Re: garbage collection and setfenv

["Matthew Armstrong" <turkeypotpie@...>]

I'm only using the __gc method for cleanup detection.  If it is creating another reference to the environment, is there another way to detect collection that doesn't maintain a reference?

On Tue, Mar 18, 2008 at 7:02 PM, Daniel Stephens <daniel@danielstephens.com> wrote:

The __gc closure you create inside tryThis will have inherited the
global environment from tryThis at the time it was executed, so it's
going to have a reference to that environment, but I'm not sure that
would be a reachable reference.

Daniel.

Matthew Armstrong wrote:
> I had already tried the setfenv(tryThis, {}) idea, and it didn't
> work.  After your mail, I also tried tryThis = nil, which also didn't
> work.  Here is my non-trimmed code:
>
> function tryThis()
>     myVar = GfcTimer()
>     local mt = getmetatable(myVar)
>     mt.__gc = function()
>         print("!!! cleanup")
>         ldb()
>     end
>
>     --myVar = nil
> end
>
> function yup()
>     local env = {}
>     setmetatable(env, { __index = _G })
>     setfenv(tryThis, env)
>
>     tryThis()
>
>     setfenv(tryThis, {})
>     tryThis = nil
>     env = nil
>
>     collectgarbage()
> end
>
> yup()
>
> Note:  there is one external function, GfcTimer, which generates a
> userdata object from our library.
>
> If I uncomment the line:
>
> -- myVar = nil
>
> ... then I get a confirmed call to the __gc method.
>
> Can you see anything else which would maintain a reference?
>
> On Tue, Mar 18, 2008 at 5:55 PM, Roberto Ierusalimschy

> <roberto@inf.puc-rio.br <mailto:roberto@inf.puc-rio.br>> wrote:
>
>     > So let's say I say:
>     >
>     > function tryThis()
>     >     myVar = { foo="baz" }
>     > end
>     >
>     > local env = {}
>     > setfenv(tryThis, env)
>     > tryThis()
>     >
>     > My question is: when does myVar get collected?  With my current
>     testing, it
>     > seems that myVar never gets collected.  If so, how do I
>     "convince" it to be
>     > collected?
>
>     'env' is the environment of 'tryThis' (which is global), so it
>     cannot be
>     collected until tryThis is garbage or until you change its environment
>     again. You may try "tryThis = nil" or "setfenv(tryThis, {})".
>
>     -- Roberto
>
>