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.CamelContext;
027    import org.apache.camel.Exchange;
028    import org.apache.camel.Navigate;
029    import org.apache.camel.Processor;
030    import org.apache.camel.impl.LoggingExceptionHandler;
031    import org.apache.camel.impl.ServiceSupport;
032    import org.apache.camel.processor.resequencer.ResequencerEngine;
033    import org.apache.camel.processor.resequencer.SequenceElementComparator;
034    import org.apache.camel.processor.resequencer.SequenceSender;
035    import org.apache.camel.spi.ExceptionHandler;
036    import org.apache.camel.util.ObjectHelper;
037    import org.apache.camel.util.ServiceHelper;
038    
039    /**
040     * A resequencer that re-orders a (continuous) stream of {@link Exchange}s. The
041     * algorithm implemented by {@link ResequencerEngine} is based on the detection
042     * of gaps in a message stream rather than on a fixed batch size. Gap detection
043     * in combination with timeouts removes the constraint of having to know the
044     * number of messages of a sequence (i.e. the batch size) in advance.
045     * <p>
046     * Messages must contain a unique sequence number for which a predecessor and a
047     * successor is known. For example a message with the sequence number 3 has a
048     * predecessor message with the sequence number 2 and a successor message with
049     * the sequence number 4. The message sequence 2,3,5 has a gap because the
050     * sucessor of 3 is missing. The resequencer therefore has to retain message 5
051     * until message 4 arrives (or a timeout occurs).
052     * <p>
053     * Instances of this class poll for {@link Exchange}s from a given
054     * <code>endpoint</code>. Resequencing work and the delivery of messages to
055     * the next <code>processor</code> is done within the single polling thread.
056     * 
057     * @version $Revision: 18209 $
058     * 
059     * @see ResequencerEngine
060     */
061    public class StreamResequencer extends ServiceSupport implements SequenceSender<Exchange>, Processor, Navigate<Processor>, Traceable {
062    
063        private static final long DELIVERY_ATTEMPT_INTERVAL = 1000L;
064    
065        private final CamelContext camelContext;
066        private final ExceptionHandler exceptionHandler;
067        private final ResequencerEngine<Exchange> engine;
068        private final Processor processor;
069        private Delivery delivery;
070        private int capacity;
071        
072        /**
073         * Creates a new {@link StreamResequencer} instance.
074         * 
075         * @param processor next processor that processes re-ordered exchanges.
076         * @param comparator a sequence element comparator for exchanges.
077         */
078        public StreamResequencer(CamelContext camelContext, Processor processor, SequenceElementComparator<Exchange> comparator) {
079            ObjectHelper.notNull(camelContext, "CamelContext");
080            this.camelContext = camelContext;
081            this.exceptionHandler = new LoggingExceptionHandler(getClass());
082            this.engine = new ResequencerEngine<Exchange>(comparator);
083            this.engine.setSequenceSender(this);
084            this.processor = processor;
085        }
086    
087        /**
088         * Returns this resequencer's exception handler.
089         */
090        public ExceptionHandler getExceptionHandler() {
091            return exceptionHandler;
092        }
093    
094        /**
095         * Returns 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. (Processor)
120         * @see ResequencerEngine#setTimeout(long)
121         */
122        public long getTimeout() {
123            return engine.getTimeout();
124        }
125    
126        public void setCapacity(int capacity) {
127            this.capacity = capacity;
128        }
129    
130        public void setTimeout(long timeout) {
131            engine.setTimeout(timeout);
132        }
133    
134        @Override
135        public String toString() {
136            return "StreamResequencer[to: " + processor + "]";
137        }
138    
139        public String getTraceLabel() {
140            return "streamResequence";
141        }
142    
143        @Override
144        protected void doStart() throws Exception {
145            ServiceHelper.startServices(processor);
146            delivery = new Delivery();
147            engine.start();
148            delivery.start();
149        }
150    
151        @Override
152        protected void doStop() throws Exception {
153            // let's stop everything in the reverse order
154            // no need to stop the worker thread -- it will stop automatically when this service is stopped
155            engine.stop();
156            ServiceHelper.stopServices(processor);
157        }
158    
159        /**
160         * Sends the <code>exchange</code> to the next <code>processor</code>.
161         * 
162         * @param exchange exchange to send.
163         */
164        public void sendElement(Exchange exchange) throws Exception {
165            processor.process(exchange);
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        public boolean hasNext() {
177            return processor != null;
178        }
179    
180        public List<Processor> next() {
181            if (!hasNext()) {
182                return null;
183            }
184            List<Processor> answer = new ArrayList<Processor>(1);
185            answer.add(processor);
186            return answer;
187        }
188    
189        private class Delivery extends Thread {
190    
191            private Lock deliveryRequestLock = new ReentrantLock();
192            private Condition deliveryRequestCondition = deliveryRequestLock.newCondition();
193            
194            public Delivery() {
195                super(camelContext.getExecutorServiceStrategy().getThreadName("Resequencer Delivery"));
196            }
197            
198            @Override
199            public void run() {
200                while (isRunAllowed()) {
201                    try {
202                        deliveryRequestLock.lock();
203                        try {
204                            deliveryRequestCondition.await(DELIVERY_ATTEMPT_INTERVAL, TimeUnit.MILLISECONDS);
205                        } finally {
206                            deliveryRequestLock.unlock();
207                        }
208                    } catch (InterruptedException e) {
209                        break;
210                    }
211                    try {
212                        engine.deliver();
213                    } catch (Throwable t) {
214                        // a fail safe to handle all exceptions being thrown
215                        getExceptionHandler().handleException(t);
216                    }
217                }
218            }
219    
220            public void cancel() {
221                interrupt();
222            }
223            
224            public void request() {
225                deliveryRequestLock.lock();
226                try {
227                    deliveryRequestCondition.signal();
228                } finally {
229                    deliveryRequestLock.unlock();
230                }
231            }
232            
233        }
234        
235    }