Netty - 优化 - 参数调优

2. 参数调优

2.1 CONNECT_TIMEOUT_MILLIS

在客户端建立连接时，如果在指定毫秒内无法连接，则抛出 timeout 异常

package com.sw.netty._07;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelOption;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;

@Slf4j
public class ConnTimeoutTest {
    public static void main(String[] args) {
        NioEventLoopGroup worker = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap()
                    .group(worker)
                    .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 300)
                    .channel(NioSocketChannel.class)
                    .handler(new LoggingHandler(LogLevel.DEBUG));
            ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 8088);
            channelFuture.sync().channel().closeFuture().sync();
        } catch (Exception e) {
            log.error("ConnTimeoutTestClient error: ", e);
        } finally {
            worker.shutdownGracefully();
        }
    }
}

2.2 SO_BACKLOG

tcp 完成三次握手后，服务端会将客户端的请求从 sync queue（半连接队列）放入 accept queue（全连接队列）

在 linux 2.2 之前，backlog 参数同时包括了两个队列的大小，2.2 之后：

• sync queue

  • 通过 /proc/sys/net/ipv4/tcp_max_syn_backlog 指定

• accept queue

  • 通过 /proc/sys/net/core/somaxconn 指定，同时内核会根据用户态传入的 backlog 参数与系统参数作比较，取二者中较小的值
  • 当队列满了时，会拒绝连接客户端的请求

BacklogServerTest

package com.sw.netty._07;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

public class BacklogServerTest {
    public static void main(String[] args) {
        new ServerBootstrap()
                .group(new NioEventLoopGroup())
                // 以 windows idea 环境演示为例，指定全连接队列大小为 2
                .option(ChannelOption.SO_BACKLOG, 2)
                .channel(NioServerSocketChannel.class)
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
                    }
                }).bind(8088);
    }
}

注：netty 对客户端的连接是来一个处理一个，所以需要在 NioEventLoop 源码中通过断点阻塞住 ACCEPT 事件，即：io.netty.channel.nio.NioEventLoop#processSelectedKey 方法

BacklogClientTest

package com.sw.netty._07;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;

@Slf4j
public class BacklogClientTest {
    public static void main(String[] args) {
        NioEventLoopGroup worker = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap()
                    .group(worker)
                    .channel(NioSocketChannel.class)
                    .handler(new LoggingHandler(LogLevel.DEBUG));
            ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 8088);
            channelFuture.sync().channel().closeFuture().sync();
        } catch (Exception e) {
            log.error("BacklogClientTest error: ", e);
        } finally {
            worker.shutdownGracefully();
        }
    }
}

建立第三个连接时，服务端全连接队列已满