kotlinlang #coroutines

import kotlinx.coroutines.*

@JvmName("_memoize_receiver")
fun <T,R> (suspend (T) -> R).memoize(): suspend (T) -> R {
    val memos = mutableMapOf<T, Deferred<R>>()
    val f = this
    return { t ->
        coroutineScope {
            withContext(coroutineContext + <http://Dispatchers.IO|Dispatchers.IO>) {
                synchronized(memos) {
                    memos.computeIfAbsent(t) { async { f(t) } }
                }
            }.await()
        }
    }
}

fun <T,R> memoize(f: suspend (T) -> R): suspend (T) -> R = f.memoize()

Pablichjenkov

08/06/2019, 7:59 PM

I have the code bellow:

suspend fun doSomethingAndThrow() { throw(MyException()) }

val coroutineScope = CoroutineScope(Job())

coroutineScope.launch {
  
  try { doSomethingAndThrow() } catch(exception: Exception) { Log.d("MyException got caught")  }

}

Is the exception thrown in the suspended fun doSomethingAndThrow(…) caught by my try/catch block or it gets caught through the CoroutineScope hierarchy. What would be a good practice to catch this exception?

Animesh Sahu

08/07/2019, 3:35 AM

Is there another use of suspend functions other than delay()? I don't get it which function can be used in suspend to actually suspend it. For example if i call any api or something it will definitely block the coroutine right? So how should i use coroutine there so i can do something till the response is recieved from the server?

hyunghui

08/07/2019, 10:16 AM

I’m planning to implement

rx's take(1)

with coroutine. Is there a good way to do it? for example, run 10 random jobs and wait only until the fastest job finishes.

Dias

08/07/2019, 12:36 PM

what are the Flow use-cases? is it mostly to replace reactive streams and all of it's implementations?

Ruckus

08/07/2019, 2:18 PM

Out of idle curiosity, is there any plans to expand the functionality of

kotlinx-coroutines-javafx

to provide helpers for common patterns, or is it only meant to provide a UI context?

➕ 1

👀 1

aerb

08/07/2019, 3:11 PM

is there a way to assert which dispatcher you’re on?

aerb

08/07/2019, 3:12 PM

to enforce

io

main

for example?

fangzhzh

08/07/2019, 9:44 PM

Hi, I did search in this channel, and google, but not found. SO my question is

kotlin
//
    var subject = PublishSubject.create<Location>()

 subject
            .buffer(1L, SECONDS)
            .subscribe( {
            list ->
               list.lastOrNull()?.let {}
            }, {}, {})

The subscribe's on Next is called every 1 second, and it process only the first one. This is helpful that I have too many log and I just want print every seconds How I do it in coroutines? Thanks

Wilson Castiblanco

08/07/2019, 11:20 PM

Hello guys! I have these two implementations in a

DeepLinkPresenter

. Which of those are the "best" approach having in mind the CoroutineScope implementation.

addamsson

08/08/2019, 9:11 AM

How can I block while a coroutine is running? My use case is that I'm confining operations to one thread in a class which has shared mutable state so I have to use a single threaded coroutine dispatcher, but I also want to provide a synchronous interface for my users. How can I do this?

sam

08/08/2019, 7:44 PM

What’s the best way to mix a long running loop with coroutines. For example, I want to do something like

while (true) { consumer.take() }

, where consumer.take is a blocking call on a JMS client. Normally, I’d launch a new thread for this, and then shut down the thread once the program exits.

Marko Mitic

08/08/2019, 9:06 PM

Latest Room alpha has Flow support http://commonsware.com/blog/2019/08/08/room-flow.html

groostav

08/08/2019, 9:36 PM

hmm. I'm curious about the

Job

and parent-child'ing.

suspend fun doLongRunningWork {
  val myContext = coroutineContext
  requireNotNull(myContext[Job])

  val async1 = someScope.async { 
    //...
  }
  val async2 = someScope.async(myContext) {
    //...
  }

  //maybe this code joins on async1 & async2, maybe not. should that impact my approach?
}

the latter exerts a rather strange back-pressure on the callers coroutine-entrypoint. Why the distinction?

rook

08/08/2019, 9:44 PM

I’m trying to make a

suspend

function execute its contents on a specific dispatcher. So far:``` suspend fun getFoo(): Foo? = coroutineScope { withContext(Dispatchers.IO) { retrieveFoo() } }``` Is this the best way to go about it?

jkbbwr

08/09/2019, 12:43 PM

Is there a way to send a value to a continuation. (not channels)

Aslam Hossin

08/09/2019, 4:40 PM

How to repeat a task within a duration of delay using coroutines in Android?

kevinherron

08/09/2019, 5:08 PM

anybody know if support for declaring anonymous suspending functions is coming?

kevinherron

08/09/2019, 5:09 PM

or suspending lambdas i guess

Vsevolod Tolstopyatov [JB]

08/09/2019, 6:32 PM

📣 📣 📣

kotlinx.coroutines

1.3.0-RC2 is here! Changelog: * New flow operator families *

combine

and

combineTransform

flatMapLatest

mapLatest

transformLatest

and

collectLatest

* R8-friendly

ServiceLoader

usage to enable SL optimization on Android toolchain 3.6.0+ * Stacktrace recovery for minified Android builds * Full-blown interop between coroutine context and Reactor context * Various fixes and improvements * Full changelog: https://github.com/Kotlin/kotlinx.coroutines/releases/tag/1.3.0-rc2

