Async-Await Apologia

This update is long overdue. Previously, I wrote:

But as I learned today, once you do hit the await statement, you are still leaving the stack. And when the await returns, the place you come back to may not be identical to the place you left, depending on how it got there.

…

The fsw.Created handler is called on a different thread than the one you just came from. That’s a pretty well-known fact and is why the FileSystemWatcher has a SynchronizingObject property to help WinForms programmers navigate their way back to the UI thread.

Well, it turns out my analysis was completely wrong. Actually, my application was modifying files in a folder that belonged to an ASP.NET website. Modifying folders inside of ASP.NET can cause application restarts. Though I’ve moved on from this project, I now believe that the behavior I was seeing had to do with the timing of the ASP.NET restart, and had nothing whatsoever to do with crossing thread boundaries. Since async/await uses continuations, any differences I was seeing between where I came from and where I got to had to occur outside of the bounds of my program.

We live, we learn.