kotlinlang #coroutines

@Jonathan Walsh I have a nagging feeling this could be due to Long overflows, where a MAX_VALUE after a delay (adding to MAX_VALUE) becomes a negative number…. i.e. no delay or waiting…

kevinherron

02/27/2019, 7:09 PM

does anybody know the status/plans/roadmap for kotlinx-io?

obobo

02/27/2019, 7:16 PM

What's the right way for setting off a 'fire and forget' Job via

launch

? Should I just instance a new scope for the call? Documentation says that any uncaught exceptions will cancel the parent job.

dewildte

02/28/2019, 12:07 AM

I have this crazy error:

java.lang.NoClassDefFoundError: kotlinx/coroutines/BuildersKt
	at RandomPanelAction.actionPerformed(RandomPanelAction.kt:17)
	at com.intellij.openapi.actionSystem.ex.ActionUtil$1.run(ActionUtil.java:220)
	at com.intellij.openapi.actionSystem.ex.ActionUtil.performActionDumbAware(ActionUtil.java:237)
	at com.intellij.ide.actions.GotoActionAction.lambda$performAction$7(GotoActionAction.java:352)
	at com.intellij.openapi.application.TransactionGuardImpl.runSyncTransaction(TransactionGuardImpl.java:88)
	at com.intellij.openapi.application.TransactionGuardImpl.lambda$submitTransaction$1(TransactionGuardImpl.java:111)
	at com.intellij.openapi.application.TransactionGuardImpl.submitTransaction(TransactionGuardImpl.java:120)
	at com.intellij.openapi.application.TransactionGuardImpl.lambda$submitTransactionLater$4(TransactionGuardImpl.java:271)
	at com.intellij.openapi.application.impl.LaterInvocator$FlushQueue.doRun(LaterInvocator.java:447)
	at com.intellij.openapi.application.impl.LaterInvocator$FlushQueue.runNextEvent(LaterInvocator.java:431)
	at com.intellij.openapi.application.impl.LaterInvocator$FlushQueue.run(LaterInvocator.java:415)
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:762)
	at java.awt.EventQueue.access$500(EventQueue.java:98)
	at java.awt.EventQueue$3.run(EventQueue.java:715)
	at java.awt.EventQueue$3.run(EventQueue.java:709)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:732)
	at com.intellij.ide.IdeEventQueue.defaultDispatchEvent(IdeEventQueue.java:781)
	at com.intellij.ide.IdeEventQueue._dispatchEvent(IdeEventQueue.java:722)
	at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.java:382)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
Caused by: java.lang.ClassNotFoundException: kotlinx.coroutines.BuildersKt PluginClassLoader[IntelliGlo.intelliglo-plugin, 0.0.1] com.intellij.ide.plugins.cl.PluginClassLoader@6d3678f6
	at com.intellij.ide.plugins.cl.PluginClassLoader.loadClass(PluginClassLoader.java:63)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	... 28 more

sitepodmatt

02/28/2019, 3:36 AM

Is there a way to get the parent Job from coroutinecontext's Job without using reflection to get privates?

sitepodmatt

02/28/2019, 7:46 AM

@elizarov is there a reason Job doesn't expose parentJob : Job?. My use case would be logging/debugging aids - wanting to log the path of jobs to the root when one fails, a job trace vs a stack trace. Ive managed to hack around it with this evil code but I wondering if there a strong reason for concealing

@UseExperimental(InternalCoroutinesApi::class)
fun Job.getParent() : Job? {
    return (AbstractCoroutine::class.java as Class<*>)?.
        getDeclaredField("parentContext")?.
        also { it.isAccessible = true }?.
        let { it.get(this) as? CoroutineContext? }?.
        let { it[Job] }
}

sitepodmatt

02/28/2019, 10:20 AM

class RequestContextTest : StringSpec({
    "playing with human context" {

        runBlocking {

            supervisorScope {


                try {
                    val repoSize = async<String> {
                        // do remote
                        val somenestedOp = async<String> {
                            delay(100)
                            throw DomainException("oh no", Exception("400"))
                        }
                        somenestedOp.await()
                    }

                    repoSize.await()
                } catch (de: DomainException) {
                    println("we will swallow")

                }


            }


        }
        println("we exited okay")
    }


})

class DomainException(msg: String, t: Throwable) : Exception(msg, t)

louiscad

02/28/2019, 11:15 AM

Hi, I'm working again on Android's callback hell based Camera2 API, resuming work on an open source library to implement structured concurrency in the bast possible way. My questions are the following: 1. How to cancel a scope (based on an error callback) with a specific exception? In my case, in a local

coroutineScope { ... }

, I have an

async

block that needs to be cancelled if some error callback comes in, and that exception coming in is the cause of the cancellation, so

