Hey all I am pretty new to using coroutines in general and I

Question

Hey all I am pretty new to using coroutines in general and I m still struggling with Kotlin coroutines I have dabbled with some async in Javascript and Python but nothing in Kotlin I wrote the following code after some reading and I m wondering why this may be a bad idea ```fun asyncOp nums List lt Int gt mult Int id String = GlobalScope async println 1 $id $mult times list computing asynchronously Thread sleep 2000L mult println 2 $id $mult times list computing asynchronously Thread sleep 1000L mult nums map it mult suspend fun main val nums = listOf 1 2 3 4 5 6 val double = asyncOp nums 2 first val triple = asyncOp nums 3 second println Double requested $double println Triple requested $triple println Waiting println awaitAll triple double ``` This works as intended but Intellij suggested this instead ```suspend fun asyncOp nums List lt Int gt mult Int id String = withContext Dispatchers Default println 1 $id $mult times list computing asynchronously Thread sleep 2000L mult println 2 $id $mult times list computing asynchronously Thread sleep 1000L mult nums map it mult ``` But this runs it in a blocking way which is not what I wanted What do you guys think Where might I be going wrong

octylFractal · Answer

1 you should almost never use GlobalScope 2 you should use `delay` instead of `Thread sleep` `delay` is suspending

octylFractal · Answer

you should probably read <https medium com elizarov structured concurrency 722d765aa952> and other kotlin related coroutine posts

octylFractal · Answer

not sure what you re really going for here but I think this is a better approximation ```suspend fun op nums List lt Int gt mult Int id String List lt Int gt println 1 $id $mult times list computing asynchronously delay 2000L mult println 2 $id $mult times list computing asynchronously delay 1000L mult return nums map it mult suspend fun main val nums = listOf 1 2 3 4 5 6 coroutineScope val double = async op nums 2 first val triple = async op nums 3 second println Double requested $double println Triple requested $triple println Waiting println awaitAll triple double ```

Hasan · Answer

They were mainly toy functions to observe some async behavior

Hasan · Answer

The coroutine scope inside the `main` does that run in a blocking way in your example

octylFractal · Answer

what part of it

Hasan · Answer

As in will the main function finish running before the `coroutineScope` finishes

octylFractal · Answer

no but it does not block it suspends

Hasan · Answer

Yeah alright

Hasan · Answer

Thanks for your help That honestly makes a lot more sense

Hasan · Answer

I ll have a look at those resources too Thanks again

Hasan · Answer

Sorry again but why is using `GlobalScope` not right

octylFractal · Answer

it s part of structured concurrency I think that blog post explains it well but as a quick summary it basically means establishing a tree of Jobs so that when you cancel a Job all of its children and its children s children etc all get cancelled and clean up all resources associated with those jobs

octylFractal · Answer

e g if you called `coroutineContext Job cancel ` in `main ` from our example after starting the two async ops in your example they would still proceed to do the `nums map` code where as in my code they immediately stop after resuming from delay or potentially sooner don t recall when cancellation is detected by `delay`

Hasan · Answer

Ahh I see That makes sense actually