Why this indeterminate jProgressBar don't work in this simple code?

Question

I want use an indeterminate jProgressBar on a JForm but I don't know why in my code don't work. The jProgressBar must be in the indeterminate status until the thread receives a latch.await() signal. This is the simple part of code when I push a button:

private void jButton5ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    // TODO add your handling code here:
    jProgressBar1.setVisible(true);
    jProgressBar1.setIndeterminate(true);

    inizio.sbuff.setLength(0);
    inizio.latch.reset();
    OutputStream outStream = inizio.p.getOutputStream();
    PrintWriter pWriter = new PrintWriter(outStream);
    pWriter.println("17");
    pWriter.flush();

    try {
        inizio.latch.await();
    } catch (InterruptedException ex) {
        Logger.getLogger(menu.class.getName()).log(Level.SEVERE, null, ex);
    }

    new risultati().setVisible(true);



     jProgressBar1.setIndeterminate(false);

    //jProgressBar1.setVisible(false);
    //this.setEnabled(false);
}

The jProgressBar does not activate before the arrival of the signal. If I remove the jProgressBar1.setIndeterminate(false); the jProgressBar activates after the signal of countdown arrived and not before. This is the part of the code when I do the countdown:

p = Runtime.getRuntime().exec("testpad -i -c"+can+" -n"+pad+" "+pathFile);
            final InputStream inStream = p.getInputStream();

            Thread uiThread = new Thread("UIHandler") {
                @Override
                public void run() {
                  InputStreamReader reader = new InputStreamReader(inStream);
                  Scanner scan = new Scanner(reader);
                  prec=null;

                  while (scan.hasNextLine()) {

                    prec=scan.nextLine();
                    System.out.println(prec);
                    sbuff.append(prec);
                    sbuff.append('\n');

                    if(err.equals(prec)){
                        //flag[0] = 1;
                        bandiera = 1;
                        //latch.countDown();
                    }

                    if(prec.contains("Quit")){
                        //System.out.println("STO DENTRO "+prec);
                        latch.countDown();
                    }

                  }

               }
            };
            uiThread.start();

Can I activate the jProgressBar first of the arrival of countdown signal? Thanks.

Answer 1

Is your latch variable a CountDownLatch or a CyclicBarrier? If so, or if it is a similar construct, then calling await() is a blocking call, and since you're calling this on the Swing event thread, something that should never be done, you're locking the thread rendering the GUI frozen. The solution is simple -- don't do this sort of stuff on the Swing event thread but rather within a background thread such as by calling it within the doInBackground method of a SwingWorker. Please check out Lesson: Concurrency in Swing for more on this.