coldacid on Why do asynchronous calls in ASP.NET MVC need to be declared as such if the method they reside in is declared with the 'async' keyword already? - http://www.reddit.com/r...
Mar 31, 2015
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"The TL;DR is that `async` decorates a method in the *language*, but doesn't emit any attributes or descriptive IL that would let ASP.NET MVC decide for itself whether or not your controller action is asynchronous."
- Chris Charabaruk