deliveryRequestLock.unlock();
222                }
223            }
224            
225        }
226        
227    }