kotlinlang #coroutines

People interested in, or using GraalVM, there's a dev version supporting coroutines for you to try! https://github.com/oracle/graal/issues/366#issuecomment-603767026

🎉 1

👍 1

rrva

03/25/2020, 1:19 PM

https://stackoverflow.com/questions/53558215/guava-loadingcache-with-kotlin-coroutines

Sam Garfinkel

03/25/2020, 2:32 PM

Is it an anti-pattern to mixin a

CoroutineScope

(with a delegate) on a class so that you can use

Deferred

as the value of its properties? This is kind of useful for creating lazily computed properties that are backed by network I/O (I’m using Ktor):

class Foo(val client: HttpClient) : CoroutineScope by GlobalScope {
  val bar: Deferred<String> by lazy {
    async { 
      client.get<String>("<https://www.example.com>")
    }
  }
}

:yes: 2

vineethraj49

03/25/2020, 5:46 PM

what's a good naming convention if I'm writing a suspending implementation of an existing method?

vineethraj49

03/25/2020, 5:49 PM

what's a good way to handle jdbi handles? I'm checking if the following will work, but wanting to check if this is a "solved" problem already

suspend fun foo() {
    val context = coroutineContext
    dbi.withHandle { conn ->
        async(context) {
            bizLogic.suspendingFunction()
        }
    }.await()
}

Maciek

03/25/2020, 8:08 PM

I've got a test with

runBlockingTest

function. From this test I'm running code that launches coroutine from

MainScope

object that is suppose to have

TestCoroutineDispatcher

but I can't seem to run

delay

function inside that coroutine because I'm getting

UncompletedCoroutinesError

exception. Is my test setup wrong or I just can't test a code that has

delay

functions? I don't really need that delay but was just wondering why it doesn't work, I thought that runBlocking and TestCoroutineDispatcher will take care of such cases

thana

03/26/2020, 10:02 AM

i feel that coroutines have the great disadvantage, that ehy cmopletly spoil the stack traces. so currenyly im profiling an application and all i see is that

invokeSuspend

takes a considerbale amount of time. How do you cope with this situation? can we expect the situation will improve when the jvm itself supports suspendable methods?

Pacane

03/26/2020, 2:19 PM

Hi, I'm trying to understand how to use coroutines in my use case... I am using the JVM (and not android). My code doesn't current use coroutines, I'm using Java CompleteableFuture to do async work. The type of work I'm doing is Fire and Forget type of stuff (I have an infinite while loop doing video/image processing. I currently have no

suspend

functions, but I could get my code to work with the

GlobalScope.launch

function. Now I've read in several places that I should avoid using the GlobalScope. So my question is, how can I create a coroutine scope for a given method (not the main) and still use coroutines for a fire and forget type of work. I've tried doing something like

fun myMethod() = runBlocking { .... }

and then inside use

CoroutineScope.launch

but the code after the

launch

block is still blocked by the

launch

block. What could I do to make this work?

Czar

03/26/2020, 2:57 PM

Hi, I have something like this:

fun serviceSseRequest(sseEmitter: SseEmitter) {
  
  val liveOutput: Channel<String> = doSomethingInBackground()
  
  liveOutput.consumeAsFlow().collect { sseEmitter.emitServerSideEvent(it) }
}

How do I determine that there won't be any more messages in the channel? Maybe there is some other component that I can use instead of the channel here?

Orhan Tozan

03/26/2020, 3:53 PM

In the context of viewmodels/android, which one of the following three is recommended (in general for events from view => viewmodel)

// option 1
interface HomeViewModel {
    fun onLoginButtonClick()
}

// option 2
interface HomeViewModel {
    val loginButtonClicks: SendChannel<ButtonClick>
    object ButtonClick
}

// option 3
interface HomeViewModel {
    val loginButtonClicks: Flow<ButtonClick>
    object ButtonClick
}

David Glasser

03/26/2020, 5:51 PM

ok i swear i knew the answer to this one but — if I want to run some Java function that blocks and might be slow and get a timeout from it, how do I do that? will this do the trick?

withTimeout(5000L) {
  withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
    somePotentiallySlowThreadBlockingFunction()
  }
}

Note that I'm perfectly fine with the fact that the timeout won't actually stop the work from happening in

somePotentiallySlowThreadBlockingFunction

. This is happening at global process shutdown so the important thing is being able to move on to the next step of shutdown in finite time, not absolutely making sure that

somePotentiallySlowThreadBlockingFunction

doesn't continue. Like, I know

withTimeout

alone won't work with non-cooperative code, but does the withContext maybe make it work?

