小编Nil*_*sta的帖子

我创建了一个具有多个工作线程的 Netty 服务器，以检查线程数量的增加如何改变吞吐量。这是我使用的代码。它是编写和回显服务器的稍微修改版本，可以在 Netty 网站中找到。

Echo服务器计算

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class EchoServerCompute {

    private int port;

    public EchoServerCompute(int port) {
        this.port = port;
    }

    public void run(int threadCount) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup(threadCount);
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .childHandler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ch.pipeline().addLast(new EchoServerComputeHandler());
                 } …

我创建了一个小型 Netty 服务器来计算 BigInteger 的阶乘并发送结果。代码如下。

因子.java

public class Factorial {

    private int port;

    public Factorial(int port) {
        this.port = port;
    }

    public void run(int threadcount) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup(threadcount);
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .childHandler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ch.pipeline().addLast(new FactorialHandler());
                 }
             })
             .option(ChannelOption.SO_BACKLOG, 128)          
             .childOption(ChannelOption.SO_KEEPALIVE, true); 

            ChannelFuture f = b.bind(port).sync(); 

            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }

    public …

我通过打印 JVM 参数来检查 JVM 上的默认 MaxMetaspaceSize，如下所示

java -XX:+PrintFlagsFinal -version | grep MaxMetaspaceSize
    uintx MaxMetaspaceSize                          = 18446744073709547520                    {product}
java version "1.8.0_152"
Java(TM) SE Runtime Environment (build 1.8.0_152-b16)
Java HotSpot(TM) 64-Bit Server VM (build 25.152-b16, mixed mode)

鉴于这些 JVM 参数值以字节为单位显示，默认 MaxMetaspaceSize 约为 18 艾字节！

有人可以解释一下为什么默认的 MaxMetaspaceSize 值这么大吗？