How to send notifications from grain to client preserving order?

[artemiusgreat]

Assume, there is a grain that every microsecond compares time series from several sources, e.g. files, and sends notification with the next smallest value to its subscribers.

Example

File A: 1, 3, 10
File B: 2, 20

Expected behavior

• Tick 1 picks 1 from File A and sends it to subscribers
• Tick 2 picks 2 from File B and sends it to subscribers
• Tick 3 picks 3
• Tick 4 picks 10
• Tick 5 picks 20

Combining time series and picking next smallest value from two sources works fine within the grain but when notification is sent outside, the order gets lost. Tried to use Orleans streams and IGrainObserver but their async nature and probably back pressure shuffles notifications so client receives them in random order.

Pseudo-code

public class PublisherGrain 
{
    IAsyncStream<int> DataStream;

    public Task Start()
    {
      var interval = new Timer(1);
      var linesA = File.ReadAllLines("FileA").GetEnumerator();
      var linesB = File.ReadAllLines("FileB").GetEnumerator();

      interval.Enabled = true;
      interval.AutoReset = true;
      interval.Elapsed += (sender, e) => 
      {
          if (linesA.Current <= linesB.Current) 
          {
                DataStream.OnNextAsync(linesA.Current);
                linesA.MoveNext();
          }
          else 
          {
                DataStream.OnNextAsync(linesB.Current);
                linesB.MoveNext();
          }
      };
    }
}

Actual implementation

https://github.com/Indemos/Terminal/blob/orleans/Gateways/Simulation/Libs/Grains/ConnectionGrain.cs

Question: If the sequence inside the grain is 1, 2, 3, 10, 20, how to ensure that it stays the same when these numbers are sent one by one outside the grain?

[artemiusgreat]

That appeared to be my fault because I was not awaiting delegate executed on timer and timer was creating multiple threads calling grains in a random order.