How does `AutofreeScope` and `Arena` work? do they automatically free the allocated memory when the...

# kotlin-native

[Leon Kiefer]

How does AutofreeScope and Arena work? do they automatically free the allocated memory when they are garbage collected, or is there some other mean to ensure native memory is freed if a kotlin object is garbage collected? We are currently wrapping a native library with a common code api and can not expose native memory management in the common code api.

[Leon Kiefer]

this is the project for reference https://github.com/voize-gmbh/pytorch-lite-multiplatform/pull/16

[Landry Norris]

Arena has a clear method. When you alloc an object, the Arena adds the pointer to a linked list. When you call clear , it loops through this linked list and frees each pointer.

[Landry Norris]

It is not safe to manually free a pointer allocated by an arena or other AutoFreeScope, other than by using methods provided by the AutoFreeScope.

[Landry Norris]

Looking at the comment on the PR, it looks like the maintainer wants to use common APIs, potentially to move the tests to common code. I’m not familiar with PLMScope, but it looks like it is the same thing as memScoped, but common.

[Arkadii Ivanov]

There is cleaner to automatically clean when the holding object is garbage collected. Here is how I use it - https://github.com/arkivanov/MVIKotlin/blob/62fceaaab920c7ea2460ec82c22c99a35cf12b95/rx-internal/src/nativeMain/kotlin/com/arkivanov/mvikotlin/rx/internal/Lock.kt#L25

[Leon Kiefer]

From the name "AutofreeScope" I would expect that the native memory is automatically freed when the holding object is garbage collected

[Leon Kiefer]

@Landry Norris we want to use common API, so we can use the library in common code without duplicating business logic for multiple platforms

[Leon Kiefer]

We use the expected class PLMScope to wrap a native placement, so we can pass it into our common api

[Landry Norris]

I see

[Landry Norris]

It would be hard to say for sure without seeing the PLMScope source. Scopes should work with C structs, so it shouldn’t be shareable regardless.

[Leon Kiefer]

https://github.com/voize-gmbh/pytorch-lite-multiplatform/blob/787131fec09252b6831caeb74e34957e133abfc2/src/iosMain/kotlin/de/voize/pytorch_lite_multiplatform/PLMScope.kt