how can i retrieve MDC from a CoroutineContext in ...

# kotlin-logging

[Nikky]

how can i retrieve MDC from a CoroutineContext in a exception handler ?
the code looks like so currently

private val exceptionHandler = CoroutineExceptionHandler { context, e -> GlobalScope.launch(MDCContext() + context) {

can i somehow do context.getCopyOfContextMap() ?

[oshai]

How about keeping MDCContext() in a var?

[Nikky]

the issue seems to be that on coroutine boundary the contextMap from the coroutineContext is used to restore the MDC

ie. when you put MDC.put("extra", "value") inside the coroutineScope and before a suspending call
then after that call the new value will be gone

so i tried something where i manually "save" the MDC state to the coroutineContext

fun CoroutineScope.storeMDC() {
    <http://logger.info|logger.info> { "storeMDC" }
    coroutineContext[MyMDCContext.Key]?.apply {
        contextMap = MDC.getCopyOfContextMap()
    }
}

but this does not work.. first of all contextMap is readonly
and even when i made a copy of the class (MyMDCContext ) it does not work.. something still restores a empty MDC context after a suspending call

[Nikky]

all that because its kinda ugly to only be able to safely use MDC inside a withContext(MDCContext()) { ... }
causing very indented code even faster

[oshai]

if i remember correctly the map is copied to the coroutine, and poped when return, so yes, its not possible to add values and get them outside

[Nikky]

i was hoping i could update the coroutineCOntext varaible from inside the context, so it ALSO restores that value, but nothing is that easy

[oshai]

I think the place to ask for it is coroutines

[Nikky]

i did