If I create instance of Kotlin Class in Swift Code and have strong reference to it, I can see this i...

# multiplatform

[Dmitry Motyl]

If I create instance of Kotlin Class in Swift Code and have strong reference to it, I can see this instance in memory graph.
I expected if I set null to reference, instance will be disposed.
Unfortunately I see this instance in memory.

Why GC doesn’t clear memory?

[kpgalligan]

1.3.40?

[Dmitry Motyl]

yes

[kpgalligan]

The runtime caches a few allocations to cut down on alloc calls. May be that? https://github.com/JetBrains/kotlin-native/blob/master/runtime/src/main/cpp/Memory.cpp#L1171

[kpgalligan]

If you're creating a single object, that will be tough to avoid. Maybe try creating a bunch and see if.the runtime is "leaking" them (i doubt it)

[Dmitry Motyl]

I dont understand. Do you want to say that is correct case for one object?

[kpgalligan]

Yeah, I would expect a single object not to have it's memory cleared, but usually I confirm things before saying them. However, currently on a boat

[kpgalligan]

So, it might be that

[Dmitry Motyl]

Kotlin/Native provides an automated memory management scheme, similar to what Java or Swift provides. The current implementation includes an automated reference counter with a cycle collector to collect cyclical garbage.

I thought that

reference counter

must clear memory

[kpgalligan]

In 1.3.31 and earlier it would clear immediately. 1.3.40 has some optimizations. One of which is to queue deallocations and reuse allocations if appropriate

[Dmitry Motyl]

I’ve tried to create several instances and after each creation I delete reference.
All objects are in memory

[kpgalligan]

How many is several?

[Dmitry Motyl]

15

[kpgalligan]

Threshold is 32 as I recall. Try 100, 1000, etc

[kpgalligan]

https://github.com/JetBrains/kotlin-native/blob/master/runtime/src/main/cpp/Memory.cpp#L85

[Dmitry Motyl]

100, 1000 - all in memory

[kpgalligan]

Are you checking at a breakpoint?

[kpgalligan]

Assume you're creating with a loop. Make sure you have an autorelease pool in Swift and check outside of it

[Dmitry Motyl]

I use Debug Memory Graph in Xcode

[kpgalligan]

Post code

[Dmitry Motyl]

I tried with autorelease pool. It is same

[kpgalligan]

Well, again, post code, but if you think you found a legit bug where Kotlin native is leaking memory in simple allocations that would be interesting news. Im on a phone and can't see your code so it's difficult to comment further

[Dmitry Motyl]

var kotlinClass = KotlinClass()
        
        for _ in 1...1000 {
            autoreleasepool {
                kotlinClass = KotlinClass()
            }
        }

[Dmitry Motyl]

class KotlinClass {
    fun foo() {
    }
}

[kpgalligan]

Why are you assigning the variable outside of the Auto release pool?

[kpgalligan]

Put the autorelease around the loop

[Dmitry Motyl]

autoreleasepool {
            var kotlinClass = KotlinClass()
            for _ in 1...1000 {
                kotlinClass = KotlinClass()
            }
            print(kotlinClass)
        }

[Dmitry Motyl]

same

[Dmitry Motyl]

[kpgalligan]

That leaks 1000 kotlin instances? Ok, well, I'd suggest creating a small sample project and posting to GitHub.

[kpgalligan]

Can you screenshot the whole tool window?

[Dmitry Motyl]

[kpgalligan]

With the memory debugger. Ideally a video of it. I want to verify what you're doing and I can try later. I'd be surprised if kotlin is leaking simple objects with no references to them, but I want to verify what you're doing to replicate. Presumably the memory debugger is stopping on some line. If you're measuring after 'viewDidLoad' that would be very interesting

[Dmitry Motyl]

I hope it is enough.
On 1.3.30 Everything is fine - no memory leak

[kpgalligan]

There also appears to be a min size trigger on GC, but I haven't tested much with that. I will say I've done large alloc tests and don't have macro size leaks

[kpgalligan]

My guess is those objects are queued to be removed, but again, on a koat

[kpgalligan]

*boat

[kpgalligan]

Can't run anything directly

[Dmitry Motyl]

Thank for discuss)
Strange for me that it was introduced so conceptual change.
I know that for Java world it is ok, but not for Swift.

Kotlin/Native provides an automated memory management scheme, similar to what Java or Swift provides.

[kpgalligan]

New for me too. I'm used to the kotlin native model from earlier versions. However, they've improved performance significantly (or so I'm told ;)

[olonho]

@Dmitry Motyl please report an issue with reproducer. Could be problem in either K/N, Swift or your memory debugger.

[svyatoslav.scherbina]

autoreleasepool shouldn’t be required in this particular case.
This behaviour is likely caused by deferred reference counting implemented in 1.3.40.
Add kotlin.native.internal.GC.collect() call to process the objects to be released.

[olonho]

@kpgalligan BTW, threshold of GC is 16384 at the moment, 32 is finalization queue threshold

[svyatoslav.scherbina]

Also note that manual GC.collect is not required for your application to work properly, because K/N memory manager invokes it automatically after the threshold has been reached.