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: 747062 $
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 processor next processor that processes re-ordered exchanges.
067         * @param comparator a sequence element comparator for exchanges.
068         */
069        public StreamResequencer(Processor processor, SequenceElementComparator<Exchange> comparator) {
070            this.exceptionHandler = new LoggingExceptionHandler(getClass());
071            this.engine = new ResequencerEngine<Exchange>(comparator);
072            this.engine.setSequenceSender(this);
073            this.processor = processor;
074        }
075    
076        /**
077         * Returns this resequencer's exception handler.
078         */
079        public ExceptionHandler getExceptionHandler() {
080            return exceptionHandler;
081        }
082    
083        /**
084         * Returns the next processor.
085         */
086        public Processor getProcessor() {
087            return processor;
088        }
089    
090        /**
091         * Returns this resequencer's capacity. The capacity is the maximum number
092         * of exchanges that can be managed by this resequencer at a given point in
093         * time. If the capacity if reached, polling from the endpoint will be
094         * skipped for <code>timeout</code> milliseconds giving exchanges the
095         * possibility to time out and to be delivered after the waiting period.
096         * 
097         * @return this resequencer's capacity.
098         */
099        public int getCapacity() {
100            return capacity;
101        }
102    
103        /**
104         * Returns this resequencer's timeout. This sets the resequencer engine's
105         * timeout via {@link ResequencerEngine#setTimeout(long)}. This value is
106         * also used to define the polling timeout from the endpoint.
107         * 
108         * @return this resequencer's timeout. (Processor)
109         * @see ResequencerEngine#setTimeout(long)
110         */
111        public long getTimeout() {
112            return engine.getTimeout();
113        }
114    
115        public void setCapacity(int capacity) {
116            this.capacity = capacity;
117        }
118    
119        public void setTimeout(long timeout) {
120            engine.setTimeout(timeout);
121        }
122    
123        @Override
124        public String toString() {
125            return "StreamResequencer[to: " + processor + "]";
126        }
127    
128        @Override
129        protected void doStart() throws Exception {
130            ServiceHelper.startServices(processor);
131            delivery = new Delivery();
132            engine.start();
133            delivery.start();
134        }
135    
136        @Override
137        protected void doStop() throws Exception {
138            // let's stop everything in the reverse order
139            // no need to stop the worker thread -- it will stop automatically when this service is stopped
140            engine.stop();
141            ServiceHelper.stopServices(processor);
142        }
143    
144        /**
145         * Sends the <code>exchange</code> to the next <code>processor</code>.
146         * 
147         * @param exchange exchange to send.
148         */
149        public void sendElement(Exchange exchange) throws Exception {
150            processor.process(exchange);
151        }
152    
153        public void process(Exchange exchange) throws Exception {
154            while (engine.size() >= capacity) {
155                Thread.sleep(getTimeout());
156            }
157            engine.insert(exchange);
158            delivery.request();
159        }
160    
161        private class Delivery extends Thread {
162    
163            private volatile boolean cancelRequested;
164            
165            public Delivery() {
166                super("Resequencer Delivery Thread");
167            }
168            
169            @Override
170            public void run() {
171                while (true) {
172                    try {
173                        Thread.sleep(DELIVERY_ATTEMPT_INTERVAL);
174                    } catch (InterruptedException e) {
175                        if (cancelRequested) {
176                            return;
177                        }
178                    }
179                    try {
180                        engine.deliver();
181                    } catch (Exception e) {
182                        exceptionHandler.handleException(e);
183                    }
184                }
185            }
186    
187            public void cancel() {
188                cancelRequested = true;
189                interrupt();
190            }
191            
192            public void request() {
193                interrupt();
194            }
195            
196        }
197        
198    }