CoroutineScope.cancel()

doesn't suit my needs. 2. Is using

CompleteableDeferred<T>(coroutineContext[Job])

safe? My guess is that it will cancel the scope with the proper exception if its

completeExceptionnaly(…)

function is called, and it will itself be cancelled if the scope is cancelled from another place. Am I right about this? If so, I'm wondering why there's no

completableDeferred<T>()

extension function for

CoroutineScope

that would do it without needing to pass

coroutineContext[Job]

Dias

02/28/2019, 12:41 PM

Hi, let's say I have 3 coroutines: A,B and C. I want A and B be related, as in when A fails B cancels as well, and vice-a-versa. I also want C depend on A and B, but only one direction, so A and B failure would cancel C, but not other way around. There is probably simple way to do it, but I am confused now. I know of supervisor scope, but that makes all children equally unrelated, while I have some sort of downward hierarchy: PARENT / \ A - B \ / C

Martin Devillers

02/28/2019, 2:19 PM

I’m running into some difficulties when trying to process items in parallel with coroutines. My current scenario is that I have a large collection of items, and I need to do a CPU-consuming transformation on each of them (deciphering data, if you’re curious). As I process these items, I want to broadcast the progress, which is the count of the number of items processed. My idea was that after each item is processed, it would send a

Unit

to a channel, which would count the number of items received and update that information. The items are processed by simply mapping the list to

async

calls which process the item then

send

to the progress channel, then doing

awaitAll

on this channel. See the code. The issue I’m running into is that the progress isn’t being broadcast along as items are processed. Instead, all the items are processed, then all the progress updates are sent, which isn’t very useful. As I understand it, this is because the dispatcher’s queue is “fair”, therefore it handles all the

async

calls before handling the

receive

calls of the actor. If you have ideas on a better way to do this, I would really appreciate it. One solution that I see is to use the “fan-out” technique described in the coroutine guide, but this seems weird to me since I have a list, not a channel, and also because I lose the benefit of leaving the responsibility of determining the parallelism of processing to the coroutine dispatcher. Thanks 🙂

-.kt

rrva

02/28/2019, 4:20 PM

Want to advertise a light-weight server microframework for HTTP services we've been using in production for over a year: Jooby. 1.x has been around for many years and to my mind has a great balance between noninvasiveness (you can easily move off jooby as a framework should you decide to do so), productivity and lightness, but still with great basic feature set. It also has a nice Kotlin DSL for HTTP routes. Tastefully built in my opinion, and you go for a more annotation/injection free style of programming for microservices where application logic code can be given a greater focus because the rest "never gets in the way". Good set of plugins for common use cases. Now 2.x is under development, and a notable feature is Kotlin coroutine support 1.x: https://jooby.org/ (We've been using it for over a year in production) 2.x: https://jooby.io/ (Now with Kotlin coroutines)

👍 3

Ryota

03/01/2019, 2:17 AM

Hi folks - I’m sorry for a newbie question, but my research didn’t conclude in clear understanding of

runBlocking

usages and I’d love to get some pointer. My goal is to start a blocking process with AWS Lambda, which would kick off a bunch of heavy tasks concurrently, and then returns the aggregate of the tasks when they are all completed (or when any canceled). Because the Lamdba interface itself is not a suspending function (i.e.

RequestHandler<I, O>

interface needs function with signature of

public O handleRequest(I input, Context context)

), I will need a coroutine builder inside

handleRequest

method to await for the tasks. I have read in a few places how

runBlocking

is only meant to be used for unit testing mainly, and should not be used in production. What I want to achieve seems to require

runBlocking

for good reason, but I am unsure if I’m missing something obvious. Given serverless function requiring a blocking call, is

runBlocking

a legitimate approach in this scenario? Or is there something that I’m missing? Thanks in advance for your support!

03/01/2019, 2:38 AM

yep. i usually put the loop in a method to be the worker and then do 9 launch/asyncs and one "synchronous" call of it.

serebit

03/01/2019, 3:10 AM

Well that’s interesting! Adding

coroutineScope

supervisorScope

to one of my suspend functions not only stops the build, but breaks the Kotlin compiler completely!

