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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.commons.pool.impl;
19  
20  import java.util.Iterator;
21  import java.util.NoSuchElementException;
22  import java.util.Stack;
23  
24  import org.apache.commons.pool.BaseObjectPool;
25  import org.apache.commons.pool.ObjectPool;
26  import org.apache.commons.pool.PoolableObjectFactory;
27  
28  /**
29   * A simple, {@link java.util.Stack Stack}-based {@link ObjectPool} implementation.
30   * <p>
31   * Given a {@link PoolableObjectFactory}, this class will maintain
32   * a simple pool of instances.  A finite number of "sleeping"
33   * or idle instances is enforced, but when the pool is
34   * empty, new instances are created to support the new load.
35   * Hence this class places no limit on the number of "active"
36   * instances created by the pool, but is quite useful for
37   * re-using <tt>Object</tt>s without introducing
38   * artificial limits.
39   *
40   * @author Rodney Waldhoff
41   * @author Dirk Verbeeck
42   * @author Sandy McArthur
43   * @version $Revision: 777748 $ $Date: 2009-05-22 20:00:44 -0400 (Fri, 22 May 2009) $
44   * @since Pool 1.0
45   */
46  public class StackObjectPool extends BaseObjectPool implements ObjectPool {
47      /**
48       * Create a new pool using
49       * no factory.
50       * Clients must first {@link #setFactory(PoolableObjectFactory) set the factory}
51       * else this pool will not behave correctly.
52       * Clients may first populate the pool
53       * using {@link #returnObject(java.lang.Object)}
54       * before they can be {@link #borrowObject borrowed} but this useage is <strong>discouraged</strong>.
55       *
56       * @see #StackObjectPool(PoolableObjectFactory)
57       */
58      public StackObjectPool() {
59          this((PoolableObjectFactory)null,DEFAULT_MAX_SLEEPING,DEFAULT_INIT_SLEEPING_CAPACITY);
60      }
61  
62      /**
63       * Create a new pool using
64       * no factory.
65       * Clients must first {@link #setFactory(PoolableObjectFactory) set the factory}
66       * else this pool will not behave correctly.
67       * Clients may first populate the pool
68       * using {@link #returnObject(java.lang.Object)}
69       * before they can be {@link #borrowObject borrowed} but this useage is <strong>discouraged</strong>.
70       *
71       * @param maxIdle cap on the number of "sleeping" instances in the pool
72       * @see #StackObjectPool(PoolableObjectFactory, int)
73       */
74      public StackObjectPool(int maxIdle) {
75          this((PoolableObjectFactory)null,maxIdle,DEFAULT_INIT_SLEEPING_CAPACITY);
76      }
77  
78      /**
79       * Create a new pool using
80       * no factory.
81       * Clients must first {@link #setFactory(PoolableObjectFactory) set the factory}
82       * else this pool will not behave correctly.
83       * Clients may first populate the pool
84       * using {@link #returnObject(java.lang.Object)}
85       * before they can be {@link #borrowObject borrowed} but this useage is <strong>discouraged</strong>.
86       *
87       * @param maxIdle cap on the number of "sleeping" instances in the pool
88       * @param initIdleCapacity initial size of the pool (this specifies the size of the container,
89       *             it does not cause the pool to be pre-populated.)
90       * @see #StackObjectPool(PoolableObjectFactory, int, int)
91       */
92      public StackObjectPool(int maxIdle, int initIdleCapacity) {
93          this((PoolableObjectFactory)null,maxIdle,initIdleCapacity);
94      }
95  
96      /**
97       * Create a new <tt>StackObjectPool</tt> using
98       * the specified <i>factory</i> to create new instances.
99       *
100      * @param factory the {@link PoolableObjectFactory} used to populate the pool
101      */
102     public StackObjectPool(PoolableObjectFactory factory) {
103         this(factory,DEFAULT_MAX_SLEEPING,DEFAULT_INIT_SLEEPING_CAPACITY);
104     }
105 
106     /**
107      * Create a new <tt>SimpleObjectPool</tt> using
108      * the specified <i>factory</i> to create new instances,
109      * capping the number of "sleeping" instances to <i>max</i>.
