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Hiya,
We’ve been using tolua++ for one of our projects and finding it an absolute joy to work with, very easy to use and understand. However we’ve recently hit a snag as our game gets further along, we’re finding a memory issue with tolua++ user objects and the lua GC. I tried to e-mail the tolua++ author at tolua@codenix.com but I got a rejection from their mailserver.
Anywhere we expect tolua++ objects to be garbage collected (such as a local Vector3 in a function), the GC seems to ignore the userdata pointer in the lua state every cycle, and at the same time constantly increase the GCThreshold until eventually our memory store runs out. The __gc metamethod is being called and tolua++ is calling the correct collector, allowing us to release our App side memory, but when I monitor the lua memory we get the above issue.
Example:
function update()
local vec = Entity:GetPos()
end
This is the result of a basic script for the GC, each time the allocations hit the threshold, the threshold practically doubles.
Mem Usage: 213469, Esti. Mem Usage: 195549, GC Threshold: 391000, GC Dept: 0, GC State: pause
Mem Usage: 213593, Esti. Mem Usage: 195549, GC Threshold: 391000, GC Dept: 0, GC State: pause
Mem Usage: 213685, Esti. Mem Usage: 195549, GC Threshold: 391000, GC Dept: 0, GC State: pause
Mem Usage: 213841, Esti. Mem Usage: 195549, GC Threshold: 391000, GC Dept: 0, GC State: pause
Mem Usage: 213997, Esti. Mem Usage: 195549, GC Threshold: 391000, GC Dept: 0, GC State: pause
Mem Usage: 214025, Esti. Mem Usage: 195549, GC Threshold: 391000, GC Dept: 0, GC State: pause
...
Mem Usage: 390981, Esti. Mem Usage: 195549, GC Threshold: 391000, GC Dept: 0, GC State: pause
Mem Usage: 391009, Esti. Mem Usage: 195549, GC Threshold: 392033, GC Dept: 9, GC State: propagate
Mem Usage: 391037, Esti. Mem Usage: 195549, GC Threshold: 392033, GC Dept: 9, GC State: propagate
Mem Usage: 391065, Esti. Mem Usage: 195549, GC Threshold: 392033, GC Dept: 9, GC State: propagate
Mem Usage: 391093, Esti. Mem Usage: 195549, GC Threshold: 392033, GC Dept: 9, GC State: propagate
Mem Usage: 391121, Esti. Mem Usage: 195549, GC Threshold: 392033, GC Dept: 9, GC State: propagate
Mem Usage: 391149, Esti. Mem Usage: 195549, GC Threshold: 392033, GC Dept: 9, GC State: propagate
Mem Usage: 391177, Esti. Mem Usage: 195549, GC Threshold: 392033, GC Dept: 9, GC State: propagate
Mem Usage: 391205, Esti. Mem Usage: 195549, GC Threshold: 392033, GC Dept: 9, GC State: propagate
...
Mem Usage: 401733, Esti. Mem Usage: 195549, GC Threshold: 402393, GC Dept: 129, GC State: propagate
Mem Usage: 467297, Esti. Mem Usage: 195549, GC Threshold: 467297, GC Dept: 64009, GC State: propagate
Mem Usage: 467297, Esti. Mem Usage: 394325, GC Threshold: 467297, GC Dept: 55845, GC State: finalize
Mem Usage: 467325, Esti. Mem Usage: 298325, GC Threshold: 467325, GC Dept: 47681, GC State: finalize
Mem Usage: 467353, Esti. Mem Usage: 205125, GC Threshold: 410200, GC Dept: 0, GC State: pause
Mem Usage: 467381, Esti. Mem Usage: 205125, GC Threshold: 467381, GC Dept: 48989, GC State: propagate
Mem Usage: 467409, Esti. Mem Usage: 205125, GC Threshold: 467409, GC Dept: 40825, GC State: propagate
Mem Usage: 410093, Esti. Mem Usage: 409425, GC Threshold: 818800, GC Dept: 0, GC State: pause
Mem Usage: 410121, Esti. Mem Usage: 409425, GC Threshold: 818800, GC Dept: 0, GC State: pause
Mem Usage: 410149, Esti. Mem Usage: 409425, GC Threshold: 818800, GC Dept: 0, GC State: pause
Mem Usage: 410177, Esti. Mem Usage: 409425, GC Threshold: 818800, GC Dept: 0, GC State: pause
Mem Usage: 410205, Esti. Mem Usage: 409425, GC Threshold: 818800, GC Dept: 0, GC State: pause
We’ve not modified the GC in any way, and to make sure this wasn’t something general I did the same but creating an empty lua table every frame, the GC behaved correctly.
To add to the confusion, if I force a full garbage collection every frame, the issue goes away and the object is collected correctly.
Any ideas what could be prevent the lua GC from picking up tolua++ objects correctly?
Regards,
Christopher Redden