Java Executors Check TCP Connection Alive

Question

I am trying to recognize that hosts are alive or dead with using executor in Java. In my case, I have severeal hosts which kept in a list.

My goal is to create threads with the number of hosts and checking them. When thread connect with the host, host doesnt close the connection, and sending a situation code such as 50 (dead) or 51(alive) continiously.

My problem is threads can only connect on host. For example;

I have two host 192.168.1.1 and 192.168.1.2. Threads should check both of them in the background but I can only connect in 1.1

CONNECTION

List <Host> hosts = LoadBalancer.getHostList();
ExecutorService executor = Executors.newFixedThreadPool(hosts.size());

executor.submit(()->{
    for (Host host:hosts) {
        try {
            connect(host,"message",1);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
});

Also I have syncronized setActive function inside of HOST.java

HOST.JAVA

public class Host {
    private String ip;
    private int port;
    private boolean isActive;

    public Host(String ip, int port) {
        this.ip = ip;
        this.port = port;
        this.isActive = true;
    }

    public synchronized boolean isActive() {
        return isActive;
    }

    public synchronized void setActive(boolean active) {
        isActive = active;
    }

    public String getIp() {
        return ip;
    }

    public void setIp(String ip) {
        this.ip = ip;
    }

    public int getPort() {
        return port;
    }

    public void setPort(int port) {
        this.port = port;
    }
}

Connect function

public static void connect(Host host, String message, int mode) throws Exception {
EventLoopGroup group = new NioEventLoopGroup();
try {
    Bootstrap clientBootstrap = new Bootstrap();

    clientBootstrap.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 500);

    clientBootstrap.group(group);
    clientBootstrap.channel(NioSocketChannel.class);
    clientBootstrap.remoteAddress(new InetSocketAddress(host.getIp(), host.getPort()));

    clientBootstrap.handler(new ChannelInitializer<SocketChannel>() {
        protected void initChannel(SocketChannel socketChannel) {

            //TODO, TIMEOUT BILGISI ILE DOLDUR BURAYI
            //socketChannel.pipeline().addLast(new ReadTimeoutHandler(1));
            //socketChannel.pipeline().addLast("idleStateHandler", new IdleStateHandler(1, 1, 2));

            socketChannel.pipeline().addLast(new ClientHandler(host, message, mode));
        }
    });

    ChannelFuture channelFuture = clientBootstrap.connect().sync();
    channelFuture.channel().closeFuture().sync();
} catch (Exception e) {
    System.err.println("Connection timed out --> " + e);
    host.setActive(false); //connection kurulamadı demektir. Bir sonraki mesaj geldiğinde bu hostun açılıp açılmadığı denenecek.
} finally {
    group.shutdownGracefully().sync();
}

}

Answer 1

This:

executor.submit(()->{
     for (Host host:hosts) {
        try {
            connect(host,"message",1);
            } catch (Exception e) {
            e.printStackTrace();
        }
    }
});

results in all hosts being connected to in a single Thread. You want it to read something like

for (Host host: hosts) {
    executor.submit(()->{
        try {
            connect(host,"message",1);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
});