Tmpod

03/26/2020, 11:30 PM

Hey! I did a quick search on this channel about asynchronous and coroutine safe subprocesses, and I didn't find anything relevant. Any suggestions on how to achieve this properly? (thinking of Python's
asyncio.create_subprocess_shell
)

03/27/2020, 12:16 PM

Is there a way to produce a UML class diagram from the coroutines library source code? Or has anyone produced it already? I thought it would be helpful to have it to learn better about coroutines, as a beginner.

Adam Grzybkowski

03/27/2020, 12:25 PM

Hi! I have a problem with testing the Flow using FlowAssert from SqlDelight library. It might be related to FlowAssert, but tbh I feel like I know nothing right now :D I created a repo with the problem here, you can find there two branches

master

and

sqldelight

On master branch I've tried to reproduce the original problem I've encountered when testing SqlDelight but without the SqlDelight code. The problem Tests are stuck when

TestCoroutineDipsatcher

is injected and used in

flowOn

operator here.

fun getData(): Flow<Pair<String?, String?>> {
    val flow1 = channel1.asFlow()
        .flowOn(dispatcher)
    val flow2 = channel2.asFlow()
        .flowOn(dispatcher)
    return flow1.combine(flow2) { data1, data2 ->
            data1 to data2
        }
        .flowOn(dispatcher)
}

suspend fun addData1(value: String?) = withContext(dispatcher) {
    channel1.send(value)
}

@Test
fun `receives data1`() = runBlocking {
    exampleDataSource.getData()
        .test {
            assertEquals(null to null, expectItem())

            exampleDataSource.addData1("data1")
            assertEquals("data1" to null, expectItem())

            cancel()
        }
}

So far I've been able to make the tests pass by removing the

flowOn

operator or by changing the injected dispatcher to

Dispatchers.Unconfined

Question Why is this happening? Could anyone explain me why using

flowOn

operator is causing this? I may be using this wrong coming from Rx word 😕 repository url https://github.com/AdamGrzybkowski/coroutineTestingProblem

Michael de Kaste

03/27/2020, 1:07 PM

Anyone know any good parallel sequence library? I'd like the same functional equivalent of parallelstreams, but not in streams. (because switching between kotlin-style collection operators and stream operators are tedious and ugly)

Orhan Tozan

03/28/2020, 4:27 PM

I'm trying to define a

val textField: Flow<String>

that depends on a

val textInputEvents: Channel<TextInputEvent>

and a

val clearTextFieldEvents: Channel<ClearTextInputEvent>

. I'm trying to initialize the textField flow by combining the textInputEvents and clearTextFieldEvents channels and decide the value of the text field based of those two event streams, only problem is that just

val textField: Flow<String> = textInputEvents
    .consumeAsFlow()
    .combine(clearTextFieldEvents.consumeAsFlow()) { textInputEvent, clearTextFieldEvent ->
        // Which one of the two just emitted?
        // return textInputEvent.text or ""
    }

wouldn't do it, since I have to know which one of the channels emitted value is the most recent one, which isnt possible. So my question kinda is: is there a combine operator that also tells you which flow emitted the most recent value? EDIT: perhaps this is a usecase for the select expression (https://kotlinlang.org/docs/reference/coroutines/select-expression.html) ?

Erik

03/28/2020, 8:30 PM

Edit: questions 1 and 2 answered in thread, question 3 remains unanswered. --- I'm trying to broadcast values to multiple flow collectors. The goal is to have all collectors receive the same values. In this example, values -1, 0, 1 and 2 are sent over the channel. There are three collectors, so the goal is to have all three collectors receive the four values, for a total of 12 collect events. I tried using a

Channel

and

bro.receiveAsFlow()

, but that results in the fan-out principle where the four values sent are handled once by any of the available collectors, but not each by all collectors. The alternative is to use a

BroadcastChannel

and

bro.asFlow()

instead, but then the collectors receive... nothing! :\ 1. Why don't they receive any values? I.e. what am I doing wrong? 2. How can I make this work? As far as I understand

BroadcastChannel

can be used to send a value to multiple receivers. And the

asFlow()

extension on it should open a new subscription for every collector? Clearly I'm doing something wrong, but I don't see it. Bonus questions I don't know the answer of: 3. Is this possible at all with channels and flows? I found this open issue (https://github.com/Kotlin/kotlinx.coroutines/issues/1261) about a

Flow.share

operator, which obviously doesn't exist yet. Is this what I might be looking for?

broadcast.kts

jeggy

03/29/2020, 4:02 PM

When using

runBlockingTest

and my test fails with "This job has not completed yet" what are some ways of figuring out what is causing this? I like that it does fail, but it doesn't bring any information on where the problem is.

myanmarking

03/29/2020, 6:56 PM

hey guys. is there any ETA for the DataFlow api for flows ?

