Shulou(Shulou.com)06/03 Report--

This article mainly explains "what is the startup process of server". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what is the startup process of server".

1. A demo of NettyServer

If you want to have an in-depth understanding of a framework, you usually have to use demo as a starting point. Below, we can see a simple process of creating nettyServer, that is, the quick start sample of netty.

@ Slf4jpublic class NettyServerHelloApplication {/ * A sample of server * / public static void main (String [] args) throws Exception {/ / 1. Create a corresponding EventLoop thread pool, bossGroup and workerGroup EventLoopGroup bossGroup = new NioEventLoopGroup (1); EventLoopGroup workerGroup = new NioEventLoopGroup (4); try {/ / 2. Create the entry core class ServerBootstrap ServerBootstrap b = new ServerBootstrap (); / / 3 corresponding to netty. Set the parameters of server And application processor b.group (bossGroup, workerGroup) .channel (NioServerSocketChannel.class) .option (ChannelOption.SO_BACKLOG) ChildHandler (new ChannelInitializer () {@ Override public void initChannel (SocketChannel ch) throws Exception {/ / 3.2. Most importantly, bind each channelHandler to the context of netty (for now) ChannelPipeline p = ch.pipeline (); p.addLast (new LoggingHandler (LogLevel.INFO)); p.addLast ("encoder", new MessageEncoder ()); p.addLast ("decoder", new MessageDecoder ()) P.addLast (new EchoServerHandler ());}}); / / 4. Bind the tcp port to enable server listening, and sync () ensures that all tasks ChannelFuture f = b.bind (ServerConstant.PORT). Sync (); / / 5. Waiting for the shutdown signal, let the business thread serve the business f.channel (). CloseFuture (). Sync ();} finally {/ / 6. After receiving the shutdown signal, gracefully close the thread pool of server to protect the application bossGroup.shutdownGracefully (); workerGroup.shutdownGracefully ();}

The above is the whole framework of a simplified version of nettyServer, which is basically the whole programming paradigm of nettyServer. It is mainly divided into the following steps:

1. Create a corresponding EventLoop thread pool, which is divided into bossGroup and workerGroup

two。 Create the entry core class ServerBootstrap corresponding to netty

3. Set the parameters of server and the application processor (the necessary channelHandler service access process)

4. Bind tcp port to enable server listening

5. Waiting for the shutdown signal, let the business thread to serve the business.

6. After receiving the shutdown signal, gracefully close the thread pool of server to protect the application

In fact, wouldn't it be much different if we were directly based on the ServerSocketChannel provided by jdk? Yes, at least on the surface, but we have to deal with a lot of exceptions and may be faced with a wide variety of business types. What should we do?

After all, the success of a framework is no accident. Let's take a look at how netty is handled in these processes.

2. The creation of EventLoop

EventLoop is literally translated as an event loop, but here we can also understand it as a thread pool because all events are submitted to it for processing. So, what kind of cycle is it?

First, let's take a look at its class inheritance:

As you can see from the class diagram, EventLoop is also an implementation of executor or thread pool, and they may have something in common.

/ / the calling method is as follows: EventLoopGroup bossGroup = new NioEventLoopGroup (1); EventLoopGroup workerGroup = new NioEventLoopGroup (4); / / io.netty.channel.nio.NioEventLoopGroup#NioEventLoopGroup (int, java.util.concurrent.ThreadFactory) / * Create a new instance using the specified number of threads, the given {@ link ThreadFactory} and the * {@ link SelectorProvider} which is returned by {@ link SelectorProvider#provider ()}. * / public NioEventLoopGroup (int nThreads, ThreadFactory threadFactory) {this (nThreads, threadFactory, SelectorProvider.provider ());} public NioEventLoopGroup (int nThreads, Executor executor, final SelectorProvider selectorProvider) {this (nThreads, executor, selectorProvider, DefaultSelectStrategyFactory.INSTANCE) } public NioEventLoopGroup (int nThreads, Executor executor, final SelectorProvider selectorProvider, final SelectStrategyFactory selectStrategyFactory) {super (nThreads, executor, selectorProvider, selectStrategyFactory, RejectedExecutionHandlers.reject ());} / io.netty.channel.MultithreadEventLoopGroup#MultithreadEventLoopGroup (int, java.util.concurrent.Executor, java.lang.Object...) Protected MultithreadEventLoopGroup (int nThreads, Executor executor, Object... Args) {/ / the default thread is cpu * 2 super (nThreads = = 0? DEFAULT_EVENT_LOOP_THREADS: nThreads, executor, args);} / / io.netty.util.concurrent.MultithreadEventExecutorGroup#MultithreadEventExecutorGroup (int, java.util.concurrent.Executor, java.lang.Object...) / * * Create a new instance. * * @ param nThreads the number of threads that will be used by this instance. * @ param executor the Executor to use, or {@ code null} if the default should be used. * @ param args arguments which will passed to each {@ link # newChild (Executor, Object...)} call * / protected MultithreadEventExecutorGroup (int nThreads, Executor executor, Object...) Args) {this (nThreads, executor, DefaultEventExecutorChooserFactory.INSTANCE, args);} / / io.netty.util.concurrent.MultithreadEventExecutorGroup#MultithreadEventExecutorGroup (int, java.util.concurrent.Executor, io.netty.util.concurrent.EventExecutorChooserFactory, java.lang.Object...) / * * Create a new instance. * * @ param nThreads the number of threads that will be used by this instance. * @ param executor the Executor to use, or {@ code null} if the default should be used. * @ param chooserFactory the {@ link EventExecutorChooserFactory} to use. * @ param args arguments which will passed to each {@ link # newChild (Executor, Object...)} call * / protected MultithreadEventExecutorGroup (int nThreads, Executor executor, EventExecutorChooserFactory chooserFactory, Object...) Args) {if (nThreads

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