Some codes won't be executed after throwing an exception

[Tea-Ayataka]

Code:

import kotlinx.coroutines.experimental.*

fun main(args: Array<String>) {
    val job = Job()
    val context = Dispatchers.Default + job
    val scope = CoroutineScope(context)

    runBlocking {
        scope.launch { say("first") }
        delay(1000)
        scope.launch { say("second") }
        delay(1000)
    }
}

fun say(text: String) {
    println("Hello World")
    throw IllegalArgumentException(text)
}

Result:

Hello World
Exception in thread "DefaultDispatcher-worker-2" java.lang.IllegalArgumentException: first
	at test.kotlin.CoroutineTestKt.say(CoroutineTest.kt:20)
	at test.kotlin.CoroutineTestKt$main$1$1.doResume(CoroutineTest.kt:11)
	at kotlin.coroutines.experimental.jvm.internal.CoroutineImpl.resume(CoroutineImpl.kt:42)
	at kotlinx.coroutines.experimental.DispatchedTask$DefaultImpls.run(Dispatched.kt:168)
	at kotlinx.coroutines.experimental.DispatchedContinuation.run(Dispatched.kt:13)
	at kotlinx.coroutines.experimental.scheduling.Task.run(Tasks.kt:94)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:586)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler.access$runSafely(CoroutineScheduler.kt:60)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:732)
Exception in thread "DefaultDispatcher-worker-2" java.lang.IllegalArgumentException: first
	at test.kotlin.CoroutineTestKt.say(CoroutineTest.kt:20)
	at test.kotlin.CoroutineTestKt$main$1$1.doResume(CoroutineTest.kt:11)
	at kotlin.coroutines.experimental.jvm.internal.CoroutineImpl.resume(CoroutineImpl.kt:42)
	at kotlinx.coroutines.experimental.DispatchedTask$DefaultImpls.run(Dispatched.kt:168)
	at kotlinx.coroutines.experimental.DispatchedContinuation.run(Dispatched.kt:13)
	at kotlinx.coroutines.experimental.scheduling.Task.run(Tasks.kt:94)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:586)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler.access$runSafely(CoroutineScheduler.kt:60)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:732)

So, I have no idea wtf is going on.

Kotlin 1.2.71
Coroutine 0.30.2
Java 1.8.0_181

[qwwdfsad]

Please clarify what behaviour are you expecting here?

[Tea-Ayataka]

If i execute multiple launch or async with the same coroutine scope and an exception is thrown from one of them, The program stops working correctly.
This won't happen if i use GlobalScope instead.

[Tea-Ayataka]

I was excepting the following result.

Hello World
Exception in thread "DefaultDispatcher-worker-1" java.lang.IllegalArgumentException: first
	at test.kotlin.CoroutineTestKt.say(CoroutineTest.kt:20)
	at test.kotlin.CoroutineTestKt$main$1$1.doResume(CoroutineTest.kt:11)
	at kotlin.coroutines.experimental.jvm.internal.CoroutineImpl.resume(CoroutineImpl.kt:42)
	at kotlinx.coroutines.experimental.DispatchedTask$DefaultImpls.run(Dispatched.kt:168)
	at kotlinx.coroutines.experimental.DispatchedContinuation.run(Dispatched.kt:13)
	at kotlinx.coroutines.experimental.scheduling.Task.run(Tasks.kt:94)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:586)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler.access$runSafely(CoroutineScheduler.kt:60)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:732)
Hello World
Exception in thread "DefaultDispatcher-worker-1" java.lang.IllegalArgumentException: second
	at test.kotlin.CoroutineTestKt.say(CoroutineTest.kt:20)
	at test.kotlin.CoroutineTestKt$main$1$2.doResume(CoroutineTest.kt:13)
	at kotlin.coroutines.experimental.jvm.internal.CoroutineImpl.resume(CoroutineImpl.kt:42)
	at kotlinx.coroutines.experimental.DispatchedTask$DefaultImpls.run(Dispatched.kt:168)
	at kotlinx.coroutines.experimental.DispatchedContinuation.run(Dispatched.kt:13)
	at kotlinx.coroutines.experimental.scheduling.Task.run(Tasks.kt:94)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:586)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler.access$runSafely(CoroutineScheduler.kt:60)
	at kotlinx.coroutines.experimental.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:732)

[qwwdfsad]

The current behaviour is expected.
What happens:

1. scope.launch { say("first") } executes, fails with an exception and fails its parent (which is plain Job you put in the scope)
2. When line with scope.launch { say("second") } is executing, parent job is already cancelled and thus this launch is not even started and became immediately failed.

You have two options to have a desired behaviour:

1. Replace Job with SupervisorJob. SupervisorJob is not cancelled on child failure, but it cancels children when svJob.cancel() is invoked
2. Use launch(start = CoroutineStart.ATOMIC). Then coroutine will be launched anyway (but in "failing" state) and fail on first cancellable suspensin point

[hrach]

@qwwdfsad

is not even started and became immediately failed.

I get this. But I do not expect the result of this should result in

Exception in thread "DefaultDispatcher-worker-2" java.lang.IllegalArgumentException: first

but some other exception that will tell me that the parent job is in failed state.

[qwwdfsad]

Yes, this is slightly counter-intuitive.

But consider following code:

val job = Job()
CoroutineScope(job).launch {delay(Long.MAX_VALUE) }
job.cancel(IllegalArgumentException())

Do you expect to IllegalArgumentException to be printed? Presumably yes.

Now assume there is a race between lines 2 and 3 (or just swap these lines). Should behaviour be different in that case? The current answer is "no", though we can consider reworking this part