/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.catalina.tribes.group;


import java.io.IOException;
import java.io.Serializable;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import javax.management.MBeanServer;
import javax.management.ObjectName;

import org.apache.catalina.tribes.ByteMessage;
import org.apache.catalina.tribes.Channel;
import org.apache.catalina.tribes.ChannelException;
import org.apache.catalina.tribes.ChannelInterceptor;
import org.apache.catalina.tribes.ChannelListener;
import org.apache.catalina.tribes.ChannelMessage;
import org.apache.catalina.tribes.ChannelReceiver;
import org.apache.catalina.tribes.ChannelSender;
import org.apache.catalina.tribes.ErrorHandler;
import org.apache.catalina.tribes.Heartbeat;
import org.apache.catalina.tribes.JmxChannel;
import org.apache.catalina.tribes.ManagedChannel;
import org.apache.catalina.tribes.Member;
import org.apache.catalina.tribes.MembershipListener;
import org.apache.catalina.tribes.MembershipService;
import org.apache.catalina.tribes.RemoteProcessException;
import org.apache.catalina.tribes.UniqueId;
import org.apache.catalina.tribes.group.interceptors.MessageDispatchInterceptor;
import org.apache.catalina.tribes.io.BufferPool;
import org.apache.catalina.tribes.io.ChannelData;
import org.apache.catalina.tribes.io.XByteBuffer;
import org.apache.catalina.tribes.jmx.JmxRegistry;
import org.apache.catalina.tribes.util.Arrays;
import org.apache.catalina.tribes.util.Logs;
import org.apache.catalina.tribes.util.StringManager;
import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;

/**
 * The default implementation of a Channel.<br>
 * The GroupChannel manages the replication channel. It coordinates
 * message being sent and received with membership announcements.
 * The channel has an chain of interceptors that can modify the message or perform other logic.<br>
 * It manages a complete group, both membership and replication.
 */
public class GroupChannel extends ChannelInterceptorBase
        implements ManagedChannel, JmxChannel, GroupChannelMBean {

    private static final Log log = LogFactory.getLog(GroupChannel.class);
    protected static final StringManager sm = StringManager.getManager(GroupChannel.class);

    /**
     * Flag to determine if the channel manages its own heartbeat
     * If set to true, the channel will start a local thread for the heart beat.
     */
    protected boolean heartbeat = true;

    /**
     * If <code>heartbeat == true</code> then how often do we want this
     * heartbeat to run. The default value is 5000 milliseconds.
     */
    protected long heartbeatSleeptime = 5*1000;

    /**
     * Internal heartbeat future
     */
    protected ScheduledFuture<?> heartbeatFuture = null;
    protected ScheduledFuture<?> monitorFuture;

    /**
     * The  <code>ChannelCoordinator</code> coordinates the bottom layer components:<br>
     * - MembershipService<br>
     * - ChannelSender <br>
     * - ChannelReceiver<br>
     */
    protected final ChannelCoordinator coordinator = new ChannelCoordinator();

    /**
     * The first interceptor in the interceptor stack.
     * The interceptors are chained in a linked list, so we only need a reference to the
     * first one
     */
    protected ChannelInterceptor interceptors = null;

    /**
     * A list of membership listeners that subscribe to membership announcements
     */
    protected final List<MembershipListener> membershipListeners = new CopyOnWriteArrayList<>();

    /**
     * A list of channel listeners that subscribe to incoming messages
     */
    protected final List<ChannelListener> channelListeners = new CopyOnWriteArrayList<>();

    /**
     * If set to true, the GroupChannel will check to make sure that
     */
    protected boolean optionCheck = false;

    /**
     * the name of this channel.
     */
    protected String name = null;

    /**
     * the jmx domain which this channel is registered.
     */
    private String jmxDomain = "ClusterChannel";

    /**
     * the jmx prefix which will be used with channel ObjectName.
     */
    private String jmxPrefix = "";

    /**
     * If set to true, this channel is registered with jmx.
     */
    private boolean jmxEnabled = true;

    /**
     * Executor service.
     */
    protected ScheduledExecutorService utilityExecutor = null;

    /**
     * the ObjectName of this channel.
     */
    private ObjectName oname = null;

    /**
     * Creates a GroupChannel. This constructor will also
     * add the first interceptor in the GroupChannel.<br>
     * The first interceptor is always the channel itself.
     */
    public GroupChannel() {
        addInterceptor(this);
    }


