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The Netty project is an effort to provide an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.

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/*
 * Copyright 2009 Red Hat, Inc.
 *
 * Red Hat 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.jboss.netty.handler.execution;

import java.util.IdentityHashMap;
import java.util.LinkedList;
import java.util.Set;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.Executor;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;

import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelEvent;
import org.jboss.netty.channel.ChannelState;
import org.jboss.netty.channel.ChannelStateEvent;
import org.jboss.netty.util.ObjectSizeEstimator;
import org.jboss.netty.util.internal.ConcurrentIdentityWeakKeyHashMap;

/**
 * A {@link MemoryAwareThreadPoolExecutor} which makes sure the events from the
 * same {@link Channel} are executed sequentially.
 * 

 * NOTE: This thread pool inherits most characteristics of its super
 * type, so please make sure to refer to {@link MemoryAwareThreadPoolExecutor}
 * to understand how it works basically.
 *
 * 
Event execution order

 *
 * For example, let's say there are two executor threads that handle the events
 * from the two channels:
 * 
 *           -------------------------------------> Timeline ------------------------------------>
 *
 * Thread X: --- Channel A (Event A1) --.   .-- Channel B (Event B2) --- Channel B (Event B3) --->
 *                                      \ /
 *                                       X
 *                                      / \
 * Thread Y: --- Channel B (Event B1) --'   '-- Channel A (Event A2) --- Channel A (Event A3) --->
 * 

 * As you see, the events from different channels are independent from each
 * other.  That is, an event of Channel B will not be blocked by an event of
 * Channel A and vice versa, unless the thread pool is exhausted.
 * 

 * Also, it is guaranteed that the invocation will be made sequentially for the
 * events from the same channel.  For example, the event A2 is never executed
 * before the event A1 is finished.  (Although not recommended, if you want the
 * events from the same channel to be executed simultaneously, please use
 * {@link MemoryAwareThreadPoolExecutor} instead.)
 * 

 * However, it is not guaranteed that the invocation will be made by the same
 * thread for the same channel.  The events from the same channel can be
 * executed by different threads.  For example, the Event A2 is executed by the
 * thread Y while the event A1 was executed by the thread X.
 *
 * 
Using a different key other than {@link Channel} to maintain event order

 * 

 * {@link OrderedMemoryAwareThreadPoolExecutor} uses a {@link Channel} as a key
 * that is used for maintaining the event execution order, as explained in the
 * previous section.  Alternatively, you can extend it to change its behavior.
 * For example, you can change the key to the remote IP of the peer:
 *
 * 
 * public class RemoteAddressBasedOMATPE extends {@link OrderedMemoryAwareThreadPoolExecutor} {
 *
 *     ... Constructors ...
 *
 *     {@code @Override}
 *     protected ConcurrentMap<Object, Executor> newChildExecutorMap() {
 *         // The default implementation returns a special ConcurrentMap that
 *         // uses identity comparison only (see {@link IdentityHashMap}).
 *         // Because SocketAddress does not work with identity comparison,
 *         // we need to employ more generic implementation.
 *         return new ConcurrentHashMap<Object, Executor>
 *     }
 *
 *     protected Object getChildExecutorKey({@link ChannelEvent} e) {
 *         // Use the IP of the remote peer as a key.
 *         return ((InetSocketAddress) e.getChannel().getRemoteAddress()).getAddress();
 *     }
 *
 *     // Make public so that you can call from anywhere.
 *     public boolean removeChildExecutor(Object key) {
 *         super.removeChildExecutor(key);
 *     }
 * }
 * 

