How can we stop an asynchronous long -running operation task?

We can use CancellationToken and pass it in the async long-running method and in the async method, we check the token for a cancel request and if one is requested we cancel the task.

e.g

async Task DoWorkAsync(CancellationToken token)
{
    for (int i = 0; i < 100; i++)
    {
        token.ThrowIfCancellationRequested(); // stop if cancelled
        await Task.Delay(1000);              // simulate work
    }
}

in the calling code:
--------------------

var cts = new CancellationTokenSource();
var task = DoWorkAsync(cts.token);

// Cancel after 5 seconds
cts.CancelAfter(5000);

try
{
   await task;
}
catch(OperationCanceledException)
{
   Console.WriteLine("Task was canceled!");
}

Example: Reading HTTP response with cancellation

using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        var cts = new CancellationTokenSource();
        cts.CancelAfter(3000); // cancel after 3 seconds

        using var httpClient = new HttpClient();
        try
        {
            using var response = await httpClient.GetAsync(
                "https://example.com/largefile",
                HttpCompletionOption.ResponseHeadersRead,
                cts.Token); // pass the cancellation token

            using var stream = await response.Content.ReadAsStreamAsync(cts.Token);

            byte[] buffer = new byte[8192];
            int bytesRead;

            while ((bytesRead = await stream.ReadAsync(buffer, 0, buffer.Length, cts.Token)) > 0)
            {
                // Process bytes (simulate work)
                Console.WriteLine($"Read {bytesRead} bytes...");
            }

            Console.WriteLine("Download complete!");
        }
        catch (OperationCanceledException)
        {
            Console.WriteLine("Download was canceled!");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex.Message}");
        }
    }
}