Jakub Pi

03/29/2020, 10:46 PM

I have a

Map<FileKey, Deferred<String>>

where I want to cache (expensive-to-compute) SHA-512 results. My objective is to only calculate hash values once, on the first retrieval from the Map. So I know I want some kind of Future object. I know I can start the computation in the getter (unless it's already complete) and then just return the result normally. But is Deferred the best way to do this or is there a different construct/pattern I should be looking at instead? I probably want to block on the retrieval, so Deferred may not be the best choice.

vineethraj49

03/30/2020, 6:30 AM

is there a way to create a

<http://Dispatchers.IO|Dispatchers.IO>

"clone" which has an even lesser number of threads? I see that

<http://Dispatchers.IO|Dispatchers.IO>

is defined as

LimitingDispatcher(this, parallelism, TaskMode.PROBABLY_BLOCKING)

, should it be possible to re-use the same implementation?

Paul Woitaschek

03/30/2020, 3:32 PM

I'm trying to create my own version of combine because of https://github.com/Kotlin/kotlinx.coroutines/issues/1683 As the current combine implementation uses a lot of internal apis I can't just copy-past it. My code so far looks like this: https://gist.github.com/PaulWoitaschek/34225bfdea65e042431c6e57e72768f7 Can you review this and tells me if this a correct implementation?

kevinherron

03/30/2020, 8:06 PM

is there a version of

Flow.debounce

that has a “failsafe” timeout - so that in the face of continuously emitted events at a rate faster than the debounce timeout something is at least occasionally emitted

spierce7

03/31/2020, 4:54 AM

If I want to output a value from

Flow

if nothing else is output, and it completes, what’s the best way to do that?

Jan Skrasek

03/31/2020, 9:42 AM

Hi, I need share operator. The implementations seem to be quite complicated so I've written this. Do you have any idea why it shouldn't work correctly?

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
import kotlinx.coroutines.flow.*
import java.util.concurrent.atomic.*

fun <T> Flow<T>.share(): Flow<T> {
  val channel = ConflatedBroadcastChannel<T>()
  val counter = AtomicInteger()
  var job: Job? = null

  return channel
    .asFlow()
    .onStart {
      if (counter.incrementAndGet() == 1) {
        job = GlobalScope.launch {
          this@share
            .catch {
              channel.close(it)
            }
            .collect {
              channel.offer(it)
            }
        }
      }
    }
    .onCompletion {
      if (counter.decrementAndGet() == 0) {
        job?.cancelAndJoin()
        job = null
      }
    }
}

Pacane

03/31/2020, 12:26 PM

Hi, I'm trying to transform a callback-based function to a coroutine. Here's what I have so far

suspend fun fastSubscribe(path: String): Value =
            suspendCancellableCoroutine { cont: CancellableContinuation<Value> ->
                val handler = object : Handler<SubscriptionValue> {
                    override fun handle(event: SubscriptionValue) {
                        requester.unsubscribe(path, this)
                        cont.resume(event.value)
                    }
                }

                requester.subscribe(path, handler)
            }

Here I want to finish the execution with the value in the callback when I have one, but I'd like to add a timeout for if I never get a value (ie: when

handle

is never called) I think I should use a

withTimeout

in there but I don't know where exactly. On timeout I need to call

requester.unsubscribe(handler)

, so having the

withTimeout

on the call site of

fastSubscribe

isn't really a solution. Is there anything I can do with this?

Antoine Gagnon

03/31/2020, 7:06 PM

I’m having some trouble on how to design something with coroutines: I want to do multiple tasks in parallel, but if one of them throws I want to stop all the other ones (putting them in the same coroutineScope seems to do that properly) but I also want to be able to catch any error thrown by the coroutine in the function that launched them (this part is the one I’m struggling with)

rrva

04/01/2020, 5:35 PM

resilience4j ?