 *
 * Please be very careful of memory leak of the child executor map.  You must
 * call {@link #removeChildExecutor(Object)} when the life cycle of the key
 * ends (e.g. all connections from the same IP were closed.)  Also, please
 * keep in mind that the key can appear again after calling {@link #removeChildExecutor(Object)}
 * (e.g. a new connection could come in from the same old IP after removal.)
 * If in doubt, prune the old unused or stall keys from the child executor map
 * periodically:
 *
 * 
 * RemoteAddressBasedOMATPE executor = ...;
 *
 * on every 3 seconds:
 *
 *   for (Iterator<Object> i = executor.getChildExecutorKeySet().iterator; i.hasNext();) {
 *       InetAddress ip = (InetAddress) i.next();
 *       if (there is no active connection from 'ip' now &&
 *           there has been no incoming connection from 'ip' for last 10 minutes) {
 *           i.remove();
 *       }
 *   }
 * 

 *
 * If the expected maximum number of keys is small and deterministic, you could
 * use a weak key map such as ConcurrentWeakHashMap
 * or synchronized {@link WeakHashMap} instead of managing the life cycle of the
 * keys by yourself.
 *
 * @author The Netty Project
 * @author Trustin Lee
 * @author David M. Lloyd ([email protected])
 *
 * @version $Rev: 2308 $, $Date: 2010-06-17 23:23:59 +0900 (Thu, 17 Jun 2010) $
 *
 * @apiviz.landmark
 */
public class OrderedMemoryAwareThreadPoolExecutor extends
        MemoryAwareThreadPoolExecutor {

    // TODO Make OMATPE focus on the case where Channel is the key.
    //      Add a new less-efficient TPE that allows custom key.

    private final ConcurrentMap childExecutors = newChildExecutorMap();

    /**
     * Creates a new instance.
     *
     * @param corePoolSize          the maximum number of active threads
     * @param maxChannelMemorySize  the maximum total size of the queued events per channel.
     *                              Specify {@code 0} to disable.
     * @param maxTotalMemorySize    the maximum total size of the queued events for this pool
     *                              Specify {@code 0} to disable.
     */
    public OrderedMemoryAwareThreadPoolExecutor(
            int corePoolSize, long maxChannelMemorySize, long maxTotalMemorySize) {
        super(corePoolSize, maxChannelMemorySize, maxTotalMemorySize);
    }

    /**
     * Creates a new instance.
     *
     * @param corePoolSize          the maximum number of active threads
     * @param maxChannelMemorySize  the maximum total size of the queued events per channel.
     *                              Specify {@code 0} to disable.
     * @param maxTotalMemorySize    the maximum total size of the queued events for this pool
     *                              Specify {@code 0} to disable.
     * @param keepAliveTime         the amount of time for an inactive thread to shut itself down
     * @param unit                  the {@link TimeUnit} of {@code keepAliveTime}
     */
    public OrderedMemoryAwareThreadPoolExecutor(
            int corePoolSize, long maxChannelMemorySize, long maxTotalMemorySize,
            long keepAliveTime, TimeUnit unit) {
        super(corePoolSize, maxChannelMemorySize, maxTotalMemorySize,
                keepAliveTime, unit);
    }

    /**
     * Creates a new instance.
     *
     * @param corePoolSize          the maximum number of active threads
     * @param maxChannelMemorySize  the maximum total size of the queued events per channel.
     *                              Specify {@code 0} to disable.
     * @param maxTotalMemorySize    the maximum total size of the queued events for this pool
     *                              Specify {@code 0} to disable.
     * @param keepAliveTime         the amount of time for an inactive thread to shut itself down
     * @param unit                  the {@link TimeUnit} of {@code keepAliveTime}
     * @param threadFactory         the {@link ThreadFactory} of this pool
     */
    public OrderedMemoryAwareThreadPoolExecutor(
            int corePoolSize, long maxChannelMemorySize, long maxTotalMemorySize,
            long keepAliveTime, TimeUnit unit, ThreadFactory threadFactory) {
        super(corePoolSize, maxChannelMemorySize, maxTotalMemorySize,
                keepAliveTime, unit, threadFactory);
    }

