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POLua metatable Objects cannot be purge from memory?
 

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  1. POLua metatable Objects cannot be purge from memory?
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    <p>I'm using a proprietary platform that reported memory usage in realtime on screen. I decided to use a Class.lua I found on <a href="http://lua-users.org/wiki/SimpleLuaClasses" rel="nofollow noreferrer">http://lua-users.org/wiki/SimpleLuaClasses</a></p> <p>However, I noticed memory issues when purging object created by this using a simple Account class. Specifically, I would start with say 146k of memory used, create 1000 objects of a class that just holds an integer instance variable and store each object into a table. The memory used is now 300k</p> <p>I would then exit, iterating through the table and setting each element in the table to nil. But would never get back the 146k, usually after this I am left using 210k or something similar. If I run the load sequence again during the same session, it does not exceed 300k so it is not a memory leak.</p> <p>I have tried creating 1000 integers in a table and setting these to nil, which does give me back 146k.</p> <p>In addition I've tried a simpler class file (Account2.lua) that doesn't rely on a class.lua. This still incurs memory fragmentation but not as much as the one that uses Class.lua</p> <p>Can anybody explain what is going on here? How can I purge these objects and get back the memory?</p> <p>here is the code --------Class.lua------</p> <pre><code> -- class.lua -- Compatible with Lua 5.1 (not 5.0). --http://lua-users.org/wiki/SimpleLuaClasses function class(base,ctor) local c = {} -- a new class instance if not ctor and type(base) == 'function' then ctor = base base = nil elseif type(base) == 'table' then -- our new class is a shallow copy of the base class! for i,v in pairs(base) do c[i] = v end c._base = base end -- the class will be the metatable for all its objects, -- and they will look up their methods in it. c.__index = c -- expose a ctor which can be called by () local mt = {} mt.__call = function(class_tbl,...) local obj = {} setmetatable(obj,c) if ctor then ctor(obj,...) else -- make sure that any stuff from the base class is initialized! if base and base.init then base.init(obj,...) end end return obj end c.init = ctor c.instanceOf = function(self,klass) local m = getmetatable(self) while m do if m == klass then return true end m = m._base end return false end setmetatable(c,mt) return c end </code> </pre> <p>--------Account.lua------</p> <pre><code> --Import Class template require 'class' local classname = "Account" --Declare class Constructor Account = class(function(acc,balance) --Instance variables declared here. if(balance ~= nil)then acc.balance = balance else --default value acc.balance = 2097 end acc.classname = classname end) </code></pre> <p>--------Account2.lua------</p> <pre><code> local account2 = {} account2.classname = "unnamed" account2.balance = 2097 -----------Constructor 1 do local metatable = { __index = account2; } function Account2() return setmetatable({}, metatable); end end </code></pre> <p>--------Main.lua------</p> <pre><code> require 'Account' require 'Account2' MAX_OBJ = 5000; test_value = 1000; Obj_Table = {}; MODE_ACC0 = 0 --integers MODE_ACC1 = 1 --Account MODE_ACC2 = 2 --Account2 TEST_MODE = MODE_ACC0; Lua_mem = 0; function Load() for i=1, MAX_OBJ do if(TEST_MODE == MODE_ACC0 )then table.insert(Obj_Table, test_value); elseif(TEST_MODE == MODE_ACC1 )then table.insert(Obj_Table, Account(test_value)); --Account.lua elseif(TEST_MODE == MODE_ACC2 )then table.insert(Obj_Table, Account2()); --Account2.lua Obj_Table[i].balance = test_value; end end end function Purge() --metatable purge if(TEST_MODE ~= MODE_ACC0)then --purge stage 0: print("set each elements metatable to nil") for i=1, MAX_OBJ do setmetatable(Obj_Table[i], nil); end end --purge stage 1: print("set table element to nil") for i=1, MAX_OBJ do Obj_Table[i] = nil; end --purge stage 2: print("start table.remove..."); for i=1, MAX_OBJ do table.remove(Obj_Table, i); end print("...end table.remove"); --purge stage 3: print("create new object_table {}"); Obj_Table= {}; --purge stage 4: print("collectgarbage('collect')"); collectgarbage('collect'); end --Loop callback, called every tick function OnUpdate() Lua_mem = collectgarbage('count'); collectgarbage('collect'); end --Loop rendering callback function OnRender() DrawText(Lua_mem ); end ------------------- --NOTE: --code starts in idle awaiting input from user --On first input, runs Load(), on exit runs Purge() --Where DrawText() draws the string parameter passed, to screen. </code></pre> <hr> <p>--Update I've updated the code with suggestions from comments below, and will post my findings later today.</p> <hr> <p>--Update 2 Well I've tried the above code, and it does seem collectgarbage("count") reports lua giving me back all the memory in all three scenarios. Here are my results for collectgarbage('count')</p> <p>ACC0 - On start: 25.567K used - On Load: 89.334K used - On Purge: 25.567K used</p> <p>ACC1 - On start: 25.567K used - On Load: 440.567k used - On Purge: 25.567K used</p> <p>ACC2 - On start: 25.327K used - On Load: 245.34K used - On Purge: 25.327K used</p>
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    1. COHave you tried forcing a garbage collection via `collectgarbage("collect")`? http://www.lua.org/manual/5.1/manual.html#pdf-collectgarbage
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