Useless exception when offering to actor with cancelled parent

[Pitel]

Let's have this very simplified code:

val job = Job()

val actor = actor<Int>(job, Channel.UNLIMITED) {
	consumeEach {
		println(it)
	}
}

job.cancel()
actor.offer(1)

The last line (offer) causes this exception:

kotlinx.coroutines.JobCancellationException: Job was cancelled; job=JobImpl{Cancelled}@8c661fc
	at kotlinx.coroutines.JobSupport.createJobCancellationException(JobSupport.kt:615)
	at kotlinx.coroutines.JobSupport.createCauseException(JobSupport.kt:640)
	at kotlinx.coroutines.JobSupport.cancelMakeCompleting(JobSupport.kt:604)
	at kotlinx.coroutines.JobSupport.cancelImpl(JobSupport.kt:592)
	at kotlinx.coroutines.JobSupport.cancel(JobSupport.kt:575)
	at kotlinx.coroutines.JobSupport.cancel(JobSupport.kt:570)
	at cz.masterapp.annie2.coroutines.JobTest$test$1.invokeSuspend(JobTest.kt:25)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:32)
	at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:233)
	at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.kt:116)
	at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:76)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:53)
	at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:35)
	at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source)
	at cz.masterapp.annie2.coroutines.JobTest.test(JobTest.kt:16)

One would typically look at JobTest.kt:25, but on line 25 is actualy the cancel() call, making the problematic offer untracable. 😿

In practice, the offers and cancels might be in different files/classes and good luck searching which offer is the cause.

[qwwdfsad]

We have a debug mode for this (-ea flag or kotlinx.coroutines.stacktrace.recovery=on property).

We can't change general channel contract in old actors, but maybe we can fix it in new actors

[Pitel]

From what I see in the code, the kotlinx.coroutines.stacktrace.recovery is enabled by default, if you have kotlinx.coroutines.debug enabled. Which I have, and still gets this useless stack trace.

Maybe I should look att the kotlinx-coroutines-debug module, but it's something completely new for me, and from the readme, it doesn't even say anything about better exception handling.