Netty 4 Overview by Trustin Lee on 27-Feb-2013

What is Netty? an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients

Asynchronous Channel channel = ... ChannelFuture f = channel.write(message); f.addListener((f) -> { if (f.isSuccess()) { f.channel().write(nextMessage); // Async } else { f.cause().printStackTrace(); f.channel().close(); // Async } });

Synchrony via Asynchrony ChannelFuture f = channel.write(message); try { f.sync() .channel().write(nextMessage).sync(); } finally { f.channel().close(); }

Event-driven class MyInboundMessageListener extends ChannelInboundMessageHandlerAdapter { @Override void messageReceived( ChannelHandlerContext ctx, MyInboundMessage msg) { MyOutboundMessage res = ...; ctx.write(res); } }

Available events ● channelRegistered/Active ● inboundBufferUpdated ○ Most handlers have its own inbound buffer. ○ Much less GC pressure than generating event objects per message ○ CIMHAdapter.inboundBufferUpdated() invokes messageReceived() ● channelInactive/Unregistered ● exceptionCaught (Throwable) ● userEventTriggered (Object)

ChannelHandler type hierarchy ChannelHandler ChannelStateHandler ChannelOperationHandler ChannelInboundByteHandler ChannelInboundMessageHandler ChannelOutboundByteHandler ChannelOutboundMessageHandler *Adapter

ChannelInboundByteHandlerAdapter abstract class ChannelInboundByteHandlerAdapter ... { ByteBuf newInboundBuffer(ChannelHandlerContext ctx) { return ctx.alloc().buffer(); } void freeInboundBuffer(ChannelHandlerContext ctx) { ctx.inboundByteBuffer().release(); } final void inboundBufferUpdated(ChannelHandlerContext ctx) { inboundBufferUpdated(ctx, ctx.inboundByteBuffer()); } abstract void inboundBufferUpdated(ctx, ByteBuf in); ... }

ByteBufAllocator ● "ctx.alloc().buffer()" ● The default: PooledByteBufAllocator ○ Pure Java jemalloc impl with some twist ○ Beats JVM by not filling with NUL(0) ○ Takes advantage of sun.misc.Unsafe to: ■ Deallocate direct buffers timely ■ Access direct buffers directly (+10% faster) ○ Reference-counted ■ "buf.release()" and "buf.retain()" ■ Sampled leak detection enabled by '-D' flag

Pipeline: List ChannelPipeline p = ch.pipeline(); p.addLast( new HttpRequestDecoder(), // IB new HttpResponseEncoder(), // OM new MyHttpServiceHandler()); // IM p.addFirst(new SslHandler(...)); // IB //+OB

Pipeline: dynamic manipulation class HttpAndHttpsHandler extends ChannelInboundByteHandlerAdapter { void inboundBufferUpdated(ctx, inBuf) { if (isHttp(inBuf)) { addHttpHandlers(ctx, inBuf); } else if (isSsl(inBuf)) { addSslHandler(ctx, inBuf); } else { ctx.close(); // Unknown protocol } }

Pipeline: staged event threading EventExecutorGroup group = new DefaultEventExecutorGroup(16); ChannelPipeline p = channel.pipeline(); p.addLast( new RedisRequestDecoder(), // IB new RedisResponseEncoder()); // OM p.addLast( group, new RedisServiceHandler()); // IM

EventExecutor and EventLoop ● EventLoop ○ performs actual I/O ○ triggers an event to a pipeline ○ receives an operation from a pipeline ○ performs arbitrary tasks submitted by user ● EventExecutor ○ EventLoop minus I/O ○ Usually specified as an arg to ChannelPipeline. add*()

EventLoop type hierarchy ScheduledExecutorService EventExecutorGroup EventLoop EventExecutor EventLoopGroup NioEventLoopGroup AioEventLoopGroup DefaultEvtExecGrp

Putting all together NioEventLoopGroup NioSocketChannel ChannelPipeline HttpRequestDecoder EL2 ELn HttpRequestEncoder MyHttpServiceHandler DefaultEvtExecGrp EE1 EEm EL1 EE2

Code walk-through via Factorial example

Factorial example ● Sends sequential integers to multiply them ● Codec ○ NumberEncoder ○ BigIntegerDecoder ● Server ○ FactorialServerHandler ○ FactorialServerInitializer ○ FactorialServer ● Client ○ FactorialClientHandler ○ FactorialClientInitializer ○ FactorialClient

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