So. `IO.effect(IO.dispatchers().io() + MDCContext())` doesn’t work, but `IO.effect(MDCContext())` ...

# arrow

[Satyam Agarwal]

So. IO.effect(IO.dispatchers().io() + MDCContext()) doesn’t work, but IO.effect(MDCContext()) works.
I am trying to put MDC correlation id on all the logs that gets produced on IO.dispatchers().io()

[simon.vergauwen]

Are the `id`s not getting added or it’s not running on the correct pool?

[Satyam Agarwal]

id s are not getting added with IO.dispatchers().io() + MDCContext() Logs do get printed on right pool. for example, whatever log message from example above gets printed on io-arrow-kt-worker-0

[Satyam Agarwal]

but with IO.effect(MDCContext()) id s get attach too

[simon.vergauwen]

That’s super weird. If you click through on + you should be able to debug how the get added to each-other.

It sounds like something is going wrong their and IO.dispatchers().io() + MDCContext() is resulting in the wrong combination of CorotuineContext

[simon.vergauwen]

Which is strange since IO.dispatchers().io() just uses the default impl from the std

[Satyam Agarwal]

I am on it

[Satyam Agarwal]

So I gets added, along arrow io worker. I am trying to look further what happens. Just putting it here if you find anything

[simon.vergauwen]

Hmm that looks indeed correct. I’m not sure what’s going on there in that case 😕

[simon.vergauwen]

Where and how are you launching the IO? I think it’s related to the KotlinX machinery, and that ThreadContextElement is not working correctly outside of KotlinX since it’s a libray.

[simon.vergauwen]

You should be able to have it working with the KotlinX integration module that was published yesterday. Available under

implementation "io.arrow-kt:arrow-fx-kotlinx-coroutines:0.10.5-SNAPSHOT"

[simon.vergauwen]

This exposes suspendCancelable which uses the Continuation used by KotlinX under the hood instead of the Continuation from Kotlin’s standard library.

[simon.vergauwen]

It also offers unsafeRunScoped to run `IO`’s within structured concurrency with CoroutineScope

[simon.vergauwen]

Using either of those methods should allow the KotlinX machinery to work again.

[Satyam Agarwal]

I actually skimmed through the PR which made this lib yesterday. Eagerly waiting for 0.10.5 to be released 😄

[Satyam Agarwal]

by the way here is how I am trying it in ktor framework :

fun Route.sendOk() {
        get("/status") {
            IO
                .invoke(IO.dispatchers().io()) {
                    <http://log.info|log.info>("whatever")
                }
                .flatMap { IO.effect(IO.dispatchers().io()) { this.call.respond("ok") } }
                .suspended()
        }
    }

[Satyam Agarwal]

this is just an example, so I would not use io pool to log one line

[simon.vergauwen]

👍

[simon.vergauwen]

Can you try using the snapshot version of that library and use suspendCancelable instead?

[simon.vergauwen]

That way it’ll start on the KotlinX custom Continuation interface instead of the one from the standard library.

[simon.vergauwen]

I think that’s necessary for their stuff to work. Which is what ThreadContextElement<MDCContextMap> does, since ThreadContextElement is not in the standard library put specific to Kotlinx sadly.

[Satyam Agarwal]

okay.
instead of suspended() ?
Yes I can give it a try. I will post in some time how it went. And thank you again @simon.vergauwen ❤️

[simon.vergauwen]

Yes, exactly. You’re very welcome 🙂

[Satyam Agarwal]

It works yay!! Thank you so much 🙂

[Satyam Agarwal]

But I can’t use snapshots in production. So I’ll have to wait, unfortunately

[simon.vergauwen]

Awesome, thanks for the update!

We’re very actively working on the release. Should be released this month.