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 package com.sun.grizzly;

 /**

  * Implementation of an {@link ProtocolChainInstanceHandler}.

  * Contains single {@link ProtocolChain} instance, which will be returned all

  * the time {@link ProtocolChainInstanceHandler#poll()} will be called.

  *

  * @author Jeanfrancois Arcand

  */

 public class SingleProtocolChainInstanceHandler

             implements ProtocolChainInstanceHandler{

     /**

      * Single {@link ProtocolChain} instance.

      */

     protected volatile ProtocolChain protocolChain;

     public SingleProtocolChainInstanceHandler() {

         this(null);

     }

     public SingleProtocolChainInstanceHandler(ProtocolChain protocolChain) {

         this.protocolChain = protocolChain;

     }

     /**

      * Return a {@link ProtocolChain} instance. If no {@link ProtocolChain} was

      * set before, then new instance of {@link DefaultProtocolChain}

      * will be returned.

      * 

      * @return <tt>ProtocolChain</tt>

      */

     public ProtocolChain poll() {

         if (protocolChain == null) {

             synchronized(this) {

                 if (protocolChain == null) {

                     protocolChain = new DefaultProtocolChain();

                 }

             }

         }

         return protocolChain;

     }

     /**

      * Offer (add) an instance of ProtocolChain to this instance pool.

      * {@link StatelessProtocolChainInstanceHandler} has empty implementation

      * of the method.

      *

      * @param protocolChain - <tt>ProtocolChain</tt> to offer / add to the pool

      * @return boolean, true is always returned.

      */

     public boolean offer(ProtocolChain protocolChain) {

         if (this.protocolChain != protocolChain) {

             throw new IllegalArgumentException("Passed protocolChain argument " +

                     "doesn't correspond to one, holding by this handler instance");

         }

         return true;

     }

     /**

      * Get the stateless {@link ProtocolChain} instance, which is always 

      * returned via {@link StatelessProtocolChainInstanceHandler#poll()}.

      * 

      * @return the stateless {@link ProtocolChain} instance, which is always

      * returned via {@link StatelessProtocolChainInstanceHandler#poll()}.

      */

     public ProtocolChain getProtocolChain() {

         return protocolChain;

     }

     /**

      * Set the stateless {@link ProtocolChain} instance, which will be always

      * returned via {@link StatelessProtocolChainInstanceHandler#poll()}.

      *

      * @param protocolChain the stateless {@link ProtocolChain} instance, 

      * which will be always returned via

      * {@link StatelessProtocolChainInstanceHandler#poll()}.

      */

     public void setProtocolChain(ProtocolChain protocolChain) {

         this.protocolChain = protocolChain;

     }

 }