Does async/await creates new thread?

In short: no.

Longer explanation:

  • task that want to do I/O write call to driver write
  • driver operations are performed asynchronously
  • write operations on devices is done without CPU involved
  • finish of writing is done via interrupt
  • interrupt, schedules Deferred Procedure Call
  • DPC schedules Asynchronous Procedure Call
  • APC notifies thread that I/O write is done
  • task that was doing I/O is scheduled with continuation of its method after I/O is done.
  • some threads might need to be borrowed for handling APC and such but no thread is spawn to handle I/O

I recommend reading this post: https://blog.stephencleary.com/2013/11/there-is-no-thread.html. This will explain the topic much better than I can.

Further read:

https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/async/task-asynchronous-programming-model#BKMK_Threads

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