Netty（三）:IdleStateHandler源码解析

IdleStateHandler是Netty为我们提供的检测连接有效性的处理器，一共有读空闲，写空闲，读/写空闲三种监测机制。

将其添加到我们的ChannelPipline中，便可以用来检测空闲。

先通过一段代码来学习下IdleStateHandler的用法：

ConnectStateHandler：（负责监测通道的各种状态并处理空闲事件IdleStateEvent）

package com.insaneXs.netty.idlestate;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.handler.timeout.IdleState;
import io.netty.handler.timeout.IdleStateEvent;

public class ConnectStateHandler extends ChannelInboundHandlerAdapter {

    public ConnectStateHandler() {
        super();
    }

    @Override
    public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
        System.out.println("Channel Register");
        super.channelRegistered(ctx);
    }

    @Override
    public void channelUnregistered(ChannelHandlerContext ctx) throws Exception {
        System.out.println("Channel Unregister");
        super.channelUnregistered(ctx);
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("Channel Active");
        super.channelActive(ctx);
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("Channel Inactive");
        super.channelInactive(ctx);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("Channel Read");
        super.channelRead(ctx, msg);
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        System.out.println("Channel Read Complete");
        super.channelReadComplete(ctx);
    }

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        if(evt instanceof IdleStateEvent){
            if(((IdleStateEvent)evt).state().equals(IdleState.READER_IDLE)){
                System.out.println("Read Idle");
                ctx.close();
            }
        }else{
            super.userEventTriggered(ctx, evt);
        }
    }

    @Override
    public void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception {
        super.channelWritabilityChanged(ctx);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        super.exceptionCaught(ctx, cause);
    }
}

 服务器代码：

package com.insaneXs.netty.idlestate;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.timeout.IdleStateHandler;

public class NettyServer {

    public static void main(String[] args){
        EventLoopGroup boss = new NioEventLoopGroup(1);
        EventLoopGroup work = new NioEventLoopGroup(4);

        try {
        ServerBootstrap bootstrap = new ServerBootstrap();
        bootstrap.group(boss,work)
                .channel(NioServerSocketChannel.class)
                .childHandler(new ChannelInitializer<NioSocketChannel>() {
                    @Override
                    protected void initChannel(NioSocketChannel ch) throws Exception {
                        ChannelPipeline pipeline = ch.pipeline();

                        pipeline.addLast(new IdleStateHandler(30, 0, 0));
                        pipeline.addLast(new ConnectStateHandler());
                    }
                });


            bootstrap.bind(8322).sync().channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

测试客户端代码：

package com.insaneXs.netty.common;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;

public class CommonNettyClient {

    public static void main(String[] args){
        EventLoopGroup group = new NioEventLoopGroup();

        Bootstrap bootstrap = new Bootstrap();
        bootstrap.group(group)
                .channel(NioSocketChannel.class)
                .remoteAddress("localhost", 8322)
                .handler(new ChannelInboundHandlerAdapter());

        bootstrap.connect();
    }
}

测试结果：

 

 从上面的输出中我们可以看到Channel的状态变化：

1.连接建立时会从register -> active，

2.当读空闲时，我们产生了一个空闲事件，当ConnectStateHandler捕获这个事件后，会主动断开连接。 

3.断开时则是从inactive -> unregister。

接下来我们学习下IdleStateHandler源码：

/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project 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 io.netty.handler.timeout;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.Channel.Unsafe;
import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOutboundBuffer;
import io.netty.channel.ChannelPromise;

import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

/
 *
 * @see ReadTimeoutHandler
 * @see WriteTimeoutHandler
 */
public class IdleStateHandler extends ChannelDuplexHandler {
    private static final long MIN_TIMEOUT_NANOS = TimeUnit.MILLISECONDS.toNanos(1);

    // Not create a new ChannelFutureListener per write operation to reduce GC pressure.
    private final ChannelFutureListener writeListener = new ChannelFutureListener() {
        @Override
        public void operationComplete(ChannelFuture future) throws Exception {
            lastWriteTime = ticksInNanos();
            firstWriterIdleEvent = firstAllIdleEvent = true;
        }
    };

