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/*
* File: Cached.java
*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* The contents of this file are subject to the terms and conditions of
* the Common Development and Distribution License 1.0 (the "License").
*
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the License by consulting the LICENSE.txt file
* distributed with this file, or by consulting https://oss.oracle.com/licenses/CDDL
*
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing the software, include this License Header Notice in each
* file and include the License file LICENSE.txt.
*
* MODIFICATIONS:
* If applicable, add the following below the License Header, with the fields
* enclosed by brackets [] replaced by your own identifying information:
* "Portions Copyright [year] [name of copyright owner]"
*/
package com.oracle.bedrock.deferred;
import java.util.concurrent.atomic.AtomicReference;
/**
* A {@link Cached} object is a specialized {@link Deferred} that holds
* a reference to (ie: caches) an object that was successfully returned by
* another {@link Deferred}.
*
* ie: A {@link Cached} is a {@link Deferred} adapter.
*
* Copyright (c) 2012. All Rights Reserved. Oracle Corporation.
* Oracle is a registered trademark of Oracle Corporation and/or its affiliates.
*
* @author Brian Oliver
*/
public class Cached implements Deferred
{
/**
* The {@link Deferred} that will provide us with an object to cache.
*/
private Deferred deferred;
/**
* The last successfully resolved object from the {@link #deferred}.
*/
private volatile AtomicReference object;
/**
* Constructs a {@link Cached} for the specified {@link Deferred}.
*
* @param deferred the {@link Deferred}
*/
public Cached(Deferred deferred)
{
this.deferred = deferred;
this.object = null;
}
/**
* Obtains the adapted {@link Deferred}.
*
* @return the adapted {@link Deferred}
*/
public Deferred getDeferred()
{
return deferred;
}
@Override
public T get() throws TemporarilyUnavailableException, PermanentlyUnavailableException
{
if (object == null)
{
synchronized (this)
{
if (object == null)
{
try
{
T deferred = this.deferred.get();
object = new AtomicReference(deferred);
}
catch (UnavailableException e)
{
throw e;
}
catch (RuntimeException e)
{
throw new TemporarilyUnavailableException(this, e);
}
}
}
}
return object.get();
}
@Override
public Class getDeferredClass()
{
return deferred.getDeferredClass();
}
/**
* Release the currently cached object.
*
* @return the currently cached object
*/
public synchronized T release()
{
T object = this.object == null ? null : this.object.get();
this.object = null;
return object;
}
@Override
public String toString()
{
return String.format("Cached{%s}", getDeferredClass());
}
}