110      *
111      * @param factory the {@link PoolableObjectFactory} used to populate the pool
112      * @param maxIdle cap on the number of "sleeping" instances in the pool
113      */
114     public StackObjectPool(PoolableObjectFactory factory, int maxIdle) {
115         this(factory,maxIdle,DEFAULT_INIT_SLEEPING_CAPACITY);
116     }
117 
118     /**
119      * Create a new <tt>SimpleObjectPool</tt> using
120      * the specified <i>factory</i> to create new instances,
121      * capping the number of "sleeping" instances to <i>max</i>,
122      * and initially allocating a container capable of containing
123      * at least <i>init</i> instances.
124      *
125      * @param factory the {@link PoolableObjectFactory} used to populate the pool
126      * @param maxIdle cap on the number of "sleeping" instances in the pool
127      * @param initIdleCapacity initial size of the pool (this specifies the size of the container,
128      *             it does not cause the pool to be pre-populated.)
129      */
130     public StackObjectPool(PoolableObjectFactory factory, int maxIdle, int initIdleCapacity) {
131         _factory = factory;
132         _maxSleeping = (maxIdle < 0 ? DEFAULT_MAX_SLEEPING : maxIdle);
133         int initcapacity = (initIdleCapacity < 1 ? DEFAULT_INIT_SLEEPING_CAPACITY : initIdleCapacity);
134         _pool = new Stack();
135         _pool.ensureCapacity( initcapacity > _maxSleeping ? _maxSleeping : initcapacity);
136     }
137 
138     public synchronized Object borrowObject() throws Exception {
139         assertOpen();
140         Object obj = null;
141         boolean newlyCreated = false;
142         while (null == obj) {
143             if (!_pool.empty()) {
144                 obj = _pool.pop();
145             } else {
146                 if(null == _factory) {
147                     throw new NoSuchElementException();
148                 } else {
149                     obj = _factory.makeObject();
150                     newlyCreated = true;
151                   if (obj == null) {
152                     throw new NoSuchElementException("PoolableObjectFactory.makeObject() returned null.");
153                   }
154                 }
155             }
156             if (null != _factory && null != obj) {
157                 try {
158                     _factory.activateObject(obj);
159                     if (!_factory.validateObject(obj)) {
160                         throw new Exception("ValidateObject failed");
161                     }
162                 } catch (Throwable t) {
163                     try {
164                         _factory.destroyObject(obj);
165                     } catch (Throwable t2) {
166                         // swallowed
167                     } finally {
168                         obj = null;
169                     }
170                     if (newlyCreated) {
171                         throw new NoSuchElementException(
172                             "Could not create a validated object, cause: " +
173                             t.getMessage());
174                     }
175                 }
176             }
177         }
178         _numActive++;
179         return obj;
180     }
181 
182     public synchronized void returnObject(Object obj) throws Exception {
183         boolean success = !isClosed();
184         if(null != _factory) {
185             if(!_factory.validateObject(obj)) {
186                 success = false;
187             } else {
188                 try {
189                     _factory.passivateObject(obj);
190                 } catch(Exception e) {
191                     success = false;
192                 }
193             }
194         }
195 
196         boolean shouldDestroy = !success;
197 
198         _numActive--;
199         if (success) {
200             Object toBeDestroyed = null;
201             if(_pool.size() >= _maxSleeping) {
202                 shouldDestroy = true;
203                 toBeDestroyed = _pool.remove(0); // remove the stalest object
204             }
205             _pool.push(obj);
206             obj = toBeDestroyed; // swap returned obj with the stalest one so it can be destroyed
207         }
208         notifyAll(); // _numActive has changed
209 
210         if(shouldDestroy) { // by constructor, shouldDestroy is false when _factory is null
211             try {
212                 _factory.destroyObject(obj);
213             } catch(Exception e) {
214                 // ignored
215             }
216         }
217     }
218 
219     public synchronized void invalidateObject(Object obj) throws Exception {
220         _numActive--;
221         if (null != _factory) {
222             _factory.destroyObject(obj);
223         }
224         notifyAll(); // _numActive has changed
225     }
226 
227     /**
228      * Return the number of instances
229      * currently idle in this pool.
