What change does the keyword "await" make?

Question

Hello,

Without "await" keyword FileStream.ReadAsync return "Task<int>".

With "await" keyword FileStream.ReadAsync return "int".

Could you please why this happened? What happens behind the scenes?

Answer 1

This happens because FileStream.ReadAsync is an asynchronous method that returns a Task<int>, representing a pending operation.

1. Without await:
   • ReadAsync immediately returns a Task<int>, which acts as a promise for the future completion of the read operation.
   • The calling code receives this Task<int> and can later use .Result, .Wait(), or await to get the actual integer result when the operation completes.
2. With await:
   • The await keyword unwraps the Task<int> and retrieves the actual integer value when the asynchronous operation completes.
   • The execution of the calling method is paused at await until the Task<int> completes, and then execution resumes with the result of the operation.

Effectively, await does not make the operation synchronous. Instead, it allows the current method to return control to the caller while waiting for the asynchronous operation to finish. The compiler transforms an async method into a state machine, handling continuations when the awaited Task<int> completes.

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hth

Marcin