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.concurrent.TimeUnit;
020    import java.util.concurrent.locks.Condition;
021    import java.util.concurrent.locks.Lock;
022    import java.util.concurrent.locks.ReentrantLock;
023    
024    import org.apache.camel.Exchange;
025    import org.apache.camel.Processor;
026    import org.apache.camel.impl.LoggingExceptionHandler;
027    import org.apache.camel.impl.ServiceSupport;
028    import org.apache.camel.processor.resequencer.ResequencerEngine;
029    import org.apache.camel.processor.resequencer.SequenceElementComparator;
030    import org.apache.camel.processor.resequencer.SequenceSender;
031    import org.apache.camel.spi.ExceptionHandler;
032    import org.apache.camel.util.ServiceHelper;
033    
034    /**
035     * A resequencer that re-orders a (continuous) stream of {@link Exchange}s. The
036     * algorithm implemented by {@link ResequencerEngine} is based on the detection
037     * of gaps in a message stream rather than on a fixed batch size. Gap detection
038     * in combination with timeouts removes the constraint of having to know the
039     * number of messages of a sequence (i.e. the batch size) in advance.
040     * <p>
041     * Messages must contain a unique sequence number for which a predecessor and a
042     * successor is known. For example a message with the sequence number 3 has a
043     * predecessor message with the sequence number 2 and a successor message with
044     * the sequence number 4. The message sequence 2,3,5 has a gap because the
045     * sucessor of 3 is missing. The resequencer therefore has to retain message 5
046     * until message 4 arrives (or a timeout occurs).
047     * <p>
048     * Instances of this class poll for {@link Exchange}s from a given
049     * <code>endpoint</code>. Resequencing work and the delivery of messages to
050     * the next <code>processor</code> is done within the single polling thread.
051     * 
052     * @author Martin Krasser
053     * 
054     * @version $Revision: 765731 $
055     * 
056     * @see ResequencerEngine
057     */
058    public class StreamResequencer extends ServiceSupport implements SequenceSender<Exchange>, Processor {
059    
060        private static final long DELIVERY_ATTEMPT_INTERVAL = 1000L;
061        
062        private ExceptionHandler exceptionHandler;
063        private ResequencerEngine<Exchange> engine;
064        private Processor processor;
065        private Delivery delivery;
066        private int capacity;
067        
068        /**
069         * Creates a new {@link StreamResequencer} instance.
070         * 
071         * @param endpoint
072         *            endpoint to poll exchanges from.
073         * @param processor
074         *            next processor that processes re-ordered exchanges.
075         * @param comparator
076         *            a sequence element comparator for exchanges.
077         */
078        public StreamResequencer(Processor processor, SequenceElementComparator<Exchange> comparator) {
079            this.exceptionHandler = new LoggingExceptionHandler(getClass());
080            this.engine = new ResequencerEngine<Exchange>(comparator);
081            this.engine.setSequenceSender(this);
082            this.processor = processor;
083        }
084    
085        /**
086         * Returns this resequencer's exception handler.
087         * 
088         * @return this resequencer's exception handler.
089         */
090        public ExceptionHandler getExceptionHandler() {
091            return exceptionHandler;
092        }
093    
094        /**
095         * Returns the next processor.
096         * 
097         * @return the next processor.
098         */
099        public Processor getProcessor() {
100            return processor;
101        }
102    
103        /**
104         * Returns this resequencer's capacity. The capacity is the maximum number
105         * of exchanges that can be managed by this resequencer at a given point in
106         * time. If the capacity if reached, polling from the endpoint will be
107         * skipped for <code>timeout</code> milliseconds giving exchanges the
108         * possibility to time out and to be delivered after the waiting period.
109         * 
110         * @return this resequencer's capacity.
111         */
112        public int getCapacity() {
113            return capacity;
114        }
115    
116        /**
117         * Returns this resequencer's timeout. This sets the resequencer engine's
118         * timeout via {@link ResequencerEngine#setTimeout(long)}. This value is
119         * also used to define the polling timeout from the endpoint.
120         * 
121         * @return this resequencer's timeout.
122         * (Processor) 
123         * @see ResequencerEngine#setTimeout(long)
124         */
125        public long getTimeout() {
126            return engine.getTimeout();
127        }
128    
129        public void setCapacity(int capacity) {
130            this.capacity = capacity;
131        }
132    
133        public void setTimeout(long timeout) {
134            engine.setTimeout(timeout);
135        }
136    
137        @Override
138        public String toString() {
139            return "StreamResequencer[to: " + processor + "]";
140        }
141    
142        @Override
143        protected void doStart() throws Exception {
144            ServiceHelper.startServices(processor);
145            delivery = new Delivery();
146            engine.start();
147            delivery.start();
148        }
149    
150        @Override
151        protected void doStop() throws Exception {
152            // let's stop everything in the reverse order
153            // no need to stop the worker thread -- it will stop automatically when this service is stopped
154            engine.stop();
155            ServiceHelper.stopServices(processor);
156        }
157    
158        /**
159         * Sends the <code>exchange</code> to the next <code>processor</code>.
160         * 
161         * @param o
162         *            exchange to send.
163         */
164        public void sendElement(Exchange o) throws Exception {
165            processor.process(o);
166        }
167    
168        public void process(Exchange exchange) throws Exception {
169            while (engine.size() >= capacity) {
170                Thread.sleep(getTimeout());
171            }
172            engine.insert(exchange);
173            delivery.request();
174        }
175    
176        private class Delivery extends Thread {
177    
178            private Lock deliveryRequestLock = new ReentrantLock();
179            private Condition deliveryRequestCondition = deliveryRequestLock.newCondition();
180            
181            public Delivery() {
182                super("Delivery Thread");
183            }
184            
185            @Override
186            public void run() {
187                while (true) {
188                    try {
189                        deliveryRequestLock.lock();
190                        try {
191                            deliveryRequestCondition.await(DELIVERY_ATTEMPT_INTERVAL, TimeUnit.MILLISECONDS);
192                        } finally {
193                            deliveryRequestLock.unlock();
194                        }
195                    } catch (InterruptedException e) {
196                        break;
197                    }
198                    try {
199                        engine.deliver();
200                    } catch (Exception e) {
201                        exceptionHandler.handleException(e);
202                    }
203                }
204            }
205    
206            public void cancel() {
207                interrupt();
208            }
209            
210            public void request() {
211                deliveryRequestLock.lock();
212                try {
213                    deliveryRequestCondition.signal();
214                } finally {
215                    deliveryRequestLock.unlock();
216                }
217            }
218            
219        }
220        
221    }