An asynchronous callback holder that is attached to an IAsyncContextTOut, TExt. Invoking [!:Invoke] will eventually lead to OnAsyncInput being called. Dispatch an asynchronous notification. This method is thread-safe and may be invoked from external execution contexts.

public delegate void AsyncCallback<in T>(
	T element
)

type AsyncCallback = 
    delegate of 
        element : 'T -> unit