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.resequencer;
018
019 import java.util.Timer;
020
021 /**
022 * Resequences elements based on a given {@link SequenceElementComparator}.
023 * This resequencer is designed for resequencing element streams. Stream-based
024 * resequencing has the advantage that the number of elements to be resequenced
025 * need not be known in advance. Resequenced elements are delivered via a
026 * {@link SequenceSender}.
027 * <p>
028 * The resequencer's behaviour for a given comparator is controlled by the
029 * <code>timeout</code> property. This is the timeout (in milliseconds) for a
030 * given element managed by this resequencer. An out-of-sequence element can
031 * only be marked as <i>ready-for-delivery</i> if it either times out or if it
032 * has an immediate predecessor (in that case it is in-sequence). If an
033 * immediate predecessor of a waiting element arrives the timeout task for the
034 * waiting element will be cancelled (which marks it as <i>ready-for-delivery</i>).
035 * <p>
036 * If the maximum out-of-sequence time difference between elements within a
037 * stream is known, the <code>timeout</code> value should be set to this
038 * value. In this case it is guaranteed that all elements of a stream will be
039 * delivered in sequence via the {@link SequenceSender}. The lower the
040 * <code>timeout</code> value is compared to the out-of-sequence time
041 * difference between elements within a stream the higher the probability is for
042 * out-of-sequence elements delivered by this resequencer. Delivery of elements
043 * must be explicitly triggered by applications using the {@link #deliver()} or
044 * {@link #deliverNext()} methods. Only elements that are <i>ready-for-delivery</i>
045 * are delivered by these methods. The longer an application waits to trigger a
046 * delivery the more elements may become <i>ready-for-delivery</i>.
047 * <p>
048 * The resequencer remembers the last-delivered element. If an element arrives
049 * which is the immediate successor of the last-delivered element it is
050 * <i>ready-for-delivery</i> immediately. After delivery the last-delivered
051 * element is adjusted accordingly. If the last-delivered element is
052 * <code>null</code> i.e. the resequencer was newly created the first arriving
053 * element needs <code>timeout</code> milliseconds in any case for becoming
054 * <i>ready-for-delivery</i>.
055 * <p>
056 *
057 * @author Martin Krasser
058 *
059 * @version $Revision: 709173 $
060 */
061 public class ResequencerEngine<E> {
062
063 /**
064 * The element that most recently hash been delivered or <code>null</code>
065 * if no element has been delivered yet.
066 */
067 private Element<E> lastDelivered;
068
069 /**
070 * Minimum amount of time to wait for out-of-sequence elements.
071 */
072 private long timeout;
073
074 /**
075 * A sequence of elements for sorting purposes.
076 */
077 private Sequence<Element<E>> sequence;
078
079 /**
080 * A timer for scheduling timeout notifications.
081 */
082 private Timer timer;
083
084 /**
085 * A strategy for sending sequence elements.
086 */
087 private SequenceSender<E> sequenceSender;
088
089 /**
090 * Creates a new resequencer instance with a default timeout of 2000
091 * milliseconds.
092 *
093 * @param comparator a sequence element comparator.
094 */
095 public ResequencerEngine(SequenceElementComparator<E> comparator) {
096 this.sequence = createSequence(comparator);
097 this.timeout = 2000L;
098 this.lastDelivered = null;
099 }
100
101 public void start() {
102 timer = new Timer("Stream Resequencer Timer");
103 }
104
105 /**
106 * Stops this resequencer (i.e. this resequencer's {@link Timer} instance).
107 */
108 public void stop() {
109 timer.cancel();
110 }
111
112 /**
113 * Returns the number of elements currently maintained by this resequencer.
114 *
115 * @return the number of elements currently maintained by this resequencer.
116 */
117 public synchronized int size() {
118 return sequence.size();
119 }
120
121 /**
122 * Returns this resequencer's timeout value.
123 *
124 * @return the timeout in milliseconds.
125 */
126 public long getTimeout() {
127 return timeout;
128 }
129
130 /**
131 * Sets this sequencer's timeout value.
132 *
133 * @param timeout the timeout in milliseconds.
134 */
135 public void setTimeout(long timeout) {
136 this.timeout = timeout;
137 }
138
139 /**
140 * Returns the sequence sender.
