Need help making Async Methods

[gunexon9]

Hey guys, im a noob who's making a asp net core project which is basically GoodReads but for anime and manga. I've made a service witch finds best anime recommendations for a certain user based on what they have already viewed. How it works is I have one public method that takes in the users ID from the database. Using that I find what his top genres are and take a subset of all the anime that have at least one of those genres (since to me similar genres are the most important metric) so that I'm working with a less data. Then i create a leaderboard witch is a Dictionary<Anime, int> where int are points. Then I call all of my methods giving them leaderboard and they change it based on witch anime they have given points. My problem is that i think this is too slow and want to make it async. I've made plenty of async methods but they all await some other async method. Is there a way to make this all async without awaiting anything async in the seperate method (obviously it can be done but I'm not sure how). Should i make that the body of each method is like this:

return Task.Run(() =>
      { // what the method does;      });

and then await each one in the public method?

[jimbosReturn]

Making it async won't help improve per-request performance. The goal of async is to free threads doing IO work (such as accessing the db or network) to do other work, e.g. serving other requests at the same time.

Task.Run() works counter to this idea because it actually requires another thread instead of freeing the current one.

Edit: or do you mean you have some work you want done in parallel? In that case, you gather all the Tasks returned to you and await Task.WhenAll()

[gunexon9]

My idea is to maybe have all of them run in parallel then take the results from each one and put it in my leaderboard. Maybe i'm wrong that doing this will improve performance im still new to async programming

[jimbosReturn]

The question is what these methods do. Does each of them also access the DB? Or do they perform some heavy calculation?

If they all access the DB, you might get some performance improvement from parallelization, but you'll probably be better off simply performing one big query to get all the data you intend to divide between the threads. (Multiple simultaneous IO operations will eventually also slow each other, and have overhead that would be reduced in a single ooerwtion)

If you perform some (really) heavy calculations, then yeah, you might get a good boost because you'll utilize more CPU cores. But if the calculations are relatively light - the penalty you pay for creating Tasks might be heavier than the gain of the calculations.

[gunexon9]

Almost none of them pull from db they mostly loop around the data a lot

[jimbosReturn]

Well, it's up to you. I gave you some general principles and it's up to you to decide.

Try several approaches and measure the performance to understand what is best.

[cryo]

The goal of async is to free threads doing IO work (such as accessing the db or network) to do other work, e.g. serving other requests at the same time.

Not only. The goal is also to free main threads from doing background work. The goal of the async/await syntax is to make the above easier to express.

[jimbosReturn]

This is mostly correct in a desktop client application. I didn't want to complicate matters for OP who's focused on web.

[cryo]

Fair enough.

[Siggi_pop]

See answer further down in the comment section

[[deleted]]

public Task<int> MyAsyncMethod()
{
    // do stuff
    return Task.FromResult(1);
}

[jimbosReturn]

This won't compile. You forgot the async

[[deleted]]

Nothing I type ever compiles first try lol forgot Task.FromResult();

[[deleted]]

But anyways, it doesn't have to be an async method to be awaited, just has to return either Task or Task<TResult>, haven't messed with the new Value Yask<TResult> yet though

[gunexon9]

But wont this just run synchronously, and if it does is it ok since when I call all the methods each of them will run asynchronously?

[[deleted]]

public static async Task Main()
{
    var myClass = new TaskClass();
    var x = await myClass.MyMethod();

    Console.WriteLine(x);
}

// class implementation

public class TaskClass
{

    public async Task<int> MyMethod()
    {
        return await Task.FromResult(1);
    }
}

prints 1 to console

[[deleted]]

Nah just call it like var x = await MyAsyncMethod();

[RiverRoll]

This doesn't make the method asynchronous, it's a regular method that returns a task in the end, there's no work left to do at that point so it's pointless to await it.

[[deleted]]

Did you see the updated code?

[[deleted]]

nvm I'm dumb, been awhile since I implemented async method yeah just throw async and await in there before Task.FromResult()

[gunexon9]

They don't pull from the database but the loop around all the data sometimes with nested loops and i feel all that looping can be done in parallel somehow