java - 后台线程死亡时其创建的子线程是怎么处理的?

Question

java一个后台线程启动的线程默认也是后台线程，那么当这个后台线程死亡的时候但这个时候用户线程还未死亡，它创建的子线程是怎样处理的？是随着父线程一同死亡还是继续运行，直至run方法结束或者用户线程死亡

Answer 1

private class StopServer extends Thread
{
    public void start()
    {
        this.setDaemon(true);
        super.start() ;
    }

    @Override
    public void run() {
        ServerSocket serverSocket = null ;
        Socket socket = null ;
        try {
            serverSocket = new ServerSocket(8001) ;

            while (true) {
                socket = serverSocket.accept();

                String line = new BufferedReader(new InputStreamReader(socket.getInputStream())).readLine();

                if (line.equals("shutdown"))
                {
                    socket.getOutputStream().write("ok, start stop the server....\r\n".getBytes());
                    socket.getOutputStream().flush() ;

                    System.out.println("start a new thread to stop the server....") ;
                    //新创建的子线程
                    new Thread() {
                        public void start() {
                            setDaemon(true);
                            super.run();
                        }

                        public void run() {
                            System.out.println("start stopServer Thread...");
                            EchoServer2.this.stop();
                        }
                    }.start();
                    break ;
                } else
                {
                    if (!socket.isClosed())
                        socket.close();
                }
            }
        }
        catch (IOException e)
        {
            System.err.println("daemon thread exception: " + e);
            e.printStackTrace();
        }
        finally {
            System.out.println("stop stopServer...");
            if(serverSocket != null && !serverSocket.isClosed())
                 try
                 {
                     serverSocket.close();
                 }
                 catch (IOException e)
                 {
                    e.printStackTrace();
                 }
            if(socket != null && !socket.isClosed())
                 try {
                     socket.close();
                 }catch (IOException e)
                 {
                     e.printStackTrace() ;
                 }
        }
    }
}

This is a background thread of a server I wrote yesterday. This thread is mainly used to monitor port 8001. If a shutdown command is received, the server will be shut down. After shutting down the server, I started a new thread, which is this background thread. When the sub-thread is actually running, the server is not shut down, so I judge that the sub-thread will die along with the entire background thread. It seems that the operating system has to read the book again. Sorry to bother everyone

Answer 2

this.setDaemon(true);

Because it’s Daemon