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.util.Iterator;
021 import java.util.NoSuchElementException;
022 import java.util.Stack;
023
024 import org.apache.commons.pool.BaseObjectPool;
025 import org.apache.commons.pool.ObjectPool;
026 import org.apache.commons.pool.PoolUtils;
027 import org.apache.commons.pool.PoolableObjectFactory;
028
029 /**
030 * A simple, {@link java.util.Stack Stack}-based {@link ObjectPool} implementation.
031 * <p>
032 * Given a {@link PoolableObjectFactory}, this class will maintain
033 * a simple pool of instances. A finite number of "sleeping"
034 * or idle instances is enforced, but when the pool is
035 * empty, new instances are created to support the new load.
036 * Hence this class places no limit on the number of "active"
037 * instances created by the pool, but is quite useful for
038 * re-using <tt>Object</tt>s without introducing
039 * artificial limits.
040 *
041 * @author Rodney Waldhoff
042 * @author Dirk Verbeeck
043 * @author Sandy McArthur
044 * @version $Revision: 965338 $ $Date: 2010-07-18 18:09:29 -0700 (Sun, 18 Jul 2010) $
045 * @since Pool 1.0
046 */
047 public class StackObjectPool extends BaseObjectPool implements ObjectPool {
048 /**
049 * Create a new pool using no factory. Clients must first
050 * {@link #setFactory(PoolableObjectFactory) set the factory} or
051 * else this pool will not behave correctly. Clients may first populate the pool
052 * using {@link #returnObject(java.lang.Object)} before they can be {@link #borrowObject borrowed}
053 * but this usage is <strong>discouraged</strong>.
054 *
055 * @see #StackObjectPool(PoolableObjectFactory)
056 * @deprecated to be removed in pool 2.0 - use {@link #StackObjectPool(PoolableObjectFactory)}
057 */
058 public StackObjectPool() {
059 this((PoolableObjectFactory)null,DEFAULT_MAX_SLEEPING,DEFAULT_INIT_SLEEPING_CAPACITY);
060 }
061
062 /**
063 * Create a new pool using no factory.
064 * Clients must first {@link #setFactory(PoolableObjectFactory) set the factory} or
065 * else this pool will not behave correctly. Clients may first populate the pool
066 * using {@link #returnObject(java.lang.Object)} before they can be {@link #borrowObject borrowed}
067 * but this usage is <strong>discouraged</strong>.
068 *
069 * @param maxIdle cap on the number of "sleeping" instances in the pool
070 * @see #StackObjectPool(PoolableObjectFactory, int)
071 * @deprecated to be removed in pool 2.0 - use {@link #StackObjectPool(PoolableObjectFactory, int)}
072 */
073 public StackObjectPool(int maxIdle) {
074 this((PoolableObjectFactory)null,maxIdle,DEFAULT_INIT_SLEEPING_CAPACITY);
075 }
076
077 /**
078 * Create a new pool using no factory.
079 * Clients must first {@link #setFactory(PoolableObjectFactory) set the factory} or
080 * else this pool will not behave correctly. Clients may first populate the pool
081 * using {@link #returnObject(java.lang.Object)} before they can be {@link #borrowObject borrowed}
082 * but this usage is <strong>discouraged</strong>.
083 *
084 * @param maxIdle cap on the number of "sleeping" instances in the pool
085 * @param initIdleCapacity initial size of the pool (this specifies the size of the container,
086 * it does not cause the pool to be pre-populated.)
087 * @see #StackObjectPool(PoolableObjectFactory, int, int)
088 * @deprecated to be removed in pool 2.0 - use {@link #StackObjectPool(PoolableObjectFactory, int, int)}
089 */
090 public StackObjectPool(int maxIdle, int initIdleCapacity) {
091 this((PoolableObjectFactory)null,maxIdle,initIdleCapacity);
092 }
093
094 /**
095 * Create a new <tt>StackObjectPool</tt> using the specified <i>factory</i> to create new instances.
096 *
097 * @param factory the {@link PoolableObjectFactory} used to populate the pool
098 */
099 public StackObjectPool(PoolableObjectFactory factory) {
100 this(factory,DEFAULT_MAX_SLEEPING,DEFAULT_INIT_SLEEPING_CAPACITY);
101 }
102
103 /**
104 * Create a new <tt>SimpleObjectPool</tt> using the specified <i>factory</i> to create new instances,
105 * capping the number of "sleeping" instances to <i>maxIdle</i>.
