Unable to perform work on the background thread

So, I'm following this tutorial to implement a Service in my app. I implemented the Service succesfully. The service is activated and the notification is shown normally. Everything is fine except that I was not able to do work on the background thread. Please see below.

My goal is to set a mock location.

This is my onStartCommand for my Service:

@Override
public int onStartCommand(Intent intent, int flags, int startId) {



    Intent notificationIntent = new Intent(this, MainActivity.class);
    PendingIntent pendingIntent = PendingIntent.getActivity(this,
            0, notificationIntent, 0);

    Notification notification = new NotificationCompat.Builder(this, CHANNEL_ID)
            .setContentTitle("Example Service")
            .setContentText("hi")
            .setSmallIcon(R.drawable.icon)
            .setContentIntent(pendingIntent)
            .build();


    startForeground(1, notification);

    //do work on a background thread
    new Thread(new Runnable() {
        @Override
        public void run() {

            startMockLocation(); // doesn't actually mock device's location!
        }
    }).start();

    return START_NOT_STICKY;
}

However, when I do this, it works fine but it's not efficient:

@Override
public int onStartCommand(Intent intent, int flags, int startId) {



    Intent notificationIntent = new Intent(this, MainActivity.class);
    PendingIntent pendingIntent = PendingIntent.getActivity(this,
            0, notificationIntent, 0);

    Notification notification = new NotificationCompat.Builder(this, CHANNEL_ID)
            .setContentTitle("Example Service")
            .setContentText("hi")
            .setSmallIcon(R.drawable.icon)
            .setContentIntent(pendingIntent)
            .build();


    startForeground(1, notification);

// works great
timer.schedule(new TimerTask() {
    @Override
    public void run() {

        startMockLocation();
        //other stuff
    }
}, 0, 1000);

    return START_NOT_STICKY;
}

Mock location method:

public void startMockLocation(){ // this code is fine, nothing to fix here, something is wrong with the thread though :(

    FusedLocationProviderClient locationProvider =  new FusedLocationProviderClient(getApplicationContext());
    locationProvider.setMockMode(true);

    Location loc = new Location("gps");

    Location mockLocation = new Location("gps"); // a string
    mockLocation.setLatitude(48.8566);
    mockLocation.setLongitude(2.3522);
    mockLocation.setAltitude(loc.getAltitude());
    mockLocation.setTime(System.currentTimeMillis());

    mockLocation.setAccuracy(1f);
    mockLocation.setElapsedRealtimeNanos(SystemClock.elapsedRealtimeNanos());
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        mockLocation.setBearingAccuracyDegrees(0.1f);
        mockLocation.setVerticalAccuracyMeters(0.1f);
        mockLocation.setSpeedAccuracyMetersPerSecond(0.01f);
    }
    locationProvider.setMockLocation(mockLocation);

}