ServerSocket backlog

public ServerSocket(int port, int backlog) throws IOException {
    this(port, backlog, null);
}

backlog 最终作用于Linux的参数 tcp_max_syn_backlog

[root@JD1 ~]# cat /proc/sys/net/ipv4/tcp_max_syn_backlog 
256
[root@JD1 ~]# sysctl -a|grep tcp_max_syn_backlog
net.ipv4.tcp_max_syn_backlog = 256

tcp_max_syn_backlog 影响的是 半连接队列和全连接队列的大小

取64和配置值中较大的哪一个。

(somaxconn 推测是 socket max connection 缩写)

[root@JD1 ~]# sysctl -a|grep net.core.somaxconn
net.core.somaxconn = 128
[root@JD1 ~]# cat /proc/sys/net/core/somaxconn
128

代码测试backlog

import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;
public class ServerMain {
    public static void main(String[] args) throws IOException {
        //设置backlog为2， 最多只能有3个客户端（2个在全连接队列中+1个accept的）
        ServerSocket serverSocket = new ServerSocket(8888, 2);
        Socket accept = serverSocket.accept();
        InputStream inputStream = accept.getInputStream();
        inputStream.read();
    }
}

public class ClientMain {
    public static void main(String[] args) throws Exception {
        Socket socket = new Socket();
        socket.connect(new InetSocketAddress("127.0.0.1", 8888));
        InputStream inputStream = socket.getInputStream();
        inputStream.read();
    }
}