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- Subject: Re: C interface, destructor and __gc question
- From: Coda Highland <chighland@...>
- Date: Wed, 15 Apr 2015 09:15:59 -0700
On Wed, Apr 15, 2015 at 8:03 AM, Thijs Schreijer
> Op 15 apr. 2015 10:02 schreef Laurent FAILLIE <firstname.lastname@example.org>:
>> I would like to have some clarification about the way I can implement à destructor of a C object.
>> As per http://www.lua.org/pil/29.1.html, it should be implemented using __gc but ... when will it be called.
>> I have an object that is managing a windows and I would like to ensure this windows is destroyed as soon as it's representing object is not anymore used.
>> In other words,
>> for a code like
>> if somestuff then
>> wnd = SelSurface.create()
>> ... bla bla bla ..
> I think the only way is to manually destroy it. Insert something like;
> Or manually run a GC cycle.
> If you create a userdata, have a flag for it being alive or closed. When calling destroy, get rid of everything you need to clean up and flag it as closed. Any further access of the closed userdata should now result in an error. Still leaves the user data itself to be cleaned up by the GC.
To follow up on this: Lua, like Java, doesn't have proper destructors
like C++ does. __gc is more of a finalizer than a destructor -- a way
to clean up resources if they're found to not be in use, rather than
an explicit shutdown routine.
Manually running a GC cycle isn't necessarily going to do the job
anyway -- for one thing, in some cases you have to run two sweeps to
eject objects; for another, if something somewhere else is holding a
reference then the GC won't do anything either. An explicit destroy is
necessary if you need to ensure certain properties with a certain