    //是否观察出站情况；默认false
    private final boolean observeOutput;
    
    /*******三种超时情况管理*********/
    //读超时时间
    private final long readerIdleTimeNanos;
    //写超时时间
    private final long writerIdleTimeNanos;
    //读或写超时时间
    private final long allIdleTimeNanos;

    //读空闲定时任务，验证是否读超时
    private ScheduledFuture<?> readerIdleTimeout;
    //最后一次读时间
    private long lastReadTime;
    //是否第一次读超时
    private boolean firstReaderIdleEvent = true;

    //写空闲定时任务，验证是否写超时
    private ScheduledFuture<?> writerIdleTimeout;
    //最后一次写超时
    private long lastWriteTime;
    //是否第一次写超时
    private boolean firstWriterIdleEvent = true;

    //读或写超时定时任务
    private ScheduledFuture<?> allIdleTimeout;
    //是否读或写超时
    private boolean firstAllIdleEvent = true;

    //处理器状态: 0-无状态, 1-初始化, 2-销毁
    private byte state; // 0 - none, 1 - initialized, 2 - destroyed
    //读状态标志
    private boolean reading;

    /****用于观察输出情况*****/
    private long lastChangeCheckTimeStamp;
    private int lastMessageHashCode;
    private long lastPendingWriteBytes;

    //设置超时时间;默认单位为秒
    public IdleStateHandler(
            int readerIdleTimeSeconds,
            int writerIdleTimeSeconds,
            int allIdleTimeSeconds) {

        this(readerIdleTimeSeconds, writerIdleTimeSeconds, allIdleTimeSeconds,
             TimeUnit.SECONDS);
    }

    //设置三种情况超时时间与时间单位
    public IdleStateHandler(
            long readerIdleTime, long writerIdleTime, long allIdleTime,
            TimeUnit unit) {
        this(false, readerIdleTime, writerIdleTime, allIdleTime, unit);
    }

    //设置是否观察输出情况,三种情况超时时间以及时间单位
    public IdleStateHandler(boolean observeOutput,
            long readerIdleTime, long writerIdleTime, long allIdleTime,
            TimeUnit unit) {
        if (unit == null) {
            throw new NullPointerException("unit");
        }

        this.observeOutput = observeOutput;

        if (readerIdleTime <= 0) {
            readerIdleTimeNanos = 0;
        } else {
            readerIdleTimeNanos = Math.max(unit.toNanos(readerIdleTime), MIN_TIMEOUT_NANOS);
        }
        if (writerIdleTime <= 0) {
            writerIdleTimeNanos = 0;
        } else {
            writerIdleTimeNanos = Math.max(unit.toNanos(writerIdleTime), MIN_TIMEOUT_NANOS);
        }
        if (allIdleTime <= 0) {
            allIdleTimeNanos = 0;
        } else {
            allIdleTimeNanos = Math.max(unit.toNanos(allIdleTime), MIN_TIMEOUT_NANOS);
        }
    }

    /************将时间转换成毫秒级***************/
    public long getReaderIdleTimeInMillis() {
        return TimeUnit.NANOSECONDS.toMillis(readerIdleTimeNanos);
    }

    
    public long getWriterIdleTimeInMillis() {
        return TimeUnit.NANOSECONDS.toMillis(writerIdleTimeNanos);
    }

    
    public long getAllIdleTimeInMillis() {
        return TimeUnit.NANOSECONDS.toMillis(allIdleTimeNanos);
    }

    //当处理器被添加时,视情况决定是否初始化
    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        if (ctx.channel().isActive() && ctx.channel().isRegistered()) {
            //判断channel是否已经激活和注册，避免
            initialize(ctx);
        } else {
            // channelActive() event has not been fired yet.  this.channelActive() will be invoked
            // and initialization will occur there.
        }
    }

    //移除时，调用destroy销毁
    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        destroy();
    }

    //当通道被注册时,视情况决定是否初始化
    @Override
    public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
        // Initialize early if channel is active already.
        if (ctx.channel().isActive()) {
            initialize(ctx);
        }
        super.channelRegistered(ctx);
    }

