/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.pool.impl;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import org.apache.commons.pool.BaseObjectPool;
import org.apache.commons.pool.ObjectPool;
import org.apache.commons.pool.PoolUtils;
import org.apache.commons.pool.PoolableObjectFactory;
/**
* A {@link java.lang.ref.SoftReference SoftReference} based
* {@link ObjectPool}.
*
* @param <T> the type of objects held in this pool
*
* @author Rodney Waldhoff
* @author Sandy McArthur
* @version $Revision: 1222710 $ $Date: 2011-12-23 10:58:12 -0500 (Fri, 23 Dec 2011) $
* @since Pool 1.0
*/
public class SoftReferenceObjectPool<T> extends BaseObjectPool<T> implements ObjectPool<T> {
/**
* Create a <code>SoftReferenceObjectPool</code> without a factory.
* {@link #setFactory(PoolableObjectFactory) setFactory} should be called
* before any attempts to use the pool are made.
* Generally speaking you should prefer the {@link #SoftReferenceObjectPool(PoolableObjectFactory)} constructor.
*
* @see #SoftReferenceObjectPool(PoolableObjectFactory)
* @deprecated to be removed in pool 2.0. Use {@link #SoftReferenceObjectPool(PoolableObjectFactory)}.
*/
@Deprecated
public SoftReferenceObjectPool() {
_pool = new ArrayList<SoftReference<T>>();
_factory = null;
}
/**
* Create a <code>SoftReferenceObjectPool</code> with the specified factory.
*
* @param factory object factory to use.
*/
public SoftReferenceObjectPool(PoolableObjectFactory<T> factory) {
_pool = new ArrayList<SoftReference<T>>();
_factory = factory;
}
/**
* Create a <code>SoftReferenceObjectPool</code> with the specified factory and initial idle object count.
*
* @param factory object factory to use.
* @param initSize initial size to attempt to prefill the pool.
* @throws Exception when there is a problem prefilling the pool.
* @throws IllegalArgumentException when <code>factory</code> is <code>null</code>.
* @deprecated because this is a SoftReference pool, prefilled idle obejects may be garbage collected before they are used.
* To be removed in Pool 2.0.
*/
@Deprecated
public SoftReferenceObjectPool(PoolableObjectFactory<T> factory, int initSize) throws Exception, IllegalArgumentException {
if (factory == null) {
throw new IllegalArgumentException("factory required to prefill the pool.");
}
_pool = new ArrayList<SoftReference<T>>(initSize);
_factory = factory;
PoolUtils.prefill(this, initSize);
}
/**
* <p>Borrow an object from the pool. If there are no idle instances available in the pool, the configured
* factory's {@link PoolableObjectFactory#makeObject()} method is invoked to create a new instance.</p>
*
* <p>All instances are {@link PoolableObjectFactory#activateObject(Object) activated} and
* {@link PoolableObjectFactory#validateObject(Object) validated} before being returned by this
* method. If validation fails or an exception occurs activating or validating an idle instance,
* the failing instance is {@link PoolableObjectFactory#destroyObject(Object) destroyed} and another
* instance is retrieved from the pool, validated and activated. This process continues until either the
* pool is empty or an instance passes validation. If the pool is empty on activation or
* it does not contain any valid instances, the factory's <code>makeObject</code> method is used
* to create a new instance. If the created instance either raises an exception on activation or
* fails validation, <code>NoSuchElementException</code> is thrown. Exceptions thrown by <code>MakeObject</code>
* are propagated to the caller; but other than <code>ThreadDeath</code> or <code>VirtualMachineError</code>,
* exceptions generated by activation, validation or destroy methods are swallowed silently.</p>
*
* @throws NoSuchElementException if a valid object cannot be provided
* @throws IllegalStateException if invoked on a {@link #close() closed} pool
* @throws Exception if an exception occurs creating a new instance
* @return a valid, activated object instance
*/
@Override
public synchronized T borrowObject() throws Exception {
assertOpen();
T obj = null;
boolean newlyCreated = false;
while(null == obj) {
if(_pool.isEmpty()) {
if(null == _factory) {
throw new NoSuchElementException();
} else {
newlyCreated = true;
obj = _factory.makeObject();
}
} else {
SoftReference<T> ref = _pool.remove(_pool.size() - 1);
obj = ref.get();
ref.clear(); // prevent this ref from being enqueued with refQueue.
}
if (null != _factory && null != obj) {
try {
_factory.activateObject(obj);
if (!_factory.validateObject(obj)) {
throw new Exception("ValidateObject failed");
}
} catch (Throwable t) {
PoolUtils.checkRethrow(t);
try {
_factory.destroyObject(obj);
} catch (Throwable t2) {
PoolUtils.checkRethrow(t2);
// Swallowed
} finally {
obj = null;
}
if (newlyCreated) {
throw new NoSuchElementException(
"Could not create a validated object, cause: " +
t.getMessage());
}
}
}
}
_numActive++;
return obj;
}
/**
* <p>Returns an instance to the pool after successful validation and passivation. The returning instance
* is destroyed if any of the following are true:<ul>
* <li>the pool is closed</li>
* <li>{@link PoolableObjectFactory#validateObject(Object) validation} fails</li>
* <li>{@link PoolableObjectFactory#passivateObject(Object) passivation} throws an exception</li>
* </ul>
*</p>
*
* <p>Exceptions passivating or destroying instances are silently swallowed. Exceptions validating
* instances are propagated to the client.</p>
*
* @param obj instance to return to the pool
*/
@Override
public synchronized void returnObject(T obj) throws Exception {
boolean success = !isClosed();
if (_factory != null) {
if(!_factory.validateObject(obj)) {
success = false;
} else {
try {
_factory.passivateObject(obj);
} catch(Exception e) {
success = false;
}
}
}
boolean shouldDestroy = !success;
_numActive--;
if(success) {
_pool.add(new SoftReference<T>(obj, refQueue));
}
notifyAll(); // _numActive has changed
if (shouldDestroy && _factory != null) {
try {
_factory.destroyObject(obj);
} catch(Exception e) {
// ignored
}
}
}
/**
* {@inheritDoc}
*/
@Override
public synchronized void invalidateObject(T obj) throws Exception {
_numActive--;
if (_factory != null) {
_factory.destroyObject(obj);
}
notifyAll(); // _numActive has changed
}
/**
* <p>Create an object, and place it into the pool.
