EDT and SwingWorker Thread - Publish and Process

Question

EDT and SwingWorker concepts are kind of confusing. I have gone over the method definitions a couple of times now and wrote some sample programs as well.

Below is the current scenario I have,

1) I have starting a GUI window from the main method using the following,

public static void main(String[] args) {
    // TODO Auto-generated method stub
    SwingUtilities.invokeLater(new Runnable() {

        @Override
        public void run() {
            // TODO Auto-generated method stub
            final StartMainWindow StartMainWindow = new StartMainWindow();
            StartMainWindow.initActionsAndComponenets();
        }
    });
}

2) StartMainWindow is an SWT window and the main piece of code is a "RUN" button. On clicking the run button, a certain set of DB operations need to be performed which are placed in the doInBackground() method of the DBOperations class. This class extends SwingWorker.

DBOperations dbOperate = new DBOperations(currentFileToBeProcessed, currentFileListObject, unstreamOutputs, saveCanonicals, clientId, systemDestin, text, true);
dbOperate.execute();

3) I have removed all DBOperations code and put in some sample code so that its easier to understand. In DBOperations, below is the code,

public class DBOperations extends SwingWorker<Integer, String>{
    @Override
    protected Integer doInBackground() throws Exception {
        Thread.sleep(2000);
        publish("String");
        System.out.println("Entered");
        Thread.sleep(5000);
        publish("String");
        System.out.println("Entered..");
        Thread.sleep(2000);
        publish("String");
        System.out.println("Entered....");
        Thread.sleep(2000);
        publish("String");
        System.out.println("Entered......");
        publish("String");
        publish("String");
        publish("String");
        publish("String");
    }

    @Override
    protected void process(List<String> chunks) {
        // TODO Auto-generated method stub
        System.out.println("Entered text update....");
        for (String string : chunks) {
            System.out.println(string);
        }
    }
}

When I run my code, it starts a window and just prints "Entered".

After I close the window, it print whatever I have sent through using publish. So the actual sequence of events is below,

Entered
Entered..
Entered....
Entered......
**CLOSES WINDOW
String
String
String
String
String
String
String
String

On using publish, it should print to stdout immediately. Any explanations why is this happening and suggestions for fix?

SWT has it's own thread model, which, while conceptually the same, has it's own set of APIs with which to work with — MadProgrammer, Jul 19 '18 at 09:59

score 0 · Answer 1 · answered Jul 27 '18 at 21:40

I solved this without using any SwingWorker concepts. As mentioned by MadProgrammer, SWT has its own thread model. What I ended up doing is the following,

1) Implement runnable interface on my DBOperations class. And then add a method called updateTextArea which does an asyncExec (method provided in SWT) to asynchronously append strings to the text area and also output to the stdout.

public class DBOperations implements Runnable{
    @Override
    public void run() {
      try {
        Thread.sleep(2000);
        updateTextArea("String");
        System.out.println("Entered");
        Thread.sleep(5000);
        updateTextArea("String");
        System.out.println("Entered..");
        Thread.sleep(2000);
        updateTextArea("String");
        System.out.println("Entered....");
        Thread.sleep(2000);
        updateTextArea("String");
        System.out.println("Entered......");
        /****DB operations performed here****/
        /****DB operations performed here****/
        /****DB operations performed here****/
        /****DB operations performed here****/
        updateTextArea("String");
        updateTextArea("String");
        updateTextArea("String");
        updateTextArea("String");
      } catch (InterruptedException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
      }
    }

    public void updateTextArea(String updateText) {
        Display.getDefault().asyncExec(new Runnable() {

            @Override
            public void run() {
                // TODO Auto-generated method stub
                text.append(updateText + "\n");
                System.out.println(updateText);
            }
        });
    }
}

asyncExec() makes sure that the text area and stdout are updated while the DBOperations are performed and this solves the problem.

EDT and SwingWorker Thread - Publish and Process

1 Answers1