HttpContext is null after await in in ASP.NET 4.8

Question

I am trying to write async code in asp.net 4.8 but and the problem is that HttpContext is null after returning from await. This means that the async code works correctly which is good, but the HttpContext is needed by the original code. From the comments in below answer by Darin Dimitrov it shows that HttpContext is having this issue since 4.6.1. Why is HttpContext.Current null after await?

var domains = HttpContext.Current.Cache.Get("domains") as Dictionary<String, Domains>;


            if (domains == null)
            {
                var x = await TrackingMethods.GetTableForCacheAsync().ConfigureAwait(false);
                domains = x.domains;
        }

/// HttpContext.Current is null here

This should never happen in .NET > 4.6.1 unless it's WCF which is fundamentally broken in its handling of asyncs and will possibly never be fixed. Could you provide a [minimal, reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of your issue? — Wiktor Zychla, May 05 '20 at 12:25
You haven't provided a [MCVE]. Show how this code is called, all the way back to the user input. But simplify it - remove any steps that aren't absolutely necessary to reproduce the issue. — mason, May 05 '20 at 12:52
By using `ConfigureAwait(false)` you possibly disable restoration of the context after the async call completes. My advice would be to drop it there. — Wiktor Zychla, May 05 '20 at 13:20
@WiktorZychla If I don't use ConfigureAwait(false) the code will not run. — realPro, May 05 '20 at 13:38

score 5 · Accepted Answer · answered May 05 '20 at 14:10

ConfigureAwait(false) means "don't resume on the captured context". By specifying ConfigureAwait(false), your code is telling the runtime that it doesn't need the ASP.NET request context. But your code does need the ASP.NET request context, since it depends on HttpContext.Current. So using ConfigureAwait(false) here is wrong.

If I don't use ConfigureAwait(false) the code will not run.

This is likely because your code is blocking further up the call stack, causing a deadlock. The ideal solution is to remove the blocking - i.e., use async all the way. Using async all the way is preferable to blocking with ConfigureAwait(false).

However, there are a handful of scenarios where this isn't possible. For example, ASP.NET 4.8 doesn't have proper asynchronous support for MVC action filters or child actions. If you're doing something like this, then you have a couple of options:

Make it synchronous all the way instead of async all the way.
Keep the blocking-over-async-with-ConfigureAwait(false) antipattern but copy out everything your code needs from HttpContext.Current first and pass that data as explicit parameters so the code no longer has a dependency on the ASP.NET request context.

HttpContext is null after await in in ASP.NET 4.8

1 Answers1