141 *
142 * @return the sequence sender.
143 */
144 public SequenceSender<E> getSequenceSender() {
145 return sequenceSender;
146 }
147
148 /**
149 * Sets the sequence sender.
150 *
151 * @param sequenceSender a sequence element sender.
152 */
153 public void setSequenceSender(SequenceSender<E> sequenceSender) {
154 this.sequenceSender = sequenceSender;
155 }
156
157 /**
158 * Returns the last delivered element.
159 *
160 * @return the last delivered element or <code>null</code> if no delivery
161 * has been made yet.
162 */
163 E getLastDelivered() {
164 if (lastDelivered == null) {
165 return null;
166 }
167 return lastDelivered.getObject();
168 }
169
170 /**
171 * Sets the last delivered element. This is for testing purposes only.
172 *
173 * @param o an element.
174 */
175 void setLastDelivered(E o) {
176 lastDelivered = new Element<E>(o);
177 }
178
179 /**
180 * Inserts the given element into this resequencer. If the element is not
181 * ready for immediate delivery and has no immediate presecessor then it is
182 * scheduled for timing out. After being timed out it is ready for delivery.
183 *
184 * @param o an element.
185 */
186 public synchronized void insert(E o) {
187 // wrap object into internal element
188 Element<E> element = new Element<E>(o);
189 // add element to sequence in proper order
190 sequence.add(element);
191
192 Element<E> successor = sequence.successor(element);
193
194 // check if there is an immediate successor and cancel
195 // timer task (no need to wait any more for timeout)
196 if (successor != null) {
197 successor.cancel();
198 }
199
200 // start delivery if current element is successor of last delivered element
201 if (successorOfLastDelivered(element)) {
202 // nothing to schedule
203 } else if (sequence.predecessor(element) != null) {
204 // nothing to schedule
205 } else {
206 element.schedule(defineTimeout());
207 }
208 }
209
210 /**
211 * Delivers all elements which are currently ready to deliver.
212 *
213 * @throws Exception thrown by {@link SequenceSender#sendElement(Object)}.
214 *
215 * @see ResequencerEngine#deliverNext()
216 */
217 public synchronized void deliver() throws Exception {
218 while (deliverNext()) {
219 // do nothing here
220 }
221 }
222
223 /**
224 * Attempts to deliver a single element from the head of the resequencer
225 * queue (sequence). Only elements which have not been scheduled for timing
226 * out or which already timed out can be delivered. Elements are deliveref via
227 * {@link SequenceSender#sendElement(Object)}.
228 *
229 * @return <code>true</code> if the element has been delivered
230 * <code>false</code> otherwise.
231 *
232 * @throws Exception thrown by {@link SequenceSender#sendElement(Object)}.
233 *
234 */
235 public boolean deliverNext() throws Exception {
236 if (sequence.size() == 0) {
237 return false;
238 }
239 // inspect element with lowest sequence value
240 Element<E> element = sequence.first();
241
242 // if element is scheduled do not deliver and return
243 if (element.scheduled()) {
244 return false;
245 }
246
247 // remove deliverable element from sequence
248 sequence.remove(element);
249
250 // set the delivered element to last delivered element
251 lastDelivered = element;
252
253 // deliver the sequence element
254 sequenceSender.sendElement(element.getObject());
255
256 // element has been delivered
257 return true;
258 }
259
260 /**
261 * Returns <code>true</code> if the given element is the immediate
262 * successor of the last delivered element.
263 *
264 * @param element an element.
265 * @return <code>true</code> if the given element is the immediate
266 * successor of the last delivered element.
267 */
268 private boolean successorOfLastDelivered(Element<E> element) {
269 if (lastDelivered == null) {
270 return false;
271 }
272 if (sequence.comparator().successor(element, lastDelivered)) {
273 return true;
274 }
275 return false;
276 }
277
278 /**
279 * Creates a timeout task based on the timeout setting of this resequencer.
280 *
281 * @return a new timeout task.
282 */
283 private Timeout defineTimeout() {
284 return new Timeout(timer, timeout);
285 }
286
287 private static <E> Sequence<Element<E>> createSequence(SequenceElementComparator<E> comparator) {
288 return new Sequence<Element<E>>(new ElementComparator<E>(comparator));
289 }
290
291 }