Stop a loop in code from UI

General
1

Unable to stop a while loop in code from UI. Such as on button click - but the listener is fired only after complete loop execution.

Thanks in advance.

2

Hi dinesh,

you may want to break your loop.
http://docs.oracle.com/javase/tutorial/java/nutsandbolts/branch.html

3

Atleast read the question before reply ’
I want to break the loop from UI on button click’.

4

Hello dinesh,

at least you should write a real question and read how Java and threads work.

5

Hi, it does not really make sense to do what you want to do. Vaadin uses a lock to synchronize concurrent access to the user session, so if you simply loop eternally in a thread handling a request, the session also stays locked eternally and nothing else can access it.

If you really need a busy loop somewhere in your application logic, it should be in a separate thread that only acquires the session lock when it really needs it, and communicates with your event handlers using proper synchronization primitives.

6

Don’t really your use case, made below small code, hopefully it answers your question somehow. The basic idea is that your while loop should be in a separate thread.

    private volatile static boolean stop = false;

    @Override
    protected void init(VaadinRequest request) {
        final VerticalLayout layout = new VerticalLayout();
        layout.setMargin(true);
        setContent(layout);

        Button button = new Button("Click Me");
        button.addClickListener(new Button.ClickListener() {
            public void buttonClick(ClickEvent event) {
                stop=true;
                Notification.show("stop");
            }
        });
        layout.addComponent(button);
        
        new Thread(){
            public void run() {
                int count = 0;
                while(true){
                    if(stop)
                        return;
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(""+count++);
                }
            };
        }.start();
    }
7

Thanks Johannes and Haijian.