230      *
231      * @return the number of instances currently idle in this pool
232      */
233     public synchronized int getNumIdle() {
234         return _pool.size();
235     }
236 
237     /**
238      * Return the number of instances currently borrowed from this pool.
239      *
240      * @return the number of instances currently borrowed from this pool
241      */
242     public synchronized int getNumActive() {
243         return _numActive;
244     }
245 
246     /**
247      * Clears any objects sitting idle in the pool.
248      */
249     public synchronized void clear() {
250         if(null != _factory) {
251             Iterator it = _pool.iterator();
252             while(it.hasNext()) {
253                 try {
254                     _factory.destroyObject(it.next());
255                 } catch(Exception e) {
256                     // ignore error, keep destroying the rest
257                 }
258             }
259         }
260         _pool.clear();
261     }
262 
263     /**
264      * Close this pool, and free any resources associated with it.
265      * <p>
266      * Calling {@link #addObject} or {@link #borrowObject} after invoking
267      * this method on a pool will cause them to throw an
268      * {@link IllegalStateException}.
269      * </p>
270      *
271      * @throws Exception <strong>deprecated</strong>: implementations should silently fail if not all resources can be freed.
272      */
273     public void close() throws Exception {
274         super.close();
275         clear();
276     }
277 
278     /**
279      * Create an object, and place it into the pool.
280      * addObject() is useful for "pre-loading" a pool with idle objects.
281      * @throws Exception when the {@link #_factory} has a problem creating an object.
282      */
283     public synchronized void addObject() throws Exception {
284         assertOpen();
285         if (_factory == null) {
286             throw new IllegalStateException("Cannot add objects without a factory.");
287         }
288         Object obj = _factory.makeObject();
289 
290         boolean success = true;
291         if(!_factory.validateObject(obj)) {
292             success = false;
293         } else {
294             _factory.passivateObject(obj);
295         }
296 
297         boolean shouldDestroy = !success;
298 
299         if (success) {
300             Object toBeDestroyed = null;
301             if(_pool.size() >= _maxSleeping) {
302                 shouldDestroy = true;
303                 toBeDestroyed = _pool.remove(0); // remove the stalest object
304             }
305             _pool.push(obj);
306             obj = toBeDestroyed; // swap returned obj with the stalest one so it can be destroyed
307         }
308         notifyAll(); // _numIdle has changed
309 
310         if(shouldDestroy) { // by constructor, shouldDestroy is false when _factory is null
311             try {
312                 _factory.destroyObject(obj);
313             } catch(Exception e) {
314                 // ignored
315             }
316         }
317     }
318 
319     /**
320      * Sets the {@link PoolableObjectFactory factory} this pool uses
321      * to create new instances. Trying to change
322      * the <code>factory</code> while there are borrowed objects will
323      * throw an {@link IllegalStateException}.
324      *
325      * @param factory the {@link PoolableObjectFactory} used to create new instances.
326      * @throws IllegalStateException when the factory cannot be set at this time
327      */
328     public synchronized void setFactory(PoolableObjectFactory factory) throws IllegalStateException {
329         assertOpen();
330         if(0 < getNumActive()) {
331             throw new IllegalStateException("Objects are already active");
332         } else {
333             clear();
334             _factory = factory;
335         }
336     }
337 
338     /** The default cap on the number of "sleeping" instances in the pool. */
339     protected static final int DEFAULT_MAX_SLEEPING  = 8;
340 
341     /**
342      * The default initial size of the pool
343      * (this specifies the size of the container, it does not
344      * cause the pool to be pre-populated.)
345      */
346     protected static final int DEFAULT_INIT_SLEEPING_CAPACITY = 4;
347 
348     /** My pool. */
349     protected Stack _pool = null;
350 
351     /** My {@link PoolableObjectFactory}. */
352     protected PoolableObjectFactory _factory = null;
353 
354     /** The cap on the number of "sleeping" instances in the pool. */
355     protected int _maxSleeping = DEFAULT_MAX_SLEEPING;
356 
357     /** Number of object borrowed but not yet returned to the pool. */
358     protected int _numActive = 0;
359 }