Anybody work with go goroutines I have a few questions about

Question

Anybody work with go goroutines I have a few questions about concepts and how similar they are to kotlin coroutines

louiscad · Answer

I didn t use Go neither goroutines but I know in Go all functions can suspend while in Kotlin only `suspend fun` are allowed to do so

asad.awadia · Answer

Kotlin coroutines are more or less syntactic sugar to write non blocking code more nicely And if you write blocking code inside coroutine its still blocking and bad

asad.awadia · Answer

But apparently go runtime can detect blocking calls and offload them into its own worker pool

asad.awadia · Answer

Its making me confused about how to deal with blocking code in kotlin coroutine now lol we make our own fixedThreadPool asCoroutineDispatcher and run it on that

Vsevolod Tolstopyatov [JB] · Answer

gt But apparently go runtime can detect blocking calls and offload them into its own worker pool Something like this it has all its syscalls instrumented at runtime level When blocking syscall is detected current thread offloads all its work to another thread and signals that it is blocking so runtime can create or unpark one more thread gt we make our own fixedThreadPool asCoroutineDispatcher and run it on that More or less depending on your blocking frequency and CPU load Latest release has experimental dispatcher which has smarter blocking code execution though you still should directly mark code as blocking

dekans · Answer

go routines are just the CommonPool and the Channel system To compare with Kotlin

dekans · Answer

`go function ` is `launch function `

asad.awadia · Answer

< Vsevolod Tolstopyatov JB > when we talk about coroutines we talk about a new better simpler way of writing async code avoiding call backs and rx Would you agree with the statement that coroutines are syntactic sugar to avoid callbacks Because in go i never hear this All i m seeing everywhere even at work is goroutines are cheap just launch as many as you want and do whatever you want in them No talk about thread pools or blocking or anything

Vsevolod Tolstopyatov [JB] · Answer

< asad awadia> I would not Coroutines are standalone feature for example take a look at stdlib `buildSequence` Is it a wrapper over callback Is `suspend fun foo Unit` a wrapper over callback Coroutines allow to translate callback based code to sequential ish but it s not a syntactic sugar to avoid callbacks it s something bigger ~syntactic sugar over state machines~ slightly smiling face Go is a different beast goroutines have runtime support but they are tightly coupled with it so you don t have access to state machine `continuation` and therefore to handy features as `buildSequence` generators or Erlang like state machines

Vsevolod Tolstopyatov [JB] · Answer

Goroutines are rather Kotlin `async` `launch` like coroutines with powerful runtime support while coroutines are broader feature but without runtime support because we can t add feature to the JVM itself In terms of runtime cost both goroutine and `launch` have roughly the same footprint

asad.awadia · Answer

Yes that s exactly what I mean by syntactic sugar as well they allow translation from callback based code to sequential ish code

asad.awadia · Answer

Koroutines goroutines aren t magic though right That just because you can launch thousands of these you can just do more stuff if you are spinning one off for blocking work at the end of the day you are still blocking just blocking another thread

asad.awadia · Answer

The code inside still needs to be non blocking

asad.awadia · Answer

For n threads launching n+1 coroutines that all have blocking work the last 1 coroutine has to wait yes Which is no different than just running it on threads and blocking it there

Vsevolod Tolstopyatov [JB] · Answer

The fact that feature simplifies `X` doesn t automatically means that the feature is a syntactic sugar over `X` slightly smiling face gt at the end of the day you are still blocking just blocking another thread Yes gt The code inside still needs to be non blocking For Go it doesn t matter Go detects blocking calls from runtime and offloads them to blocking threadpool kind of Go scheduler is a bit more complicated For `kotlinx coroutines` yes or you should offload blocking calls to another threadpool gt For n threads launching n+1 coroutines that all have blocking work the last 1 coroutine has to wait yes Yes

Vsevolod Tolstopyatov [JB] · Answer

Note though that many APIs maybe except for file I O have non blocking API e g nio and with a help of syntactic sugar you now can write the same sequential ish code which uses non blocking API underneath making the code scalable and programming model simple E g you can t have 100000 threads bound to long polling connections with reasonable performance but you can have 100000 coroutines one per connection Without coroutines to properly handle 100000 connections you should use some callbacks event based APIs like netty or jetty s asynchronous servlets which are easy to get wrong

asad.awadia · Answer

Do you have examples of production more advanced usages of coroutines

asad.awadia · Answer

I d really like to solidify my understanding by reading code that actually demonstrate a bit more advanced usage

Vsevolod Tolstopyatov [JB] · Answer

take a look at Ktor examples Ktor has coroutine based API down to the network stack