    /**
     * Adds an interceptor to the stack for message processing<br>
     * Interceptors are ordered in the way they are added.<br>
     * <code>channel.addInterceptor(A);</code><br>
     * <code>channel.addInterceptor(C);</code><br>
     * <code>channel.addInterceptor(B);</code><br>
     * Will result in an interceptor stack like this:<br>
     * <code>A -&gt; C -&gt; B</code><br>
     * The complete stack will look like this:<br>
     * <code>Channel -&gt; A -&gt; C -&gt; B -&gt; ChannelCoordinator</code><br>
     * @param interceptor ChannelInterceptorBase
     */
    @Override
    public void addInterceptor(ChannelInterceptor interceptor) {
        if ( interceptors == null ) {
            interceptors = interceptor;
            interceptors.setNext(coordinator);
            interceptors.setPrevious(null);
            coordinator.setPrevious(interceptors);
        } else {
            ChannelInterceptor last = interceptors;
            while ( last.getNext() != coordinator ) {
                last = last.getNext();
            }
            last.setNext(interceptor);
            interceptor.setNext(coordinator);
            interceptor.setPrevious(last);
            coordinator.setPrevious(interceptor);
        }
    }

    /**
     * Sends a heartbeat through the interceptor stack.<br>
     * Invoke this method from the application on a periodic basis if
     * you have turned off internal heartbeats <code>channel.setHeartbeat(false)</code>
     */
    @Override
    public void heartbeat() {
        super.heartbeat();

        for (MembershipListener listener : membershipListeners) {
            if ( listener instanceof Heartbeat ) ((Heartbeat)listener).heartbeat();
        }

        for (ChannelListener listener : channelListeners) {
            if ( listener instanceof Heartbeat ) ((Heartbeat)listener).heartbeat();
        }
    }


    /**
     * Send a message to the destinations specified
     * @param destination Member[] - destination.length &gt; 0
     * @param msg Serializable - the message to send
     * @param options sender options, options can trigger guarantee levels and different
     *                interceptors to react to the message see class documentation for the
     *                <code>Channel</code> object.<br>
     * @return UniqueId - the unique Id that was assigned to this message
     * @throws ChannelException - if an error occurs processing the message
     * @see org.apache.catalina.tribes.Channel
     */
    @Override
    public UniqueId send(Member[] destination, Serializable msg, int options)
            throws ChannelException {
        return send(destination,msg,options,null);
    }

    /**
     *
     * @param destination Member[] - destination.length &gt; 0
     * @param msg Serializable - the message to send
     * @param options sender options, options can trigger guarantee levels and different
     *                interceptors to react to the message see class documentation for the
     *                <code>Channel</code> object.<br>
     * @param handler - callback object for error handling and completion notification,
     *                  used when a message is sent asynchronously using the
     *                  <code>Channel.SEND_OPTIONS_ASYNCHRONOUS</code> flag enabled.
     * @return UniqueId - the unique Id that was assigned to this message
     * @throws ChannelException - if an error occurs processing the message
     * @see org.apache.catalina.tribes.Channel
     */
    @Override
    public UniqueId send(Member[] destination, Serializable msg, int options, ErrorHandler handler)
            throws ChannelException {
        if ( msg == null ) throw new ChannelException(sm.getString("groupChannel.nullMessage"));
        XByteBuffer buffer = null;
        try {
            if (destination == null || destination.length == 0) {
                throw new ChannelException(sm.getString("groupChannel.noDestination"));
            }
            ChannelData data = new ChannelData(true);//generates a unique Id
            data.setAddress(getLocalMember(false));
            data.setTimestamp(System.currentTimeMillis());
            byte[] b = null;
            if ( msg instanceof ByteMessage ){
                b = ((ByteMessage)msg).getMessage();
                options = options | SEND_OPTIONS_BYTE_MESSAGE;
            } else {
                b = XByteBuffer.serialize(msg);
                options = options & (~SEND_OPTIONS_BYTE_MESSAGE);
            }
            data.setOptions(options);
            //XByteBuffer buffer = new XByteBuffer(b.length+128,false);
            buffer = BufferPool.getBufferPool().getBuffer(b.length+128, false);
            buffer.append(b,0,b.length);
            data.setMessage(buffer);
            InterceptorPayload payload = null;
            if ( handler != null ) {
                payload = new InterceptorPayload();
                payload.setErrorHandler(handler);
            }
            getFirstInterceptor().sendMessage(destination, data, payload);
            if ( Logs.MESSAGES.isTraceEnabled() ) {
                Logs.MESSAGES.trace("GroupChannel - Sent msg:" + new UniqueId(data.getUniqueId()) +
                        " at " + new java.sql.Timestamp(System.currentTimeMillis()) + " to " +
                        Arrays.toNameString(destination));
                Logs.MESSAGES.trace("GroupChannel - Send Message:" +
                        new UniqueId(data.getUniqueId()) + " is " + msg);
            }

