I am creating a new net core 2.2 API for use with a JavaScript client. Some examples in Microsoft have the controller having all async methods and some examples aren't. Should the methods on my API be async. Will be using IIS if this is a factor. An example method will involve calling another API and returning the result whilst another will be doing a database request using entity Framework.
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3 Answers
It is best practice to use async for your controller methods, especially if your services are doing things like accessing a database. Whether or not your controller methods are async or not doesn't matter to IIS, the .net core runtime will be invoking them. Both will work, but you should always try to use async when possible.
2 Comments
JimmyShoe
Ok thanks I have a colleague who is doing most of the work so far and he is not making any async methods. When I try to add async it like jumping through a rabbit hole because then I have to change a lot of other stuff and some of the methods he's written I'm not sure how I'll make them async they involve generic func. Thanks anyway for the guidance.
Matt H
Yeah that's actually totally normal. Converting a non-async program to be async has been compared to "spreading a virus" msdn.microsoft.com/en-us/magazine/jj991977.aspx The basic issue is the fact that while it is easy to call synchronous code from an async function, it isn't so easy to call an async function from synchronous code. That means that you need to start all your async stuff at the root of your call stack.
First, you need to understand what async does. Simply put, it allows the thread handling the request to be returned to the pool to field other requests, if the thread enters a wait state. This is almost invariably caused by I/O operations, such as querying a database, writing/reading a file, etc. CPU-bound work such as calculations require active use of the thread and therefore cannot be handled asynchronously. As side benefit of async is the ability to "cancel" work. If the client closes the connection prematurely, this will fire a cancellation token which can be used by supported asynchronous methods to cancel work in progress. For example, assuming you passed the cancellation token into a call to something like ToListAsync(), and the client closes the connection, EF will see this an subsequently cancel the query. It's actually a little more complex than that, but you get the idea.
Therefore, you need to simply evaluate whether async is beneficial in a particular scenario. If you're going to be doing I/O and/or want to be able to cancel work in progress, then go async. Otherwise, you can stick with sync, if you like.
That said, while there's a slight performance cost to async, it's usually negligible, and the benefits it provides in terms of scalability are generally worth the trade-off. As such, it's pretty much preferred to just always go async. Additionally, if you're doing anything async, then your action should also be async. For example, everything EF Core does is async. The "sync" methods (ToList rather than ToListAsync) merely block on the async methods. As such, if you're doing a query via EF, use async. The sync methods are only there to support certain limited scenarios where there's no choice but to process sync, and in such cases, you should run in a separate thread (Task.Run) to prevent deadlocks.
UPDATE
I should also mention that things are a little murky with actions and particularly Razor Page handlers. There's an entire request pipeline, of which an action/handler is just a part of. Having a "sync" action does not preclude doing something async in your view, or in some policy handler, view component, etc. The action itself only needs to be async if it itself is doing some sort of asynchronous work.
Razor Page handlers, in particular, will often be sync, because very little processing typically happens in the handler itself; it's all in subordinate processes.
Comments
Async is very important concept to understand and Microsoft focus too much on this. But sometimes we don't realise the importance of this. Every time you are not using Async you are blocking the caller thread.
Why Use Async
Even if your API controller is using single operation (Let's say DB fetch) you should be using Async. The reason is your server has limited number of threads to handle client requests. Let's assume your application can handle 20 requests and if you are not using Async you are blocking the handler thread to do the operation (DB operation) which could be done by other thread (Async). In turn your request queue grows because your main thread is busy dealing other things and not able to look after new requests , at some stage your application will stop responding. If you would use Async the Main thread is free to handle more client requests while other operation run in the background.
More Resources
I would recommend definitely watching very informative official video from Microsoft on Performance issues. https://www.youtube.com/watch?v=_5T4sZHbfoQ
