UseAsyncDataReceivedEvents - Firing DataReceived Out of Order?

[ykarpeev]

Hello, I am trying to figure out if I am doing something wrong, or if when UseAsyncDataReceivedEvents is enabled which it is by default - data comes in out of order.

I've created a test case here:

   internal class Program
    {
        static void Main(string[] args)
        {
            SimpleTcpServer server = new SimpleTcpServer("127.0.0.1:9000");
            server.Start();

            SimpleTcpClient client = new SimpleTcpClient("127.0.0.1:9000");
            client.Events.DataReceived += Events_DataReceived;
            client.Settings.UseAsyncDataReceivedEvents = true;
            client.Connect();

            while (!(Console.KeyAvailable && Console.ReadKey(true).Key == ConsoleKey.Escape))
            {
                var key = Console.ReadKey(false);

                Console.WriteLine(key.KeyChar);
                if (key.Key == ConsoleKey.S)
                {
                    Console.WriteLine("Sending");
                    foreach (var c in server.GetClients())
                    {
                        for (var i = 0; i < 100; i++)
                        {
                            server.Send(c, $"-------- {i}\r");
                        }
                    }
                }
            }
        }

        private static void Events_DataReceived(object? sender, DataReceivedEventArgs e)
        {
            Debug.WriteLine($"Received: {Encoding.UTF8.GetString(e.Data.Array, 0, e.Data.Count)}");
        }
    }

This is the kind of output I see:

`Received: -------- 0

Received: -------- 19

Received: -------- 25

Received: -------- 30

Received: -------- 17
-------- 18

Received: -------- 28
-------- 29

Received: -------- 43

Received: -------- 50
-------- 51

Received: -------- 44
-------- 45
-------- 46
-------- 47
-------- 48

Received: -------- 49

Received: -------- 31
-------- 32

Received: -------- 67
-------- 68

Received: -------- 52

Received: -------- 61
-------- 62
-------- 63
-------- 64
-------- 65
-------- 66

Received: -------- 60

Received: -------- 33

Received: -------- 75
-------- 76
-------- 77

Received: -------- 69

Received: -------- 70
-------- 71
-------- 72
-------- 73
-------- 74

Received: -------- 78

Received: -------- 86
-------- 87
-------- 88

Received: -------- 79
-------- 80
-------- 81
-------- 82
-------- 83
-------- 84

Received: -------- 85

Received: -------- 90
-------- 91
-------- 92
-------- 93

Received: -------- 95
-------- 96
-------- 97
-------- 98
-------- 99

Received: -------- 94

Received: -------- 34

Received: -------- 35
-------- 36
-------- 37

Received: -------- 89

Received: -------- 53
-------- 54
-------- 55
-------- 56
-------- 57
-------- 58
-------- 59

Received: -------- 27

Received: -------- 26

Received: -------- 38
-------- 39
-------- 40

Received: -------- 22

Received: -------- 23

Received: -------- 24

Received: -------- 42

Received: -------- 20

Received: -------- 21

Received: -------- 10
-------- 11
-------- 12
-------- 13
-------- 14
-------- 15
-------- 16

Received: -------- 1
-------- 2
-------- 3
-------- 4
-------- 5
-------- 6
-------- 7
-------- 8
-------- 9

Received: -------- 41`

UseAsyncDataReceivedEvents set to false will make it work as expected.

My initial guess is that the issue could be in this code and that Task.Run() doesn't run in order.

                                if (_settings.UseAsyncDataReceivedEvents)
                                {
                                    _ = Task.Run(action, token);
                                }

Am I missing something? Handling datareceived incorrectly? Should this be await Task.Run(action, token) instead? Anyone seeing the same?

[jchristn]

Hi @ykarpeev yes, this can absolutely happen if you use async events. There isn't a good way as far as I know to ensure in-order async processing. It's really up to the CLR to schedule the work at that point.

[ykarpeev]

Thank you. I'll set it to false by default on my end.