Cancellation Token signal not being received by the application code

Question

looks like there is a limitation as it can be read here

https://github.com/dotnet/aspnetcore/issues/20229#issuecomment-623289191
https://learn.microsoft.com/en-us/answers/questions/391343/cancellationtoken-in-controller-endpoint-hosted-in

but is there anything that can be done? our api needs to cancel a long running query if the user for example navigates to another page or just abort the request from one of the api client (SPA)

Answer 1

the main issue is that with http protocol, it is a request/response protocol with no cancel support. the server typically will not detect a closed socket until it sends a response. this does not help with a long running query. you can change to websocket or signal/r where you could add support for sending a cancel event on the same connection as the query request, and process cancel.

Answer 2

If your app is hosted by IIS with in-process hosting model the following article might help:

Handling aborted requests in ASP.NET Core

The IIS in-process hosting model means:

Please read the following document:

Differences between in-process and out-of-process hosting

"The following characteristics apply when hosting in-process: Client disconnects are detected. The HttpContext.RequestAborted cancellation token is cancelled when the client disconnects."

Cancellation by client includes (1) click X button on the browser, (2) depress Esc key on keyboard, or (3) abort when XMLHttpRequest is used:

Sample code:

View

@{
    ViewData["Title"] = "Cancel";
    Layout = "~/Views/Shared/_Layout.cshtml";
}
 
<h1>Cancel</h1>
 
<input type="button" id="ajaxRequest" value="Ajax Request" />
<br />
<input type="button" id="abortButton" value="Abort" />
<br />
<div id="result"></div>
 
@section Scripts {
    <script type="text/javascript">
        //<![CDATA[
 
        var xhr;
 
        $(function () {
            $('#ajaxRequest').on('click', function (e) {
                xhr = $.ajax({
                    url: '/home/cancel',
                    method: 'get',
                }).done(function (response) {
                    $("#result").empty;
                    $("#result").text(response);
                }).fail(function (jqXHR, textStatus, errorThrown) {
                    $("#result").empty;
                    $("#result").text('textStatus: ' + textStatus +
                        ', errorThrown: ' + errorThrown);
                });
            });
 
            $('#abortButton').on('click', function (e) {
                if (xhr) {
                    xhr.abort();
                }
            });
        });
        //]]>
    </script>
}

Controller / Action Method

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using MvcCore5App4.Models;
using System.Diagnostics;
using Microsoft.AspNetCore.Authorization;
using System.Threading;
using System.Threading.Tasks;
using System;
using Microsoft.AspNetCore.Identity;
using MvcCore5App4.Data;
 
namespace MvcCore5App4.Controllers
{
    public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;
 
        public HomeController(ILogger<HomeController> logger)
        {
            _logger = logger;
        }
 
        // ・・・中略・・・
 
        public async Task<IActionResult> Cancel(CancellationToken token)
        {
            _logger.LogInformation($"start: {DateTime.Now:ss.fff}");
            await Task.Delay(5000, token);
            _logger.LogInformation($"end: {DateTime.Now:ss.fff}");
            return View();
        }
    }
}

Result of [Start Debugging] the above code shown on the Output of Visual Studio 2022:

See "Start again - Cancelled" in which a client cancelled within 5 sec.