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
018 package org.apache.commons.pool.impl;
019
020 import java.lang.ref.SoftReference;
021 import java.lang.ref.ReferenceQueue;
022 import java.lang.ref.Reference;
023 import java.util.ArrayList;
024 import java.util.Iterator;
025 import java.util.List;
026 import java.util.NoSuchElementException;
027
028 import org.apache.commons.pool.BaseObjectPool;
029 import org.apache.commons.pool.ObjectPool;
030 import org.apache.commons.pool.PoolableObjectFactory;
031 import org.apache.commons.pool.PoolUtils;
032
033 /**
034 * A {@link java.lang.ref.SoftReference SoftReference} based
035 * {@link ObjectPool}.
036 *
037 * @author Rodney Waldhoff
038 * @author Sandy McArthur
039 * @version $Revision: 965338 $ $Date: 2010-07-18 18:09:29 -0700 (Sun, 18 Jul 2010) $
040 * @since Pool 1.0
041 */
042 public class SoftReferenceObjectPool extends BaseObjectPool implements ObjectPool {
043 /**
044 * Create a <code>SoftReferenceObjectPool</code> without a factory.
045 * {@link #setFactory(PoolableObjectFactory) setFactory} should be called
046 * before any attempts to use the pool are made.
047 * Generally speaking you should prefer the {@link #SoftReferenceObjectPool(PoolableObjectFactory)} constructor.
048 *
049 * @see #SoftReferenceObjectPool(PoolableObjectFactory)
050 * @deprecated to be removed in pool 2.0. Use {@link #SoftReferenceObjectPool(PoolableObjectFactory)}.
051 */
052 public SoftReferenceObjectPool() {
053 _pool = new ArrayList();
054 _factory = null;
055 }
056
057 /**
058 * Create a <code>SoftReferenceObjectPool</code> with the specified factory.
059 *
060 * @param factory object factory to use.
061 */
062 public SoftReferenceObjectPool(PoolableObjectFactory factory) {
063 _pool = new ArrayList();
064 _factory = factory;
065 }
066
067 /**
068 * Create a <code>SoftReferenceObjectPool</code> with the specified factory and initial idle object count.
069 *
070 * @param factory object factory to use.
071 * @param initSize initial size to attempt to prefill the pool.
072 * @throws Exception when there is a problem prefilling the pool.
073 * @throws IllegalArgumentException when <code>factory</code> is <code>null</code>.
074 * @deprecated because this is a SoftReference pool, prefilled idle obejects may be garbage collected before they are used.
075 * To be removed in Pool 2.0.
076 */
077 public SoftReferenceObjectPool(PoolableObjectFactory factory, int initSize) throws Exception, IllegalArgumentException {
078 if (factory == null) {
079 throw new IllegalArgumentException("factory required to prefill the pool.");
080 }
081 _pool = new ArrayList(initSize);
082 _factory = factory;
083 PoolUtils.prefill(this, initSize);
084 }
085
086 /**
087 * <p>Borrow an object from the pool. If there are no idle instances available in the pool, the configured
088 * factory's {@link PoolableObjectFactory#makeObject()} method is invoked to create a new instance.</p>
089 *
090 * <p>All instances are {@link PoolableObjectFactory#activateObject(Object) activated} and
091 * {@link PoolableObjectFactory#validateObject(Object) validated} before being returned by this
092 * method. If validation fails or an exception occurs activating or validating an idle instance,
093 * the failing instance is {@link PoolableObjectFactory#destroyObject(Object) destroyed} and another
094 * instance is retrieved from the pool, validated and activated. This process continues until either the
095 * pool is empty or an instance passes validation. If the pool is empty on activation or
096 * it does not contain any valid instances, the factory's <code>makeObject</code> method is used
097 * to create a new instance. If the created instance either raises an exception on activation or
098 * fails validation, <code>NoSuchElementException</code> is thrown. Exceptions thrown by <code>MakeObject</code>
099 * are propagated to the caller; but other than <code>ThreadDeath</code> or <code>VirtualMachineError</code>,
100 * exceptions generated by activation, validation or destroy methods are swallowed silently.</p>
101 *
102 * @throws NoSuchElementException if a valid object cannot be provided
103 * @throws IllegalStateException if invoked on a {@link #close() closed} pool
104 * @throws Exception if an exception occurs creating a new instance
105 * @return a valid, activated object instance
106 */
107 public synchronized Object borrowObject() throws Exception {
108 assertOpen();
109 Object obj = null;
110 boolean newlyCreated = false;
111 while(null == obj) {
112 if(_pool.isEmpty()) {
113 if(null == _factory) {
114 throw new NoSuchElementException();
115 } else {
116 newlyCreated = true;
117 obj = _factory.makeObject();
118 }
119 } else {
120 SoftReference ref = (SoftReference)(_pool.remove(_pool.size() - 1));
121 obj = ref.get();
122 ref.clear(); // prevent this ref from being enqueued with refQueue.
