Wrap a synchronous method in Asynchronous call c#

Question

I am looking to wrap synchronous methods into asynchronous code in order to expose those methods as asynchronous - the reason is I do not want to duplicate the code inside the synchrnous methods as I would like it to be DRY and already knowing the functionality of the syunchronous code works - no need to manage separate method as well. However I would like asynchronous methods. I understand the purpose of asynchronous methods at least what they do and why I would want to use them.

Consider the following code:

public int AddValues(int a, int b)
{
  // some really boring or extremely long DRY method code 
  return a + b;
}

Adding an Asynchronous Calling Method like below saves time writing code ; Ensures the functionality of the inner code is the same as Synchronous code. Could I or Should I do this?:

public async task AddValuesAsync(int a, int b)
{
  return await Task.FromResult(AddValues(a,b));
}

And here is my other question and maybe an answer to me; Calling the Asynch method twice will also call the sync method - and since it is behind the async I can get a cross thread exception ? IS that correct.

So what should I do in this situation - how to keep it DRY and keep it simple? I could make the sync method private and force all calls to the method be Async ..

If you say my example code is a bad way to do it, please give a short reason why and a simple example of a good way to do it ..and any suggestions on what is best and how to do this ?

I have looked here Is wrapping a synchronous call in a Task.Run() to make it asynchronous beneficial? but that does not seem to answer very clearly , what I would like to know.

EDIT

For others who are looking - aside from the answer marked here is info that points to the answer with examples and also more importantly why.

Should I expose asynchronous wrappers for synchronous methods?

Which way is best for wrapping synchronous code into an asynchronous method?

Answer 1

I am asking this because I would like to know what the proper way is to make a synchronous methods to have asynchronous versions in a class and as DRY as possible.

The proper way is "don't" .

More to the point, your API's shouldn't lie . If they're doing synchronous work, they should have a synchronous signature.

Answer 2

After comments by Stephen Cleary I found a link on related.. What is the best way for wrapping synchronous code into asynchronous method

While not worded exactly - one comment included an article link that was worded exactly to one point of my question.

The comment there by Yuval Itzchakov included this. "There is great article called Should I expose asynchronous wrappers for synchronous methods? by Stephan Toub which talks about all the reasons not to do what you're trying to do. I suggest reading it."