Quit while loop with external event

Question

I have a loop doing like this :

while (!exit){

read/write on file

}

And I have a button on my frame which his action performed change the value of "exit", the exit condition of the loop.

My problem, I am stuck in my loop, I can't click on my button because the program is all the time in the loop I think.

Someone told me to see with the Thread with the "polling" but I don't understand how i can integrate in my loop ?

EDIT :

How I call the Thread :

case "Mode Measure": {
    JOptionPane.showMessageDialog(null,"Radar in Measure Mode : ON ");
    System.out.println("READ Mode : ON ");
    JB_MeasurMode.setVisible(true);

    JB_MeasurMode.addActionListener(new ActionListener(){
    public void actionPerformed(ActionEvent arg0) {
        sortie = true;
        }      
    });

    SwingUtilities.invokeLater(new Runnable() {
    public void run() {
        CommPortIdentifier portId = null;
        try {
            portId = CommPortIdentifier.getPortIdentifier(ChoixPortCom);
            serialPort = (SerialPort) portId.open("Main Frame", 5000);
            System.out.println("serialPort ouvert");
            outputStream = serialPort.getOutputStream();
            inputStream = serialPort.getInputStream();
            serialPort.setRTS(false);
            serialPort.setInputBufferSize(8192);
            serialPort.setOutputBufferSize(8192);
            serialPort.setSerialPortParams(115400,SerialPort.DATABITS_8,SerialPort.STOPBITS_1,SerialPort.PARITY_NONE);
            serialPort.setFlowControlMode(SerialPort.FLOWCONTROL_XONXOFF_IN |SerialPort.FLOWCONTROL_XONXOFF_OUT);
            catch (NoSuchPortException e1) {
                // TODO Auto-generated catch block
                    e1.printStackTrace();
            } catch (PortInUseException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (UnsupportedCommOperationException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
    System.out.println("Dans le while");
    while(sortie == false) {
            int i = 0;
        int availableBytes = 0;
        try {
            int read = 0;
            availableBytes = inputStream.available();
            if (availableBytes > 0) {
                String tradV3 = null;
                System.out.println("je suis dans le availableBytes > 0 du while -- read = "+read);
                read = read + availableBytes;
                int raw = inputStream.read(readBuffer, read-availableBytes, availableBytes);
                traduction = new String(readBuffer, read-availableBytes, raw);          
                    System.out.println("2=>" + traduction);
                tradV3 = tradV3 + traduction;   // bytes -> String
            }

            if (read == 19){

                System.out.println("une donnee de 19 char lue -- read = "+read);
                System.out.println("Non-Traité :"+Arrays.toString(readBuffer));
                int[] tab_int2 = new int[19];
                tab_int2 = Fonction.Get_Msg_19(readBuffer);
                String Msg_affiche2 = Arrays.toString(tab_int2);
                System.out.println("Traité : "+Msg_affiche2);
                Measure t = new Measure();
                t.GetMeasure(tab_int2);
                Tab_Measure[i] = t;
                i++;
            }
            } catch (IOException e) {
                System.out.println("Problem avec le try !!!");
            }
        }
        System.out.println("Sortie du while");
                }
    });
break;
}

He was right. You need a second thread that will be able to change the value of `exit`. — user1021726, Apr 03 '14 at 08:27
Ok, but where do I put it and how do I use it. Do you got a good tutorial ? — D3fman, Apr 03 '14 at 08:28
@D3fman `While` doesn't exist in Java. It's `while`. Come on, just google it! — Christian Tapia, Apr 03 '14 at 08:28
@Christian : its because of the uppercase that you are telling me this ? ps : I edited. And if I ask here maybe I searched before coming here :D — D3fman, Apr 03 '14 at 08:31

Jakub H · Accepted Answer · 2014-04-03T08:35:10.027

1

Because read/write operation could be a really long task you should execute it in a different thread to not block the main UI thread.

SwingWorker class can be helpful, because it's created to handle such long-time tasks. Have a look here: http://docs.oracle.com/javase/tutorial/uiswing/concurrency/worker.html

If you use SwingWorker than instead of your flag you should call cancel method of SwingWorker when someone will press your button.

edited Apr 03 '14 at 08:35

answered Apr 03 '14 at 08:28

Jakub H

2,130
9
16

1

Because there is no possibility to finish the loop without changing the flag it really doesn't matter, but I was thinking more generally how such task should be handled. He has to create another thread anyway, but it's a good idea to move I/O operations to a SwingWorker class. – Jakub H Apr 03 '14 at 08:42

score 1 · Answer 2 · answered Apr 03 '14 at 08:33

1

You are probably running the loop in GUI thread, which is also responsible for handling the button click. While it is stuck in while loop, it's not available for changing value of variable 'exit'. Do the reading/writing in separate thread, there is a convenience class for it in Swing:

SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
// IO stuff
            }
        });

answered Apr 03 '14 at 08:33

Kristjan Veskimäe

992
5
16

Can you give a quick check to my code, just tell me if I am calling it the right way if no how should I call it. With this code, the button still doesn't respond. – D3fman Apr 03 '14 at 09:12
Sorry SwingUtilities' method invokeLater actually also causes code to be executed in GUI thread, actually you need to use SwingWorker that creates a new thread and doesn't execute code in GUI thread http://stackoverflow.com/questions/11255925/use-of-swingworker-to-do-complex-tasks-in-background – Kristjan Veskimäe Apr 03 '14 at 10:20
BTW you can check if you are in GUI thread with method http://docs.oracle.com/javase/7/docs/api/javax/swing/SwingUtilities.html#isEventDispatchThread() – Kristjan Veskimäe Apr 03 '14 at 10:25

Quit while loop with external event

2 Answers2