123 }
124 if (null != _factory && null != obj) {
125 try {
126 _factory.activateObject(obj);
127 if (!_factory.validateObject(obj)) {
128 throw new Exception("ValidateObject failed");
129 }
130 } catch (Throwable t) {
131 PoolUtils.checkRethrow(t);
132 try {
133 _factory.destroyObject(obj);
134 } catch (Throwable t2) {
135 PoolUtils.checkRethrow(t2);
136 // Swallowed
137 } finally {
138 obj = null;
139 }
140 if (newlyCreated) {
141 throw new NoSuchElementException(
142 "Could not create a validated object, cause: " +
143 t.getMessage());
144 }
145 }
146 }
147 }
148 _numActive++;
149 return obj;
150 }
151
152 /**
153 * <p>Returns an instance to the pool after successful validation and passivation. The returning instance
154 * is destroyed if any of the following are true:<ul>
155 * <li>the pool is closed</li>
156 * <li>{@link PoolableObjectFactory#validateObject(Object) validation} fails</li>
157 * <li>{@link PoolableObjectFactory#passivateObject(Object) passivation} throws an exception</li>
158 * </ul>
159 *</p>
160 *
161 * <p>Exceptions passivating or destroying instances are silently swallowed. Exceptions validating
162 * instances are propagated to the client.</p>
163 *
164 * @param obj instance to return to the pool
165 */
166 public synchronized void returnObject(Object obj) throws Exception {
167 boolean success = !isClosed();
168 if (_factory != null) {
169 if(!_factory.validateObject(obj)) {
170 success = false;
171 } else {
172 try {
173 _factory.passivateObject(obj);
174 } catch(Exception e) {
175 success = false;
176 }
177 }
178 }
179
180 boolean shouldDestroy = !success;
181 _numActive--;
182 if(success) {
183 _pool.add(new SoftReference(obj, refQueue));
184 }
185 notifyAll(); // _numActive has changed
186
187 if (shouldDestroy && _factory != null) {
188 try {
189 _factory.destroyObject(obj);
190 } catch(Exception e) {
191 // ignored
192 }
193 }
194 }
195
196 /**
197 * {@inheritDoc}
198 */
199 public synchronized void invalidateObject(Object obj) throws Exception {
200 _numActive--;
201 if (_factory != null) {
202 _factory.destroyObject(obj);
203 }
204 notifyAll(); // _numActive has changed
205 }
206
207 /**
208 * <p>Create an object, and place it into the pool.
209 * addObject() is useful for "pre-loading" a pool with idle objects.</p>
210 *
211 * <p>Before being added to the pool, the newly created instance is
212 * {@link PoolableObjectFactory#validateObject(Object) validated} and
213 * {@link PoolableObjectFactory#passivateObject(Object) passivated}. If validation
214 * fails, the new instance is {@link PoolableObjectFactory#destroyObject(Object) destroyed}.
215 * Exceptions generated by the factory <code>makeObject</code> or <code>passivate</code> are
216 * propagated to the caller. Exceptions destroying instances are silently swallowed.</p>
217 *
218 * @throws IllegalStateException if invoked on a {@link #close() closed} pool
219 * @throws Exception when the {@link #getFactory() factory} has a problem creating or passivating an object.
