private void DoAll()
        {
            Observable.ForkJoin(
                Observable.Start(() => DoA()),
                Observable.Start(() => DoB()),
                Observable.Start(() => DoC())
            ).Finally(() => Debug.WriteLine("Done!")).First();
        }

        private void DoA() {
            Thread.Sleep(1000);
            Debug.WriteLine("A");
        }

        private void DoB() {
            Thread.Sleep(500);
            Debug.WriteLine("B");
        }

        private void DoC() {
            Thread.Sleep(750);
            Debug.WriteLine("C");
        }