calling an async method inside a non-async method

Question

I have a class that i'm inheriting from, and i have NO access to the base class. I'm overriding a method of that base class, and this method is not async, but i need it to call an async method i've created. Like so:

public class OverridingClass : BaseClass
{
    public override bool TestMethod()
    {
        var res = engine.DoAsyncFunction().Result;
        //do stuff with res value
    }
}

is it better to use this method, where i take out the 'result' value, or should i add a new, synchronous method to the engine instead and ignore it's async function entirely, like so?

public class OverridingClass : BaseClass
{
    public override bool TestMethod()
    {
        var res = engine.DoFunction();
        //do stuff with res value
    }
}

or is there something else i can do entirely to the overridden function to make it async? If i try to make the overridden method:

public async override Task<bool> TestMethod()...

then i will get a compile error saying that the method doesn't match the base signature.

Personally I'd prefer the latter approach. If it's not "async all the way down" then there's potential for problems. And even getting around that and waiting on the task's result will only end up making it synchronous anyway, so it might as well be simply and explicitly synchronous. — David
– David, Commented Feb 16, 2016 at 19:46
@Phil: I describe a number of different approaches to this problem with pros and cons of each in an MSDN article. — Stephen Cleary
– Stephen Cleary, Commented Feb 17, 2016 at 13:21

Ehsan Sajjad · Accepted Answer · 2016-02-16 19:55:08Z

6

You can wrap it in a Task.Run() like following, if you want it to be called asynchrounously:

public override bool TestMethod()
{
    var task = Task.Run(async () => {

       return await engine.DoAsyncFunction();

    });

   var Result = task.Result; // use returned result from async method here
}

answered Feb 16, 2016 at 19:55

Ehsan Sajjad

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7 Comments

Phil Over a year ago

Honestly this totally slipped my mind. Thanks a bunch!

Servy Over a year ago

This is accomplishing nothing productive; it's doing what the OP was already doing, but wasting a whole bunch of additional resources in the process.

piedar Over a year ago

@Servy If the implementation of engine.DoAsyncFunction() yields to the caller with await and then you call Wait() on it, that's a potential deadlock. Firing up a new task is not pretty, but it won't deadlock.

Servy Over a year ago

@piedar But that's not the situation that he's in, as per the question. And even if it was, there are better ways of dealing with that problem.

Ehsan Sajjad Over a year ago

@Servy you can post your thoughts, and it will make us learn the better approach as well. :)

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