220 */
221 public synchronized void addObject() throws Exception {
222 assertOpen();
223 if (_factory == null) {
224 throw new IllegalStateException("Cannot add objects without a factory.");
225 }
226 Object obj = _factory.makeObject();
227
228 boolean success = true;
229 if(!_factory.validateObject(obj)) {
230 success = false;
231 } else {
232 _factory.passivateObject(obj);
233 }
234
235 boolean shouldDestroy = !success;
236 if(success) {
237 _pool.add(new SoftReference(obj, refQueue));
238 notifyAll(); // _numActive has changed
239 }
240
241 if(shouldDestroy) {
242 try {
243 _factory.destroyObject(obj);
244 } catch(Exception e) {
245 // ignored
246 }
247 }
248 }
249
250 /**
251 * Returns an approximation not less than the of the number of idle instances in the pool.
252 *
253 * @return estimated number of idle instances in the pool
254 */
255 public synchronized int getNumIdle() {
256 pruneClearedReferences();
257 return _pool.size();
258 }
259
260 /**
261 * Return the number of instances currently borrowed from this pool.
262 *
263 * @return the number of instances currently borrowed from this pool
264 */
265 public synchronized int getNumActive() {
266 return _numActive;
267 }
268
269 /**
270 * Clears any objects sitting idle in the pool.
271 */
272 public synchronized void clear() {
273 if(null != _factory) {
274 Iterator iter = _pool.iterator();
275 while(iter.hasNext()) {
276 try {
277 Object obj = ((SoftReference)iter.next()).get();
278 if(null != obj) {
279 _factory.destroyObject(obj);
280 }
281 } catch(Exception e) {
282 // ignore error, keep destroying the rest
283 }
284 }
285 }
286 _pool.clear();
287 pruneClearedReferences();
288 }
289
290 /**
291 * <p>Close this pool, and free any resources associated with it. Invokes
292 * {@link #clear()} to destroy and remove instances in the pool.</p>
293 *
294 * <p>Calling {@link #addObject} or {@link #borrowObject} after invoking
295 * this method on a pool will cause them to throw an
296 * {@link IllegalStateException}.</p>
297 *
298 * @throws Exception never - exceptions clearing the pool are swallowed
299 */
300 public void close() throws Exception {
301 super.close();
302 clear();
303 }
304
305 /**
306 * Sets the {@link PoolableObjectFactory factory} this pool uses
307 * to create new instances. Trying to change
308 * the <code>factory</code> while there are borrowed objects will
309 * throw an {@link IllegalStateException}.
310 *
311 * @param factory the {@link PoolableObjectFactory} used to create new instances.
312 * @throws IllegalStateException when the factory cannot be set at this time
313 * @deprecated to be removed in pool 2.0
314 */
315 public synchronized void setFactory(PoolableObjectFactory factory) throws IllegalStateException {
316 assertOpen();
317 if(0 < getNumActive()) {
318 throw new IllegalStateException("Objects are already active");
319 } else {
320 clear();
321 _factory = factory;
322 }
323 }
324
325 /**
326 * If any idle objects were garbage collected, remove their
327 * {@link Reference} wrappers from the idle object pool.
328 */
329 private void pruneClearedReferences() {
330 Reference ref;
331 while ((ref = refQueue.poll()) != null) {
332 try {
333 _pool.remove(ref);
334 } catch (UnsupportedOperationException uoe) {
335 // ignored
336 }
337 }
338 }
339
340 /**
341 * Returns the {@link PoolableObjectFactory} used by this pool to create and manage object instances.
342 *
343 * @return the factory
344 * @since 1.5.5
345 */
346 public synchronized PoolableObjectFactory getFactory() {
347 return _factory;
348 }
349
350 /** My pool. */
351 private List _pool = null;
352
353 /** My {@link PoolableObjectFactory}. */
354 private PoolableObjectFactory _factory = null;
355
356 /**
357 * Queue of broken references that might be able to be removed from <code>_pool</code>.
358 * This is used to help {@link #getNumIdle()} be more accurate with minimial
359 * performance overhead.
360 */
361 private final ReferenceQueue refQueue = new ReferenceQueue();
362
363 /** Number of active objects. */
364 private int _numActive = 0;
365 }