WaitingInMainSignalCatcherLoop Error in Android Application

Question

I have an android application that refreshes the screen every 33 milliseconds, displaying a rectangle at a pair of coordinates. Here is the code for the custom view:

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.os.Handler;
import android.util.AttributeSet;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class OurView extends SurfaceView implements SurfaceHolder.Callback {

    private SurfaceHolder holder;
    private Handler handler = new Handler();
    private Bitmap testimg;
    private int xCoord = 500;
    private int yCoord = 500;
    boolean running = false;
    int xPos;
    int yPos;

    public OurView(Context context) {
        super(context);
        init();
    }

    public OurView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public OurView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init();
    }

    private void init() {
        holder = getHolder();
        holder.addCallback(this);
        testimg = BitmapFactory.decodeResource(getResources(),R.drawable.testimg);
    }

    void moveImage(int xChange, int yChange) {
        this.xCoord = this.xCoord + xChange;
        this.yCoord = this.yCoord + yChange;
    }

    void doDraw(Canvas canvas) {
        xPos = this.xCoord + (testimg.getWidth()/2);
        yPos = this.yCoord + (testimg.getHeight()/2);
        canvas.drawARGB(255, 55, 255, 255);
        canvas.drawBitmap(testimg, xPos, yPos, null);
    }

    @Override
    public void surfaceCreated(final SurfaceHolder holder) {
        running = true;
        while(running){

            handler.postDelayed(new Runnable() {
                public void run() {

                    Canvas canvas = getHolder().lockCanvas();

                    if(canvas != null){
                        synchronized (getHolder()) {
                            doDraw(canvas);
                        }
                        holder.unlockCanvasAndPost(canvas);
                    }

                }
            }, 33);

        }
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {}


    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {}

}

I used to have a separate thread that handled the drawing, but that caused problems with variables having different values between the threads. When I run this program, I get this error:

04-20 10:54:35.577    1925-1931/com.thatoneprogrammerkid.gameminimum I/art﹕ Thread[2,tid=1931,WaitingInMainSignalCatcherLoop,Thread*=0xae668400,peer=0x12c00080,"Signal Catcher"]: reacting to signal 3
04-20 10:54:35.577    1925-1931/com.thatoneprogrammerkid.gameminimum I/art﹕ [ 04-20 10:54:35.627  1925: 1931 W/art      ]

Answer 1

That's not an error, that's the VM letting you know that your app was sent a signal 3 (SIGQUIT). The most likely cause is that the app was unresponsive and the system is doing ANR processing -- SIGQUIT causes the VM to dump a stack trace.

Do you see ANR complaints in logcat?

Looking at your code, you're looping in surfaceCreated(), which runs on the UI thread. That means your app won't be able to process messages from the system (or draw on Views, or receive user input). You can either use a separate thread as you did before (but with better synchronization), or just remove the loop from surfaceCreated() and then have your draw handler re-issue postDelayed() every time it executes.