* addObject() is useful for "pre-loading" a pool with idle objects.</p>
*
* <p>Before being added to the pool, the newly created instance is
* {@link PoolableObjectFactory#validateObject(Object) validated} and
* {@link PoolableObjectFactory#passivateObject(Object) passivated}. If validation
* fails, the new instance is {@link PoolableObjectFactory#destroyObject(Object) destroyed}.
* Exceptions generated by the factory <code>makeObject</code> or <code>passivate</code> are
* propagated to the caller. Exceptions destroying instances are silently swallowed.</p>
*
* @throws IllegalStateException if invoked on a {@link #close() closed} pool
* @throws Exception when the {@link #getFactory() factory} has a problem creating or passivating an object.
*/
@Override
public synchronized void addObject() throws Exception {
assertOpen();
if (_factory == null) {
throw new IllegalStateException("Cannot add objects without a factory.");
}
T obj = _factory.makeObject();
boolean success = true;
if(!_factory.validateObject(obj)) {
success = false;
} else {
_factory.passivateObject(obj);
}
boolean shouldDestroy = !success;
if(success) {
_pool.add(new SoftReference<T>(obj, refQueue));
notifyAll(); // _numActive has changed
}
if(shouldDestroy) {
try {
_factory.destroyObject(obj);
} catch(Exception e) {
// ignored
}
}
}
/**
* Returns an approximation not less than the of the number of idle instances in the pool.
*
* @return estimated number of idle instances in the pool
*/
@Override
public synchronized int getNumIdle() {
pruneClearedReferences();
return _pool.size();
}
/**
* Return the number of instances currently borrowed from this pool.
*
* @return the number of instances currently borrowed from this pool
*/
@Override
public synchronized int getNumActive() {
return _numActive;
}
/**
* Clears any objects sitting idle in the pool.
*/
@Override
public synchronized void clear() {
if(null != _factory) {
Iterator<SoftReference<T>> iter = _pool.iterator();
while(iter.hasNext()) {
try {
T obj = iter.next().get();
if(null != obj) {
_factory.destroyObject(obj);
}
} catch(Exception e) {
// ignore error, keep destroying the rest
}
}
}
_pool.clear();
pruneClearedReferences();
}
/**
* <p>Close this pool, and free any resources associated with it. Invokes
* {@link #clear()} to destroy and remove instances in the pool.</p>
*
* <p>Calling {@link #addObject} or {@link #borrowObject} after invoking
* this method on a pool will cause them to throw an
* {@link IllegalStateException}.</p>
*
* @throws Exception never - exceptions clearing the pool are swallowed
*/
@Override
public void close() throws Exception {
super.close();
clear();
}
/**
* Sets the {@link PoolableObjectFactory factory} this pool uses
* to create new instances. Trying to change
* the <code>factory</code> while there are borrowed objects will
* throw an {@link IllegalStateException}.
*
* @param factory the {@link PoolableObjectFactory} used to create new instances.
* @throws IllegalStateException when the factory cannot be set at this time
* @deprecated to be removed in pool 2.0
*/
@Deprecated
@Override
public synchronized void setFactory(PoolableObjectFactory<T> factory) throws IllegalStateException {
assertOpen();
if(0 < getNumActive()) {
throw new IllegalStateException("Objects are already active");
} else {
clear();
_factory = factory;
}
}
/**
* If any idle objects were garbage collected, remove their
* {@link Reference} wrappers from the idle object pool.
*/
private void pruneClearedReferences() {
Reference<? extends T> ref;
while ((ref = refQueue.poll()) != null) {
try {
_pool.remove(ref);
} catch (UnsupportedOperationException uoe) {
// ignored
}
}
}
/**
* Returns the {@link PoolableObjectFactory} used by this pool to create and manage object instances.
*
* @return the factory
* @since 1.5.5
*/
public synchronized PoolableObjectFactory<T> getFactory() {
return _factory;
}
/** My pool. */
private final List<SoftReference<T>> _pool;
/** My {@link PoolableObjectFactory}. */
private PoolableObjectFactory<T> _factory = null;
/**
* Queue of broken references that might be able to be removed from <code>_pool</code>.
* This is used to help {@link #getNumIdle()} be more accurate with minimial
* performance overhead.
*/
private final ReferenceQueue<T> refQueue = new ReferenceQueue<T>();
/** Number of active objects. */
private int _numActive = 0; //@GuardeBy("this")
}