Re: garbage collection and setfenv

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

So my non-trimmed code posted previously is actually a simplified version of my real code, which I won't post here because it's too big.  I'm still running into the problem where something is maintaining a reference to my environment table, but for the life of me I can't figure out where.

Is there a facility to trace back references for a given object?   I didn't see something like that in the debug interface.

On Tue, Mar 18, 2008 at 7:51 PM, Matthew Armstrong <turkeypotpie@gmail.com> wrote:

With response to Daniel Stephens code:

----------------------------------------------------------------------------------

function detectGc()
 print("!!! cleanup")
 ldb();
end

function tryThis(gcFunc)

 myVar = GfcTimer();
 local mt = getmetatable(myVar);

 mt.__gc = gcFunc;
end

----------------------------------------------------------------------------------

I break correctly if I define my garbage handler this way, or if I just pass it in through my environment table.  So it looks like it was just my detection method that skewed my view of what was going on :)


With response to Patrick Donnelly's code:

----------------------------------------------------------------------------------

function tryThis()
 myVar = newproxy()
 print(myVar)
 local mt = getmetatable(myVar) or {}
 debug.setmetatable(myVar, mt);

 mt.__gc = function()
   print("!!! cleanup")

 end
end

function yup()
 setfenv(tryThis, setmetatable({}, { __index = _G }))
 tryThis()
 setfenv(tryThis, {})
 collectgarbage()
end

yup();

----------------------------------------------------------------------------------

I don't break correctly, as he does, when I use the code verbatim (except for substituting newproxy for GfcTimer).   I don't know what's causing the discrepancy between our two results.
Note: I did have a local variable 'env' referencing the environment, but I set it to nil.  I'm not sure whether it would make a difference in either way.

Thanks everyone for your help :)

On Tue, Mar 18, 2008 at 7:24 PM, Patrick Donnelly <batrick.donnelly@gmail.com> wrote:

Running the following in the Lua interpretter:

function tryThis()
 myVar = newproxy()
 print(myVar)
 local mt = getmetatable(myVar) or {}
 debug.setmetatable(myVar, mt);

 mt.__gc = function()
   print("!!! cleanup")

 end
end

function yup()
 setfenv(tryThis, setmetatable({}, { __index = _G }))
 tryThis()
 setfenv(tryThis, {})
 collectgarbage()
end

yup();

The following is output:
batrick@waterdeep:~$ lua test.lua
userdata: 0x806f9ec
!!! cleanup

I believe your problem is that you are expecting the environment to be
collected when a local variable has a reference to it =)

Cheers,

--
-Patrick Donnelly

"One of the lessons of history is that nothing is often a good thing
to do and always a clever thing to say."

-Will Durant