Hi,

I'm working on sketch with a Background thread, which updates a progress bar in the main thread. But I'm fairy new to all this java stuff.

The goal is to perform heavy calculations, based on where the user clicked, but without the sketch locking up. Also I want to display a small progress bar to indicate how far the calculation is proceeding.

I tried to use SwingWorker because from the description, this seemed to do exactly what I needed, but I couldn't get it to work with processing, so I gave up.

In the end I managed to create the following sketch with FutureTask, but I have still some questions:

• 1. to update the progress bar I call getProgress() from the main thread. But since the background thread is also manipulating completedPercentage in setProgress(int, int) I'm not sure if this is (thread)safe. Is there a better or safer way to get progress feedback from a background thread like this?
• 2. This code is not yet doing any heavy calculation. It's mainly sleeping and reversing a string. When it would be doing much more intensive calculations (e.g. calculate prime numbers based on the mouse position) do I then need to keep a Thread.currentThread().sleep() statement in the code, to allow the main thread to do its drawing? And how long should it sleep for then?

The code:

background_process_sketch.pde
Code:

import java.util.concurrent.*;

boolean backgroundTaskRunning = false;
int progressBarValue = 100; // from 0 to 100
ExecutorService executor;
BackgroundTask task;

void setup() {
  size (300, 300);
  smooth();
  noStroke();
}

void draw() {
  // try every loop
  if (backgroundTaskRunning) {
    if (!task.isDone()) {
      //println("Task not yet completed.");
    } else {
      println("Here is the result..." + task.getResult());
      executor.shutdown();
      backgroundTaskRunning = false;
    }
  }
  
  background(150);
  displayProgressBar();
  fill (255);
  ellipse (mouseX, mouseY, 20, 20);
}

void mousePressed() {
  if (!backgroundTaskRunning) {
    println("Start a background process");
    executor = Executors.newSingleThreadExecutor();
    task = new BackgroundTask("foobar");
    executor.execute(task.future);
    backgroundTaskRunning = true;
  }
}

void displayProgressBar() {
  if (backgroundTaskRunning) {
    int progressX = 195;
    int progressY = 290;
    int progressHeight = 8;
    fill (100);
    progressBarValue = task.getProgress();
    rect(progressX, progressY, progressBarValue, progressHeight);
  }
}

void displayAnswer(int answer) {
  println("We have an answer: ");
  print(answer);
}
 

BackgroundTask.java
Code:

//BackgroundTask.java

import java.util.concurrent.*;

public class BackgroundTask
{
  SlowStringReverser reverser = new SlowStringReverser();
  FutureTask<String> future;
  int completedPercentage;
  
  BackgroundTask(String argument) {
    completedPercentage = 0;
    try {
      createTask(argument);
    } catch (InterruptedException ie) {
      System.out.println(ie);
    }
  }

  void createTask(final String target) throws InterruptedException {
    future = new FutureTask<String> (
      new Callable<String>()
      {
        public String call()
        {
          return reverser.reverseString(target);
        }
      });
  }
  
  boolean isDone() {
    return future.isDone();
  }
  
  String getResult() {
    try {
      try {
        return future.get();
      } catch (ExecutionException ex) {}
    } catch (InterruptedException ie) {
      System.out.println(ie);
    }
    return "";
  }

  int getProgress() {
    return completedPercentage;    
  }
  
  void setProgress(int currentValue, int maxValue) {
    completedPercentage = (currentValue * 100) / maxValue;
  }
  
  
  //-----------------------------

  class SlowStringReverser {
    StringBuffer orgString;
    StringBuffer reversedString;

    SlowStringReverser(String orgStr) {
      orgString = new StringBuffer(orgStr);
    }

    SlowStringReverser() {
    }

    public String reverseString(String str) {
      orgString = new StringBuffer(str);
      reversedString = new StringBuffer();
      for (int i = (orgString.length() - 1); i >= 0; i--) {
        reversedString.append(orgString.charAt(i));
        //setProgressBarValue((orgString.length() - i), orgString.length());
        setProgress((orgString.length() - i), orgString.length());
        System.out.println("Reversing one character per second." + reversedString);
        try {
          Thread.currentThread().sleep(1000);
        } catch (InterruptedException ie) {}
      }
      return reversedString.toString();
    }
  }
}
 

Thanks!
Dirk

Ah, Thanks a bunch!
I'm now skipping the sleep() and suddenly it's a challenge to write background threading code that will actually take so long to witness the progress bar filling up.
 

Now I ran into another problem, which is somewhat related.
How can I access sketch classes (defined in a .pde file) from this .java file?

Say I have a TestClass.pde
Code:

class TestClass {
  int foo;
  
  TestClass (int myfoo) {
    foo = myfoo;
  }
  [...]
}
 

and now I would like to use this class in the BackgroundTask.java of above.

If I mention the TestClass in the class BackgroundTask it complains:
Cannot find a class or type named "TestClass".
And import TestClass tells me:
The package "TestClass" does not exist. [...]

How can I use import this .pde (sketch) class in the .java code?

thanks,
Dirk

Thanks,
that works to access the class.

It was a bit more tricky to also create new instance of that TestClass. But I also managed to do that by supplying an instance of my sketch class. In the .pde I create the background task like this:
Code:

// name_of_my_sketch.pde
task = new BackgroundTask(this, calculateFromValue);
 

And then in the .java file
Code:

// BackgroundTask.java
  BackgroundTask(name_of_my_sketch mainSketch, int arg) {
    tc = mainSketch.new TestClass(42);
 

Thanks a lot.