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Unable to Cancel Socket.ReceiveAsync with CancellationTokenSource in Unity (Unity version: 2022.3.26

Discussion in 'Scripting' started by bbsuuo, May 10, 2024.

  1. bbsuuo


    Jul 21, 2016
    I've been experimenting with asynchronous programming in Unity for handling network communication recently, but I've encountered a tricky issue. I'm using the asynchronous method Socket.ReceiveAsync to receive data and I want to be able to cancel this operation using a CancellationTokenSource. However, no matter what I try, I can't seem to cancel the ReceiveAsync operation successfully.

    Here's a simplified version of my code:

    Code (CSharp):
    1. private async void Start()
    2. {
    3.     IPAddress ipAddress = IPAddress.Parse(ip);
    4.     IPEndPoint remoteEndPoint = new IPEndPoint(ipAddress, port);
    6.     var socket = new Socket(remoteEndPoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
    7.     Memory<byte> test = new Memory<byte>(new byte[2048]);
    8.     var tokenSource = new CancellationTokenSource();
    10.     InputSystem.onAnyButtonPress.Call(x =>
    11.     {
    12.         if (x is KeyControl keyboardCtl && keyboardCtl.keyCode == Key.E)
    13.         {
    14.             tokenSource.Cancel();
    15.             Debug.Log("token cancel");
    16.         }
    17.     });
    19.     Debug.Log("start receive");
    20.     try
    21.     {
    22.         int count = await socket.ReceiveAsync(test, SocketFlags.None, tokenSource.Token);
    23.         Debug.Log($"end receive : {count}");
    24.     }
    25.     catch (OperationCanceledException)
    26.     {
    27.         Debug.Log("ReceiveAsync cancelled");
    28.     }
    29. }
    In this code snippet, I expect the ReceiveAsync operation to be cancelled when a certain button (e.g., the E key on the keyboard) is pressed. However, no matter what I try, I can't seem to trigger the cancellation operation.

    I suspect the issue may lie with the Socket.ReceiveAsync method, as it doesn't seem to respond to the CancellationTokenSource passed to it. I expect the ReceiveAsync method to throw an OperationCanceledException when the cancellation token is triggered, but instead, it continues to block the thread
  2. bbsuuo


    Jul 21, 2016
    I discovered that I can indeed cancel the ReceiveAsync operation using the following approach:
    Code (CSharp):
    1. int count = await socket.ReceiveAsync(test, SocketFlags.None, tokenSource.Token)
    2.                     .AsUniTask<int>()
    3.                     .AttachExternalCancellation(tokenSource.Token);
    However, upon further consideration, I believe this approach may introduce some implicit issues. Using AttachExternalCancellation seems to work, but it feels like a workaround rather than a clean solution.
    Last edited: May 10, 2024
  3. Alex-Thibodeau


    Unity Technologies

    Apr 18, 2013
    Have you tried your code with a regular dotnet framework application? In general if it works there but not in Unity it is a bug that we should investigate.