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package com.sun.xml.internal.ws.util;

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

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;

import java.util.concurrent.ConcurrentLinkedQueue;
import java.lang.ref.SoftReference;


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, Tube instances.) 

This class provides a default implementation of such a pool.
TODO: improve the implementation
Author:
Kohsuke Kawaguchi/**
 * General-purpose object pool.
 *
 * <p>
 * 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.)
 *
 * <p>
 * This class provides a default implementation of such a pool.
 *
 * TODO: improve the implementation
 *
 * @author Kohsuke Kawaguchi
 */
public abstract class Pool<T> {

    // volatile since multiple threads may access queue reference
    private volatile SoftReference<ConcurrentLinkedQueue<T>> queue;

    
Gets a new object from the pool.

If no object is available in the pool, this method creates a new one.
Returns:

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

    private ConcurrentLinkedQueue<T> getQueue() {
        SoftReference<ConcurrentLinkedQueue<T>> q = queue;
        if (q != null) {
            ConcurrentLinkedQueue<T> d = q.get();
            if (d != null)
                return d;
        }

        // overwrite the queue
        ConcurrentLinkedQueue<T> d = new ConcurrentLinkedQueue<T>();
        queue = new SoftReference<ConcurrentLinkedQueue<T>>(d);

        return d;
    }

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

    
Creates a new instance of object.
 This method is used when someone wants to take an object from an empty pool. 

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


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

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

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

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

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

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

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

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

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

        
Returns:
master tubeline from pool
Deprecated:
Expected to be used in rare cases where access to master
tubeline is required and safe, such as Stub.close()."/**
         *
         * @return master tubeline from pool
         * @deprecated Expected to be used in rare cases where access to master
         * tubeline is required and safe, such as Stub.close()."
         */
        @Deprecated()
        public final Tube takeMaster() {
            return master;
        }

    }
}