MartinZaubitzer

04/01/2020, 8:35 PM

Hey people, I have already asked this in the android channel, but this channel seems to be the better choice. I am struggling to combine coroutines and callbacks for my implementation: I am developing a BLE Server-Client communication protocol which includes messages that receive a custom answer from the peripheral. Now I would like to use coroutines and channels to make a queue of messages to send and only send the next message after a successful response from the peripheral. Currently I am not able to understand how I can await the result of the ble callback since it is not a function that returns anything. Thanks in advance!

Andrey Stepankov

04/02/2020, 1:57 PM

Hi, can someone explain why exception is not consumed by try/catch? Steps to reproduce: fast clicks on button full project

class MainActivity : AppCompatActivity(), CoroutineScope by MainScope() {
  private val singleThread = this + newSingleThreadContext("SingleThread")

  override fun onCreate(savedInstanceState: Bundle?) {
    Timber.plant(Timber.DebugTree())

    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    val api = PokemonApi.createApi()
    button.setOnClickListener {
      singleThread.launch {
        try {
          val names = async { api.getPokemonNames() }
          val types = async { api.getPokemonTypes() }
          val stages = async { api.getPokemonStages() }
          val owners = async { api.getPokemonOwners() }

          names.join()
          types.join()
          stages.join()
          owners.join()
        } catch (e: UnknownHostException) {
          // exception is not consumed
        }
      }
    }

    val crashHandler = Thread.getDefaultUncaughtExceptionHandler()
    val exceptionHandler = Thread.UncaughtExceptionHandler { thread, exception ->
      try {
        Timber.tag("UncaughtException").e(exception)
      } finally {
        crashHandler?.uncaughtException(thread, exception)
      }
    }
    Thread.setDefaultUncaughtExceptionHandler(exceptionHandler)
  }

  interface PokemonApi {
    @GET("/names")
    suspend fun getPokemonNames()

    @GET("/types")
    suspend fun getPokemonTypes()

    @GET("/stages")
    suspend fun getPokemonStages()

    @GET("/owners")
    suspend fun getPokemonOwners()

    companion object {
      fun createApi(): PokemonApi {
        return Retrofit.Builder()
          .baseUrl("<https://unavailable-host.com>")
          .build()
          .create(PokemonApi::class.java)
      }
    }
  }
}

stacktrace

E/UncaughtException: <http://java.net|java.net>.UnknownHostException: Unable to resolve host "<http://unavailable-host.com|unavailable-host.com>": No address associated with hostname
        at <http://java.net|java.net>.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:156)
        at <http://java.net|java.net>.Inet6AddressImpl.lookupAllHostAddr(Inet6AddressImpl.java:103)
        at <http://java.net|java.net>.InetAddress.getAllByName(InetAddress.java:1152)
        at okhttp3.Dns$Companion$DnsSystem.lookup(Dns.kt:49)
        at okhttp3.internal.connection.RouteSelector.resetNextInetSocketAddress(RouteSelector.kt:164)
        at okhttp3.internal.connection.RouteSelector.nextProxy(RouteSelector.kt:129)
        at okhttp3.internal.connection.RouteSelector.next(RouteSelector.kt:71)
        at okhttp3.internal.connection.ExchangeFinder.findConnection(ExchangeFinder.kt:199)
        at okhttp3.internal.connection.ExchangeFinder.findHealthyConnection(ExchangeFinder.kt:108)
        at okhttp3.internal.connection.ExchangeFinder.find(ExchangeFinder.kt:76)
        at okhttp3.internal.connection.RealCall.initExchange$okhttp(RealCall.kt:245)
        at okhttp3.internal.connection.ConnectInterceptor.intercept(ConnectInterceptor.kt:32)
        at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:100)
        at okhttp3.internal.cache.CacheInterceptor.intercept(CacheInterceptor.kt:82)
        at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:100)
        at okhttp3.internal.http.BridgeInterceptor.intercept(BridgeInterceptor.kt:83)
        at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:100)
        at okhttp3.internal.http.RetryAndFollowUpInterceptor.intercept(RetryAndFollowUpInterceptor.kt:74)
        at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:100)
        at okhttp3.internal.connection.RealCall.getResponseWithInterceptorChain$okhttp(RealCall.kt:197)
        at okhttp3.internal.connection.RealCall$AsyncCall.run(RealCall.kt:502)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:919)
    	Suppressed: <http://java.net|java.net>.UnknownHostException: Unable to resolve host "<http://unavailable-host.com|unavailable-host.com>": No address associated with hostname
    		... 24 more
    	Caused by: android.system.GaiException: android_getaddrinfo failed: EAI_NODATA (No address associated with hostname)
        at libcore.io.Linux.android_getaddrinfo(Native Method)
        at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:74)
        at libcore.io.BlockGuardOs.android_getaddrinfo(BlockGuardOs.java:200)
        at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:74)
        at <http://java.net|java.net>.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:135)
        		... 23 more
     Caused by: android.system.GaiException: android_getaddrinfo failed: EAI_NODATA (No address associated with hostname)
        at libcore.io.Linux.android_getaddrinfo(Native Method)
        at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:74)
        at libcore.io.BlockGuardOs.android_getaddrinfo(BlockGuardOs.java:200)
        at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:74)
        at <http://java.net|java.net>.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:135)
        	... 23 more
E/AndroidRuntime: FATAL EXCEPTION: SingleThread
    Process: com.example.myapplication, PID: 24936

