Sehz (Mar 23 2024 at 00:06): Sehz (Mar 23 2024 at 00:06):Is post_return https://docs.rs/wasmtime/latest/wasmtime/component/struct.Func.html#method.post_return required after calling function? This seems take considerable amount of time.
Alex Crichton (Mar 23 2024 at 03:09):If no further functions are used on a component, no, it can be omitted. If another function is going to be invoked, yes, it is required.
Can you clarify why it's taking a considerable amount of time? Or do you have an example we could perhaps profile and try to optimize?
Karel Hrkal (kajacx) (Mar 23 2024 at 16:39):I think it gives the guest an opportunity to destroy the returned object after the host has read it's contents. If you are returning a complex object, it's address is returned and the host reads the data at that address and then the guest destroys the object (explicitly in Rust/C/C++, dropping a reference to in GC languages) in the post-return call, since the host cannot know how the guest manages it's memory. Or at least I think this is how it works.
Sehz (Mar 23 2024 at 17:16):does it still needed If I am invoking same function? this seems to be error prone. I am invoking same function many times repeatedly
Sehz (Mar 23 2024 at 17:20):I guess, why not call invoke object cleaning in fun call so this is invisible to API.
Alex Crichton (Mar 24 2024 at 17:09):Karel is correct, that's what post-return enables at the ABI level. At the API level splittng out post_return from call enables WasmStr and WasmList types to exist which borrow directly from linear memory. With post_return bundled in they couldn't exist.
I'll note that with bindgen!-generated APIs post_return happens automatically, so if you don't want to worry about post-return I'd recommend using those APIs instead
Last updated: Dec 23 2024 at 13:07 UTC