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/*
 * The contents of this file are subject to the terms
 * of the Common Development and Distribution License
 * (the License).  You may not use this file except in
 * compliance with the License.
 * 
 * You can obtain a copy of the license at
 * https://glassfish.dev.java.net/public/CDDLv1.0.html.
 * See the License for the specific language governing
 * permissions and limitations under the License.
 * 
 * When distributing Covered Code, include this CDDL
 * Header Notice in each file and include the License file
 * at https://glassfish.dev.java.net/public/CDDLv1.0.html.
 * If applicable, add the following below the CDDL Header,
 * with the fields enclosed by brackets [] replaced by
 * you own identifying information:
 * "Portions Copyrighted [year] [name of copyright owner]"
 * 
 * Copyright 2006 Sun Microsystems Inc. All Rights Reserved
 */

package com.sun.xml.ws.util;

import com.sun.xml.ws.api.pipe.Tube;
import com.sun.xml.ws.api.pipe.TubeCloner;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import java.util.concurrent.ConcurrentLinkedQueue;

/**
 * General-purpose object pool.
 *
 * 
 * In many parts of the runtime, we need to pool instances of objects that
 * are expensive to create (such as JAXB objects, StAX parsers, {@link Tube} instances.)
 *
 * 

 * This class provides a default implementation of such a pool.
 *
 * TODO: improve the implementation
 *
 * @author Kohsuke Kawaguchi
 */
public abstract class Pool {
    private final ConcurrentLinkedQueue queue = new ConcurrentLinkedQueue();

    /**
     * Gets a new object from the pool.
     *
     * 

     * If no object is available in the pool, this method creates a new one.
     *
     * @return
     *      always non-null.
     */
    public final T take() {
        T t = queue.poll();
        if(t==null)
            return create();
        return t;
    }

    /**
     * Returns an object back to the pool.
     */
    public final void recycle(T t) {
        queue.offer(t);
    }

    /**
     * Creates a new instance of object.
     *
     * 

     * This method is used when someone wants to
     * {@link #take() take} an object from an empty pool.
     *
     * 
     * Also note that multiple threads may call this method
     * concurrently.
     */
    protected abstract T create();


    /**
     * JAXB {@link javax.xml.bind.Marshaller} pool.
     */
    public static final class Marshaller extends Pool {
        private final JAXBContext context;

        public Marshaller(JAXBContext context) {
            this.context = context;
        }

        protected javax.xml.bind.Marshaller create() {
            try {
                return context.createMarshaller();
            } catch (JAXBException e) {
                // impossible
                throw new AssertionError(e);
            }
        }
    }

    /**
     * JAXB {@link javax.xml.bind.Marshaller} pool.
     */
    public static final class Unmarshaller extends Pool {
        private final JAXBContext context;

        public Unmarshaller(JAXBContext context) {
            this.context = context;
        }

        protected javax.xml.bind.Unmarshaller create() {
            try {
                return context.createUnmarshaller();
            } catch (JAXBException e) {
                // impossible
                throw new AssertionError(e);
            }
        }
    }

    /**
     * {@link Tube} pool.
     */
    public static final class TubePool extends Pool {
        private final Tube master;

        public TubePool(Tube master) {
            this.master = master;
            recycle(master);    // we'll use master as a part of the pool, too.
        }

        protected Tube create() {
            return TubeCloner.clone(master);
        }
    }
}