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: 1206501 $ $Date: 2011-11-26 10:11:40 -0700 (Sat, 26 Nov 2011) $
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 final List _pool;
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; //@GuardeBy("this")
365    }