    //当通道激活时,初始化
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        // This method will be invoked only if this handler was added
        // before channelActive() event is fired.  If a user adds this handler
        // after the channelActive() event, initialize() will be called by beforeAdd().
        initialize(ctx);
        super.channelActive(ctx);
    }

    //通道不活跃时，调用destroy销毁
    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        destroy();
        super.channelInactive(ctx);
    }

    //读事件
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        //开启了读空闲监测 或 读写空闲检测
        if (readerIdleTimeNanos > 0 || allIdleTimeNanos > 0) {
            //修改为正在读，并重置首次读写事件的标志位为true
            reading = true;
            firstReaderIdleEvent = firstAllIdleEvent = true;
        }
        ctx.fireChannelRead(msg);
    }

    //读完成
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        //如果开启了 读/读写标志 且 正在读
        if ((readerIdleTimeNanos > 0 || allIdleTimeNanos > 0) && reading) {
            //修改最后一次读取时间,重置正在读标识
            lastReadTime = ticksInNanos();
            reading = false;
        }
        ctx.fireChannelReadComplete();
    }

    @Override
    public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
        //如果开启了 写/读写标志
        if (writerIdleTimeNanos > 0 || allIdleTimeNanos > 0) {
            ctx.write(msg, promise.unvoid()).addListener(writeListener);
        } else {
            ctx.write(msg, promise);
        }
    }

    //初始化
    private void initialize(ChannelHandlerContext ctx) {
        //判断状态避免重复初始化
        switch (state) {
        case 1:
        case 2:
            return;
        }

        state = 1;
        //观察输出情况
        initOutputChanged(ctx);

        //初始化最后一次读写时间
        lastReadTime = lastWriteTime = ticksInNanos();

        //根据超时时间，判断是否开启超时监测
        if (readerIdleTimeNanos > 0) {
            readerIdleTimeout = schedule(ctx, new ReaderIdleTimeoutTask(ctx),
                    readerIdleTimeNanos, TimeUnit.NANOSECONDS);
        }
        if (writerIdleTimeNanos > 0) {
            writerIdleTimeout = schedule(ctx, new WriterIdleTimeoutTask(ctx),
                    writerIdleTimeNanos, TimeUnit.NANOSECONDS);
        }
        if (allIdleTimeNanos > 0) {
            allIdleTimeout = schedule(ctx, new AllIdleTimeoutTask(ctx),
                    allIdleTimeNanos, TimeUnit.NANOSECONDS);
        }
    }

    /**
     * This method is visible for testing!
     */
    long ticksInNanos() {
        return System.nanoTime();
    }

    /**
     * This method is visible for testing!
     */
    ScheduledFuture<?> schedule(ChannelHandlerContext ctx, Runnable task, long delay, TimeUnit unit) {
        return ctx.executor().schedule(task, delay, unit);
    }

    //销毁
    private void destroy() {
        //更改状态 取消定时器
        state = 2;

        if (readerIdleTimeout != null) {
            readerIdleTimeout.cancel(false);
            readerIdleTimeout = null;
        }
        if (writerIdleTimeout != null) {
            writerIdleTimeout.cancel(false);
            writerIdleTimeout = null;
        }
        if (allIdleTimeout != null) {
            allIdleTimeout.cancel(false);
            allIdleTimeout = null;
        }
    }

    /**
     * Is called when an {@link IdleStateEvent} should be fired. This implementation calls
     * {@link ChannelHandlerContext#fireUserEventTriggered(Object)}.
     */
    protected void channelIdle(ChannelHandlerContext ctx, IdleStateEvent evt) throws Exception {
        ctx.fireUserEventTriggered(evt);
    }

    /**
     * Returns a {@link IdleStateEvent}.
     */
    protected IdleStateEvent newIdleStateEvent(IdleState state, boolean first) {
        switch (state) {
            case ALL_IDLE:
                return first ? IdleStateEvent.FIRST_ALL_IDLE_STATE_EVENT : IdleStateEvent.ALL_IDLE_STATE_EVENT;
            case READER_IDLE:
                return first ? IdleStateEvent.FIRST_READER_IDLE_STATE_EVENT : IdleStateEvent.READER_IDLE_STATE_EVENT;
            case WRITER_IDLE:
                return first ? IdleStateEvent.FIRST_WRITER_IDLE_STATE_EVENT : IdleStateEvent.WRITER_IDLE_STATE_EVENT;
            default:
                throw new IllegalArgumentException("Unhandled: state=" + state + ", first=" + first);
        }
    }

