Is using `AtomicRef` and `Deferred` a good approac...

# coroutines

[Marc Knaup]

Is using AtomicRef and Deferred a good approach to ensure that concurrent calls to update() never cause more than one updateAsync() execution in parallel?

For example let’s say updateAsync() execution takes 10 seconds and there are 4 calls to update() with 2 seconds in between. updateAsync() would only be called once and they all share the same result, right?

[Dominaezzz]

The code you have might call updateAsync() multiple times. (Unless it's just an illustration then nvm).
The function pass to updateAndGet should be pure.

[Dominaezzz]

Instead of AtomicRef , I think you should use a Semaphore .

[Marc Knaup]

What do you mean by pure?

[Dominaezzz]

Without side effect. As the lambda could be executed multiple times.

[Marc Knaup]

Oh, really. Damn.
It launches a coroutine 😅

[Dominaezzz]

Haha yeah. You could have 8 `updateAsync()`s running concurrently without it's result being consumed.

[Marc Knaup]

I guess I have to fall back to a Mutex then?
Mutex basically seems to be a Semaphore with permits = 1, doesn’t it?

[Dominaezzz]

It is but Semaphore was quite recently optimised and currently performs better than Mutex . (I checked this a month ago, not sure if Mutex has been updated since).

[Marc Knaup]

Interesting. Thanks for the heads ups 🙂

[Casey Brooks]

What’s the intention here? Is it that if updateAsync is running that it won’t try to update again? Or that new updates cancel/replace the previous one? There are a handful of things you can do with Channels or Flows that can solve both those cases pretty elegantly

[Marc Knaup]

New update requests should join the current pending update.
I’ve already rewritten it as a Flow 🙂

[Dominaezzz]

If you've got time or can be bothered. Can you share the rewrite? I can't imagine how this can be rewritten with a Flow .

[Marc Knaup]

It’s merged with other functionality by now, esp. caching. So the behavior has changed slightly which makes it work with Flows 🙂

[Marc Knaup]

It now comes close to something like flow { while(true) { emit(update()); delay(refreshInterval) } }.stateIn(…)

[Dominaezzz]

Ah, stateIn off course, that makes a lot of sense.