org.apache.commons.pool2.impl

Class SoftReferenceObjectPool<T>

java.lang.Object

org.apache.commons.pool2.BaseObjectPool<T>

org.apache.commons.pool2.impl.SoftReferenceObjectPool<T>

Type Parameters:

T - Type of element pooled in this pool.

All Implemented Interfaces:

ObjectPool<T>

public class SoftReferenceObjectPool<T>
extends BaseObjectPool<T>

A SoftReference based ObjectPool.

This class is intended to be thread-safe.

Since:

2.0

Version:

$Revision: 1622090 $

Field Summary

Fields

Modifier and Type	Field and Description
private java.util.ArrayList<PooledSoftReference<T>>	allReferences All references - checked out or waiting to be borrowed.
private long	createCount Total number of instances that have been created
private long	destroyCount Total number of instances that have been destroyed
private PooledObjectFactory<T>	factory Factory to source pooled objects
private LinkedBlockingDeque<PooledSoftReference<T>>	idleReferences Idle references - waiting to be borrowed
private int	numActive Count of instances that have been checkout out to pool clients
private java.lang.ref.ReferenceQueue<T>	refQueue Queue of broken references that might be able to be removed from _pool.

Constructor Summary

Constructors

Constructor and Description
SoftReferenceObjectPool(PooledObjectFactory<T> factory) Create a SoftReferenceObjectPool with the specified factory.

Method Summary

Modifier and Type	Method and Description
void	addObject() Create an object, and place it into the pool.
T	borrowObject() Borrow an object from the pool.
void	clear() Clears any objects sitting idle in the pool.
void	close() Close this pool, and free any resources associated with it.
private void	destroy(PooledSoftReference<T> toDestroy) Destroy a PooledSoftReference and remove it from the idle and all references pools.
private PooledSoftReference<T>	findReference(T obj) Find the PooledSoftReference in allReferences that points to obj.
PooledObjectFactory<T>	getFactory() Returns the PooledObjectFactory used by this pool to create and manage object instances.
int	getNumActive() Return the number of instances currently borrowed from this pool.
int	getNumIdle() Returns an approximation not less than the of the number of idle instances in the pool.
void	invalidateObject(T obj) Invalidates an object from the pool.
private void	pruneClearedReferences() If any idle objects were garbage collected, remove their Reference wrappers from the idle object pool.
private void	removeClearedReferences(java.util.Iterator<PooledSoftReference<T>> iterator) Clears cleared references from iterator's collection
void	returnObject(T obj) Returns an instance to the pool after successful validation and passivation.

Methods inherited from class org.apache.commons.pool2.BaseObjectPool

assertOpen, isClosed

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

factory

private final PooledObjectFactory<T> factory

Factory to source pooled objects

refQueue

private final java.lang.ref.ReferenceQueue<T> refQueue

Queue of broken references that might be able to be removed from _pool. This is used to help getNumIdle() be more accurate with minimal performance overhead.

numActive

private int numActive

Count of instances that have been checkout out to pool clients

destroyCount

private long destroyCount

Total number of instances that have been destroyed

createCount

private long createCount

Total number of instances that have been created

idleReferences

private final LinkedBlockingDeque<PooledSoftReference<T>> idleReferences

Idle references - waiting to be borrowed

allReferences

private final java.util.ArrayList<PooledSoftReference<T>> allReferences

All references - checked out or waiting to be borrowed.

Constructor Detail

SoftReferenceObjectPool

public SoftReferenceObjectPool(PooledObjectFactory<T> factory)

Create a SoftReferenceObjectPool with the specified factory.

Parameters:

factory - object factory to use.

Method Detail

borrowObject

public T borrowObject()
               throws java.lang.Exception

Borrow an object from the pool. If there are no idle instances available in the pool, the configured factory's PooledObjectFactory.makeObject() method is invoked to create a new instance.

All instances are activated and validated before being returned by this method. If validation fails or an exception occurs activating or validating an idle instance, the failing instance is 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 makeObject method is used to create a new instance. If the created instance either raises an exception on activation or fails validation, NoSuchElementException is thrown. Exceptions thrown by MakeObject are propagated to the caller; but other than ThreadDeath or VirtualMachineError, exceptions generated by activation, validation or destroy methods are swallowed silently.

