Re: The life cycle of userdata values?

[Thomas Jericke <tjericke@...>]

On 07/26/2016 09:24 AM, Marc Balmer wrote:
> > Am 25.07.2016 um 21:03 schrieb Roberto Ierusalimschy <roberto@inf.puc-rio.br>:
> >
> > > > p = lua_newuserdate(L, sizeof int)
> > > > *p = 42
> > > >
> > > > /* Do a Lua API call that might error (longjmp) out */
> > > This has the risk of the memory being invalidated by the
> > > garbage collector.
> > No, if the userdata is properly anchored (e.g, in the stack). Just
> > leave the the userdata in the stack (where lua_newuserdate put it)
> > and everything should work fine.
>
> Thanks to all that replied.  After I sprinkled some lua_checkstack()
> calls, the crashes went away.  Time for a release...
>
> Out of curiosity, why does lua_newuserdata() not call lua_checkstack()
> internally?  When calling lua_newuserdata(), isn't it quite obvious
> that you want the result on the stack?
>
> - mb
To my knowledge, performance.
You should know how many stack slots you have available in your C code. 
Just call lua_checkstack with the number of slots you need at the beginning.
 And if you are called by Lua you always have some slots reserved 
already (I think 20 by default).
--
Thomas