how to pause and resume a surfaceView thread

I have a surfaceView setup and running, but when I resume it I get an error that the thread has already been started. What's the proper way to handle when the app goes to the background and then back to the foreground? I've tinkered around and managed to get the app to come back without crashing... but the surfaceView doesn't draw anything anymore. My code:

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
           Log.e("sys","surfaceCreated was called.");
           if(systemState==BACKGROUND){
                  thread.setRunning(true);

           }
           else {
        thread.setRunning(true);
               thread.start();
               Log.e("sys","started thread");
               systemState=READY;
           }



    }
    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
           Log.e("sys","surfaceDestroyed was called.");
           thread.setRunning(false);
           systemState=BACKGROUND;
    }