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Xiaobian to share with you the example analysis of thread names in Netty, I believe most people still do not know how, so share this article for your reference, I hope you have a lot of harvest after reading this article, let us go to understand it together!

NioEventLoop creation process. The first step is to create the ThreadPerTaskExecutor, which is used to create Netty's underlying threads. When learning Java Thread, the default thread names are something like thread-0,thread-1,thread-2... And so on. The name of the thread for us to troubleshoot the problem is also played a great role, so we design the thread pool, according to certain rules to the thread pool named, this is also a good habit. In Netty, the threads in the thread pool are naturally named, so let's analyze the naming rules.

There are two thread pools in the diagram above, one called bossGroup and the other called workerGroup. They are all of type EventLoopGroup. We also mentioned earlier that bossGroup is responsible for receiving client requests, workerGroup, as its name suggests, is a 'worker' responsible for handling client IO read and write operations.

There are many NioEventLoops inside these two groups.

If we create EventLoopGroup without thread count, then each thread pool creates 2*CPU threads by default. The naming convention for each thread: nioEventLoop-n-n, e.g. nioEventLoop-2-1

Next we explain how the last two numbers are determined.

Let's take nioEventLoop-2-1 as an example.

Note: Frameworks like dubbo and RocketMQ have similar underlying code when using Netty, as follows

EventLoopGroup bossGroup = new NioEventLoopGroup(1);EventLoopGroup workerGroup = new NioEventLoopGroup(); When the main thread of the above code is executed from top to bottom, the first bossGroup is the first thread pool, and the second workerGroup is the second thread pool. And so on, if five NioEventLoopGroups are new in the code, then the fifth group is the fifth thread pool. So the number 2 in nioEventLoop-2-1 in our example means the second thread pool. The thread named nioEventLoop-2-1 is in the second thread pool.

We continue to analyze the origin of the number 1 in nioEventLoop-2-1.

Each EventLoopGroup has multiple NioEventLoop. NioEventLoop creates the underlying thread when it starts. According to the selector EventExecutorSelector, the NioEventLoop selected first from the thread pool to serve the client is the first thread, the NioEventLoop selected second from the thread pool to serve the client is the second thread, and so on. So the number 1 in the example nioEventLoop-2-1 represents the first thread in the thread pool, and the whole represents the first thread in the second thread pool.

Note: The nioEventLoop name in the example nioEventLoop-2-1 is fixed.

actual combat

So let's actually look at their names.

The server code is as follows

import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.ChannelFuture;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.codec.FixedLengthFrameDecoder;import io.netty.handler.codec.string.StringDecoder;import io.netty.handler.codec.string.StringEncoder;import io.netty.handler.logging.LogLevel;import io.netty.handler.logging.LoggingHandler;import io.netty.handler.timeout.IdleStateHandler;

import java.util.concurrent.TimeUnit;

public class Server {

public static void main(String[] args) throws Exception {

EventLoopGroup bossGroup = new NioEventLoopGroup(1); EventLoopGroup workerGroup = new NioEventLoopGroup();

ServerBootstrap serverBootstrap = new ServerBootstrap();

try { serverBootstrap.group(bossGroup, workerGroup) .channel(NioServerSocketChannel.class) .handler(new LoggingHandler(LogLevel.INFO)) .childHandler(new ChannelInitializer() { @Override protected void initChannel(NioSocketChannel ch) {

ChannelPipeline channelPipeline = ch.pipeline(); // ... } });

//Bind port synchronization waiting for success ChannelFuture channelFuture1 = serverBootstrap.bind("127.0.0.1", 8080).sync();

//Wait for the server listening port to close channelFuture1.channel().closeFuture().sync(); } finally { //This means that the server has been closed. bossGroup.shutdownGracefully(); workerGroup.shutdownGracefully(); }

}

}

We start the above code and connect to the server via telnet 127.0.0.1 8080. We use jvisualvm, which comes with JDK, to view threads.

to telnet

We found two more threads because we connected twice via telnet. One of the second numbers is-1, the other is-2, meaning the first and second threads.

but

According to the above server-side code and the previous explanation, we clearly created two thread pools, then the first number should be-1 and-2, but we actually observed that it is-2 and-3. (More precisely, nioEventLoopGroup-2 stands for bossGroup, nioEventLoopGroup-3 stands for workerGroup). Our code clearly only new out 2 NioEventLoopGroup, but now actual observation found that nioEventLoopGroup-1 was occupied by others.

We look for answers in the source code

When we instantiate NioEventLoopGroup with new in our code, since NioEventLoopGroup inherits MultithreadEventExecutorGroup, this MultithreadEventExecutorGroup will also be instantiated.

From the diagram we see that a DefaultPromise is instantiated with GlobalEventExecutor.INSTANCE. Create GlobalEventExecutor using Singleton pattern. where GlobalEventExecutor has an attribute

final ThreadFactory threadFactory = new DefaultThreadFactory(DefaultThreadFactory.toPoolName(getClass()), false, Thread.NORM_PRIORITY, null);

Follow DefaultThreadFactory

We see the truth in the bottom right corner, -1 is used by globalEventExecutor-1-.

Note: DefaultThreadFactory This factory class is used to create bossGroups and workerGroups.

The above is all the content of this article "Example Analysis of Thread Names in Netty", thank you for reading! I believe that everyone has a certain understanding, hope to share the content to help everyone, if you still want to learn more knowledge, welcome to pay attention to the industry information channel!

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