106 *
107 * @param factory the {@link PoolableObjectFactory} used to populate the pool
108 * @param maxIdle cap on the number of "sleeping" instances in the pool
109 */
110 public StackObjectPool(PoolableObjectFactory factory, int maxIdle) {
111 this(factory,maxIdle,DEFAULT_INIT_SLEEPING_CAPACITY);
112 }
113
114 /**
115 * <p>Create a new <tt>StackObjectPool</tt> using the specified <code>factory</code> to create new instances,
116 * capping the number of "sleeping" instances to <code>maxIdle</code>, and initially allocating a container
117 * capable of containing at least <code>initIdleCapacity</code> instances. The pool is not pre-populated.
118 * The <code>initIdleCapacity</code> parameter just determines the initial size of the underlying
119 * container, which can increase beyond this value if <code>maxIdle > initIdleCapacity.</code></p>
120 *
121 * <p>Negative values of <code>maxIdle</code> are ignored (i.e., the pool is created using
122 * {@link #DEFAULT_MAX_SLEEPING}) as are non-positive values for <code>initIdleCapacity.</code>
123 *
124 * @param factory the {@link PoolableObjectFactory} used to populate the pool
125 * @param maxIdle cap on the number of "sleeping" instances in the pool
126 * @param initIdleCapacity initial size of the pool (this specifies the size of the container,
127 * it does not cause the pool to be pre-populated.)
128 */
129 public StackObjectPool(PoolableObjectFactory factory, int maxIdle, int initIdleCapacity) {
130 _factory = factory;
131 _maxSleeping = (maxIdle < 0 ? DEFAULT_MAX_SLEEPING : maxIdle);
132 int initcapacity = (initIdleCapacity < 1 ? DEFAULT_INIT_SLEEPING_CAPACITY : initIdleCapacity);
133 _pool = new Stack();
134 _pool.ensureCapacity( initcapacity > _maxSleeping ? _maxSleeping : initcapacity);
135 }
136
137 /**
138 * <p>Borrows an object from the pool. If there are idle instances available on the stack,
139 * the top element of the stack is popped to activate, validate and return to the client. If there
140 * are no idle instances available, the {@link PoolableObjectFactory#makeObject() makeObject}
141 * method of the pool's {@link PoolableObjectFactory} is invoked to create a new instance.</p>
142 *
143 * <p>All instances are {@link PoolableObjectFactory#activateObject(Object) activated} and
144 * {@link PoolableObjectFactory#validateObject(Object) validated} before being returned to the
145 * client. If validation fails or an exception occurs activating or validating an instance
146 * popped from the idle instance stack, the failing instance is
147 * {@link PoolableObjectFactory#destroyObject(Object) destroyed} and the next instance on
148 * the stack is popped, validated and activated. This process continues until either the
149 * stack is empty or an instance passes validation. If the stack is empty on activation or
150 * it does not contain any valid instances, the factory's <code>makeObject</code> method is used
151 * to create a new instance. If a null instance is returned by the factory or the created
152 * instance either raises an exception on activation or fails validation, <code>NoSuchElementException</code>
153 * is thrown. Exceptions thrown by <code>MakeObject</code> are propagated to the caller; but
154 * other than <code>ThreadDeath</code> or <code>VirtualMachineError</code>, exceptions generated by
155 * activation, validation or destroy methods are swallowed silently.</p>
156 *
157 * @return an instance from the pool
158 */
159 public synchronized Object borrowObject() throws Exception {
160 assertOpen();
161 Object obj = null;
162 boolean newlyCreated = false;
163 while (null == obj) {
164 if (!_pool.empty()) {
165 obj = _pool.pop();
166 } else {
167 if(null == _factory) {
168 throw new NoSuchElementException();
169 } else {
170 obj = _factory.makeObject();
171 newlyCreated = true;
172 if (obj == null) {
173 throw new NoSuchElementException("PoolableObjectFactory.makeObject() returned null.");
174 }
175 }
176 }
177 if (null != _factory && null != obj) {
178 try {
179 _factory.activateObject(obj);
180 if (!_factory.validateObject(obj)) {
181 throw new Exception("ValidateObject failed");
