/*
* 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.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Stack;
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 simple, {@link java.util.Stack Stack}-based {@link ObjectPool} implementation.
* <p>
* Given a {@link PoolableObjectFactory}, this class will maintain
* a simple pool of instances. A finite number of "sleeping"
* or idle instances is enforced, but when the pool is
* empty, new instances are created to support the new load.
* Hence this class places no limit on the number of "active"
* instances created by the pool, but is quite useful for
* re-using <tt>Object</tt>s without introducing
* artificial limits.
*
* @param <T> the type of objects held in this pool
*
* @author Rodney Waldhoff
* @author Dirk Verbeeck
* @author Sandy McArthur
* @version $Revision: 1222396 $ $Date: 2011-12-22 14:02:25 -0500 (Thu, 22 Dec 2011) $
* @since Pool 1.0
*/
public class StackObjectPool<T> extends BaseObjectPool<T> implements ObjectPool<T> {
/**
* Create a new pool using no factory. Clients must first
* {@link #setFactory(PoolableObjectFactory) set the factory} or
* else this pool will not behave correctly. Clients may first populate the pool
* using {@link #returnObject(java.lang.Object)} before they can be {@link #borrowObject borrowed}
* but this usage is <strong>discouraged</strong>.
*
* @see #StackObjectPool(PoolableObjectFactory)
* @deprecated to be removed in pool 2.0 - use {@link #StackObjectPool(PoolableObjectFactory)}
*/
@Deprecated
public StackObjectPool() {
this(null,DEFAULT_MAX_SLEEPING,DEFAULT_INIT_SLEEPING_CAPACITY);
}
/**
* Create a new pool using no factory.
* Clients must first {@link #setFactory(PoolableObjectFactory) set the factory} or
* else this pool will not behave correctly. Clients may first populate the pool
* using {@link #returnObject(java.lang.Object)} before they can be {@link #borrowObject borrowed}
* but this usage is <strong>discouraged</strong>.
*
* @param maxIdle cap on the number of "sleeping" instances in the pool
* @see #StackObjectPool(PoolableObjectFactory, int)
* @deprecated to be removed in pool 2.0 - use {@link #StackObjectPool(PoolableObjectFactory, int)}
*/
@Deprecated
public StackObjectPool(int maxIdle) {
this(null,maxIdle,DEFAULT_INIT_SLEEPING_CAPACITY);
}
/**
* Create a new pool using no factory.
* Clients must first {@link #setFactory(PoolableObjectFactory) set the factory} or
* else this pool will not behave correctly. Clients may first populate the pool
* using {@link #returnObject(java.lang.Object)} before they can be {@link #borrowObject borrowed}
* but this usage is <strong>discouraged</strong>.
*
* @param maxIdle cap on the number of "sleeping" instances in the pool
* @param initIdleCapacity initial size of the pool (this specifies the size of the container,
* it does not cause the pool to be pre-populated.)
* @see #StackObjectPool(PoolableObjectFactory, int, int)
* @deprecated to be removed in pool 2.0 - use {@link #StackObjectPool(PoolableObjectFactory, int, int)}
*/
@Deprecated
public StackObjectPool(int maxIdle, int initIdleCapacity) {
this(null,maxIdle,initIdleCapacity);
}
/**
* Create a new <tt>StackObjectPool</tt> using the specified <i>factory</i> to create new instances.
*
* @param factory the {@link PoolableObjectFactory} used to populate the pool
*/
public StackObjectPool(PoolableObjectFactory<T> factory) {
this(factory,DEFAULT_MAX_SLEEPING,DEFAULT_INIT_SLEEPING_CAPACITY);
}
/**
* Create a new <tt>SimpleObjectPool</tt> using the specified <i>factory</i> to create new instances,
* capping the number of "sleeping" instances to <i>maxIdle</i>.
*
* @param factory the {@link PoolableObjectFactory} used to populate the pool
* @param maxIdle cap on the number of "sleeping" instances in the pool
*/
public StackObjectPool(PoolableObjectFactory<T> factory, int maxIdle) {
this(factory,maxIdle,DEFAULT_INIT_SLEEPING_CAPACITY);
}
/**
* <p>Create a new <tt>StackObjectPool</tt> using the specified <code>factory</code> to create new instances,
* capping the number of "sleeping" instances to <code>maxIdle</code>, and initially allocating a container
* capable of containing at least <code>initIdleCapacity</code> instances. The pool is not pre-populated.
* The <code>initIdleCapacity</code> parameter just determines the initial size of the underlying
* container, which can increase beyond this value if <code>maxIdle > initIdleCapacity.</code></p>
*
* <p>Negative values of <code>maxIdle</code> are ignored (i.e., the pool is created using
* {@link #DEFAULT_MAX_SLEEPING}) as are non-positive values for <code>initIdleCapacity.</code>
*
* @param factory the {@link PoolableObjectFactory} used to populate the pool
* @param maxIdle cap on the number of "sleeping" instances in the pool
* @param initIdleCapacity initial size of the pool (this specifies the size of the container,
* it does not cause the pool to be pre-populated.)
