Execute Futures until a parameter becomes true

Question

I launch a request to a server with a future "requestServer". I would like to poll a system for a specific value (passed from false to true, when request is done) and return when finished.

Code could be like that, but "while" synchronous and "checkOperation" is asynchronous?

return requestServer().then((operation) {
  var done = false;
  while (done)
    return checkOperation(operation).then((result) {
      done = (result == true);
    });
    sleep(10);
  }
});

Any ideas ?

Answer 1

I guess this is not exactly what you want but as far as I know there is no way to block execution so you have to use callbacks.

void main(List<String> args) {

  // polling
  new Timer.periodic(new Duration(microseconds: 100), (t) {
    if(isDone) {
      t.cancel();
      someCallback();
    }
  });

  // set isDone to true sometimes in the future
  new Future.delayed(new Duration(seconds: 10), () => isDone = true);
}

bool isDone = false;

void someCallback() {
  print('isDone: $isDone');
  // continue processing
}

You can of course pass the callback as parameter instead of hardcode it, because functions are first class members in Dart.