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ConfigureAwaitOptions in .NET 8

If you have ever used async/await in C#, you probably also used the ConfigureAwait method. In this post I want you to show how this method got some enhancements in .NET 8. But before I do that let's first recap the original behavior (just in case you forgot).

Understanding ConfigureAwait in .NET

The ConfigureAwait method in .NET plays a crucial role when awaiting tasks. It allows developers to configure how asynchronous operations resume after completion. Specifically, it determines whether the continuation should happen on the original captured context or on an available thread pool thread.

Original ConfigureAwait Behavior

When you await a task (such as Task, Task<T>, ValueTask, or ValueTask<T>), the default behavior is to capture a “context.” This context is either SynchronizationContext.Current or TaskScheduler.Current (falling back to the thread pool context if none is provided). The async method then resumes execution in that context when the task completes.

You could originally use the ConfigureAwait in two ways:

  • ConfigureAwait(true): This explicitly continues on the captured context.
  • ConfigureAwait(false): Useful when you don’t want to resume on the captured context. It allows the async method to resume on any available thread pool thread.

ConfigureAwait(false) was typically used in library code because a library author could not make any assumptions on how the code would be consumed but you should generally avoid it in application code..

With improvements like dropping SynchronizationContext in ASP.NET Core, there has been a move away from ConfigureAwait(false).

Still there are some places where this method can be useful and with .NET 8,a new type ConfigureAwaitOptions is added that provides all the different ways to configure awaitables:

  • None: No specific configuration Equivalent to ConfigureAwait(false)..
  • ContinueOnCapturedContext: Equivalent to ConfigureAwait(true).
  • SuppressThrowing: Suppresses exceptions during await.
  • ForceYielding: Forces the await to always behave asynchronously

Developers can now fine-tune their await behavior using these options. Whether you’re building libraries or applications, understanding and leveraging ConfigureAwaitOptions will empower you to write more efficient and context-aware asynchronous code.

For more details, I would recommend to check out Stephen Cleary’s insightful blog post on ConfigureAwait in .NET 8

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