Async/Await easy cancellation in c#

#csharp #dotnet #webdev #productivity

Using async/await is so fun but in the same time there are plenty of situations which the awaiting part can stuck forever, specially when there is any involvement of programming over the network. Other than that there are situations which the app must not wait more than a timeout for a response.

Therefore, the ability to set a timeout for a asynchronous operation is a must, by using CancellationToken one can achieve this and this post will demonstrate an easier method of using these CancellationTokens by applying an extension method for the Task object type.

Implementation

NuGet Installation

.Net CLI
dotnet add package easyAsyncCancel

Package Manager
Install-Package easyAsyncCancel

Usage

Let's say there is a Task which it can take unknown amount of time to finish

private async Task Task_NetworkBound()
{
    await new HttpClient().GetStringAsync("https://dotnetfoundation.org");
}

In order for the task to get canceled after 1 seconds

await Task_NetworkBound().CancelAfter(1000);
OR
await Task_NetworkBound().CancelAfter(1000,"Custom OperationCanceledException message");

Test it

[TestFixture]
public class TaskCancellationTest
{
    private async Task Task_NetworkBound()
    {
        await new HttpClient().GetStringAsync("https://dotnetfoundation.org");
    }

    private async Task<string> Task_NetworkBound_T()
    {
        return await new HttpClient().GetStringAsync("https://dotnetfoundation.org");
    }

    [Test]
    public void Test_CancelWithMilliseconds()
    {
        Assert.ThrowsAsync<OperationCanceledException>(
            async () => { await Task_NetworkBound().CancelAfter(1000); });

        Assert.ThrowsAsync<OperationCanceledException>(
            async () => { await Task_NetworkBound_T().CancelAfter(1000); });
    }


    [Test]
    public void Test_CancelWithToken()
    {
        Assert.ThrowsAsync<OperationCanceledException>(async () =>
        {
            var cts = new CancellationTokenSource();
            cts.CancelAfter(1000);
            await Task_NetworkBound().CancelAfter(cts.Token);
        });


        Assert.ThrowsAsync<OperationCanceledException>(async () =>
        {
            var cts = new CancellationTokenSource();
            cts.CancelAfter(1000);
            await Task_NetworkBound_T().CancelAfter(cts.Token);
        });
    }
}

Full source code here

Happy coding :)

Top comments (6)

John Gonyo • Apr 14 '19

A word of caution. This only cancels the await, it does not cancel the running task. Any additional code inside the awaited task will continue to execute.

Instead, you should add and pass a cancellation token to the awaited method so that the task itself is also cancelled.

That is, Task.Delay (and almost all other awaitable methods) accept(s) a cancellation token to cancel the delay before the time out expires.

Ali Alp • Apr 14 '19

thanks bro :) Very important point you have mentioned
I have updated the post to be more clear about the IO bound operations.
good examples will be web requests or waiting on TcpClient stream and ...