uncatchable error with JViewport.setView

Question

I CANNOT provide an SSCCE as I can't make error repeatable outside of my large App.

But here is a snippet and the output:

            if (vp != null) {
                try {
                    starterModule.writePaneln("Sigma.show() 4.1 vp: "+vp);
                    starterModule.writePaneln("Sigma.show() 4.1 P: "+P);
                    starterModule.writePaneln("Sigma.show() 4.1 scrollPane: "+scrollPane);

                    vp.setView(P);
                    starterModule.writePaneln("Sigma.show() 4.2");

                } catch (Exception e) {
                    PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("C:\\javaout2.txt", true)));
                    out.println("ERROR SIGMA e:");
                    out.flush();
                    out.close();
                }
            }

Output is:

    Sigma.show() 4.1 vp: javax.swing.JViewport[,0,0,902x800,layout=javax.swing.ViewportLayout,alignmentX=0.0,alignmentY=0.0,border=,flags=25165832,maximumSize=,minimumSize=,preferredSize=,isViewSizeSet=true,lastPaintPosition=,scrollUnderway=false]
    Sigma.show() 4.1 P: javax.swing.JPanel[,0,0,0x0,invalid,layout=javax.swing.BoxLayout,alignmentX=0.0,alignmentY=0.0,border=com.devexperts.dxpro.shared.swing.styles.support.border.DefaultBorderSetter$PaddingBorder@4719dad8,flags=9,maximumSize=,minimumSize=,preferredSize=]
    Sigma.show() 4.1 scrollPane: javax.swing.JScrollPane[,0,30,917x800,layout=javax.swing.ScrollPaneLayout$UIResource,alignmentX=0.0,alignmentY=0.0,border=com.devexperts.dxpro.shared.swing.styles.support.border.DefaultBorderSetter$PaddingBorder@14716d46,flags=328,maximumSize=,minimumSize=,preferredSize=,columnHeader=,horizontalScrollBar=javax.swing.JScrollPane$ScrollBar[,0,0,0x0,hidden,layout=com.devexperts.dxpro.shared.swing.styles.laf.impl.basic.StyledScrollBarUI,alignmentX=0.0,alignmentY=0.0,border=,flags=4194632,maximumSize=,minimumSize=,preferredSize=,blockIncrement=10,orientation=HORIZONTAL,unitIncrement=1],horizontalScrollBarPolicy=HORIZONTAL_SCROLLBAR_AS_NEEDED,lowerLeft=,lowerRight=,rowHeader=,upperLeft=,upperRight=,verticalScrollBar=javax.swing.JScrollPane$ScrollBar[,902,0,15x800,layout=com.devexperts.dxpro.shared.swing.styles.laf.impl.basic.StyledScrollBarUI,alignmentX=0.0,alignmentY=0.0,border=,flags=4194632,maximumSize=,minimumSize=,preferredSize=,blockIncrement=10,orientation=VERTICAL,unitIncrement=1],verticalScrollBarPolicy=VERTICAL_SCROLLBAR_ALWAYS,viewport=javax.swing.JViewport[,0,0,902x800,layout=javax.swing.ViewportLayout,alignmentX=0.0,alignmentY=0.0,border=,flags=25165832,maximumSize=,minimumSize=,preferredSize=,isViewSizeSet=true,lastPaintPosition=,scrollUnderway=false],viewportBorder=]

Then the program appears to freeze on vp.setView(P); as the next writePaneln is not called.

HOWEVER, the error is not trapped either....

Here writePaneln ( for completeness)

public static void writePaneln(String txt){
    if(DEBUG){
    try {
        synchronized (textPane) {
            //textPane.getDocument().insertString(textPane.getDocument().getLength(), txt + "\n", null);

            PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("C:\\javaout.txt", true)));
            out.println(txt);
            out.flush();
            out.close();
        }
    } catch (IOException e) {
        // TODO Auto-generated catch block
        JOptionPane.showMessageDialog(null,"writePaneln ERROR: "+e);
    }   
    }
}

EDIT 1

I have changed to using invokeLater in my java.util.timer:

        class RemindTask extends TimerTask {

               @Override
               public void run() {
                   SwingUtilities.invokeLater(
                           new Runnable(){

                               @Override
                                public void run() {
                                   handleGO();
                                };
                           }
                   );
               }
       }

Answer 1

Use one of the approaches cited here to find EDT violations.

Should I put CheckThreadViolationRepaintManager in Factory?

As shown here, you can replace the RepaintManager with an instance of CheckThreadViolationRepaintManager to catch violations.

RepaintManager.setCurrentManager(new CheckThreadViolationRepaintManager());

Answer 2

If the calling thread neither returns nor throws an exception, it is obviously stuck somewhere. You can try two things:

1. Attach a debugger and see what happened starting from the setView call (as suggested by @DeltaLima)
2. Run the thing and create a thread dump (instructions differ based on OS, unfortunately you didn't mention yours). The thread dump will show you exactly where your program is stuck and why it is stuck, i.e. what other thread may hold a lock that yours wants.

I'd recommend to start with 2., as it is cheap and quick.

Good luck.