The danger of using Task.Result to synchronously retrieve the result of an async operation in C#

Pretty long title ;-) I was aware that a deadlock could occur when using Task<TResult>.Result , but I did not fully understand the reason for it until today

It is generally considered dangerous to use Task<TResult>.Result to synchronously retrieve the result of an asynchronous operation in C# because it can cause a deadlock.

When you call Task<TResult>.Result, the calling thread is blocked until the Task completes. If the Task is not already completed, the calling thread will wait indefinitely until the task completes.

The problem arises when the Task is running on the same thread as the calling thread. If the Task is running on the same thread as the calling thread, and the Task is blocked waiting for a resource that is being used by the calling thread, a deadlock occurs.

Additionally, when you use Task<TResult>.Result, the exception thrown by the task is wrapped in an AggregateException and re-thrown.

Instead of using Task<TResult>.Result, it is recommended to use await keyword which will not block the calling thread and also handle the exception in a more elegant way