How to Recursively Schedule Async Tasks in ASP.NET Core?

Implementing Recurring Asynchronous Tasks in ASP.NET Core

ASP.NET Core applications often require the periodic execution of background tasks without impacting user requests. This article explores a solution for creating a recurring asynchronous task, similar to JavaScript's setInterval().

The Challenge:

The goal is to regularly execute an asynchronous method (e.g., sending collected data to a remote service) without blocking user interactions. The difficulty lies in scheduling this asynchronous task appropriately.

A Simple Solution (with caveats):

.NET's Timer class, using its Elapsed event, provides a straightforward approach. However, the required signature (void MethodName(object e, ElapsedEventArgs args)) is incompatible with an async method signature (async Task MethodName(object e, ElapsedEventArgs args)).

Workaround using Task.Delay():

This incompatibility can be overcome using a while loop and Task.Delay(), which internally utilizes a timer:

<code class="language-csharp">public async Task PeriodicFooAsync(TimeSpan interval, CancellationToken cancellationToken)
{
    while (!cancellationToken.IsCancellationRequested)
    {
        await FooAsync();
        await Task.Delay(interval, cancellationToken);
    }
}</code>

This effectively executes FooAsync() at the specified interval. The critical addition is cancellationToken, enabling graceful task termination, especially important during application shutdown.

Important Considerations for ASP.NET Core:

While functional in general .NET applications, this approach requires caution within ASP.NET Core. The "fire-and-forget" nature of this method can lead to issues. For robust background task management in ASP.NET Core, consider established solutions like Hangfire or the techniques detailed in Stephen Cleary's "Fire and Forget on ASP.NET" and Scott Hanselman's "How to run Background Tasks in ASP.NET." These resources provide more sophisticated and reliable methods for handling long-running or asynchronous background processes within the ASP.NET Core environment.

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