Title

Andrey Stepankov

04/02/2020, 1:57 PM

Hi, can someone explain why exception is not consumed by try/catch? Steps to reproduce: fast clicks on button full project

class MainActivity : AppCompatActivity(), CoroutineScope by MainScope() {
  private val singleThread = this + newSingleThreadContext("SingleThread")

  override fun onCreate(savedInstanceState: Bundle?) {
    Timber.plant(Timber.DebugTree())

    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    val api = PokemonApi.createApi()
    button.setOnClickListener {
      singleThread.launch {
        try {
          val names = async { api.getPokemonNames() }
          val types = async { api.getPokemonTypes() }
          val stages = async { api.getPokemonStages() }
          val owners = async { api.getPokemonOwners() }

          names.join()
          types.join()
          stages.join()
          owners.join()
        } catch (e: UnknownHostException) {
          // exception is not consumed
        }
      }
    }

    val crashHandler = Thread.getDefaultUncaughtExceptionHandler()
    val exceptionHandler = Thread.UncaughtExceptionHandler { thread, exception ->
      try {
        Timber.tag("UncaughtException").e(exception)
      } finally {
        crashHandler?.uncaughtException(thread, exception)
      }
    }
    Thread.setDefaultUncaughtExceptionHandler(exceptionHandler)
  }

  interface PokemonApi {
    @GET("/names")
    suspend fun getPokemonNames()

    @GET("/types")
    suspend fun getPokemonTypes()

    @GET("/stages")
    suspend fun getPokemonStages()

    @GET("/owners")
    suspend fun getPokemonOwners()

    companion object {
      fun createApi(): PokemonApi {
        return Retrofit.Builder()
          .baseUrl("<https://unavailable-host.com>")
          .build()
          .create(PokemonApi::class.java)
      }
    }
  }
}

stacktrace

E/UncaughtException: <http://java.net|java.net>.UnknownHostException: Unable to resolve host "<http://unavailable-host.com|unavailable-host.com>": No address associated with hostname
        at <http://java.net|java.net>.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:156)
        at <http://java.net|java.net>.Inet6AddressImpl.lookupAllHostAddr(Inet6AddressImpl.java:103)
        at <http://java.net|java.net>.InetAddress.getAllByName(InetAddress.java:1152)
        at okhttp3.Dns$Companion$DnsSystem.lookup(Dns.kt:49)
        at okhttp3.internal.connection.RouteSelector.resetNextInetSocketAddress(RouteSelector.kt:164)
        at okhttp3.internal.connection.RouteSelector.nextProxy(RouteSelector.kt:129)
        at okhttp3.internal.connection.RouteSelector.next(RouteSelector.kt:71)
        at okhttp3.internal.connection.ExchangeFinder.findConnection(ExchangeFinder.kt:199)
        at okhttp3.internal.connection.ExchangeFinder.findHealthyConnection(ExchangeFinder.kt:108)
        at okhttp3.internal.connection.ExchangeFinder.find(ExchangeFinder.kt:76)
        at okhttp3.internal.connection.RealCall.initExchange$okhttp(RealCall.kt:245)
        at okhttp3.internal.connection.ConnectInterceptor.intercept(ConnectInterceptor.kt:32)
        at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:100)
        at okhttp3.internal.cache.CacheInterceptor.intercept(CacheInterceptor.kt:82)
        at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:100)
        at okhttp3.internal.http.BridgeInterceptor.intercept(BridgeInterceptor.kt:83)
        at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:100)
        at okhttp3.internal.http.RetryAndFollowUpInterceptor.intercept(RetryAndFollowUpInterceptor.kt:74)
        at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:100)
        at okhttp3.internal.connection.RealCall.getResponseWithInterceptorChain$okhttp(RealCall.kt:197)
        at okhttp3.internal.connection.RealCall$AsyncCall.run(RealCall.kt:502)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:919)
    	Suppressed: <http://java.net|java.net>.UnknownHostException: Unable to resolve host "<http://unavailable-host.com|unavailable-host.com>": No address associated with hostname
    		... 24 more
    	Caused by: android.system.GaiException: android_getaddrinfo failed: EAI_NODATA (No address associated with hostname)
        at libcore.io.Linux.android_getaddrinfo(Native Method)
        at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:74)
        at libcore.io.BlockGuardOs.android_getaddrinfo(BlockGuardOs.java:200)
        at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:74)
        at <http://java.net|java.net>.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:135)
        		... 23 more
     Caused by: android.system.GaiException: android_getaddrinfo failed: EAI_NODATA (No address associated with hostname)
        at libcore.io.Linux.android_getaddrinfo(Native Method)
        at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:74)
        at libcore.io.BlockGuardOs.android_getaddrinfo(BlockGuardOs.java:200)
        at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:74)
        at <http://java.net|java.net>.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:135)
        	... 23 more
E/AndroidRuntime: FATAL EXCEPTION: SingleThread
    Process: com.example.myapplication, PID: 24936