*/
public StackObjectPool(PoolableObjectFactory<T> factory, int maxIdle, int initIdleCapacity) {
_factory = factory;
_maxSleeping = (maxIdle < 0 ? DEFAULT_MAX_SLEEPING : maxIdle);
int initcapacity = (initIdleCapacity < 1 ? DEFAULT_INIT_SLEEPING_CAPACITY : initIdleCapacity);
_pool = new Stack<T>();
_pool.ensureCapacity( initcapacity > _maxSleeping ? _maxSleeping : initcapacity);
}
/**
* <p>Borrows an object from the pool. If there are idle instances available on the stack,
* the top element of the stack is popped to activate, validate and return to the client. If there
* are no idle instances available, the {@link PoolableObjectFactory#makeObject() makeObject}
* method of the pool's {@link PoolableObjectFactory} 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 to the
* client. If validation fails or an exception occurs activating or validating an instance
* popped from the idle instance stack, the failing instance is
* {@link PoolableObjectFactory#destroyObject(Object) destroyed} and the next instance on
* the stack is popped, validated and activated. This process continues until either the
* stack is empty or an instance passes validation. If the stack 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 a null instance is returned by the factory or 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>
*
* @return an instance from the pool
*/
@Override
public synchronized T borrowObject() throws Exception {
assertOpen();
T obj = null;
boolean newlyCreated = false;
while (null == obj) {
if (!_pool.empty()) {
obj = _pool.pop();
} else {
if(null == _factory) {
throw new NoSuchElementException();
} else {
obj = _factory.makeObject();
newlyCreated = true;
if (obj == null) {
throw new NoSuchElementException("PoolableObjectFactory.makeObject() returned null.");
}
}
}
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, pushing it on top of the idle instance stack 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>
* If adding a validated, passivated returning instance to the stack would cause
* {@link #getMaxSleeping() maxSleeping} to be exceeded, the oldest (bottom) instance on the stack
* is destroyed to make room for the returning instance, which is pushed on top of the stack.</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(null != _factory) {
if(!_factory.validateObject(obj)) {
success = false;
} else {
try {
_factory.passivateObject(obj);
} catch(Exception e) {
success = false;
}
}
}
boolean shouldDestroy = !success;
_numActive--;
if (success) {
T toBeDestroyed = null;
if(_pool.size() >= _maxSleeping) {
shouldDestroy = true;
toBeDestroyed = _pool.remove(0); // remove the stalest object
}
_pool.push(obj);
obj = toBeDestroyed; // swap returned obj with the stalest one so it can be destroyed
}
notifyAll(); // _numActive has changed
if(shouldDestroy) { // by constructor, shouldDestroy is false when _factory is null
try {
_factory.destroyObject(obj);
} catch(Exception e) {
// ignored
}
}
}
/**
* {@inheritDoc}
*/
@Override
public synchronized void invalidateObject(T obj) throws Exception {
_numActive--;
if (null != _factory) {
_factory.destroyObject(obj);
}
notifyAll(); // _numActive has changed
}
/**
* Return the number of instances
* currently idle in this pool.
*
* @return the number of instances currently idle in this pool
*/
@Override
public synchronized int getNumIdle() {
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. Silently swallows any
* exceptions thrown by {@link PoolableObjectFactory#destroyObject(Object)}.
*/
@Override
public synchronized void clear() {
if(null != _factory) {
Iterator<T> it = _pool.iterator();
while(it.hasNext()) {
try {
_factory.destroyObject(it.next());
} catch(Exception e) {
// ignore error, keep destroying the rest
}
}
}
_pool.clear();
}
/**
* <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();
}
/**
* <p>Create an object, and place it on top of the stack.
* This method 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>
*
* <p>If a new instance is created and successfully validated and passivated and adding this
* instance to the pool causes {@link #getMaxSleeping() maxSleeping} to be exceeded, the oldest
* (bottom) instance in the pool is destroyed to make room for the newly created instance, which
* is pushed on top of the stack.
*
* @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) {
T toBeDestroyed = null;
if(_pool.size() >= _maxSleeping) {
shouldDestroy = true;
toBeDestroyed = _pool.remove(0); // remove the stalest object
}
_pool.push(obj);
obj = toBeDestroyed; // swap returned obj with the stalest one so it can be destroyed
}
notifyAll(); // _numIdle has changed
if(shouldDestroy) { // by constructor, shouldDestroy is false when _factory is null
try {
_factory.destroyObject(obj);
} catch(Exception e) {
// ignored
}
}
}
/**
* 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;
}
}
/**
* The cap on the number of "sleeping" instances in the pool.
*/
protected static final int DEFAULT_MAX_SLEEPING = 8;
/**
* The default initial size of the pool
* (this specifies the size of the container, it does not
* cause the pool to be pre-populated.)
*/
protected static final int DEFAULT_INIT_SLEEPING_CAPACITY = 4;
/**
* My pool.
* @deprecated to be made private in pool 2.0
*/
@Deprecated
protected Stack<T> _pool = null;
/**
* My {@link PoolableObjectFactory}.
* @deprecated to be made private in pool 2.0 - use {@link #getFactory()}
*/
@Deprecated
protected PoolableObjectFactory<T> _factory = null;
/**
* The cap on the number of "sleeping" instances in the pool.
* @deprecated to be made private in pool 2.0 - use {@link #getMaxSleeping()}
*/
@Deprecated
protected int _maxSleeping = DEFAULT_MAX_SLEEPING;
/**
* Number of objects borrowed but not yet returned to the pool.
* @deprecated to be made private in pool 2.0 - use {@link #getNumActive()}
*/
@Deprecated
protected int _numActive = 0;
/**
* 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;
}
/**
* Returns the maximum number of idle instances in the pool.
*
* @return maxSleeping
* @since 1.5.5
*/
public int getMaxSleeping() {
return _maxSleeping;
}
}