Java threading, shutting down a server thread from a main JFrame GUI

Question

I have a program that starts up a passive server that spawns a connection handler for each connection to the server socket. I would like to find an eloquent way to shutdown the server socket and release the port. Currently, I am not sure how to interrupt the Socket.accept method. I have been using a synchronized method to set a flag in another Thread, but Socket.accpet blocks until a connection is made.

My passive server code

package NetSecConsole;

import java.io.*;
import java.net.*;
import javax.swing.SwingUtilities;


public class PassiveServer implements Runnable
{
    Thread runner;
    int port = 20000;
    MainFrame mainFrame;
    ServerSocket s = null;

    public PassiveServer(MainFrame mf, int hostPort) 
    {
        mainFrame = mf;
        port = hostPort;
        try 
        {
            s = new ServerSocket(hostPort);
        } 
        catch (Exception e) 
        {
            newStatus("Server [Constructor]: Could not open server socket! " + e);
        }
    }

    public void start() 
    {
        if (runner == null) 
        {
            runner = new Thread(this);
            runner.start();
        } 
    }

    @Override
    public void run() 
    {
        try 
        {
            int connCount = 1;
            for (;;) 
            {
                // Sit and wait for a connection
                newStatus("Server [run]: Waiting for connection to port " + Integer.toString(port) + "...");
                Socket incomingConnection =  s.accept();

                // Pass the connection off to a connection handler thread
                newStatus("Server [run]: Got connection on port " + Integer.toString(port));
                final ConnectionHandler conHand = new ConnectionHandler(mainFrame, incomingConnection, connCount); 

                // Start the connection handler, then continue;
                conHand.start();
                connCount++;
            } 
        } 
        catch (IOException e) 
        {
            newStatus("Server [run]: IOException: "  + e);
        }
    }

    public final void newStatus(final String arg)
    {
        Runnable sendMsg = new Runnable() 
        {
            @Override
            public void run() 
            {
                    mainFrame.newStatusLine(arg);
            }
        };
        SwingUtilities.invokeLater(sendMsg);
    }

 }

score 1 · Accepted Answer · answered Feb 26 '14 at 18:28

If you don't want to force an exception by closing the listening socket, (which is perfectly fine IME), then set a volatile boolean 'shutdown' flag that that is checked after every accept() return. Then make the accept() call return by opening a localhost client connection.

score 0 · Answer 2 · edited May 23 '17 at 12:28

0

You can call interrupt on the server/background thread or close
on the server socket. I didn't know about the latter, just Googled it.

Java threading, shutting down a server thread from a main JFrame GUI

3 Answers3