Re: Is there any circumstance that needs to invoke lua_newstate () to create two or more Lua states in a single C\C++ process?

[JeanHeyd Meneide <phdofthehouse@...>]

Dear Sunshilong,

     Sandboxing in a single Lua State is achieved by overriding the
"environment" in which a Lua function call is run. Since all scripts
are just function calls, this applies to script loading/running as
well. Some light reading on the subject (in English; sorry, I have
nothing in other languages: http://lua-users.org/wiki/SandBoxes)

     This is what I mean by "without hijacking tables"; using multiple
states means that there is no need to try to substitute a
function/script's environment table. You just transfer information
explicitly between lua_States.

     This is one of the primary reasons I see multiple Lua States in a
single threaded program. There are other use cases but those are
outside of my understanding.

Sincerely,
Derp

On Tue, Oct 20, 2020 at 11:16 PM 孙世龙 sunshilong <sunshilong369@gmail.com> wrote:
>
> Dear Derp:
>
> Thank you for your detailed explanation.
>
> >Even for non-multithreaded programs, a common way to guarantee
> >sandboxing without hijacking tables is to create a Lua State for each
> >participant.
>
> I can't fully understand it.
> What is "sandboxing without hijacking tables'?
> Could you please explain that more in detail for me or suggest some
> documents for me to go through?
>
> Thank you for your attention to my question.
> Best regards
> Sunshilong
>
> On Wed, Oct 21, 2020 at 9:55 AM JeanHeyd Meneide
> <phdofthehouse@gmail.com> wrote:
> >
> > Dear Sunshilong,
> >
> >      Each Lua state is entirely self-contained, and therefore you can
> > make 10s or even 100s of them in one C/C++ process. The common way to
> > do multithreading with Lua is to create multiple lua_State's, and then
> > let them run independently while setting up ways to communicate
> > information across threads in specific ways to need it.
> >
> >     Even for non-multithreaded programs, a common way to guarantee
> > sandboxing without hijacking tables is to create a Lua State for each
> > participant.
> >
> >      Note if you have 2 or more Lua States, you cannot use a reference
> > (Table, Userdata, etc.) that came from Lua State #1 with Lua State #2
> > without invoking undefined behavior (and, in severe cases, a crash).
> >
> > Hope that helps,
> > Derp
> >
> > On Tue, Oct 20, 2020 at 9:50 PM 孙世龙 sunshilong <sunshilong369@gmail.com> wrote:
> > >
> > > HI, list
> > >
> > > Is there any circumstance that needs to invoke lua_newstate () to
> > > create two or more Lua states in a single C\C++ process?
> > > It would be better if you can give me a few simple examples.
> > > What aspects should I consider(or be aware of) when creating two or
> > > more Lua states in a single C\C++ process?
> > >
> > > Best regards
> > > Sunshilong