so the above issue is actually rooted in using `CoroutineWorker.execute` with `CompletableDeferred`....

# multiplatform

[Kris Wong]

so the above issue is actually rooted in using CoroutineWorker.execute with CompletableDeferred. anyone have an idea why completing the deferred might deadlock when used from execute?

[basher]

do you have a code sample?

[Kris Wong]

i can distill it down into a basic example

[Kris Wong]

@Test fun testSomething() = runBlocking {
    val deferred = CompletableDeferred<Unit>()
    CoroutineWorker.execute {
        ...
        deferred.complete(Unit)
    }
    deferred.await()
}

[Kris Wong]

it deadlocks on deferred.complete

[basher]

is this using native mt branch or something?

[Kris Wong]

no

[basher]

that's going to freeze deferred then, which could do bad things

[basher]

there's probably internal state you're freezing

[basher]

it may not be deadlocking as much as crashing on a bg thread and dying silently

[Kris Wong]

any problems from that would throw an exception, would it not?

[basher]

and then your main thread never finishes waiting on the deferred

[basher]

yes but exceptions in Worker do not crash the app

[basher]

they just log

[Kris Wong]

hmmm

[basher]

that's why CoroutineWorker has a special mechanism for capturing Worker exceptions so that you can manually crash, if that's what you want

[Kris Wong]

i've always gotten a stack trace when i've had issues with freezing in the past

[basher]

you won't get the exception when you freeze, you'll get it later in the background when you try to complete the deferred

[Kris Wong]

understood

[basher]

that function btw: https://github.com/Autodesk/coroutineworker/blob/master/src/nativeMain/kotlin/com/autodesk/coroutineworker/BackgroundCoroutineWorkQueueExecutor.kt#L144

[basher]

logs might show the exception, assuming my guess is correct

[Kris Wong]

i'll give it a shot

[basher]

Best documentation I can find about worker uncaught exceptions is just the param for Worker.start: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.native.concurrent/-worker/start.html

[basher]

IIRC, it was just something we observed when testing things for our first App Store release

[Kris Wong]

the handler is not receiving an exception in this case

[Kris Wong]

well, whatever the actual root cause is, seems like I am going to be rolling my own kind of Deferred to fix this, so I might as well just do that

[Kris Wong]

so strange, now that's fixed (something about COROUTINE_SUSPENDED seems to cause the dead lock), but now I have the same behavior with Semaphore

[basher]

What's COROUTINE_SUSPENDED?

[basher]

Semaphore also can't be frozen, if you mean the one from coroutines lib

[Kris Wong]

it's a special value used with suspendCoroutine

[Kris Wong]

i replaced semaphore with the same class I used in place of deferred

[Kris Wong]

now it's all working

[basher]

Huh 👌

[Kris Wong]

¯\_(ツ)_/¯