Lua memory leak when add lua table in userdata object

Question

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When I pressed the 'btn' memory rose up from 80M to 240M. And I pressed the 'btn2' to remove the object(self.sprite) include many lua table, but the memory didn't go down.

What wrong with this code? Or it is a lua bug?

I used cocos2dx-3.8.1/xcode7/ios simulator.

local MainScene = class("MainScene", cc.load("mvc").ViewBase)
function MainScene:onCreate()
    local btn = ccui.Button:create("res/Button_Normal.png","res/Button_Press.png","res/Button_Disable.png")
    btn:setScale9Enabled(true)
    btn:setContentSize(cc.size(70,70))
    btn:setPosition(100,100)
    btn:setTitleColor(cc.c3b(0,0,0))
    btn:setTitleFontSize(30)
    btn:setTitleText("Add")
    btn:addTouchEventListener(function(ref,typ)
        if typ == ccui.TouchEventType.ended then
            self.sprite = cc.Sprite:create("res/Button_Normal.png")
            for i=1,1000000 do
                self.sprite["s_"..i] = {"abc",123}
            end
            self.sprite:setPosition(100, 200)
            self:addChild(self.sprite)
        end
    end)
    self:addChild(btn)
    local btn2 = ccui.Button:create("res/Button_Normal.png","res/Button_Press.png","res/Button_Disable.png")
    btn2:setScale9Enabled(true)
    btn2:setContentSize(cc.size(70,70))
    btn2:setPosition(200,100)
    btn2:setTitleColor(cc.c3b(0,0,0))
    btn2:setTitleFontSize(30)
    btn2:setTitleText("remove")
    btn2:addTouchEventListener(function(ref,typ)
        if typ == ccui.TouchEventType.ended then
            if self.sprite then
            self.sprite:removeFromParent(true)
            self.sprite = nil
            end
        end
    end)
    self:addChild(btn2)
end
return MainScene

Please bring the code directly to the post. That way, no one has to click on a link to view what code you have. Additionally, see if you can break it down to what specifically is causing the increase. Thank you! — Josh, Oct 27 '15 at 04:06
Did you wait for the garbage collector to run? Did you force it to run? Did you force it twice? — Etan Reisner, Oct 27 '15 at 04:38
@EtanReisner Run twice and the memory added twice. I try to garbage collection, but the memory did not return to the initial state. — superyyl, Oct 27 '15 at 05:07
You ran the *collector* twice? Did you actually see the gc run? Do your objects have `__gc` metamethods? Did they get called? Do the objects have deletion functions you can call manually? — Etan Reisner, Oct 27 '15 at 11:35

score 1 · Accepted Answer · answered Oct 27 '15 at 15:18

It's probably not a memory leak. You can use Lua garbage collection methods to see how much memory Lua allocates to those structures. For example, try the following:

collectgarbage("count") -- #1 returns something like 2574.62890625 (in Kb)
-- allocate and release memory
collectgarbage() -- collect memory
collectgarbage()
collectgarbage("count") -- #2 check the amount of memory

You should see about the same amount of memory used in 1 and 2 (assuming everything that was allocated was released as it doesn't have anything holding a reference), but in general you should not expect the memory reported by the operating system to go down to the original amount because of the fragmentation. You should expect Lua to continue reusing the memory it released, so if you allocate the same structures again, the total amount of memory will stay approximately the same.

I doubt there is a memory leak in Lua unless you can demonstrate it on a much simpler script that doesn't involve cocos2dx API.

This means that Lua collected and released all the memory it allocated between the calls, which is what you'd normally expect. This doesn't mean that the OS gets the memory back or that there are no leaks in cocos2dx. — Paul Kulchenko, Oct 28 '15 at 05:40

Lua memory leak when add lua table in userdata object

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