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     * @version $Revision: 14059 $
053     * 
054     * @see ResequencerEngine
055     */
056    public class StreamResequencer extends ServiceSupport implements SequenceSender<Exchange>, Processor {
057    
058        private static final long DELIVERY_ATTEMPT_INTERVAL = 1000L;
059        
060        private ExceptionHandler exceptionHandler;
061        private ResequencerEngine<Exchange> engine;
062        private Processor processor;
063        private Delivery delivery;
064        private int capacity;
065        
066        /**
067         * Creates a new {@link StreamResequencer} instance.
068         * 
069         * @param endpoint
070         *            endpoint to poll exchanges from.
071         * @param processor
072         *            next processor that processes re-ordered exchanges.
073         * @param comparator
074         *            a sequence element comparator for exchanges.
075         */
076        public StreamResequencer(Processor processor, SequenceElementComparator<Exchange> comparator) {
077            this.exceptionHandler = new LoggingExceptionHandler(getClass());
078            this.engine = new ResequencerEngine<Exchange>(comparator);
079            this.engine.setSequenceSender(this);
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            ServiceHelper.startServices(processor);
143            delivery = new Delivery();
144            engine.start();
145            delivery.start();
146        }
147    
148        @Override
149        protected void doStop() throws Exception {
150            // let's stop everything in the reverse order
151            // no need to stop the worker thread -- it will stop automatically when this service is stopped
152            engine.stop();
153            ServiceHelper.stopServices(processor);
154        }
155    
156        /**
157         * Sends the <code>exchange</code> to the next <code>processor</code>.
158         * 
159         * @param o
160         *            exchange to send.
161         */
162        public void sendElement(Exchange o) throws Exception {
163            processor.process(o);
164        }
165    
166        public void process(Exchange exchange) throws Exception {
167            while (engine.size() >= capacity) {
168                Thread.sleep(getTimeout());
169            }
170            engine.insert(exchange);
171            delivery.request();
172        }
173    
174        private class Delivery extends Thread {
175    
176            private Lock deliveryRequestLock = new ReentrantLock();
177            private Condition deliveryRequestCondition = deliveryRequestLock.newCondition();
178            
179            public Delivery() {
180                super("Delivery Thread");
181            }
182            
183            @Override
184            public void run() {
185                while (true) {
186                    try {
187                        deliveryRequestLock.lock();
188                        try {
189                            deliveryRequestCondition.await(DELIVERY_ATTEMPT_INTERVAL, TimeUnit.MILLISECONDS);
190                        } finally {
191                            deliveryRequestLock.unlock();
192                        }
193                    } catch (InterruptedException e) {
194                        break;
195                    }
196                    try {
197                        engine.deliver();
198                    } catch (Exception e) {
199                        exceptionHandler.handleException(e);
200                    }
201                }
202            }
203    
204            public void cancel() {
205                interrupt();
206            }
207            
208            public void request() {
209                deliveryRequestLock.lock();
210                try {
211                    deliveryRequestCondition.signal();
212                } finally {
213                    deliveryRequestLock.unlock();
214                }
215            }
216            
217        }
218        
219    }