Estou tentando girar esta imagem usando um thread. O que devo fazer?

     public class Start extends Activity {
        View base;
            Bitmap rotate, base1, rotate1;
        ImageView rotator;
        float angle, pivX, pivY;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.start);
            base = findViewById(R.id.base);
            rotator = (ImageView) findViewById(R.id.rotator);
            pivX = (rotator.getLeft()) / 2;
            pivY = (rotator.getTop()) / 2;
            Thread thread = new Thread() {
        @Override
        public void run() {
            for (angle = 0; angle < 50; angle++) {
                Matrix matrix = new Matrix();
                rotator.setScaleType(ScaleType.MATRIX); // required
                matrix.postRotate((float) angle, pivX, pivY);
                rotator.setImageMatrix(matrix);
                if (angle == 40) {`enter code here`
                    angle = 0;
                    return;
                }
            }
        }
    };

    thread.start();

        }
    }