Specified by:

borrowObject in interface ObjectPool<T>

Specified by:

borrowObject in class BaseObjectPool<T>

Returns:

a valid, activated object instance

Throws:

java.util.NoSuchElementException - if a valid object cannot be provided

java.lang.IllegalStateException - if invoked on a closed pool

java.lang.Exception - if an exception occurs creating a new instance

returnObject

public void returnObject(T obj)
                  throws java.lang.Exception

Returns an instance to the pool after successful validation and passivation. The returning instance is destroyed if any of the following are true:

• the pool is closed
• validation fails
• passivation throws an exception

Exceptions passivating or destroying instances are silently swallowed. Exceptions validating instances are propagated to the client.

Specified by:

returnObject in interface ObjectPool<T>

Specified by:

returnObject in class BaseObjectPool<T>

Parameters:

obj - instance to return to the pool

Throws:

java.lang.IllegalStateException - if an attempt is made to return an object to the pool that is in any state other than allocated (i.e. borrowed). Attempting to return an object more than once or attempting to return an object that was never borrowed from the pool will trigger this exception.

java.lang.Exception - if an instance cannot be returned to the pool

invalidateObject

public void invalidateObject(T obj)
                      throws java.lang.Exception

Invalidates an object from the pool.

By contract, obj must have been obtained using ObjectPool.borrowObject() or a related method as defined in an implementation or sub-interface.

This method should be used when an object that has been borrowed is determined (due to an exception or other problem) to be invalid.

Specified by:

invalidateObject in interface ObjectPool<T>

Specified by:

invalidateObject in class BaseObjectPool<T>

Parameters:

obj - a borrowed instance to be disposed.

Throws:

java.lang.Exception - if the instance cannot be invalidated

addObject

public void addObject()
               throws java.lang.Exception

Create an object, and place it into the pool. addObject() is useful for "pre-loading" a pool with idle objects.

Before being added to the pool, the newly created instance is validated and passivated. If validation fails, the new instance is destroyed. Exceptions generated by the factory makeObject or passivate are propagated to the caller. Exceptions destroying instances are silently swallowed.

Specified by:

addObject in interface ObjectPool<T>

Overrides:

addObject in class BaseObjectPool<T>

Throws:

java.lang.IllegalStateException - if invoked on a closed pool

java.lang.Exception - when the factory has a problem creating or passivating an object.

getNumIdle

public int getNumIdle()

Returns an approximation not less than the of the number of idle instances in the pool.

Specified by:

getNumIdle in interface ObjectPool<T>

Overrides:

getNumIdle in class BaseObjectPool<T>

Returns:

estimated number of idle instances in the pool

getNumActive

public int getNumActive()

Return the number of instances currently borrowed from this pool.

Specified by:

getNumActive in interface ObjectPool<T>

Overrides:

getNumActive in class BaseObjectPool<T>

Returns:

the number of instances currently borrowed from this pool

clear

public void clear()

Clears any objects sitting idle in the pool.

Specified by:

clear in interface ObjectPool<T>

Overrides:

clear in class BaseObjectPool<T>

close

public void close()

Close this pool, and free any resources associated with it. Invokes clear() to destroy and remove instances in the pool.

Calling addObject() or borrowObject() after invoking this method on a pool will cause them to throw an IllegalStateException.

Specified by:

close in interface ObjectPool<T>

Overrides:

close in class BaseObjectPool<T>

getFactory

public PooledObjectFactory<T> getFactory()

Returns the PooledObjectFactory used by this pool to create and manage object instances.

Returns:

the factory

pruneClearedReferences

private void pruneClearedReferences()

If any idle objects were garbage collected, remove their Reference wrappers from the idle object pool.

findReference

private PooledSoftReference<T> findReference(T obj)

Find the PooledSoftReference in allReferences that points to obj.

Parameters:

obj - returning object

Returns:

PooledSoftReference wrapping a soft reference to obj

destroy

private void destroy(PooledSoftReference<T> toDestroy)
              throws java.lang.Exception

Destroy a PooledSoftReference and remove it from the idle and all references pools.

Parameters:

toDestroy - PooledSoftReference to destroy

Throws:

java.lang.Exception - If an error occurs while trying to destroy the object

removeClearedReferences

private void removeClearedReferences(java.util.Iterator<PooledSoftReference<T>> iterator)

Clears cleared references from iterator's collection

Parameters:

iterator - iterator over idle/allReferences