Lua - decrementing "class" object count when object is removed from memory

Question

I'm currently working on a MOAI project using Lua. I"m trying to set up some stress tests for some of the game objects, and in turn tracking when the Lua objects I have are created and destroyed during a game session. I can easily track when an "class" object/table has been initialized by incrementing the count in the constructor or initializer. However, because Lua does not have destructors, I'm not sure how I can track when an object has been removed from memory.

Would appreciate any help or suggestions on this matter. Thanks!

score 2 · Answer 1 · edited Mar 14 '13 at 19:17

2

To be notified when a Lua object (I assume full userdata or table) is gone, you set a _gc metamethod for it.

edited Mar 14 '13 at 19:17

hugomg

68,213
24
160
246

answered Mar 14 '13 at 18:02

lhf

70,581
9
108
149

1

I don't think this will work in MOAI as it uses Lua 5.1. Also `debug` and `newproxy` are not available. – finnw Mar 14 '13 at 23:24
@finnw, you're right, if the objects are pure Lua tables, then there is no way to get gc notifications. I thought they were userdata created in C. – lhf Mar 15 '13 at 00:30

score 1 · Answer 2 · answered Mar 18 '13 at 22:11

Perhaps weak tables is your answer, with nesting. Here's a snippet:

objectArray={}

function newObj(...)
   --your OOP code here
   --obj is the new table you made
   objectArray[#objectArray+1]=setmetatable({obj},{__mode='v'})
end

Now, in a function/block that runs every frame:

for i=1,#objectArray do --no pairs for efficiency, being run every frame this matters
   local stillThere=#objectArray[i]
   stillThere=stillThere==1
   if not stillThere then deconstruct() end
end

Unfortunately, you can't get the table back. I'm not sure if there's an easy solution to this, because __index halts GC.

Lua - decrementing "class" object count when object is removed from memory

2 Answers2