182 }
183 } catch (Throwable t) {
184 PoolUtils.checkRethrow(t);
185 try {
186 _factory.destroyObject(obj);
187 } catch (Throwable t2) {
188 PoolUtils.checkRethrow(t2);
189 // swallowed
190 } finally {
191 obj = null;
192 }
193 if (newlyCreated) {
194 throw new NoSuchElementException(
195 "Could not create a validated object, cause: " +
196 t.getMessage());
197 }
198 }
199 }
200 }
201 _numActive++;
202 return obj;
203 }
204
205 /**
206 * <p>Returns an instance to the pool, pushing it on top of the idle instance stack after successful
207 * validation and passivation. The returning instance is destroyed if any of the following are true:<ul>
208 * <li>the pool is closed</li>
209 * <li>{@link PoolableObjectFactory#validateObject(Object) validation} fails</li>
210 * <li>{@link PoolableObjectFactory#passivateObject(Object) passivation} throws an exception</li>
211 * </ul>
212 * If adding a validated, passivated returning instance to the stack would cause
213 * {@link #getMaxSleeping() maxSleeping} to be exceeded, the oldest (bottom) instance on the stack
214 * is destroyed to make room for the returning instance, which is pushed on top of the stack.</p>
215 *
216 * <p>Exceptions passivating or destroying instances are silently swallowed. Exceptions validating
217 * instances are propagated to the client.</p>
218 *
219 * @param obj instance to return to the pool
220 */
221 public synchronized void returnObject(Object obj) throws Exception {
222 boolean success = !isClosed();
223 if(null != _factory) {
224 if(!_factory.validateObject(obj)) {
225 success = false;
226 } else {
227 try {
228 _factory.passivateObject(obj);
229 } catch(Exception e) {
230 success = false;
231 }
232 }
233 }
234
235 boolean shouldDestroy = !success;
236
237 _numActive--;
238 if (success) {
239 Object toBeDestroyed = null;
240 if(_pool.size() >= _maxSleeping) {
241 shouldDestroy = true;
242 toBeDestroyed = _pool.remove(0); // remove the stalest object
243 }
244 _pool.push(obj);
245 obj = toBeDestroyed; // swap returned obj with the stalest one so it can be destroyed
246 }
247 notifyAll(); // _numActive has changed
248
249 if(shouldDestroy) { // by constructor, shouldDestroy is false when _factory is null
250 try {
251 _factory.destroyObject(obj);
252 } catch(Exception e) {
253 // ignored
254 }
255 }
256 }
257
258 /**
259 * {@inheritDoc}
260 */
261 public synchronized void invalidateObject(Object obj) throws Exception {
262 _numActive--;
263 if (null != _factory) {
264 _factory.destroyObject(obj);
265 }
266 notifyAll(); // _numActive has changed
267 }
268
269 /**
270 * Return the number of instances
271 * currently idle in this pool.
272 *
273 * @return the number of instances currently idle in this pool
274 */
275 public synchronized int getNumIdle() {
276 return _pool.size();
277 }
278
279 /**
280 * Return the number of instances currently borrowed from this pool.
281 *
282 * @return the number of instances currently borrowed from this pool
283 */
284 public synchronized int getNumActive() {
285 return _numActive;
286 }
287
288 /**
289 * Clears any objects sitting idle in the pool. Silently swallows any
290 * exceptions thrown by {@link PoolableObjectFactory#destroyObject(Object)}.
291 */
292 public synchronized void clear() {
293 if(null != _factory) {
294 Iterator it = _pool.iterator();
295 while(it.hasNext()) {
296 try {
297 _factory.destroyObject(it.next());
298 } catch(Exception e) {
299 // ignore error, keep destroying the rest
300 }
301 }
302 }
303 _pool.clear();
304 }
305
306 /**
307 * <p>Close this pool, and free any resources associated with it. Invokes
308 * {@link #clear()} to destroy and remove instances in the pool.</p>
309 *
310 * <p>Calling {@link #addObject} or {@link #borrowObject} after invoking
311 * this method on a pool will cause them to throw an
312 * {@link IllegalStateException}.</p>
313 *
314 * @throws Exception never - exceptions clearing the pool are swallowed
315 */
316 public void close() throws Exception {
317 super.close();
318 clear();
319 }
320
321 /**
322 * <p>Create an object, and place it on top of the stack.
