Curious about implementing deallocators for buffer returned from Rust

[hsfzxjy]

Assume I am writing an API where a heap-allocated byte buffer is returned from Rust to Dart side. The byte buffer will be processed by some Dart code, and then it should be deallocated.

I was wondering if there's any approach to automatically do the deallocation job by, for example, calling a Rust deallocator function when the Dart object is about to be GCed, or I must manually call the deallocator by myself?

[fzyzcjy]

if there's any approach to automatically do the deallocation job by, for example, calling a Rust deallocator function when the Dart object is about to be GCed, or I must manually call the deallocator by myself?

If you say ZeroCopyBuffer<Vec<u8>>, then it is auto deallocated when Dart decides to dispose it. Details can be found in allo-isolate, which is a wrapper around Dart's C api.

if you say any arbitrary data, they are copied (instead of zero-copy) to Flutter, and it is still Flutter's job to deallocate.

[hsfzxjy]

@fzyzcjy Thanks for your reply!

btw, is it possible to implement zero-copied arbitary struct that can also be auto-deallocated? Currently only typed arrays support this feature.

I've spotted there's Dart_CObject.value.as_native_pointer in dart_native_api.h , which seemingly wraps a struct pointer along with a native deallocator. May this be used for the purpose?

[fzyzcjy]

implement zero-copied arbitary struct that can also be auto-deallocated
I've spotted there's Dart_CObject.value.as_native_pointer in dart_native_api.h , which seemingly wraps a struct pointer along with a native deallocator. May this be used for the purpose?

Seems no. We have had some discussions with the dart team and realized impossible. You may search in this repo and dart repo, and possibly also #293.

[hsfzxjy]

Many thanks again for the instruction.

[fzyzcjy]

You are welcome!