Re: Confused by Lua garbage collection tear down order when there are references between objects

[Coda Highland <chighland@...>]

On Wed, May 21, 2014 at 3:07 PM, Philipp Janda <siffiejoe@gmx.net> wrote:
> Am 21.05.2014 21:04 schröbte Tim Hill:
>>
>>
>> On May 20, 2014, at 6:49 PM, Philipp Janda <siffiejoe@gmx.net> wrote:
>>>
>>>
>>> They are collected in the reverse order that they were marked for
>>> finalization[1] (usually by setting the metatable), so B will always be
>>> collected before A if both become garbage at the same time, because it was
>>> created/marked last.
>>>
>>
>> I’m not sure this is true; the Lua docs say “in the reverse order
>> they were marked for COLLECTION” (not finalization). So my reading is
>> that the order depends entirely on the order in which the GC
>> determines objects to be unreachable, and (in my reading of it at
>> least) I don’t see a clear guarantee of that ordering in the docs.
>
>
> Good point. The wording is definitely ambiguous (given that Lua uses a
> _mark_ and sweep collector) and should be cleared up in the manual.

I'm not certain I agree. This feels like an implementation detail and
formalizing it as a required behavior carries a smell to me. My
opinion is the opposite -- the documentation should be removed to
avoid asserting any sort of guarantee about the behavior, since not
every Lua implementation is going to necessarily have the same
behavior as PUC-Rio Lua.

/s/ Adam