Re: Problem with circular refrence and garbage collection

["Sam Roberts" <vieuxtech@...>]

On Sat, Jan 10, 2009 at 12:05 AM,  <malobu@cox.net> wrote:
> I am creating a Lua api for a gui toolkit i am working on and have run
> into a snag with garbage collection not happening when there is a
> circular refrence.
>
> --After this chunk is run there is no refrence to frame, it is collected
> eventually the problem is col and the button that is attached to it is
> never collected
> local frame = cwl:createFrame("Hello World")
>
> --attachTo will create a refrence to col in frame, which goes away when
> the frame is collected
> local col = cwl:createColumn():attachTo(frame)
>
> --attachTo will create a refrence to button in col
> local button = cwl:createButton():attachTo(col)
>
> --the function is refrenced by the button to lock it into existence
> until the button is collected.
> --but when I create this closure with col as an upvalue, it locks col
> into existence, when frame is collected, col is not becuase of this
> refrence.
> button:onEvent("click", function(b) col:selectRow(i) end)

How does button (a userdata, I assume?), keep the reference to the function,
using luaL_ref()? I "think" that if it uses the userdata's fenv, that
lua would see the cycle, and be able to collect.

Sam