ThreadStatic in asynchronous ASP.NET Web API

Question

Is there a possibility to use thread static like variables within a single request? The current code uses a thread static variable for logging purposes and now we want to use async controller methods (with async and await pattern) which results in problems because the variable is null when a new thread is opened.

Ehrenberg

Answer 1

await can cause thread jumps, so thread static variables will naturally cause problems.

To work around this, you can either use AsyncLocal<T> (available in .NET 4.6), or (if you must) HttpContext.Current.Items. Of those two, I would definitely recommend AsyncLocal<T> over Items, if it's available on your platform.

Merlynmermaid

Can I ask you the reason why you recommend AsyncLocal over Items? – Helico

I recommend AsyncLocal<T> over HttpContext.Current because HttpContext.Current is considered a poor design and has been removed in ASP.NET Core. – Merlynmermaid