Question

I have a thread in my screen recording application that won’t cooperate:

package recorder;

import java.awt.AWTException;
import java.awt.Insets;
import java.io.IOException;

import javax.swing.JFrame;

public class RepeatThread extends Thread {
    volatile boolean stop;
    public volatile Thread recordingThread;
    JFrame frame;
    int count = 0;

    RepeatThread( JFrame myFrame ) {
        stop = false;
        frame = myFrame;
    }

    public void run() {
        while( stop == false ) {
            int loopDelay = 33; // 33 is approx. 1000/30, or 30 fps
            long loopStartTime = System.currentTimeMillis();
            Insets insets = frame.getInsets(); // Get the shape we're recording

            try {
                ScreenRecorder.capture( frame.getX() + insets.left, 
                        frame.getY() + insets.top, frame.getWidth()
                        - ( insets.left + insets.right ), 
                        frame.getHeight() - ( insets.top + insets.bottom ) );
            }
            catch( AWTException e1 ) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
            catch( IOException e1 ) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            } // Add another picture

            long loopEndTime = System.currentTimeMillis();
            int loopTime = (int )( loopEndTime - loopStartTime );
            if( loopTime < loopDelay ) {
                try {
                    sleep( loopDelay - loopTime ); // If we have extra time,
                                                   // sleep
                }
                catch( Exception e ) {
                } // If something interrupts it, I don't give a crap; just
                  // ignore it
            }
        }

    }

    public void endThread() {
        stop = true;
        count = 0;
        ScreenRecorder.reset();
        // Once I get this annoying thread to work, I have to make the pictures
        // into a video here!
    }
}

It’s been bugging me for ages. It periodically takes screenshots to the specified area.

When you start recording, it hides (decativates) the window. On a Mac, when you give an application focus, any hidden windows will activate. In my class WListener (which I have confirmed to work), I have:

    public void windowActivated(WindowEvent e) {
        if(ScreenRecorder.recordingThread != null) {
            ScreenRecorder.recordingThread.endThread();
        }
    }

So what SHOULD happen is, the screenshot-taking thread stops when he clicks on the application. However, I must be brutally screwing something up, because when the thread is running, it won’t even let the window reappear. This is my first thread, so I expected a weird problem like this. Do you know what’s wrong?

EDIT: Okay, I made stop volatile, and here is the place where I make the thread:

package recorder;

import java.awt.AWTException;
import java.awt.Robot;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.io.*;
import javax.imageio.ImageIO;
import javax.swing.JFrame;

public class ScreenRecorder {

    static RepeatThread recordingThread;
    static int count;

    public static void record(JFrame frame) {

        if(recordingThread == null) { //Make a new thread if we don't have one
            recordingThread = new RepeatThread(frame);
            recordingThread.start();
        }
    }

    public static void capture(int x, int y, int width, int height) throws AWTException, IOException {
        // capture the whole screen
        //BufferedImage screencapture = new Robot().createScreenCapture(
        //      new Rectangle(Toolkit.getDefaultToolkit().getScreenSize()) );

        BufferedImage screencapture = new Robot().createScreenCapture(
                new Rectangle( x, y, width, height));

        // Save as JPEG
        File directory = new File("/Users/stuart/Movies/temp");
        if(directory.exists() == false) {
            directory.mkdirs();
        }

        count ++;
        File file = new File("/Users/stuart/Movies/temp/screencapture" + count + ".jpg");
        ImageIO.write(screencapture, "jpg", file);


        // Save as PNG
        // File file = new File("screencapture.png");
        // ImageIO.write(screencapture, "png", file);

    }

    public static void stop() {

    }

    public static void reset() {
        count = 0;
    }
}

Answer 1

Since you are clearly trying to execute a unit of work every X milliseconds, this will be far far easier if you use Java’s Executors:

ScheduledExecutorService service = executors.newSingleThreadScheduledExecutor();
service.scheduleAtFixedRate(new Runnable() {
  public void run() {
    // do one iteration of your work
    ScreenRecorder.capture(...);
    ...
  }
}, 0L, 33L, TimeUnit.MILLISECONDS);

...
service.shutdown(); // to stop

Doing this manually with Thread isn’t nearly as messy as you’re making it (not a dig at you, just saying it’s not that terrible in Java), but the above is still by far the simplest option.