    /**
     * @see #hasOutputChanged(ChannelHandlerContext, boolean)
     */
    private void initOutputChanged(ChannelHandlerContext ctx) {
        if (observeOutput) {
            Channel channel = ctx.channel();
            Unsafe unsafe = channel.unsafe();
            ChannelOutboundBuffer buf = unsafe.outboundBuffer();
            //初始化消息内容的HashCode和byte
            if (buf != null) {
                lastMessageHashCode = System.identityHashCode(buf.current());
                lastPendingWriteBytes = buf.totalPendingWriteBytes();
            }
        }
    }

    //判断输出是否有变化
    private boolean hasOutputChanged(ChannelHandlerContext ctx, boolean first) {
        if (observeOutput) {

            // We can take this shortcut if the ChannelPromises that got passed into write()
            // appear to complete. It indicates "change" on message level and we simply assume
            // that there's change happening on byte level. If the user doesn't observe channel
            // writability events then they'll eventually OOME and there's clearly a different
            // problem and idleness is least of their concerns.
            if (lastChangeCheckTimeStamp != lastWriteTime) {
                lastChangeCheckTimeStamp = lastWriteTime;

                // But this applies only if it's the non-first call.
                if (!first) {
                    return true;
                }
            }

            Channel channel = ctx.channel();
            Unsafe unsafe = channel.unsafe();
            ChannelOutboundBuffer buf = unsafe.outboundBuffer();

            if (buf != null) {
                int messageHashCode = System.identityHashCode(buf.current());
                long pendingWriteBytes = buf.totalPendingWriteBytes();

                if (messageHashCode != lastMessageHashCode || pendingWriteBytes != lastPendingWriteBytes) {
                    lastMessageHashCode = messageHashCode;
                    lastPendingWriteBytes = pendingWriteBytes;

                    if (!first) {
                        return true;
                    }
                }
            }
        }

        return false;
    }

    //监测任务的父类
    private abstract static class AbstractIdleTask implements Runnable {

        private final ChannelHandlerContext ctx;

        AbstractIdleTask(ChannelHandlerContext ctx) {
            this.ctx = ctx;
        }

        @Override
        public void run() {
            if (!ctx.channel().isOpen()) {
                return;
            }

            run(ctx);
        }

        protected abstract void run(ChannelHandlerContext ctx);
    }

    //读监测定时任务
    private final class ReaderIdleTimeoutTask extends AbstractIdleTask {

        ReaderIdleTimeoutTask(ChannelHandlerContext ctx) {
            super(ctx);
        }

        @Override
        protected void run(ChannelHandlerContext ctx) {
            long nextDelay = readerIdleTimeNanos;
            if (!reading) {//不在读的过程中
                //计算是否超时
                nextDelay -= ticksInNanos() - lastReadTime;
            }

            if (nextDelay <= 0) {//已经超时
                //下次空闲监测
                readerIdleTimeout = schedule(ctx, this, readerIdleTimeNanos, TimeUnit.NANOSECONDS);

                boolean first = firstReaderIdleEvent;
                firstReaderIdleEvent = false;

                try {
                    //出发读超时事件
                    IdleStateEvent event = newIdleStateEvent(IdleState.READER_IDLE, first);
                    channelIdle(ctx, event);
                } catch (Throwable t) {
                    ctx.fireExceptionCaught(t);
                }
            } else {
                // Read occurred before the timeout - set a new timeout with shorter delay.
                readerIdleTimeout = schedule(ctx, this, nextDelay, TimeUnit.NANOSECONDS);
            }
        }
    }

    //写监测定时任务
    private final class WriterIdleTimeoutTask extends AbstractIdleTask {

        WriterIdleTimeoutTask(ChannelHandlerContext ctx) {
            super(ctx);
        }