323 * This method is useful for "pre-loading" a pool with idle objects.</p>
324 *
325 * <p>Before being added to the pool, the newly created instance is
326 * {@link PoolableObjectFactory#validateObject(Object) validated} and
327 * {@link PoolableObjectFactory#passivateObject(Object) passivated}. If validation
328 * fails, the new instance is {@link PoolableObjectFactory#destroyObject(Object) destroyed}.
329 * Exceptions generated by the factory <code>makeObject</code> or <code>passivate</code> are
330 * propagated to the caller. Exceptions destroying instances are silently swallowed.</p>
331 *
332 * <p>If a new instance is created and successfully validated and passivated and adding this
333 * instance to the pool causes {@link #getMaxSleeping() maxSleeping} to be exceeded, the oldest
334 * (bottom) instance in the pool is destroyed to make room for the newly created instance, which
335 * is pushed on top of the stack.
336 *
337 * @throws Exception when the {@link #getFactory() factory} has a problem creating or passivating an object.
338 */
339 public synchronized void addObject() throws Exception {
340 assertOpen();
341 if (_factory == null) {
342 throw new IllegalStateException("Cannot add objects without a factory.");
343 }
344 Object obj = _factory.makeObject();
345
346 boolean success = true;
347 if(!_factory.validateObject(obj)) {
348 success = false;
349 } else {
350 _factory.passivateObject(obj);
351 }
352
353 boolean shouldDestroy = !success;
354
355 if (success) {
356 Object toBeDestroyed = null;
357 if(_pool.size() >= _maxSleeping) {
358 shouldDestroy = true;
359 toBeDestroyed = _pool.remove(0); // remove the stalest object
360 }
361 _pool.push(obj);
362 obj = toBeDestroyed; // swap returned obj with the stalest one so it can be destroyed
363 }
364 notifyAll(); // _numIdle has changed
365
366 if(shouldDestroy) { // by constructor, shouldDestroy is false when _factory is null
367 try {
368 _factory.destroyObject(obj);
369 } catch(Exception e) {
370 // ignored
371 }
372 }
373 }
374
375 /**
376 * Sets the {@link PoolableObjectFactory factory} this pool uses
377 * to create new instances. Trying to change
378 * the <code>factory</code> while there are borrowed objects will
379 * throw an {@link IllegalStateException}.
380 *
381 * @param factory the {@link PoolableObjectFactory} used to create new instances.
382 * @throws IllegalStateException when the factory cannot be set at this time
383 * @deprecated to be removed in pool 2.0
384 */
385 public synchronized void setFactory(PoolableObjectFactory factory) throws IllegalStateException {
386 assertOpen();
387 if(0 < getNumActive()) {
388 throw new IllegalStateException("Objects are already active");
389 } else {
390 clear();
391 _factory = factory;
392 }
393 }
394
395 /**
396 * The cap on the number of "sleeping" instances in the pool.
397 */
398 protected static final int DEFAULT_MAX_SLEEPING = 8;
399
400 /**
401 * The default initial size of the pool
402 * (this specifies the size of the container, it does not
403 * cause the pool to be pre-populated.)
404 */
405 protected static final int DEFAULT_INIT_SLEEPING_CAPACITY = 4;
406
407 /**
408 * My pool.
409 * @deprecated to be made private in pool 2.0
410 */
411 protected Stack _pool = null;
412
413 /**
414 * My {@link PoolableObjectFactory}.
415 * @deprecated to be made private in pool 2.0 - use {@link #getFactory()}
416 */
417 protected PoolableObjectFactory _factory = null;
418
419 /**
420 * The cap on the number of "sleeping" instances in the pool.
421 * @deprecated to be made private in pool 2.0 - use {@link #getMaxSleeping()}
422 */
423 protected int _maxSleeping = DEFAULT_MAX_SLEEPING;
424
425 /**
426 * Number of objects borrowed but not yet returned to the pool.
427 * @deprecated to be made private in pool 2.0 - use {@link #getNumActive()}
428 */
429 protected int _numActive = 0;
430
431 /**
432 * Returns the {@link PoolableObjectFactory} used by this pool to create and manage object instances.
433 *
434 * @return the factory
435 * @since 1.5.5
436 */
437 public synchronized PoolableObjectFactory getFactory() {
438 return _factory;
439 }
440
441 /**
442 * Returns the maximum number of idle instances in the pool.
443 *
444 * @return maxSleeping
445 * @since 1.5.5
446 */
447 public int getMaxSleeping() {
448 return _maxSleeping;
449 }
450
451
452 }