            return new UniqueId(data.getUniqueId());
        } catch (RuntimeException | IOException e) {
            throw new ChannelException(e);
        } finally {
            if ( buffer != null ) BufferPool.getBufferPool().returnBuffer(buffer);
        }
    }


    /**
     * Callback from the interceptor stack. <br>
     * When a message is received from a remote node, this method will be
     * invoked by the previous interceptor.<br>
     * This method can also be used to send a message to other components
     * within the same application, but its an extreme case, and you're probably
     * better off doing that logic between the applications itself.
     * @param msg ChannelMessage
     */
    @Override
    public void messageReceived(ChannelMessage msg) {
        if ( msg == null ) return;
        try {
            if ( Logs.MESSAGES.isTraceEnabled() ) {
                Logs.MESSAGES.trace("GroupChannel - Received msg:" +
                        new UniqueId(msg.getUniqueId()) + " at " +
                        new java.sql.Timestamp(System.currentTimeMillis()) + " from " +
                        msg.getAddress().getName());
            }

            Serializable fwd = null;
            if ( (msg.getOptions() & SEND_OPTIONS_BYTE_MESSAGE) == SEND_OPTIONS_BYTE_MESSAGE ) {
                fwd = new ByteMessage(msg.getMessage().getBytes());
            } else {
                try {
                    fwd = XByteBuffer.deserialize(msg.getMessage().getBytesDirect(), 0,
                            msg.getMessage().getLength());
                }catch (Exception sx) {
                    log.error(sm.getString("groupChannel.unable.deserialize", msg),sx);
                    return;
                }
            }
            if ( Logs.MESSAGES.isTraceEnabled() ) {
                Logs.MESSAGES.trace("GroupChannel - Receive Message:" +
                        new UniqueId(msg.getUniqueId()) + " is " + fwd);
            }

            //get the actual member with the correct alive time
            Member source = msg.getAddress();
            boolean rx = false;
            boolean delivered = false;
            for (ChannelListener channelListener : channelListeners) {
                if (channelListener != null && channelListener.accept(fwd, source)) {
                    channelListener.messageReceived(fwd, source);
                    delivered = true;
                    //if the message was accepted by an RPC channel, that channel
                    //is responsible for returning the reply, otherwise we send an absence reply
                    if (channelListener instanceof RpcChannel) rx = true;
                }
            }//for
            if ((!rx) && (fwd instanceof RpcMessage)) {
                //if we have a message that requires a response,
                //but none was given, send back an immediate one
                sendNoRpcChannelReply((RpcMessage)fwd,source);
            }
            if ( Logs.MESSAGES.isTraceEnabled() ) {
                Logs.MESSAGES.trace("GroupChannel delivered[" + delivered + "] id:" +
                        new UniqueId(msg.getUniqueId()));
            }

        } catch ( Exception x ) {
            //this could be the channel listener throwing an exception, we should log it
            //as a warning.
            if ( log.isWarnEnabled() ) log.warn(sm.getString("groupChannel.receiving.error"),x);
            throw new RemoteProcessException(sm.getString("groupChannel.receiving.error"),x);
        }
    }

    /**
     * Sends a <code>NoRpcChannelReply</code> message to a member<br>
     * This method gets invoked by the channel if an RPC message comes in
     * and no channel listener accepts the message. This avoids timeout
     * @param msg RpcMessage
     * @param destination Member - the destination for the reply
     */
    protected void sendNoRpcChannelReply(RpcMessage msg, Member destination) {
        try {
            //avoid circular loop
            if ( msg instanceof RpcMessage.NoRpcChannelReply) return;
            RpcMessage.NoRpcChannelReply reply =
                    new RpcMessage.NoRpcChannelReply(msg.rpcId, msg.uuid);
            send(new Member[]{destination},reply,Channel.SEND_OPTIONS_ASYNCHRONOUS);
        } catch ( Exception x ) {
            log.error(sm.getString("groupChannel.sendFail.noRpcChannelReply"),x);
        }
    }

