How Does Code Execution Resume After an `await` Keyword in C#?

Understanding Code Execution After the await Keyword

In a single-threaded application, the await keyword can be confusing. When the code encounters the await keyword within an async method, it yields back to the calling method and relinquishes control to the UI thread. However, understanding how the code after the await is executed can be challenging.

Contrary to the assumption that the main thread remains locked, the code after the await may be executed by a different thread. This behavior is determined by the synchronization context. By default, the awaitable pattern for Task employs the synchronization context current at the time of the await expression.

For instance, if the code is executed within the UI thread, the continuation (the part following the await) will resume execution on the same UI thread. However, in the case of thread-pool threads, the continuation might not necessarily resume on the same thread.

It is crucial to recognize that blocking the UI thread, as with the Wait() call in the provided code sample, can prevent the continuation from executing. In scenarios where tasks may involve work on the current thread and their completion status is unknown, resorting to Wait() or Result is ill-advised.

To avoid relying on the default synchronization context, the Task.ConfigureAwait method can be used. This allows you to specify that the continuation can execute on any thread, making it suitable for library methods that lack thread preference. By leveraging the ConfigureAwait(false) syntax, you indicate a desire to detach the continuation from the current context, facilitating more robust multithreaded code.

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