SWT UI Thread is not Responding - Printing Error

Question

I have a Print Button in my SWT TitleAreaDialog.

viewPDFButton.addSelectionListener(new SelectionAdapter() {
     public void widgetSelected(SelectionEvent e) {
        try {

           startPdfPrintOperation();
        }
        catch (Exception e1) {
           // TODO Auto-generated catch block
           e1.printStackTrace();
        }
     }
  }); 

I am getting a existing PDF filename and path from a user selection from a table. I am then wantinf to print the pdf file out to a local printer. The user needs to be allowed to select the local printer of choice.

public void startPdfPrintOperation() throws Exception {
  File file = new File(getPDFFileName());
  RandomAccessFile raf;
  raf = new RandomAccessFile(file, "r");
  FileChannel channel = raf.getChannel();
  ByteBuffer buf = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());
  pdfFile = new PDFFile(buf);
  PDFPrintPage pages = new PDFPrintPage(pdfFile);

  // Create Print Job
  pjob = PrinterJob.getPrinterJob();
  pjob.setPrintable(new MyPrintable());
  final HashPrintRequestAttributeSet attset;
  attset = new HashPrintRequestAttributeSet ();
  attset.add (new PageRanges (1, pdfFile.getNumPages ()));
  if (pjob.printDialog (attset)) {
      try {
           pjob.print (attset);
      }
      catch (PrinterException e) {
           e.printStackTrace();
      }
  }             
}
class MyPrintable implements Printable {
  public int print (Graphics g, PageFormat format, int index) throws PrinterException {
     int pagenum = index+1;
        if (pagenum < 1 || pagenum > pdfFile.getNumPages ())
            return NO_SUCH_PAGE;

        Graphics2D g2d = (Graphics2D) g;
        AffineTransform at = g2d.getTransform ();
        PDFPage pdfPage = pdfFile.getPage (pagenum);

        Dimension dim;
        dim = pdfPage.getUnstretchedSize ((int) format.getImageableWidth (),
                                       (int) format.getImageableHeight (),
                                       pdfPage.getBBox ());

        Rectangle bounds = new Rectangle ((int) format.getImageableX (),
                                       (int) format.getImageableY (),
                                       dim.width,
                                       dim.height);

        PDFRenderer rend = new PDFRenderer (pdfPage, (Graphics2D) g, bounds, null, null);

        try
        {
           pdfPage.waitForFinish ();
           rend.run ();
        }
        catch (InterruptedException ie)
        {
           MessageDialog.openError(null, "PDF Error Message", "Needs");
        }
        g2d.setTransform (at);
        g2d.draw (new Rectangle2D.Double (format.getImageableX (),
                                       format.getImageableY (),
                                       format.getImageableWidth (),
                                       format.getImageableHeight ()));
     return PAGE_EXISTS;
  }
}

I am getting the above error from line 315

if (pjob.printDialog (attset)) {

The printer dialog opens the entire application is frozen and goes unresponsive. Then in about 30 secs, I get the above error.

I have tried to use Display.getDefault().asyncExec(new Runnable() ) in multiple spots but that did not help.

Could it be because the base dialog is SWT and the printer dialog is AWT?

Answer 1

Since you didn't define "in multiple spots", I would suggest you refactor the print job in its own class, extends Thread and implement starting the print job in the run method.
I'm not familiar with all classes in above code, you can try simply starting this thread and it will run in parallel with the SWT thread. Try avoiding shared ressources, this may help resolving your deadlock. If you want to have a UI response from this thread, you can wrap e.g. the SWT messagebox ("Printing done!") in a call to Display.getDefault().asyncExec(new Runnable() { ... }.
Furthermore, please test if the printing code without UI code produces the same exception. If it does, the environment may be misconfigured.