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Still trying to wrap my head around how suspending...
# coroutines
a
Still trying to wrap my head around how suspending functions and coroutines come into play in a full complete production grade app (non android)
g
How Gradle or even Android related to this? What is source of your confusion? What exactly do you want to see? There are many concepts in kotlinx.coroutines: channels, actors, mutexes, lifecycle management etc Do you need particular examples or you just want to see how this works?
a
Because android mainly uses coroutines to switch work from main thread - I m more interested in writing backend apps
https://github.com/konrad-kaminski/spring-kotlin-coroutine/tree/master/spring-kotlin-coroutine-demo/src/main/kotlin/demo/app i basically want to see something like this - but something that does real work and isn’t spring or ktor
g
mainly uses coroutines to switch work from main thread
Not only
I think you have too narrow requirements for your example. It’s obvious reasons why Ktor (based on coroutines) or Sprint (most popular JVM framework for BE). Probably you also can find some Vertex samples
all the examples are there, maybe from different parts of kotlinx.coroutines and from different types of project
kotlinx.coroutines reached 1.0 only a month ago
if you have particular questions about implementation details or some patterns for backend development, there is also #server and this channel
It’s just not very clear example of what you want to see, just full sized app based on coroutines? Someone will do this of course at some point, but most adoptions now are not open sources, maybe you could just write such sample yourself with help of community and Kotlin team
d
You should a video by Roman elizarov explaining coroutines, there are a couple. Preferably more recent ones.
a
@Dico I have seen all of them - they are all very scoped just to coroutines and have a lot of placeholder code
I understand the coroutines part - i m trying to understand how they fit into the entire app as a whole
A lot of those slides just call delay - that doesn’t really help much
g
delay
can be replaced with ANY async operation: db request, network request, any other IO, depending on you use case and your project
What do you expect to see there instead?
a
A blocking library call
And/or a suspend function wrapping a blocking call
Also maybe explanation of what the thread is doing when the coroutine is suspended
And also how everything ties into main()
g
But this is very particular use case, why do you need whole project for this?
a
As a template more than anything
It’s very easy to use coroutines incorrectly
g
I agree guide should contain examples and limitations of blocking call wrapping, it was discussed some time ago, but it's not a rocket since, just wrap any blocking call with 
withContext(<http://Dispatchers.IO|Dispatchers.IO>)
But you don't have cancellation support with this approach (blocking call cannot be cancelled)
As a template more than anything
Template for what? You can use coroutines with any project that have async libraries. Ideally you shouldn't wrap blocking calls, but use async API and coroutines adapter for this API
a
Yes - I read that as soon as it came out lol
g
@asad.awadia https://github.com/vert-x3/vertx-examples/blob/3.6.0-SNAPSHOT/kotlin-examples/coroutines/src/main/kotlin/movierating/App.kt is not fully updated to Vert.x 3.6 but it shows how coroutines can be used on a single thread
a
Thanks - I have seen most of these
s
Write a dispatcher and eventloop yourself. Takes only a couple of lines and you get to see how it works in detail. Especially logging when the dispatcher is invoked helped me to understand it.
f
I've some slides on the subject that eventually may help, namely 1) On how 
suspendCoroutine
works 2) An example using a Spring Controller https://speakerdeck.com/pmhsfelix/using-kotlin-coroutines-for-asynchronous-and-concurrent
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