excutor class ()sakib vai !!!

// init on a clas
    private static volatile CartDatabase INSTANCE;
    private static final int NUMBER_OF_THREADS = 2;
    public static final ExecutorService databaseWriteExecutor =
            Executors.newFixedThreadPool(NUMBER_OF_THREADS);

    public static CartDatabase getDatabase(final Context context) {
        if (INSTANCE == null) {
            synchronized (CartDatabase.class) {
                if (INSTANCE == null) {
                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
                            CartDatabase.class, DB_NAME)
                            .fallbackToDestructiveMigration()
                            .allowMainThreadQueries()
                            .build();
                }
            }
        }
        return INSTANCE;
    }

}


//calling
CartDatabase.databaseWriteExecutor.execute(new Runnable() {
                        @Override
                        public void run() {
                            CartDatabase.getDatabase(getApplicationContext()).dao().nukeCartTable();
                            runOnUiThread(new Runnable() {
                                @Override
                                public void run() {
                                    dialog.dismiss();
                                    Intent p = new Intent(getApplicationContext(), OrderDone.class);
                                    startActivity(p);
                                    finish();
                                }
                            });
                        }

                    });