Shutdown netty programmatically

Question

I'm using netty 4.0.24.Final.

I need to start/stop netty server programmatically.
On starting the server, the thread gets blocked at

f.channel().closeFuture().sync()

Please help with some hints how to do it correctly. Below is the EchoServer that is called by the Main class. Thanks.

package nettytests;

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;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

public class EchoServer {

    private final int PORT = 8007;
    private EventLoopGroup bossGroup;
    private EventLoopGroup workerGroup;

    public void start() throws Exception {
        // Configure the server.
        bossGroup = new NioEventLoopGroup(1);
        workerGroup = new NioEventLoopGroup(1);
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .option(ChannelOption.SO_BACKLOG, 100)
             .handler(new LoggingHandler(LogLevel.INFO))
             .childHandler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ch.pipeline().addLast(new EchoServerHandler());
                 }
             });

            // Start the server.
            ChannelFuture f = b.bind(PORT).sync();

            // Wait until the server socket is closed. Thread gets blocked.
            f.channel().closeFuture().sync();
        } finally {
            // Shut down all event loops to terminate all threads.
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public void stop(){
        bossGroup.shutdownGracefully();
        workerGroup.shutdownGracefully();
    }
}


package nettytests;

public class Main {
    public static void main(String[] args) throws Exception {
        EchoServer server = new EchoServer();
        // start server
        server.start();

        // not called, because the thread is blocked above
        server.stop();
    }
}

UPDATE: I changed the EchoServer class in the following way. The idea is to start the server in a new thread and preserve the links to the EventLoopGroups. Is this the right way?

package nettytests;

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;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

/**
 * Echoes back any received data from a client.
 */
public class EchoServer {

    private final int PORT = 8007;
    private EventLoopGroup bossGroup;
    private EventLoopGroup workerGroup;

    public void start() throws Exception {
        new Thread(() -> {
            // Configure the server.
            bossGroup = new NioEventLoopGroup(1);
            workerGroup = new NioEventLoopGroup(1);
            Thread.currentThread().setName("ServerThread");
            try {
                ServerBootstrap b = new ServerBootstrap();
                b.group(bossGroup, workerGroup)
                        .channel(NioServerSocketChannel.class)
                        .option(ChannelOption.SO_BACKLOG, 100)
                        .handler(new LoggingHandler(LogLevel.INFO))
                        .childHandler(new ChannelInitializer<SocketChannel>() {
                            @Override
                            public void initChannel(SocketChannel ch) throws Exception {
                                ch.pipeline().addLast(new EchoServerHandler());
                            }
                        });

                // Start the server.
                ChannelFuture f = b.bind(PORT).sync();

                // Wait until the server socket is closed.
                f.channel().closeFuture().sync();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                // Shut down all event loops to terminate all threads.
                bossGroup.shutdownGracefully();
                workerGroup.shutdownGracefully();
            }
        }).start();
    }

    public void stop() throws InterruptedException {
        workerGroup.shutdownGracefully();
        bossGroup.shutdownGracefully();
    }
}

Answer 1

One way is to make something like:

// once having an event in your handler (EchoServerHandler)
// Close the current channel
ctx.channel().close();
// Then close the parent channel (the one attached to the bind)
ctx.channel().parent().close();

Doing this way will end up the following:

// Wait until the server socket is closed. Thread gets blocked.
f.channel().closeFuture().sync();

No need for an extra thread on main part. Now the question is: what kind of event? It's up to you... Might be a message in the echo handler as "shutdown" that will be taken as an order of shutdown and not only "quit" which will turn as closing only the client channel. Might be something else...

If you do not handle the shutdown from a child channel (so through your handler) but through another process (for instance looking for a stop file existing), then you need an extra thread that will wait for this event and then directly make a channel.close() where channel will be the parent one (from f.channel()) for instance...

Many other solutions exist.