How Async/Await Really Works in C#

Several weeks ago, the .NET Blog featured a post What is .NET, and why should you choose it?. It provided a high-level overview of the platform, summarizing various components and design decisions, and promising more in-depth posts on the covered areas. This post is the first such follow-up, deep-diving into the history leading to, the design decisions behind, and implementation details of async/await in C# and .NET.

The support for async/await has been around now for over a decade. In that time, it’s transformed how scalable code is written for .NET, and it’s both viable and extremely common to utilize the functionality without understanding exactly what’s going on under the covers. You start with a synchronous method like the following (this method is “synchronous” because a caller will not be able to do anything else until this whole operation completes and control is returned back to the caller):

Then you sprinkle a few keywords, change a few method names, and you end up with the following asynchronous method instead (this method is “asynchronous” because control is expected to be returned back to its caller very quickly and possibly before the work associated with the whole operation has completed):

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