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
e

Exerosis

01/11/2022, 10:24 PM
Can anyone recommend any resources that cover the internal implementation of courotines? I've been using suspendCoroutineUninterceptedOrReturn in my networking library. When I made it I looked into what suspending functions compiled down to, so I know that at least at some point in the past a suspend function was basically a function that takes a continuation and has a big switch statement over continuation.label which it uses to determine where it will resume from each time it gets called. Even if this is still true I don't fully understand how the continuation itself is created and how confined vs unconfined works etc. The actual issue I'm having is understanding where exceptions end up going since it seems to be based on what scope is being used or something along those lines.
e

ephemient

01/11/2022, 10:48 PM
1. a suspend function gets compiled into a state machine - so yes, a switch statement additional fields for local state. except in cases where that can be optimized out such as if there are no suspend points or they are only in tail position. see https://github.com/JetBrains/kotlin/blob/master/compiler/backend/src/org/jetbrains/kotlin/codegen/coroutines/coroutines-codegen.md for details 2. a coroutine can be dispatched - run by the dispatcher - or undispatched - executed in place, at least until the first suspension point. unconfined is just a special dispatcher that doesn't actually dispatch, and runs in place. 3. if you're talking about kotlinx.coroutines (structured concurrency) specifically and not just kotlin.coroutines (low level infrastructure for any kind of coroutine), then exceptions always bubble up to the root coroutine, which is created by launch(), async(), supervisorScope() 4. don't use suspendCoroutineUninterceptedOrReturn or other intrinsics unless you're trying to build your own coroutine system
e

Exerosis

01/11/2022, 11:35 PM
So when it's dispatched the initial call is dispatched and resumes are dispatched? Undispatched only resumes are dispatched? Unconfined there is no dispatching at all? "then exceptions always bubble up to the root coroutine" meaning any sub routines that use the parents scope? eg: GlobalScope.launch { GlobalScope.launch { } } would both be root, but: GlobalScope.launch { launch {} } only the outer would be a root? Why not use suspendCoroutineUninterceptedOrReturn? If I know the code that will be resuming it won't resume twice or return value and then resume etc. I also would like to remain as close as possible to constant memory profile as physically possible.
e

ephemient

01/11/2022, 11:56 PM
resumes are always* dispatched to avoid blowing up the stack. no, the inner launch is also a root.
suspendCoroutine
is type-safe, unlike
suspendCoroutineUninterceptedOrReturn
.
e

Exerosis

01/12/2022, 12:06 AM
Humm, why would the stack blow up unless you otherwise would have a StackOverflow? Can't you do like:
suspend fun switchThreads() = suspendCoroutineUninterceptedOrReturn<Unit> {
    Thread({
        it.resumeWith(Result.success(Unit))
    }, "Example Thread").start()
    COROUTINE_SUSPENDED
}
fun main() = runBlocking {
    println(Thread.currentThread())
    switchThreads()
    println(Thread.currentThread())
}
To print:
Thread[main,...]
Thread[Test,...]
e

ephemient

01/12/2022, 12:26 AM
suspend functions do not StackOverflow, even in situations where non-suspending functions would StackOverflow
to give a quick example,
val fib = DeepRecursiveFunction { if (it < 2) it else callRecursive(it - 1) + callRecursive(it - 2) }
uses kotlin.coroutines (not concurrency nor kotlinx.coroutines) and does not StackOverflow
e

Exerosis

01/12/2022, 12:35 AM
But would that functionality not work when dealing with Unconfined dispatcher and or bypassing intercepted resumes?
e

ephemient

01/12/2022, 12:40 AM
there's no use of any dispatchers in that example
e

Exerosis

01/12/2022, 12:51 AM
"resumes are always* dispatched to avoid blowing up the stack." Then I don't really understand this? Ultimately what I want to take an ExecutorService and pass it to an async thread group, then I will resume a continuation from a CompletionHandler (which will be invoked on an executor service thread). Then when I write something like this:
val provider = SocketProvider(executor)
val dispatcher = executor.asCoroutineDispatcher()
GlobalScope.launch(dispatcher) {
  while (provider.isOpen) {
    val client = provider.accept() //suspends
    launch(dispatcher) {
      while (client.isOpen) {
        val length = <http://client.read.int|client.read.int>() //suspends
        val bytes = client.read.bytes(length)
        println(bytes.toString(UTF_8))
      }
    }
  }
}
I want it to for example resume from int() on some executor thread... and call bytes on the same thread... rather than scheduling a new task when I resume from int() b/c I'm already on a thread pool thread. And I want to minimize overhead to the greatest possible degree since ofc the number of calls to something like int or bytes might be incredibly high. I've gone to great lengths to make sure that it has an almost constant memory overhead already.
n

Nick Allen

01/12/2022, 5:47 PM
resumes are always* dispatched to avoid blowing up the stack
DeepRecursiveFunction
avoids stack overflows because its implementation trampolines. There's nothing inherent to continuations that avoids stack overflow.
I want it to for example resume from int() on some executor thread... and call bytes on the same thread... rather than scheduling a new task when I resume from int() b/c I'm already on a thread pool thread.
All the built in Dispatchers either schedule the task or trampoline (even Unconfined may not resume directly) If you want to guarantee you don't schedule, then
Executor { it.run() }.asCoroutineDispatcher()
is an option but it's a very dangerous option. Personally, I'd prefer it over
suspendCoroutineUninterceptedOrReturn
since it's the caller aiming at their own foot rather than the implementation ignoring the caller's interceptor.
Kotlin's Coroutines have an implied contract that your code is always running where you told it to run.
I would expect this to work well enough:
val provider = SocketProvider(executor)
val dispatcher = executor.asCoroutineDispatcher()
GlobalScope.launch(dispatcher) {
  while (provider.isOpen) {
    val client = provider.accept() //suspends
    withContext(Dispatchers.Unconfined) {
      while (client.isOpen) {
        //Assuming int always resumes from executor
        val length = <http://client.read.int|client.read.int>() //suspends
        val bytes = client.read.bytes(length)
        println(bytes.toString(UTF_8))
      }
    }
  }
}
e

Exerosis

01/13/2022, 6:28 AM
The problem with this: Executor { it.run() }.asCoroutineDispatcher() is that it wouldn't be parallel anymore. Let me see if withContext(Unconfined) works well. I'll also try benching it vs unintercepted.