    /**
     * Creates a new instance.
     *
     * @param corePoolSize          the maximum number of active threads
     * @param maxChannelMemorySize  the maximum total size of the queued events per channel.
     *                              Specify {@code 0} to disable.
     * @param maxTotalMemorySize    the maximum total size of the queued events for this pool
     *                              Specify {@code 0} to disable.
     * @param keepAliveTime         the amount of time for an inactive thread to shut itself down
     * @param unit                  the {@link TimeUnit} of {@code keepAliveTime}
     * @param threadFactory         the {@link ThreadFactory} of this pool
     * @param objectSizeEstimator   the {@link ObjectSizeEstimator} of this pool
     */
    public OrderedMemoryAwareThreadPoolExecutor(
            int corePoolSize, long maxChannelMemorySize, long maxTotalMemorySize,
            long keepAliveTime, TimeUnit unit,
            ObjectSizeEstimator objectSizeEstimator, ThreadFactory threadFactory) {
        super(corePoolSize, maxChannelMemorySize, maxTotalMemorySize,
                keepAliveTime, unit, objectSizeEstimator, threadFactory);
    }

    protected ConcurrentMap newChildExecutorMap() {
        return new ConcurrentIdentityWeakKeyHashMap();
    }

    protected Object getChildExecutorKey(ChannelEvent e) {
        return e.getChannel();
    }

    protected Set getChildExecutorKeySet() {
        return childExecutors.keySet();
    }

    protected boolean removeChildExecutor(Object key) {
        // FIXME: Succeed only when there is no task in the ChildExecutor's queue.
        //        Note that it will need locking which might slow down task submission.
        return childExecutors.remove(key) != null;
    }

    /**
     * Executes the specified task concurrently while maintaining the event
     * order.
     */
    @Override
    protected void doExecute(Runnable task) {
        if (!(task instanceof ChannelEventRunnable)) {
            doUnorderedExecute(task);
        } else {
            ChannelEventRunnable r = (ChannelEventRunnable) task;
            getChildExecutor(r.getEvent()).execute(task);
        }
    }

    private Executor getChildExecutor(ChannelEvent e) {
        Object key = getChildExecutorKey(e);
        Executor executor = childExecutors.get(key);
        if (executor == null) {
            executor = new ChildExecutor();
            Executor oldExecutor = childExecutors.putIfAbsent(key, executor);
            if (oldExecutor != null) {
                executor = oldExecutor;
            }
        }

        // Remove the entry when the channel closes.
        if (e instanceof ChannelStateEvent) {
            Channel channel = e.getChannel();
            ChannelStateEvent se = (ChannelStateEvent) e;
            if (se.getState() == ChannelState.OPEN &&
                !channel.isOpen()) {
                childExecutors.remove(channel);
            }
        }
        return executor;
    }

    @Override
    protected boolean shouldCount(Runnable task) {
        if (task instanceof ChildExecutor) {
            return false;
        }

        return super.shouldCount(task);
    }

    void onAfterExecute(Runnable r, Throwable t) {
        afterExecute(r, t);
    }

    private final class ChildExecutor implements Executor, Runnable {
        private final LinkedList tasks = new LinkedList();

        ChildExecutor() {
            super();
        }

        public void execute(Runnable command) {
            boolean needsExecution;
            synchronized (tasks) {
                needsExecution = tasks.isEmpty();
                tasks.add(command);
            }

            if (needsExecution) {
                doUnorderedExecute(this);
            }
        }

        public void run() {
            Thread thread = Thread.currentThread();
            for (;;) {
                final Runnable task;
                synchronized (tasks) {
                    task = tasks.getFirst();
                }

                boolean ran = false;
                beforeExecute(thread, task);
                try {
                    task.run();
                    ran = true;
                    onAfterExecute(task, null);
                } catch (RuntimeException e) {
                    if (!ran) {
                        onAfterExecute(task, e);
                    }
                    throw e;
                } finally {
                    synchronized (tasks) {
                        tasks.removeFirst();
                        if (tasks.isEmpty()) {
                            break;
                        }
                    }
                }
            }
        }
    }
}
 















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