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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 ProtocolChain
     */
    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 - ProtocolChain 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;
    }
}




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