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package com.jme3.network.kernel;

import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.atomic.AtomicLong;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *  Base implementation of the Kernel interface providing several
 *  useful default implementations of some methods.  This implementation
 *  assumes that the kernel will be managing its own internal threads
 *  and queuing any results for the caller to retrieve on their own
 *  thread.
 *
 *  @version   $Revision$
 *  @author    Paul Speed
 */
public abstract class AbstractKernel implements Kernel
{
    private static final Logger log = Logger.getLogger(AbstractKernel.class.getName());

    private AtomicLong nextId = new AtomicLong(1);

    /**
     *  Contains the pending endpoint events waiting for the caller
     *  to retrieve them.
     */
    private ConcurrentLinkedQueue endpointEvents = new ConcurrentLinkedQueue<>();

    /**
     *  Contains the pending envelopes waiting for the caller to
     *  retrieve them.
     */
    private LinkedBlockingQueue envelopes = new LinkedBlockingQueue<>();

    protected AbstractKernel()
    {
    }

    protected void reportError( Exception e )
    {
        // Should really be queued up so the outer thread can
        // retrieve them.  For now we'll just log it.  FIXME
        log.log( Level.SEVERE, "Unhandled kernel error", e );
    }

    protected void wakeupReader() {
        // If there are no pending messages then add one so that the
        // kernel-user knows to wake up if it is only listening for
        // envelopes.
        if( !hasEnvelopes() ) {
            // Note: this is not really a race condition.  At worst, our
            // event has already been handled, and it does no harm
            // to check again.
            addEnvelope( EVENTS_PENDING );
        }
    }

    protected long nextEndpointId()
    {
        return nextId.getAndIncrement();
    }

    /**
     *  Returns true if there are waiting envelopes.
     */
    @Override
    public boolean hasEnvelopes()
    {
        return !envelopes.isEmpty();
    }

    /**
     *  Removes one envelope from the received messages queue or
     *  blocks until one is available.
     */
    @Override
    public Envelope read() throws InterruptedException
    {
        return envelopes.take();
    }

    /**
     *  Removes and returns one endpoint event from the event queue or
     *  null if there are no endpoint events.
     */
    @Override
    public EndpointEvent nextEvent()
    {
        return endpointEvents.poll();
    }

    protected void addEvent( EndpointEvent e )
    {
        endpointEvents.add( e );
    }

    protected void addEnvelope( Envelope env )
    {
        if( !envelopes.offer( env ) ) {
            throw new KernelException( "Critical error, could not enqueue envelope." );
        }            
    }
}