org.apache.commons.pool.impl.StackObjectPool Maven / Gradle / Ivy
/*
* 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.PoolableObjectFactory;
/**
* A simple, {@link java.util.Stack Stack}-based {@link ObjectPool} implementation.
*
* 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 Objects without introducing
* artificial limits.
*
* @author Rodney Waldhoff
* @author Dirk Verbeeck
* @author Sandy McArthur
* @version $Revision: 777748 $ $Date: 2009-05-22 20:00:44 -0400 (Fri, 22 May 2009) $
* @since Pool 1.0
*/
public class StackObjectPool extends BaseObjectPool implements ObjectPool {
/**
* Create a new pool using
* no factory.
* Clients must first {@link #setFactory(PoolableObjectFactory) set the factory}
* 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 useage is discouraged.
*
* @see #StackObjectPool(PoolableObjectFactory)
*/
public StackObjectPool() {
this((PoolableObjectFactory)null,DEFAULT_MAX_SLEEPING,DEFAULT_INIT_SLEEPING_CAPACITY);
}
/**
* Create a new pool using
* no factory.
* Clients must first {@link #setFactory(PoolableObjectFactory) set the factory}
* 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 useage is discouraged.
*
* @param maxIdle cap on the number of "sleeping" instances in the pool
* @see #StackObjectPool(PoolableObjectFactory, int)
*/
public StackObjectPool(int maxIdle) {
this((PoolableObjectFactory)null,maxIdle,DEFAULT_INIT_SLEEPING_CAPACITY);
}
/**
* Create a new pool using
* no factory.
* Clients must first {@link #setFactory(PoolableObjectFactory) set the factory}
* 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 useage is discouraged.
*
* @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)
*/
public StackObjectPool(int maxIdle, int initIdleCapacity) {
this((PoolableObjectFactory)null,maxIdle,initIdleCapacity);
}
/**
* Create a new StackObjectPool using
* the specified factory to create new instances.
*
* @param factory the {@link PoolableObjectFactory} used to populate the pool
*/
public StackObjectPool(PoolableObjectFactory factory) {
this(factory,DEFAULT_MAX_SLEEPING,DEFAULT_INIT_SLEEPING_CAPACITY);
}
/**
* Create a new SimpleObjectPool using
* the specified factory to create new instances,
* capping the number of "sleeping" instances to max.
*
* @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 factory, int maxIdle) {
this(factory,maxIdle,DEFAULT_INIT_SLEEPING_CAPACITY);
}
/**
* Create a new SimpleObjectPool using
* the specified factory to create new instances,
* capping the number of "sleeping" instances to max,
* and initially allocating a container capable of containing
* at least init instances.
*
* @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 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();
_pool.ensureCapacity( initcapacity > _maxSleeping ? _maxSleeping : initcapacity);
}
public synchronized Object borrowObject() throws Exception {
assertOpen();
Object 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) {
try {
_factory.destroyObject(obj);
} catch (Throwable t2) {
// swallowed
} finally {
obj = null;
}
if (newlyCreated) {
throw new NoSuchElementException(
"Could not create a validated object, cause: " +
t.getMessage());
}
}
}
}
_numActive++;
return obj;
}
public synchronized void returnObject(Object 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) {
Object 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
}
}
}
public synchronized void invalidateObject(Object 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
*/
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
*/
public synchronized int getNumActive() {
return _numActive;
}
/**
* Clears any objects sitting idle in the pool.
*/
public synchronized void clear() {
if(null != _factory) {
Iterator it = _pool.iterator();
while(it.hasNext()) {
try {
_factory.destroyObject(it.next());
} catch(Exception e) {
// ignore error, keep destroying the rest
}
}
}
_pool.clear();
}
/**
* Close this pool, and free any resources associated with it.
*
* Calling {@link #addObject} or {@link #borrowObject} after invoking
* this method on a pool will cause them to throw an
* {@link IllegalStateException}.
*
*
* @throws Exception deprecated: implementations should silently fail if not all resources can be freed.
*/
public void close() throws Exception {
super.close();
clear();
}
/**
* Create an object, and place it into the pool.
* addObject() is useful for "pre-loading" a pool with idle objects.
* @throws Exception when the {@link #_factory} has a problem creating an object.
*/
public synchronized void addObject() throws Exception {
assertOpen();
if (_factory == null) {
throw new IllegalStateException("Cannot add objects without a factory.");
}
Object obj = _factory.makeObject();
boolean success = true;
if(!_factory.validateObject(obj)) {
success = false;
} else {
_factory.passivateObject(obj);
}
boolean shouldDestroy = !success;
if (success) {
Object 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 factory 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
*/
public synchronized void setFactory(PoolableObjectFactory factory) throws IllegalStateException {
assertOpen();
if(0 < getNumActive()) {
throw new IllegalStateException("Objects are already active");
} else {
clear();
_factory = factory;
}
}
/** The default 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. */
protected Stack _pool = null;
/** My {@link PoolableObjectFactory}. */
protected PoolableObjectFactory _factory = null;
/** The cap on the number of "sleeping" instances in the pool. */
protected int _maxSleeping = DEFAULT_MAX_SLEEPING;
/** Number of object borrowed but not yet returned to the pool. */
protected int _numActive = 0;
}