https://kotlinlang.org logo
Channels
100daysofcode
100daysofkotlin
100daysofkotlin-2021
advent-of-code
aem
ai
alexa
algeria
algolialibraries
amsterdam
android
android-architecture
android-databinding
android-studio
androidgithubprojects
androidthings
androidx
androidx-xprocessing
anime
anko
announcements
apollo-kotlin
appintro
arabic
argentina
arkenv
arksemdevteam
armenia
arrow
arrow-contributors
arrow-meta
ass
atlanta
atm17
atrium
austin
australia
austria
awesome-kotlin
ballast
bangladesh
barcelona
bayarea
bazel
beepiz-libraries
belgium
benchmarks
berlin
big-data
books
boston
brazil
brikk
budapest
build
build-tools
bulgaria
bydgoszcz
cambodia
canada
carrat
carrat-dev
carrat-feed
chicago
chile
china
chucker
cincinnati-user-group
cli
clikt
cloudfoundry
cn
cobalt
code-coverage
codeforces
codemash-precompiler
codereview
codingame
codingconventions
coimbatore
collaborations
colombia
colorado
communities
competitive-programming
competitivecoding
compiler
compose
compose-android
compose-desktop
compose-hiring
compose-ios
compose-mp
compose-ui-showcase
compose-wear
compose-web
confetti
connect-audit-events
corda
cork
coroutines
couchbase
coursera
croatia
cryptography
cscenter-course-2016
cucumber-bdd
cyprus
czech
dagger
data2viz
databinding
datascience
dckotlin
debugging
decompose
decouple
denmark
deprecated
detekt
detekt-hint
dev-core
dfw
docs-revamped
dokka
domain-driven-design
doodle
dsl
dublin
dutch
eap
eclipse
ecuador
edinburgh
education
effective-kotlin
effectivekotlin
emacs
embedded-kotlin
estatik
event21-community-content
events
exposed
failgood
fb-internal-demo
feed
firebase
flow
fluid-libraries
forkhandles
forum
fosdem
fp-in-kotlin
framework-elide
freenode
french
fritz2
fuchsia
functional
funktionale
gamedev
ge-kotlin
general-advice
georgia
geospatial
german-lang
getting-started
github-workflows-kt
glance
godot-kotlin
google-io
gradle
graphic
graphkool
graphql
graphql-kotlin
graviton-browser
greece
grpc
gsoc
gui
hackathons
hacktoberfest
hamburg
hamkrest
helios
helsinki
hexagon
hibernate
hikari-cp
hire-me
hiring
hongkong
hoplite
http4k
hungary
hyderabad
image-processing
india
indonesia
inkremental
intellij
intellij-plugins
intellij-tricks
internships
introduce-yourself
io
ios
iran
israel
istanbulcoders
italian
jackson-kotlin
jadx
japanese
jasync-sql
java-to-kotlin-refactoring
javadevelopers
javafx
javalin
javascript
jdbi
jhipster-kotlin
jobsworldwide
jpa
jshdq
juul-libraries
jvm-ir-backend-feedback
jxadapter
k2-early-adopters
kaal
kafka
kakao
kalasim
kapt
karachi
karg
karlsruhe
kash_shell
kaskade
kbuild
kdbc
kgen-doc-tools
kgraphql
kinta
klaxon
klock
kloudformation
kmdc
kmm-español
kmongo
knbt
knote
koalaql
koans
kobalt
kobweb
kodein
kodex
kohesive
koin
koin-dev
komapper
kondor-json
kong
kontent
kontributors
korau
korean
korge
korim
korio
korlibs
korte
kotest
kotest-contributors
kotless
kotlick
kotlin-asia
kotlin-beam
kotlin-by-example
kotlin-csv
kotlin-data-storage
kotlin-foundation
kotlin-fuel
kotlin-in-action
kotlin-inject
kotlin-latam
kotlin-logging
kotlin-multiplatform-contest
kotlin-mumbai
kotlin-native
kotlin-pakistan
kotlin-plugin
kotlin-pune
kotlin-roadmap
kotlin-samples
kotlin-sap
kotlin-serbia
kotlin-spark
kotlin-szeged
kotlin-website
kotlinacademy
kotlinbot
kotlinconf
kotlindl
kotlinforbeginners
kotlingforbeginners
kotlinlondon
kotlinmad
kotlinprogrammers
kotlinsu
kotlintest
kotlintest-devs
kotlintlv
kotlinultimatechallenge
kotlinx-datetime
kotlinx-files
kotlinx-html
kotrix
kotson
kovenant
kprompt
kraph
krawler
kroto-plus
ksp
ktcc
ktfmt
ktlint
ktor
ktp
kubed
kug-leads
kug-torino
kvision
kweb
lambdaworld_cadiz
lanark
language-evolution
language-proposals
latvia
leakcanary
leedskotlinusergroup
lets-have-fun
libgdx
libkgd
library-development
lincheck
linkeddata
lithuania
london
losangeles
lottie
love
lychee
macedonia
machinelearningbawas
madrid
malaysia
mathematics
meetkotlin
memes
meta
metro-detroit
mexico
miami
micronaut
minnesota
minutest
mirror
mockk
moko
moldova
monsterpuzzle
montreal
moonbean
morocco
motionlayout
mpapt
mu
multiplatform
mumbai
munich
mvikotlin
mvrx
myndocs-oauth2-server
naming
navigation-architecture-component
nepal
new-mexico
new-zealand
newname
nigeria
nodejs
norway
npm-publish
nyc
oceania
ohio-kotlin-users
oldenburg
oolong
opensource
orbit-mvi
osgi
otpisani
package-search
pakistan
panamá
pattern-matching
pbandk
pdx
peru
philippines
phoenix
pinoy
pocketgitclient
polish
popkorn
portugal
practical-functional-programming
proguard
prozis-android-backup
pyhsikal
python
python-contributors
quasar
random
re
react
reaktive
realm
realworldkotlin
reductor
reduks
redux
redux-kotlin
refactoring-to-kotlin
reflect
refreshversions
reports
result
rethink
revolver
rhein-main
rocksdb
romania
room
rpi-pico
rsocket
russian
russian_feed
russian-kotlinasfirst
rx
rxjava
san-diego
science
scotland
scrcast
scrimage
script
scripting
seattle
serialization
server
sg-user-group
singapore
skia-wasm-interop-temp
skrape-it
slovak
snake
sofl-user-group
southafrica
spacemacs
spain
spanish
speaking
spek
spin
splitties
spotify-mobius
spring
spring-security
squarelibraries
stackoverflow
stacks
stayhungrystayfoolish
stdlib
stlouis
strife-discord-lib
strikt
students
stuttgart
sudan
swagger-gradle-codegen
swarm
sweden
swing
swiss-user-group
switzerland
talking-kotlin
tallinn
tampa
teamcity
tegal
tempe
tensorflow
terminal
test
testing
testtestest
texas
tgbotapi
thailand
tornadofx
touchlab-tools
training
tricity-kotlin-user-group
trójmiasto
truth
tunisia
turkey
turkiye
twitter-feed
uae
udacityindia
uk
ukrainian
uniflow
unkonf
uruguay
utah
uuid
vancouver
vankotlin
vertx
videos
vienna
vietnam
vim
vkug
vuejs
web-mpp
webassembly
webrtc
wimix_sentry
wwdc
zircon
Powered by
Title
a

