Question

I am trying on RX for the first time and I have a couple questions.

1) Is there a better way to accomplish the Async of my collection?

2) I need to block on the thread until all Async Tasks are complete, how do I do that?

class Program
{

    internal class MyClass
    {
        private readonly List<int> _myData = new List<int>() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

        private readonly Random random = new Random();

        public int DoSomething(int j)
        {
            int i = random.Next(j * 1000) - (j * 200);
            i = i < 0 ? 1000 : i;
            Thread.Sleep(i);
            Console.WriteLine(j);
            return j;
        }

        public IObservable<int> DoSomethingAsync(int j)
        {
            return Observable.CreateWithDisposable<int>(
                o => Observable.ToAsync<int, int>(DoSomething)(j).Subscribe(o)
                );
        }

        public void CreateTasks()
        {
            _myData.ToObservable(Scheduler.NewThread).Subscribe(
            onNext: (i) => DoSomethingAsync(i).Subscribe(),
            onCompleted: () => Console.WriteLine("Completed")
                );
        }
    }

    static void Main(string[] args)
    {
        MyClass test = new MyClass();

        test.CreateTasks();

        Console.ReadKey(); 
    } 
}

(Note: I know I could have used Observable.Range for my list of Int but my list is not of type Int in the real program).

Answer 1

I’d probably try

public void CreateTasks()                
{                       
    _myData.ToObservable(Scheduler.NewThread)
        .SelectMany(i => Observable.Start(() => DoSomething(i)))
        .Subscribe(j => Console.WriteLine("j is {0}", j), 
                  () => Console.WriteLine("Completed"));       
} 

So firstly I’ve changed the DoSomethingAsync so that it uses Observable.Start. Observable.Start will run the DoSomething method asyncronously and return the value through IObservable.OnNext when the method completes.

Then the CreateTasks method runs over each item in the collection as it did before, but feeds each value into a SelectMany which continues with a call the DoSomethingAsync method. The result is, that you’ll then recieve an OnNext for each completed call to DoSomethingAsync and an OnComplete when they are all complete.