org.xnio

Class AutomaticReference<T>

java.lang.Object

java.lang.ref.Reference<T>

java.lang.ref.PhantomReference<T>

org.xnio.AutomaticReference<T>

public abstract class AutomaticReference<T>
extends PhantomReference<T>

An automatic reference is a phantom reference which is automatically freed by a background thread when it is enqueued. Since this type of garbage collection imposes considerable overhead, it should only be used sparingly, when it is impossible to achieve correctness any other way.

Author:

David M. Lloyd

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AutomaticReference(T referent, Object permit) Construct a new instance.

Method Summary

Modifier and Type	Method and Description
void	clear() Not supported.
boolean	enqueue() Not supported.
protected abstract void	free() Free this reference.
T	get() Always returns null.
static Object	getPermit() Get the security authorization permit to create automatic references.
boolean	isEnqueued() Determine whether this reference has been enqueued by the garbage collector.

Methods inherited from class java.lang.Object

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

Constructor Detail

AutomaticReference

protected AutomaticReference(T referent,
                             Object permit)

Construct a new instance. In order to maximize performance, the only security check performed by this constructor is to verify the permit which was passed in.

Parameters:

referent - the object to monitor

permit - the permit object originally acquired from getPermit()

Method Detail

getPermit

public static Object getPermit()

Get the security authorization permit to create automatic references.

Returns:

the permit

Throws:

SecurityException - if a security manager is enabled and the caller does not have the createAutomaticReference RuntimePermission

get

public final T get()

Always returns null.

Overrides:

get in class PhantomReference<T>

Returns:

null

clear

public final void clear()

Not supported.

Overrides:

clear in class Reference<T>

Throws:

UnsupportedOperationException - always

isEnqueued

public final boolean isEnqueued()

Determine whether this reference has been enqueued by the garbage collector.

Overrides:

isEnqueued in class Reference<T>

Returns:

true if the reference has been enqueued, false otherwise

enqueue

public final boolean enqueue()

Not supported.

Overrides:

enqueue in class Reference<T>

Returns:

nothing

Throws:

UnsupportedOperationException - always

free

protected abstract void free()

Free this reference. This method will be called from a dedicated thread or threads so this method should execute as quickly as possible.