        @Override
        protected void run(ChannelHandlerContext ctx) {

            long lastWriteTime = IdleStateHandler.this.lastWriteTime;
            long nextDelay = writerIdleTimeNanos - (ticksInNanos() - lastWriteTime);
            if (nextDelay <= 0) {//写超时
                //下一次超时检查时间 
                writerIdleTimeout = schedule(ctx, this, writerIdleTimeNanos, TimeUnit.NANOSECONDS);

                boolean first = firstWriterIdleEvent;
                firstWriterIdleEvent = false;

                try {
                    //输入内容是否发生变化:观察输出模式下且输出内容发生变化则不认为写超时
                    if (hasOutputChanged(ctx, first)) {
                        return;
                    }
                    //传递写超时事件
                    IdleStateEvent event = newIdleStateEvent(IdleState.WRITER_IDLE, first);
                    channelIdle(ctx, event);
                } catch (Throwable t) {
                    ctx.fireExceptionCaught(t);
                }
            } else {
                // Write occurred before the timeout - set a new timeout with shorter delay.
                writerIdleTimeout = schedule(ctx, this, nextDelay, TimeUnit.NANOSECONDS);
            }
        }
    }

    //读写监测定时任务
    private final class AllIdleTimeoutTask extends AbstractIdleTask {

        AllIdleTimeoutTask(ChannelHandlerContext ctx) {
            super(ctx);
        }

        @Override
        protected void run(ChannelHandlerContext ctx) {

            long nextDelay = allIdleTimeNanos;
            if (!reading) {
                nextDelay -= ticksInNanos() - Math.max(lastReadTime, lastWriteTime);
            }
            if (nextDelay <= 0) {
                // Both reader and writer are idle - set a new timeout and
                // notify the callback.
                allIdleTimeout = schedule(ctx, this, allIdleTimeNanos, TimeUnit.NANOSECONDS);

                boolean first = firstAllIdleEvent;
                firstAllIdleEvent = false;

                try {
                    if (hasOutputChanged(ctx, first)) {
                        return;
                    }

                    IdleStateEvent event = newIdleStateEvent(IdleState.ALL_IDLE, first);
                    channelIdle(ctx, event);
                } catch (Throwable t) {
                    ctx.fireExceptionCaught(t);
                }
            } else {
                // Either read or write occurred before the timeout - set a new
                // timeout with shorter delay.
                allIdleTimeout = schedule(ctx, this, nextDelay, TimeUnit.NANOSECONDS);
            }
        }
    }
}

 代码的关键部分都已经给出了注释。

这里主要关注几个问题，带着这些问题去思考代码设计的目的：

1.代码中firstXXXIdleEvent的标志位的作用是什么?

2.ObserveOutput标志位的作用是什么?

3.reading的标志的作用是什么？

4.lastReadTime和lastWriteTime会在什么时候被重置？

首先来回答第一个问题，为什么会有firstXXXIdleEvent的标识。

这是因为一次读写事件中，可能会产生多次的空闲超时事件。比如当我设置写空闲时间为5秒，而在某些情况下，我整个写过程需要30秒。那么这一次写过程就会产生多个写空闲事件。firstXXXIdleEvent标志位就是用来表明此次空闲事件是否为第一次空闲事件。

知道了第一个问题后，我们在看ObserveOutput标志的作用。ObserveOutput标志用来解决上述的慢输出的问题。如果设置为true，那么即使写过程中发生了写空闲事件，但是只要hasOutputChanged方法判断此时仍然在向外写（写缓存发生变化），那么就不会为此次超时产生写超时事件。

那么reading标志的作用是什么?reading的标志是在read方法开始时，被设置为true，在readComplete方法中又被设置为false。也就是reading标志表示正在发生读的过程。

最后的问题,lastReadTime和lastWriteTime在什么时候被重置？lastReadTime和lastWriteTime会在相应的定时器中被用来和空闲时间作比较，以此来检测在这段空闲时间中，是否发生过完整的读或写过程。因此，它们在handler初始化时被初始化值。lastReadTime会在readComplete时更新值。而lastWriteTime则是在WriterListener中设置（写过程完成后的回掉中）。