    /**
     * memberAdded gets invoked by the interceptor below the channel
     * and the channel will broadcast it to the membership listeners
     * @param member Member - the new member
     */
    @Override
    public void memberAdded(Member member) {
        //notify upwards
        for (MembershipListener membershipListener : membershipListeners) {
            if (membershipListener != null) membershipListener.memberAdded(member);
        }
    }

    /**
     * memberDisappeared gets invoked by the interceptor below the channel
     * and the channel will broadcast it to the membership listeners
     * @param member Member - the member that left or crashed
     */
    @Override
    public void memberDisappeared(Member member) {
        //notify upwards
        for (MembershipListener membershipListener : membershipListeners) {
            if (membershipListener != null) membershipListener.memberDisappeared(member);
        }
    }

    /**
     * Sets up the default implementation interceptor stack
     * if no interceptors have been added
     * @throws ChannelException Cluster error
     */
    protected synchronized void setupDefaultStack() throws ChannelException {
        if (getFirstInterceptor() != null &&
                ((getFirstInterceptor().getNext() instanceof ChannelCoordinator))) {
            addInterceptor(new MessageDispatchInterceptor());
        }
        Iterator<ChannelInterceptor> interceptors = getInterceptors();
        while (interceptors.hasNext()) {
            ChannelInterceptor channelInterceptor = interceptors.next();
            channelInterceptor.setChannel(this);
        }
        coordinator.setChannel(this);
    }

    /**
     * Validates the option flags that each interceptor is using and reports
     * an error if two interceptor share the same flag.
     * @throws ChannelException Error with option flag
     */
    protected void checkOptionFlags() throws ChannelException {
        StringBuilder conflicts = new StringBuilder();
        ChannelInterceptor first = interceptors;
        while ( first != null ) {
            int flag = first.getOptionFlag();
            if ( flag != 0 ) {
                ChannelInterceptor next = first.getNext();
                while ( next != null ) {
                    int nflag = next.getOptionFlag();
                    if (nflag!=0 && (((flag & nflag) == flag ) || ((flag & nflag) == nflag)) ) {
                        conflicts.append('[');
                        conflicts.append(first.getClass().getName());
                        conflicts.append(':');
                        conflicts.append(flag);
                        conflicts.append(" == ");
                        conflicts.append(next.getClass().getName());
                        conflicts.append(':');
                        conflicts.append(nflag);
                        conflicts.append("] ");
                    }//end if
                    next = next.getNext();
                }//while
            }//end if
            first = first.getNext();
        }//while
        if ( conflicts.length() > 0 ) throw new ChannelException(sm.getString("groupChannel.optionFlag.conflict",
                conflicts.toString()));

    }

    protected boolean ownExecutor = false;

    /**
     * Starts the channel.
     * @param svc int - what service to start
     * @throws ChannelException Start error
     * @see org.apache.catalina.tribes.Channel#start(int)
     */
    @Override
    public synchronized void start(int svc) throws ChannelException {
        setupDefaultStack();
        if (optionCheck) checkOptionFlags();
        // register jmx
        JmxRegistry jmxRegistry = JmxRegistry.getRegistry(this);
        if (jmxRegistry != null) this.oname = jmxRegistry.registerJmx(",component=Channel", this);
        if (utilityExecutor == null) {
            log.warn(sm.getString("groupChannel.warn.noUtilityExecutor"));
            utilityExecutor = new ScheduledThreadPoolExecutor(1);
            ownExecutor = true;
        }
        super.start(svc);
        monitorFuture = utilityExecutor.scheduleWithFixedDelay(this::startHeartbeat, 0, 60, TimeUnit.SECONDS);
    }

    protected void startHeartbeat() {
        if (heartbeat && (heartbeatFuture == null || (heartbeatFuture != null && heartbeatFuture.isDone()))) {
            if (heartbeatFuture != null && heartbeatFuture.isDone()) {
                // There was an error executing the scheduled task, get it and log it
                try {
                    heartbeatFuture.get();
                } catch (InterruptedException | ExecutionException e) {
                    log.error(sm.getString("groupChannel.unable.sendHeartbeat"), e);
                }
            }
            heartbeatFuture = utilityExecutor.scheduleWithFixedDelay(new HeartbeatRunnable(),
                    heartbeatSleeptime, heartbeatSleeptime, TimeUnit.MILLISECONDS);
        }
    }

