pixelherodev commented on PR #578:
URL: https://github.com/apache/arrow-go/pull/578#issuecomment-3573675481
I'm just going to write up the design notes as one place to explain all the
weirdness:
- Looking over the existing code for Message/MessageReader, there's a few
requirements:
- Buffers get released when the last reference to them is erased.
- When buffers get released, we also nil out the pointer to them.
- When 1 object is released, we want to walk every object it references
and release those too.
- This is often done by _value at the time of Release_, not when the
object is created, and includes a "if != nil" check. The object may not be
created until _after the object is initialized_, if ever, and should be
released regardless. e.g. `MessageReader.msg` is a `*Message`, and has a
different value for each Message that is read.
So, in trying to _separate_ the concerns of reference counting and object
management, and trying to make it all declarative and only called on object
initialization - keeping the refcount graph _static_, even as the objects in it
may be dynamic! - I settled on using two-level-pointers. The address of
`MessageReader.msg` is fixed, even as its value may change - we want to release
whatever the _final value is_ when MessageReader gets released, and we don't
want to insert a lot more code dynamically shifting around the reference graph.
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