👏 22

👍 3

🐿 2

👀 3

🍻 1

🎉 5

😒uspend: 3

bogdoll

08/10/2019, 8:27 AM

For working non blocking the AWS2 SDK provides methods which returns CompleteableFuture<T>. Wrapping them into coroutines I wrote the following extension function (I don't like the name). My question would be, is that extension okay, or even already implemented in the standard coroutines library? If that extension is okay, what would you suggest as name for it?

suspend fun <T> CompletableFuture<T>.suspending() : T = suspendCoroutine { cont ->
    whenComplete { v, e -> if(e==null) cont.resume(v) else cont.resumeWithException(e) }
}

It can be used for example to wrap the following AWS SDK method:

CompletableFuture<CopyObjectResponse> copyObject(CopyObjectRequest copyObjectRequest)

into

suspend fun S3AsyncClient.suspendingCopyObject(copyObjectRequest: CopyObjectRequest) : CopyObjectResponse = copyObject(copyObjectRequest).suspending()

voddan

08/10/2019, 10:17 AM

what does

BOM

in the new

kotlinx-coroutines-bom

stand for?

sjthn

08/10/2019, 5:38 PM

Hi all, I am using the following scope to launch the coroutine on button click. But the app crashes w/o any logs. Do you know what I am missing?

private val scope = CoroutineScope(Dispatchers.Main + SupervisorJob())
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    presenter = ProductPresenter(ProductRepository(Network(), Database()), scope)

    button_fetch.setOnClickListener {
        presenter.onFetchClick()
    }
}

---------------------------------------------------------------------

    fun onFetchClick() {
        loadingState.value = true

        scope.launch {
            //...
        }
    }

Robert Menke

08/11/2019, 1:43 AM

Just want to say thank you to whoever put https://play.kotlinlang.org/hands-on/Introduction%20to%20Coroutines%20and%20Channels/01_Introduction together. That was a really useful tutorial and I appreciate the work that went into it!

👍 4

Kulwinder Singh

08/11/2019, 9:39 AM

Hi, can i convert this Firebase Phone Auth code to coroutines friendly, in below method i have two options first is that i can scope this call to activity and second is that i can add some Executor(which i don't know how works). but here i don't want this request to be scoped on Activity because i don't want this request inside Activity instead i want to move it inside ViewModel or Repository.

phoneAuth.verifyPhoneNumber(
number, 1, TimeUnit.MINUTES,
executor or Activity // but here i don't wanna scope it to activity instead i want to use it inside ViewModel using coroutines
,authCallback)

dharrigan

08/11/2019, 12:14 PM

If I have, lets say 3 functions that write to a database. They are independent of each other (in that the writes of one function does not affect the writes of another function into the db) and I want to run each in their own coroutine, not caring about any return code or status.

dharrigan

08/11/2019, 12:15 PM

Which of these two approaches would be better? (and are they idomatic?)

dharrigan

08/11/2019, 12:15 PM

fun doSomething() = GlobalScope.launch(<http://Dispatchers.IO|Dispatchers.IO>) {
    writeIntoTable1()
    writeIntoTable2()
    writeIntoTable3()
}

suspend fun writeIntoTable1() {...}
suspend fun writeIntoTable2() {...}
suspend fun writeIntoTable3() {...}

Title

dharrigan

08/11/2019, 12:15 PM

fun doSomething() = GlobalScope.launch(<http://Dispatchers.IO|Dispatchers.IO>) {
    writeIntoTable1()
    writeIntoTable2()
    writeIntoTable3()
}

suspend fun writeIntoTable1() {...}
suspend fun writeIntoTable2() {...}
suspend fun writeIntoTable3() {...}

gildor

08/11/2019, 2:29 PM

okay, there are a few layers in this question 1. First option will run writes in parallel, second sequentially, choose what is suits your use case better 2. Implementing doSomething in a such way is a very bad approach, especially with GlobalScope. Instead, I would just make doSomething suspendable and use

coroutineScope {}

to group writes, so client could launch this suscpend function in own scope using launch, or just call suspend function (which is even better) 3. To make parallel version of this code less awkward I would use something like:

listOf(::writeIntoTable1, ::writeIntoTable2, ::writeIntoTable3).forEach { launch ( it() } }

Or any other way to group operations and do not copy paste invocation strategy 4. i see that you use IO dispatcher which looks suspicious in this case, because you call suspend function which itself never should block, so if write is blocking, just move this IO dispatcher to those functions or make them blocking explicitly, remove suspend modifier and add Blocking suffix

dharrigan

08/11/2019, 3:51 PM

thanks for the great tips! 🙂

Dico

08/11/2019, 10:33 PM

What is Blocking suffix?

@gildor

gildor

08/12/2019, 3:50 AM

I mean if

writeIntoTableN

is blocking better to remove suspend modifier which is probably useless and rather confusing for blocking function and rename it to writeIntoTableBlocking, so it will be clear that function is blocking and should be called from corresponding context

Dico

08/12/2019, 9:38 AM

Oh name suffix of course, I'm an idiot

I thought you meant there's some kind of unified marker thing

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