View Javadoc

    1   /*
    2    * Copyright 2009 Red Hat, Inc.
    3    *
    4    * Red Hat licenses this file to you under the Apache License, version 2.0
    5    * (the "License"); you may not use this file except in compliance with the
    6    * License.  You may obtain a copy of the License at:
    7    *
    8    *    http://www.apache.org/licenses/LICENSE-2.0
    9    *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
    12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
    13   * License for the specific language governing permissions and limitations
    14   * under the License.
    15   */
    16  package org.jboss.netty.handler.execution;
    17
    18  import java.util.concurrent.Executor;
    19
    20  import org.jboss.netty.bootstrap.ServerBootstrap;
    21  import org.jboss.netty.channel.Channel;
    22  import org.jboss.netty.channel.ChannelDownstreamHandler;
    23  import org.jboss.netty.channel.ChannelEvent;
    24  import org.jboss.netty.channel.ChannelHandler;
    25  import org.jboss.netty.channel.ChannelHandlerContext;
    26  import org.jboss.netty.channel.ChannelPipeline;
    27  import org.jboss.netty.channel.ChannelPipelineFactory;
    28  import org.jboss.netty.channel.ChannelState;
    29  import org.jboss.netty.channel.ChannelStateEvent;
    30  import org.jboss.netty.channel.ChannelUpstreamHandler;
    31  import org.jboss.netty.channel.Channels;
    32  import org.jboss.netty.channel.ChannelHandler.Sharable;
    33  import org.jboss.netty.util.ExternalResourceReleasable;
    34  import org.jboss.netty.util.internal.ExecutorUtil;
    35
    36  /**
    37   * Forwards an upstream {@link ChannelEvent} to an {@link Executor}.
    38   * <p>
    39   * {@link ExecutionHandler} is often used when your {@link ChannelHandler}
    40   * performs a blocking operation that takes long time or accesses a resource
    41   * which is not CPU-bound business logic such as DB access.  Running such
    42   * operations in a pipeline without an {@link ExecutionHandler} will result in
    43   * unwanted hiccup during I/O because an I/O thread cannot perform I/O until
    44   * your handler returns the control to the I/O thread.
    45   * <p>
    46   * In most cases, an {@link ExecutionHandler} is coupled with an
    47   * {@link OrderedMemoryAwareThreadPoolExecutor} because it guarantees the
    48   * correct event execution order and prevents an {@link OutOfMemoryError}
    49   * under load:
    50   * <pre>
    51   * public class DatabaseGatewayPipelineFactory implements {@link ChannelPipelineFactory} {
    52   *
    53   *     <b>private final {@link ExecutionHandler} executionHandler;</b>
    54   *
    55   *     public DatabaseGatewayPipelineFactory({@link ExecutionHandler} executionHandler) {
    56   *         this.executionHandler = executionHandler;
    57   *     }
    58   *
    59   *     public {@link ChannelPipeline} getPipeline() {
    60   *         return {@link Channels}.pipeline(
    61   *                 new DatabaseGatewayProtocolEncoder(),
    62   *                 new DatabaseGatewayProtocolDecoder(),
    63   *                 <b>executionHandler, // Must be shared</b>
    64   *                 new DatabaseQueryingHandler());
    65   *     }
    66   * }
    67   * ...
    68   *
    69   * public static void main(String[] args) {
    70   *     {@link ServerBootstrap} bootstrap = ...;
    71   *     ...
    72   *     <b>{@link ExecutionHandler} executionHandler = new {@link ExecutionHandler}(
    73   *             new {@link OrderedMemoryAwareThreadPoolExecutor}(16, 1048576, 1048576))
    74   *     bootstrap.setPipelineFactory(
    75   *             new DatabaseGatewayPipelineFactory(executionHandler));</b>
    76   *     ...
    77   *     bootstrap.bind(...);
    78   *     ...
    79   *
    80   *     while (!isServerReadyToShutDown()) {
    81   *         // ... wait ...
    82   *     }
    83   *
    84   *     bootstrap.releaseExternalResources();
    85   *     <b>executionHandler.releaseExternalResources();</b>
    86   * }
    87   * </pre>
    88   *
    89   * Please refer to {@link OrderedMemoryAwareThreadPoolExecutor} for the
    90   * detailed information about how the event order is guaranteed.
    91   *
    92   * <h3>SEDA (Staged Event-Driven Architecture)</h3>
    93   * You can implement an alternative thread model such as
    94   * <a href="http://en.wikipedia.org/wiki/Staged_event-driven_architecture">SEDA</a>
    95   * by adding more than one {@link ExecutionHandler} to the pipeline.
    96   *
    97   * <h3>Using other {@link Executor} implementation</h3>
    98   *
    99   * Although it's recommended to use {@link OrderedMemoryAwareThreadPoolExecutor},
    100  * you can use other {@link Executor} implementations.  However, you must note
    101  * that other {@link Executor} implementation might break your application
    102  * because they often do not maintain event execution order nor interact with
    103  * I/O threads to control the incoming traffic and avoid {@link OutOfMemoryError}.
    104  *
    105  * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
    106  * @author <a href="http://gleamynode.net/">Trustin Lee</a>
    107  *
    108  * @version $Rev: 2295 $, $Date: 2010-06-03 18:01:46 +0900 (Thu, 03 Jun 2010) $
    109  *
    110  * @apiviz.landmark
    111  * @apiviz.has java.util.concurrent.ThreadPoolExecutor
    112  */
    113 @Sharable
    114 public class ExecutionHandler implements ChannelUpstreamHandler, ChannelDownstreamHandler, ExternalResourceReleasable {
    115
    116     private final Executor executor;
    117
    118     /**
    119      * Creates a new instance with the specified {@link Executor}.
    120      * Specify an {@link OrderedMemoryAwareThreadPoolExecutor} if unsure.
    121      */
    122     public ExecutionHandler(Executor executor) {
    123         if (executor == null) {
    124             throw new NullPointerException("executor");
    125         }
    126         this.executor = executor;
    127     }
    128
    129     /**
    130      * Returns the {@link Executor} which was specified with the constructor.
    131      */
    132     public Executor getExecutor() {
    133         return executor;
    134     }
    135
    136     /**
    137      * Shuts down the {@link Executor} which was specified with the constructor
    138      * and wait for its termination.
    139      */
    140     public void releaseExternalResources() {
    141         ExecutorUtil.terminate(getExecutor());
    142     }
    143
    144     public void handleUpstream(
    145             ChannelHandlerContext context, ChannelEvent e) throws Exception {
    146         executor.execute(new ChannelEventRunnable(context, e));
    147     }
    148
    149     public void handleDownstream(
    150             ChannelHandlerContext ctx, ChannelEvent e) throws Exception {
    151         if (e instanceof ChannelStateEvent) {
    152             ChannelStateEvent cse = (ChannelStateEvent) e;
    153             if (cse.getState() == ChannelState.INTEREST_OPS &&
    154                 (((Integer) cse.getValue()).intValue() & Channel.OP_READ) != 0) {
    155
    156                 // setReadable(true) requested
    157                 boolean readSuspended = ctx.getAttachment() != null;
    158                 if (readSuspended) {
    159                     // Drop the request silently if MemoryAwareThreadPool has
    160                     // set the flag.
    161                     e.getFuture().setSuccess();
    162                     return;
    163                 }
    164             }
    165         }
    166
    167         ctx.sendDownstream(e);
    168     }
    169 }