streetsofboston

04/02/2020, 2:02 PM

Have you installed a CoroutineException handling in the top-most CoroutineScope? https://medium.com/the-kotlin-chronicle/coroutine-exceptions-3378f51a7d33

👎 1

Andrey Stepankov

04/02/2020, 2:03 PM

Handle do not help me. I think that crash in same reason with https://jakewharton.com/exceptions-and-proxies-and-coroutines-oh-my/

louiscad

04/02/2020, 2:03 PM

Yes I can explain: you need to wrap all your calls to

async

in a local

coroutineScope

, and put your

try

block around it. Without it, the

launch

gets the crash, cancels all children coroutines and crashes its parent scope.

streetsofboston

04/02/2020, 2:05 PM

But wouldn’t calling

await()

on async calls’

Deferred<T>

results be sufficient?

Andrey Stepankov

04/02/2020, 2:05 PM

Hm.. it works. One moment i need to check it on real project.

louiscad

04/02/2020, 2:10 PM

@streetsofboston You need to understand structured concurrency. A crashing child coroutine (i.e. unhandled exception that is not a

CancellationException

) will cancel its parent scope. So if you want to handle errors without crashing the parent scope, you need a middle scope (

coroutineScope { ... }

), and catch exceptions/throwables around it. The intent of the behavior is to cancel fast work in the same scope if one fails, to avoid pursuing unneeded work that cannot be used as a part already failed.

streetsofboston

04/02/2020, 2:12 PM

But installing a

SupervisorJob

MainActivity’s CoroutineScope in the should be sufficient to not cancel the MainActivity’s CoroutineScope after a failure happens. In my opinion, if

names

fails, you want the others (

types

stages

, etc) to be cancelled as well.

(And I do understand structure concurrency 🙂 )

Andrey Stepankov

04/02/2020, 2:13 PM

So... in case like that: I will get error on launch coroute?

launch {
  try {
    getCats()
  } catch() {
    // no-op
  }
}

// getCats will throw UnknownHostException
suspend fun callApi() = httpClient.getCats()

louiscad

04/02/2020, 2:15 PM

If it's an Activity, you should use

lifecycleScope

extension brought by AndroidX Lifecycle runtime KTX 2.2.0+ that already uses a

SupervisorJob

for the case where you use independant

async

where one can fail while letting the other still be useful on its own.

💯 1

Andrey Stepankov

04/02/2020, 2:17 PM

No its not an activity. its

MainScope() + newSingleThreadContext("SingleThread")

streetsofboston

04/02/2020, 2:17 PM

val names = async { api.getPokemonNames() }
          val types = async { api.getPokemonTypes() }
          val stages = async { api.getPokemonStages() }
          val owners = async { api.getPokemonOwners() }

          val listOfResults = listOf(names, types, stages, owners).awaitAll()
          ... or call `await()` on each one individually depending on your use-case...

Your MainActivity implements a CoroutineScope. But as Louis said, use the

lifecycleScope

instead. It is all set up correctly already (

lifecycleScope.launch { …. }

) 🙂

Andrey Stepankov

04/02/2020, 2:28 PM

Yeah. All you advice works well with example. Samething another is wrong on real project. Thx.

Oh.. 🤦 As result is it my bad. I forget to add try catch in another place. Place with flow and async works perfectly.

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