Netty支持多种服务端的server实例,包括mina、netty等,如下所示:
由于开发者目前使用dubbo几乎都是基于Netty4的,因此下面的分析就以netty4的NettyServer为例,dubbo启动过程中会调用 NettyServer#doOpen 初始化和启动netty server。这里主要操作就是初始化 bossGroup 和 workerGroup,然后进行bind、设置channelHandler,一个标准的netty初始化启动流程,具体代码如下:
<code>protected
void
doOpen
()
throws
Throwable { bootstrap =new
ServerBootstrap(); bossGroup =new
NioEventLoopGroup(1
,new
DefaultThreadFactory("NettyServerBoss"
,true
)); workerGroup =new
NioEventLoopGroup(getUrl().getPositiveParameter(IO_THREADS_KEY, Constants.DEFAULT_IO_THREADS),new
DefaultThreadFactory("NettyServerWorker"
,true
));final
NettyServerHandler nettyServerHandler =new
NettyServerHandler(getUrl(),this
); channels = nettyServerHandler.getChannels(); bootstrap.group(bossGroup, workerGroup) .channel(NioServerSocketChannel.
class
) .childOption
(ChannelOption
.TCP_NODELAY
,Boolean
.TRUE
) .childOption
(ChannelOption
.SO_REUSEADDR
,Boolean
.TRUE
) .childOption
(ChannelOption
.ALLOCATOR
,PooledByteBufAllocator
.DEFAULT
) .childHandler
(new
ChannelInitializer
<NioSocketChannel
>() {protected
void
initChannel
(NioSocketChannel ch)
throws
Exception {int
idleTimeout = UrlUtils.getIdleTimeout(getUrl()); NettyCodecAdapter adapter =new
NettyCodecAdapter(getCodec(), getUrl(), NettyServer.this
);if
(getUrl().getParameter(SSL_ENABLED_KEY,false
)) { ch.pipeline().addLast("negotiation"
, SslHandlerInitializer.sslServerHandler(getUrl(), nettyServerHandler)); } ch.pipeline() .addLast("decoder"
, adapter.getDecoder()) .addLast("encoder"
, adapter.getEncoder()) .addLast("server-idle-handler"
,new
IdleStateHandler(0
,0
, idleTimeout, MILLISECONDS)) .addLast("handler"
, nettyServerHandler); } }); ChannelFuture channelFuture = bootstrap.bind(getBindAddress()); channelFuture.syncUninterruptibly(); channel = channelFuture.channel(); }/<code>
dubbo启动netty server时,会创建心跳检查的ChannelHandler,从IdleStateHandler的实现来看,它提供针对了 读空闲检测readerIdleTime、写空闲检测writerIdleTime和读写空闲检测allIdleTime的能力,当readerIdleTime、writerIdleTime或者allIdleTime大于0时,会在channelActive时初始化对应的netty的延时任务。
<code>public
IdleStateHandler
(
long
readerIdleTime,long
writerIdleTime,long
allIdleTime, TimeUnit unit) {this
(false
, readerIdleTime, writerIdleTime, allIdleTime, unit); }/<code>
当任务到期执行时,会检查上次的读写时间戳是否大于设定的最大空闲时间,如果大于则发送 IdleStateEvent 事件,这时就会触发用户设定的ChannelHandler的fireUserEventTriggered回调,针对上述代码来说,就会走到dubbo中org.apache.dubbo.remoting.transport.netty4.NettyServerHandler#userEventTriggered方法中:
<code>public
void
userEventTriggered
(ChannelHandlerContext ctx, Object evt)
throws
Exception {if
(evtinstanceof
IdleStateEvent) { NettyChannel channel = NettyChannel.getOrAddChannel(ctx.channel(), url, handler);try
{ logger.info("IdleStateEvent triggered, close channel "
+ channel); channel.close(); }finally
{ NettyChannel.removeChannelIfDisconnected(ctx.channel()); } }super
.userEventTriggered(ctx, evt); }/<code>
默认的心跳超时时间是心跳间隔的3倍,从实现来看,如果心跳超时了,dubbo provider端会主动断开连接,这说明comsumer端可能已经挂了或者重启了。
从上述dubbo启动netty的初始化代码来看,当consumer发出的请求达到provider时,首先要经过解码器InternalDecoder,注意这个解码器只是简单的转发作用,实际上解码工作是靠具体协议对应的解码器的,比如针对dubbo协议来说就是DubboCountCodec。
注意:dubbo provider端的解码流程不是本文的关注重点,因此大家只需知道其流程即可,关于编解码这块后续我会写专门的文章来分析。
consumer的请求数据经过解码之后就到达了dubbo业务处理的ChannelHandler — NettyServerHandler。
<code>public
void
channelRead
(ChannelHandlerContext ctx, Object msg)
throws
Exception { NettyChannel channel = NettyChannel.getOrAddChannel(ctx.channel(), url, handler); handler.received(channel, msg); }/<code>
关于dubbo中处理各种IO事件,和netty中处理类似也定义了一套处理回调接口,定义如下:
<code>public
interface
ChannelHandler
{void
connected
(Channel channel)
throws
RemotingException;void
disconnected
(Channel channel)
throws
RemotingException;
void
sent
(Channel channel, Object message)
throws
RemotingException;void
received
(Channel channel, Object message)
throws
RemotingException;void
caught
(Channel channel, Throwable exception)
throws
RemotingException; }/<code>
传递给dubbo处理器,会走到MultiMessageHandler处理器,由于dubbo定义的各种处理器实际上就是责任链的体现,为了方便看流程,先看下大致的处理涉及的类图:
- MultiMessageHandler:提供了针对多请求的处理能力;
- HeartbeatHandler:是针对心跳请求的处理逻辑,如果是心跳请求,则更新心跳时间戳,然后直接返回,这时是不会传递给接下来的处理器的;
- AllChannelHandler:all线程模型的实现,这是dubbo provider端默认的线程模型,这种线程模型把所有事件都直接交给业务线程池进行处理了。
注意:dubbo的provider线程池模型不是本文关注的重点,因此大家理解节课,后续dubbo provider线程池模型这块后续我会写专门的文章来分析。
将请求数据传递给dubbo provider端的线程池来处理之后,接下来就是dubbo真正的业务处理流程了。也到了本文该结束的时刻了,关于dubbo provider后续的处理流程解析,欢迎大家看接下来的文章哈。