Question

my code :

    private  AtomicBoolean fetched1 = new AtomicBoolean(false);

    private int  rowCount;

    public int getRowCount() {
            data.getRealm().exec(new Runnable(){
                @Override
                public  void run() {
                    rowCount = data.size();
                    fetched1.set(true);
                }
            });
            while(!fetched1.get()){
            }
            fetched1.set(false);
            return rowCount;
        }

it seems work for me right now, but I am not familiar with threading(it always confuse me), should I do it like above code any way?

Answer 1

should I do it like above code any way?

This looks to be a spin loop which will use unnecessary CPU. It is better to use wait and notify to signal that the data has been fetched. Something like:

   private final Object lock = new Object();
   private volatile Integer rowCount = null;
   ...

      public void run() {
         rowCount = data.size();
         synchronized (lock) {
            lock.notify();
         }
      }

  synchronized (lock) {
     // we loop here in case of race conditions or spurious interrupts
     while (rowCount == null) {
        lock.wait();
     }
  }
  ...

I don’t think you need a fetched AtomicBoolean at all. You should make the rowCount be volatile and then you can test its value. The while loop is a good pattern to follow because of producer/consumer race conditions and spurious interrupts.