Hello, World! I have a behavior difference when using the new memory manager or not with this very s...

# kotlin-native

[bod]

Hello, World! I have a behavior difference when using the new memory manager or not with this very simple app (on Apple):

fun main() {
    runBlocking {
        withContext(Dispatchers.Main) {
            println("Hello, World!")
        }
    }
}

With the new memory manager enabled, the message is never printed, the thread seems to be stuck on withContext.
I’m not sure if this is to be expected - something like runBlocking blocking the main thread and making dispatching ineffective? … But then again it feels like this should work, and also looks like a regression since it works with the old MM? 🤔
Any insight would be appreciated! 🙏
Repro project here.

[Arkadii Ivanov]

This looks like a reasonable deadlock. runBlocking blocks the main thread, and so withContext can't submit its job.

[Arkadii Ivanov]

It's an equivalent to Rx:

completableFromFunction { println() }
    .subscribeOn(mainScheduler)
    .blockingAwait()

[bod]

That sounds reasonable but still wondering why it works without the new MM.

[bod]

as a side note: using Dispatchers.Main.immediate avoids the hang

[Arkadii Ivanov]

I thought the immediate dispatcher is only available on Android, unless something has changed recently.

Also it looks like you don't need to switch context at all, because you are already on the main thread.

[Arkadii Ivanov]

The doc says it's not supported on native and JS - https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-dispatchers/-main.html

[bod]

Interesting about immediate! Wondering if the doc is outdated. Will look at the source 🙂

You are right about not really needing this, just exploring and trying to understand why some of our tests are now failing (well, not failing but hanging).

[bod]

I think that's it

[Arkadii Ivanov]

Cool! Good to know!