Async Method Call Non-Async Method Best Practices

Question

For some reason I need to inherit a class to implement an Async method which is the below implementation that it is best practices

1.

protected override Task<TResult> OnExecuteAsync<TResult><TResult>()
{
        return Task.Run<TResult>(() => DoSomething());
}

protected override async Task<TResult> OnExecuteAsync<TResult><TResult>()
{
        return await Task.Run<TResult>(() => DoSomething());
}

I want to know which one is the best implementation?

Thank you

Answer 1

In short, if the base class or interface is expecting a Task result and you have synchronous method and it doesn't need to run in a task, all you need to do is give it a pre-completed task .

The simplest thing to do, would be just leave the async keyword , return the result, and ignore (or pragma out) the warning. You do not need to spin-up a new task via Task.Run (this would be an inefficient way of achieving nothing). In this case the compiler automatically takes care of everything for you (albeit with a warning that you have nothing to await)

protected override async Task<TResult> OnExecuteAsync<TResult>()
{
    return DoSomething();
}

You could also use Task.FromResult to create the pre-completed task . The only caveat is if the consumer is calling await , in which case you should be nice and make sure any exceptions are returned on the resulting Task with Task.FromException . This is analogous to what the compiler generated IAsyncStateMachine implementation ( async and await pattern ) would automatically do.

protected override Task<TResult> OnExecuteAsync<TResult>()
{
    try
    {
        return Task.FromResult(DoSomething());
    }
    catch(exception ex)
    { 
        // place any exception on the returned task
        return Task.FromException<TResult>(ex);
    }
}