Re: Is Lua the next big thing?

[Rici Lake <lua@...>]

Brent Fulgham wrote:
> My main concern is threading support.  Our application is heavily 
> threaded, and I want to ensure that any embedded scripting engine is 
> able to be isolated from other threads.  I have spent quite a bit of 
> time cleaning up an earlier home-grown interpreter (previously created 
> in a typical fit of NIH syndrome) that had horrible thread isolation 
> problems (such that if the same loop variable was used in two separate 
> instances of the interpreter, both variables would be incremented during 
> the loop).  Needless to say, it's not hard to exceed this level of 
> quality but not that I've cleaned up the old mess, I want to *enhance* 
> things, rather than run the risk of creating new problems.

Lua uses no mutable globals at all (aside from the ones in the standard 
C library: errno and stdin&friends). A Lua_State is entirely 
self-contained, and will not interfere with any independently created
Lua_State, which is more or less the equivalent of an "interpreter
instance". So you're not going to run into any threading issues which 
you don't create yourself :)

The coroutine mechanism is not implemented with threads, although the 
API calls them threads (which they are, but not OS threads); Lua threads 
are exposed as instances of a Lua_State, and those Lua_States are 
related to each other. You probably don't want to run those 
simultaneously in different OS threads, but it is theoretically 
possible; the language does not provide any synchronization primitives, 
though, so you need to implement your own so that related Lua_States 
don't trod on each other's globals.
> If anyone can give me a pep talk about Lua in a C++ environment, I'd 
> love to be pointed to any references or success stories.  I have just 
> read Roberto's Lua book (2nd Edition) but don't have much practical 
> experience with the language.

I'm not sure what you need to know. Lua can be compiled as C++, and if 
you do that it will use C++ exceptions instead of setjmp/longjmp for 
error handling (this is all tweakable, but that's the default.) I 
personally don't do a lot of C++ programming, so I can't really give you 
a C++ pep talk, but it's wonderfully simple to integrate into a C 
application and I don't see why C++ would be any different.