    /**
     * Stops the channel.
     * @param svc int
     * @throws ChannelException Stop error
     * @see org.apache.catalina.tribes.Channel#stop(int)
     */
    @Override
    public synchronized void stop(int svc) throws ChannelException {
        if (monitorFuture != null) {
            monitorFuture.cancel(true);
            monitorFuture = null;
        }
        if (heartbeatFuture != null) {
            heartbeatFuture.cancel(true);
            heartbeatFuture = null;
        }
        super.stop(svc);
        if (ownExecutor) {
            utilityExecutor.shutdown();
            utilityExecutor = null;
            ownExecutor = false;
        }
        if (oname != null) {
            JmxRegistry.getRegistry(this).unregisterJmx(oname);
            oname = null;
        }
    }

    /**
     * Returns the first interceptor of the stack. Useful for traversal.
     * @return ChannelInterceptor
     */
    public ChannelInterceptor getFirstInterceptor() {
        if (interceptors != null) return interceptors;
        else return coordinator;
    }

    @Override
    public ScheduledExecutorService getUtilityExecutor() {
        return utilityExecutor;
    }

    @Override
    public void setUtilityExecutor(ScheduledExecutorService utilityExecutor) {
        this.utilityExecutor = utilityExecutor;
    }

    /**
     * Returns the channel receiver component
     * @return ChannelReceiver
     */
    @Override
    public ChannelReceiver getChannelReceiver() {
        return coordinator.getClusterReceiver();
    }

    /**
     * Returns the channel sender component
     * @return ChannelSender
     */
    @Override
    public ChannelSender getChannelSender() {
        return coordinator.getClusterSender();
    }

    /**
     * Returns the membership service component
     * @return MembershipService
     */
    @Override
    public MembershipService getMembershipService() {
        return coordinator.getMembershipService();
    }

    /**
     * Sets the channel receiver component
     * @param clusterReceiver ChannelReceiver
     */
    @Override
    public void setChannelReceiver(ChannelReceiver clusterReceiver) {
        coordinator.setClusterReceiver(clusterReceiver);
    }

    /**
     * Sets the channel sender component
     * @param clusterSender ChannelSender
     */
    @Override
    public void setChannelSender(ChannelSender clusterSender) {
        coordinator.setClusterSender(clusterSender);
    }

    /**
     * Sets the membership component
     * @param membershipService MembershipService
     */
    @Override
    public void setMembershipService(MembershipService membershipService) {
        coordinator.setMembershipService(membershipService);
    }

    /**
     * Adds a membership listener to the channel.<br>
     * Membership listeners are uniquely identified using the equals(Object) method
     * @param membershipListener MembershipListener
     */
    @Override
    public void addMembershipListener(MembershipListener membershipListener) {
        if (!this.membershipListeners.contains(membershipListener) )
            this.membershipListeners.add(membershipListener);
    }

    /**
     * Removes a membership listener from the channel.<br>
     * Membership listeners are uniquely identified using the equals(Object) method
     * @param membershipListener MembershipListener
     */

    @Override
    public void removeMembershipListener(MembershipListener membershipListener) {
        membershipListeners.remove(membershipListener);
    }

    /**
     * Adds a channel listener to the channel.<br>
     * Channel listeners are uniquely identified using the equals(Object) method
     * @param channelListener ChannelListener
     */
    @Override
    public void addChannelListener(ChannelListener channelListener) {
        if (!this.channelListeners.contains(channelListener) ) {
            this.channelListeners.add(channelListener);
        } else {
            throw new IllegalArgumentException(sm.getString("groupChannel.listener.alreadyExist",
                    channelListener,channelListener.getClass().getName()));
        }
    }

    /**
     *
     * Removes a channel listener from the channel.<br>
     * Channel listeners are uniquely identified using the equals(Object) method
     * @param channelListener ChannelListener
     */
    @Override
    public void removeChannelListener(ChannelListener channelListener) {
        channelListeners.remove(channelListener);
    }

