Re: light userdata (Was: Fastest way to transfer data from C to Lua ?)

[David Demelier <demelier.david@...>]

2013/6/9 Tim Hill <drtimhill@gmail.com>:
> Agreed, the real problem is without __gc on light userdata you can never be
> sure when Lua has released the last pointer, so it is of limited use unless
> the pointer is to static memory or heap memory that will not be released
> until after the Lua state is closed. I'm with you, I tend to wrap C pointers
> in full userdata so that I can track GC correctly.
>
> --Tim
>
> On Jun 9, 2013, at 2:01 AM, David Heiko Kolf <david@dkolf.de> wrote:
>
> In my opinion the term "light userdata" is a bit misleading, as I see
> only a very limited value in using it for storing actual data.  You
> cannot assign different metatables to each light userdata.  That means
> it is later very hard to find out what was actually stored in it.  And I
> don't see any way of making sure that Lua has no stray pointers left --
> except by closing the entire Lua state.  So even when I need to do
> memory handling in C I would store a pointer in a full userdata.
>

For me, lightuserdata is best to use with closure, I usually use them
to store a temporary buffer which will be only used by the closure as
an upvalue, so the script will never know the usage of that userdata
and will never rely on it at anytime. I think nobody should give
lightuserdata to a script just like a variable.


--
Demelier David