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- Subject: Re: Using Lua's memory allocator
- From: Gavin Wraith <gavin@...>
- Date: Tue, 11 Oct 2011 15:54:36 +0100
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<[email protected]>
<[email protected]>
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In message <[email protected]> you wrote:
> > If I grab some memory using lua_newuserdata, and after using that memory
> > for the above-mentioned operations simply throw away the pointer to it
> > (i.e. never push it on the Lua stack), then that memory will be reclaimed
> > - have I got that right?
>
> First, to use automatic stack management, i.e. to have dedicated stack frame,
> all your functions should be "Lua C functions" (see lua_CFunction) and be called
> from Lua or using lua_call() etc. Big work here. Otherwise, you can only use
> initial Lua stack, where *you* must lua_pop() chunks, because first frame never
> returns. Not very useful too, better stay with malloc/free.
> Second, lua_newuserdata() creates and pushes(!) new userdata on stack.
If you lua_pop() it, it may be immediately reclaimed.
Thanks. I had not thought of that. I do not think I dare go the route of freezing
the gc temporarily, so I will take your advice and stick with calloc/free for
intermediate values. It means some work disciminating the library's use of its
memory allocations, to separate those which should use lua_newuserdata from those
which should not.
> Anyway, leave internal allocations to malloc/free, and only allocate exported
> objects with lua_newuserdata().
> Never store result of lua_touserdata() to permanent places, and you are fine.
>
> [1] http://lua-users.org/lists/lua-l/2010-10/msg00246.html
Many thanks to all for taking the time to answer. Very useful for me.
--
Gavin Wraith ([email protected])
Home page: http://www.wra1th.plus.com/