:youtrack: 1

Davide Giuseppe Farella

03/01/2019, 12:58 PM

Hello, this is my code flow from DB to ViewModel, I can’t figure out why my Use Case’s `Channel`s don’t emit anything:

Davide Giuseppe Farella

03/01/2019, 1:08 PM

TLDR; this is what worries me more, is there anything wrong here?

override suspend fun observeCount() = coroutineScope {
    queries.count().asChannel().mapToOne( coroutineContext ).map { it.toInt() }
}

louiscad

03/01/2019, 2:37 PM

Contracts for suspending functions! That means we will get it in

withContext

and

coroutineScope

at some point!

😒uspend: 8

🎉 1

marcoferrer

03/01/2019, 5:02 PM

I was trying something like this but noticed that the exception is already unwrapped at this point.

coroutineContext[Job]?.invokeOnCompletion {
        if(it is CancellationException){
            call.cancel(it.message,it.cause ?: it)
        }
    }

otakusenpai

03/01/2019, 6:15 PM

How do I include kotlinx.coroutines.experimental ? In my project, which I'm starting from new

ansman

03/01/2019, 10:14 PM

I was pretty surprised that a coroutine scope won’t complete if there are any unstarted coroutines in it. This function will never return for example:

coroutineScope {
  launch(start = LAZY) {}
}

asad.awadia

03/01/2019, 11:55 PM

@elizarov hey Roman - can we get a post or a video on idiomatic use of kotlin coroutines? Rob pike has one for go and it seems like a really good way of suggesting patterns for real world usages

➕ 2

Matej Kormuth

03/02/2019, 3:14 PM

Hi, I launch a coroutine with

while(true) { ... delay(3000) }

code in it. Is is possible to somehow trigger skip of the delay (waiting 3s) and run the while loop body immediately?

asad.awadia

03/03/2019, 6:42 AM

And i get into the foreach lambda for the result set I cant call send on a channel?

asad.awadia

03/03/2019, 7:25 AM

I can’t come out of reading a channel loop? Its a hard block on the execution?

bogdoll

03/03/2019, 6:27 PM

How would a SuspendingQueue analog to a BlockingQueue look like? Are there some example sources for that available?

aksh1618

03/03/2019, 7:09 PM

On trying to run this code in playground: https://pl.kotl.in/r1dZNoYIE, it says "No main method found in project". However, on uncommenting

await()

on both, it runs. Is this a bug with the playground?

groostav

03/03/2019, 7:39 PM

I'm trying to get a good grip on the result using

Unconfined

to try and keep stacks neat. Namely I'd like to use an unconfined consumer to keep the producer on the stack trace, But I think there's a races making my life hard. AFAIK the contract with unconfined is so weak (and is aimed at performance, not debugability) that perhaps this isn't a bug per se, but Id still like to see it. Proof-of-concept: https://gist.github.com/Groostav/f8ef01ed830c14c394ac5b992d981aa1 if you put a breakpoint on
send
and walk-through the the downstack implementation it will eventually invoke the receiver, If you just run the test, on my machine, the

runBlocking

event loop will invoke the receiver.

Alexjok

03/04/2019, 9:16 AM

Hello to all! How can I define an interface for this method

suspend fun CoroutineScope.removeDuplicateTerminal(objectId: MutableList<Int>, token: String) = async { }

Title

Alexjok

03/04/2019, 9:16 AM

Hello to all! How can I define an interface for this method

suspend fun CoroutineScope.removeDuplicateTerminal(objectId: MutableList<Int>, token: String) = async { }

antonis

03/04/2019, 9:24 AM

Hello. I don’t think an extension function can be extracted in an interface

What is your use case?

Alexjok

03/04/2019, 9:27 AM

I use it in spring and want to make an autowired implementation through the interface.

antonis

03/04/2019, 9:28 AM

It seems that I’m wrong. This looks valid

interface YourInterface { suspend fun CoroutineScope.removeDuplicateTerminal(objectId: MutableList<Int>, token: String) } class YourClass: YourInterface { override suspend fun CoroutineScope.removeDuplicateTerminal(objectId: MutableList<Int>, token: String) { } }

Alexjok

03/04/2019, 9:45 AM

Thank! I hurried with the question 🙂

suspend fun CoroutineScope.removeDuplicateTerminal(objectId: MutableList<Int>, token: String): Deferred<Unit>

👍 1

tseisel

03/04/2019, 4:16 PM

If your function starts a coroutine that doesn't need to return a result, you may consider returning a

Job

instead of

Deferred<Unit>

, replacing

async

with

launch

. You can then

job.join()

to wait for the coroutine to complete its work.

👍 1

Alexjok

03/04/2019, 5:27 PM

Yes, you are right! Thank you

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