Hi guys, can anyone help me figure out how to call...

# ktor

[Sander Ploegsma]

Hi guys, can anyone help me figure out how to call two suspend functions in parallel inside a route? This compiles but crashes at runtime with `io.ktor.util.pipeline.SuspendFunctionGun cannot be cast to kotlinx.coroutines.CoroutineScope`:

fun Routing.test() {
    get("/") {
        val firstResultDeferred = async { firstCall() }
        val secondResultDeferred = async { secondCall() }
        
        val firstResult = firstResultDeferred.await()
        val secondResult = secondResultDeferred.await()

        call.respond(listOf(firstResult, secondResult))
    }
}

[gildor]

Could you show full stacktrace, looks like some ktor bug (make sense to create an issue)

[gildor]

because your code in general is completely fine

[gildor]

See, this works with coroutines:
https://pl.kotl.in/BymrGQ-8N

[Sander Ploegsma]

Sure

[e5l]

@cy

[Sander Ploegsma]

And on a related note, is there any cleaner way of writing this? I can't seem to .await() inside the call.respond()

[gildor]

@Sander Ploegsma what do you mean “inside the `call.respond()`“? You can, because get block is suspendable lambda, I showed above example that it works

[Sander Ploegsma]

I would like to do this:

get("/test") {
        val a = async { a() }
        val b = async { b() }

        call.respond(listOf(a.await(), b.await()))
    }

EDIT: Oh wait, never mind. In my example it works, but my production code uses call.respondHtmlTemplate with a block function parameter that is not suspendable

[cy]

This looks like a classloaders related issue since SuspendFunctionGun implements the interface

[cy]

Do you have hot-reload configured?

[Sander Ploegsma]

Yes

[Sander Ploegsma]

And if I disable it, it looks like it does work.

[cy]

Then for sure it is a bug. Could you please report it https://github.com/ktorio/ktor/issues/new

[Sander Ploegsma]

I set up a small MVP to recreate the bug but it looks like that works: https://github.com/sanderploegsma/ktor-route-async-await

So, it's probably an issue with our current setup, let me look into it

[gildor]

but my production code uses call.respondHtmlTemplate with a block function parameter that is not suspendable

Yes, it make sense. You can create a feature request to make respondHtmlTemplate suspendable.
For now I think the only way is suspend before this block. receive data and than use it in respondHtmlTemplate block

[Sander Ploegsma]

Thanks @gildor, I submitted a feature request for it: https://github.com/ktorio/ktor/issues/976

[Sander Ploegsma]

@cy It looks like an issue with AppEngine, which is what my application runs on. If I run it using io.ktor.server.jetty.EngineMain everything works as expected, also with hot reloading enabled

[cy]

What engine did you use before?

[Sander Ploegsma]

kotlin-server-servlet, basically the same as https://github.com/ktorio/ktor-samples/tree/master/deployment/google-appengine-standard