Question

I am currently trying to make a little game for Android.
I try to measure the time between two actions of the game but the begin time stays 0 when I try to call the currentTimeMillis() method after I called the gameThread.run() method (gameThread is a runnable).
When I place it before the run() call, it delivers the right value.

Class Gameview:

@Override
public void surfaceCreated(SurfaceHolder holder)
{
    // at this point the surface is created and we start the gameloop
    gameThread.setRunning(true);
    gameThread.run();
    begin=System.currentTimeMillis();
}

/**
 * This is the game update method. It iterates through all the objects and
 * calls their update method
 */
public void update()
{
    for (GuiElement element : guiElements)
    {
        element.update();
    }
    count++;
    if (ball.getPosY() >= Statics.DISPLAY_HEIGTH - ball.getRadius())
    {
        Log.d(TAG, "Displayhoehe : " + Statics.DISPLAY_HEIGTH);
        Log.d(TAG, "DisplayfactorHeight : " + Statics.DISPLAY_FACTOR_HEIGHT);
        Log.d(TAG, "speedvalue : " + ball.getSpeedY());
        Log.d(TAG, "ballradius : " + ball.getRadius());
        Log.d(TAG, "am boden mit " + count + " schritten");
        gameThread.setRunning(false);
        end = System.currentTimeMillis();
        Log.d(TAG, "begin, end " + begin + " " + end);
        Log.d(TAG, "time " + (end - begin));
    }
}

Class GameThread (implements runnable)

public void run()
{
    Canvas canvas;
    Log.d(TAG, "Starting game loop");

    long beginTime; // the time when the cycle begun
    long timeDiff; // the time it took for the cycle to execute
    int sleepTime; // ms to sleep (<0 if we're behind)
    int framesSkipped; // number of frames being skipped

    while (running)
    {
        canvas = null;
        // try locking the canvas for exclusive pixel editing in the surface
        try
        {
            canvas = surfaceHolder.lockCanvas();

            synchronized (surfaceHolder)
            {
                beginTime = System.currentTimeMillis();
                framesSkipped = 0; // resetting the frames skipped
                // update game state
                gameView.update();
                // draw state to the screen
                gameView.draw(canvas);
                // calculate how long did the cycle take
                timeDiff = System.currentTimeMillis() - beginTime;
                // calculate sleep time
                sleepTime = (int) (FRAME_PERIOD - timeDiff);

                if (sleepTime > 0)
                {
                    // if sleepTime > 0 we're OK
                    try
                    {
                        // send the thread to sleep for a short period very
                        // (useful for battery saving)
                        Thread.sleep(sleepTime);
                    }
                    catch (InterruptedException e)
                    {
                    }
                }

                while (sleepTime < 0 && framesSkipped < MAX_FRAME_SKIPS)
                {
                    // we need to catch up (skip some draw() calls)
                    this.gameView.update(); // update without rendering
                    sleepTime += FRAME_PERIOD; // add frame period to check
                                                // if we catched up
                    framesSkipped++;
                }
            }
        }
        finally
        {
            // in case of an exception the surface is not left in an inconsistent state
            if (canvas != null)
            {
                surfaceHolder.unlockCanvasAndPost(canvas);
            }
        }
    }
}

EDIT: i tried to Log the return value of currentMillis() at the beginning point and it seems that the method gets called after the run() method has finished. Shouldn’t it run synchronous?

@Override
public void surfaceCreated(SurfaceHolder holder)
{
    // at this point the surface is created and we start the gameloop
    gameThread.setRunning(true);
    gameThread.run();
    begin=System.currentTimeMillis();
    Log.d(TAG, "currentMillis at beginning " + System.currentTimeMillis());
}

Log:

10-21 19:43:17.480: D/GameView(19767): Displayhoehe : 480
10-21 19:43:17.480: D/GameView(19767): DisplayfactorHeight : 1.0
10-21 19:43:17.480: D/GameView(19767): speedvalue : 1.6666666666666667
10-21 19:43:17.480: D/GameView(19767): ballradius : 20
10-21 19:43:17.480: D/GameView(19767): am boden mit 133 schritten
10-21 19:43:17.480: D/GameView(19767): begin, end 0 1350841397483
10-21 19:43:17.480: D/GameView(19767): time 1350841397483
10-21 19:43:17.480: D/GameView(19767): currentMillis at beginning 1350841397484

Solution: I started the Runnable incorrectly. That’s the right way to start the Runnable:

gameThread.setRunning(true);
Thread t = new Thread(gameThread);
t.start();
begin=System.currentTimeMillis();

Answer 1

That’s because you’re calling the run() method directly instead of calling the Thread’s start() method.