    /**
     * Returns an iterator of all the interceptors in this stack
     * @return Iterator
     */
    @Override
    public Iterator<ChannelInterceptor> getInterceptors() {
        return new InterceptorIterator(this.getNext(),this.coordinator);
    }

    /**
     * Enables/disables the option check<br>
     * Setting this to true, will make the GroupChannel perform a conflict check
     * on the interceptors. If two interceptors are using the same option flag
     * and throw an error upon start.
     * @param optionCheck boolean
     */
    public void setOptionCheck(boolean optionCheck) {
        this.optionCheck = optionCheck;
    }

    /**
     * Configure local heartbeat sleep time<br>
     * Only used when <code>getHeartbeat()==true</code>
     * @param heartbeatSleeptime long - time in milliseconds to sleep between heartbeats
     */
    public void setHeartbeatSleeptime(long heartbeatSleeptime) {
        this.heartbeatSleeptime = heartbeatSleeptime;
    }

    /**
     * Enables or disables local heartbeat.
     * if <code>setHeartbeat(true)</code> is invoked then the channel will start an internal
     * thread to invoke <code>Channel.heartbeat()</code> every <code>getHeartbeatSleeptime</code> milliseconds
     * @param heartbeat boolean
     */
    @Override
    public void setHeartbeat(boolean heartbeat) {
        this.heartbeat = heartbeat;
    }

    /**
     * @see #setOptionCheck(boolean)
     * @return boolean
     */
    @Override
    public boolean getOptionCheck() {
        return optionCheck;
    }

    /**
     * @see #setHeartbeat(boolean)
     * @return boolean
     */
    @Override
    public boolean getHeartbeat() {
        return heartbeat;
    }

    /**
     * Returns the sleep time in milliseconds that the internal heartbeat will
     * sleep in between invocations of <code>Channel.heartbeat()</code>
     * @return long
     */
    @Override
    public long getHeartbeatSleeptime() {
        return heartbeatSleeptime;
    }

    @Override
    public String getName() {
        return name;
    }

    @Override
    public void setName(String name) {
        this.name = name;
    }

    @Override
    public boolean isJmxEnabled() {
        return jmxEnabled;
    }

    @Override
    public void setJmxEnabled(boolean jmxEnabled) {
        this.jmxEnabled = jmxEnabled;
    }

    @Override
    public String getJmxDomain() {
        return jmxDomain;
    }

    @Override
    public void setJmxDomain(String jmxDomain) {
        this.jmxDomain = jmxDomain;
    }

    @Override
    public String getJmxPrefix() {
        return jmxPrefix;
    }

    @Override
    public void setJmxPrefix(String jmxPrefix) {
        this.jmxPrefix = jmxPrefix;
    }

    @Override
    public ObjectName preRegister(MBeanServer server, ObjectName name)
            throws Exception {
        // NOOP
        return null;
    }

    @Override
    public void postRegister(Boolean registrationDone) {
        // NOOP
    }

    @Override
    public void preDeregister() throws Exception {
        // NOOP
    }

    @Override
    public void postDeregister() {
        JmxRegistry.removeRegistry(this, true);
    }

    /**
     *
     * <p>Title: Interceptor Iterator</p>
     *
     * <p>Description: An iterator to loop through the interceptors in a channel</p>
     *
     * @version 1.0
     */
    public static class InterceptorIterator implements Iterator<ChannelInterceptor> {
        private final ChannelInterceptor end;
        private ChannelInterceptor start;
        public InterceptorIterator(ChannelInterceptor start, ChannelInterceptor end) {
            this.end = end;
            this.start = start;
        }

        @Override
        public boolean hasNext() {
            return start!=null && start != end;
        }

        @Override
        public ChannelInterceptor next() {
            ChannelInterceptor result = null;
            if ( hasNext() ) {
                result = start;
                start = start.getNext();
            }
            return result;
        }

        @Override
        public void remove() {
            //empty operation
        }
    }

    /**
     * <p>Title: Internal heartbeat runnable</p>
     *
     * <p>Description: if <code>Channel.getHeartbeat()==true</code> then a thread of this class
     * is created</p>
     */
    public class HeartbeatRunnable implements Runnable {
        @Override
        public void run() {
            heartbeat();
        }
    }

}