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?
g

groostav

03/03/2019, 7:53 PM
I cant come out of a channel loop
meaning a for-each loop on a receive channel? Yeah, it only exits when the channel has completed. You might consider using a
withTimeoutOrNull
+
receieve
or
select { channel.onReceieve {} ...
instead of a for-each loop if you need more control
Its a hard block on the execution
Certainly not, the caller is suspended, and there's no execution in a channel per-se. Remember most of the time you wire a producer up to your channel that you're then consuming. When the consumer attempts to read an element it does so fully asynchronous concurrently with the producer
a

asad.awadia

03/03/2019, 7:54 PM
How do i get to the next line from the ‘read from a channel’ without sending a close?
Lets say theres a bunch of coroutines sending a string to a channel - can i stop the infinite loop over reading the channel? And get to the next line without sending close - because I cant guarantee that the close will be sent after all the values have been sent
g

groostav

03/03/2019, 7:58 PM
I'm not sure what you mean by "next line", but cant you detect your cercomstance and
break
?
for(element in foreverChannel){
  if(state + element > threshold){
    break;
  }
}
?
a

asad.awadia

03/03/2019, 7:58 PM
Is that how you’re supposed to do it though?
I can but that looks unclean and unkotlin like
g

groostav

03/03/2019, 7:59 PM
so, you do have to ask about cancellation, if the consumer doesnt ever consume any more elements from
foreverChannel
, do you want it to cancel that channel?
if that is true, then
consumeEach
is what you want, and if thats true you can use the standard functional
first
combinator
ie
val result = foreverChannel.first { state + it > threshold }
that will cause
foreverChannel
to be cancelled after the first element that matches that criteria, which causes your producers to all get signalled next time they try to produce
a

asad.awadia

03/03/2019, 8:01 PM
Hmm 🤔
Surprised kotlin doesn’t already have syntactic sugar for this
In go you can create a buffered channel and then read that many elements in a loop
I guess I could do that
Is it bad to have a channel - read n elements from it and then proceed and not ever send a close?
g

groostav

03/03/2019, 8:08 PM
I think its a problem only if you dont have reasonable assurances that there are producers and consumers --as long as there will be another consumer that's taking elements n+1 until the close signal. But I just had this same thought: what I'd really like is a
take(n)
that doesn't cancel the channel after receiving those elements.
quick point, you cant
close
a
ReceiveChannel
, you can only
cancel
it. Producers
close
the `SendChannel`s.
If you think about your program as being a kind of parser then trying to look ahead on a channel some number of tokens (messages) without cancelling or closing the channel is totally reasonable.
v

Vsevolod Tolstopyatov [JB]

03/04/2019, 8:49 AM
We don’t have a built-in mechanism that loops
n
times and then returns without cancelling a channel (otherwise, you can use
take
). If you think this is a frequent use-case that keeps popping here and there, feel free to create an issue on github.
in you project you can just create a specific extension:
suspend inline fun <E> ReceiveChannel<E>.iterate(limit: Int, action: suspend (element: E) -> Unit) {
        var consumed = 0
        for (element in this) {
            action(element)
            if (++consumed == limit) {
                break
            }
        }
    }
a

asad.awadia

03/04/2019, 5:59 PM
@Vsevolod Tolstopyatov [JB] thank you. Much appreciated.
I read Roman’s answer on stack Overflow that not closing a channel is nbd - that’s still applies?
Thats my biggest concern - reading from a channel and then just moving on without closing it
g

gildor

03/05/2019, 1:39 AM
In this case channel will leak
a

asad.awadia

03/05/2019, 1:40 AM
If someone writes to it?
What if nothing will write to it?
g

gildor

03/05/2019, 1:40 AM
if this channel blocks some coroutine (like in case of
produce
)
it depends on channel implementation, it can be garbage collected if there are no more links on this channel
it depends on implementation, for example:
val channel = produce { 
   while(true) {
      send("something")
   }
}
if you never close this channel it will leak coroutine and channel, but it’s not so bad, because now you can call produce only in CoroutineScope, this channel will be closed together with scope