Re: Lua and preemptive scheduling for coroutines

[Leo Romanoff <romixlev@...>]

----- Ursprüngliche Message -----
> Von: Sean Conner <sean@conman.org>
> An: Leo Romanoff <romixlev@yahoo.com>; Lua mailing list <lua-l@lists.lua.org>
> CC: 
> Gesendet: 10:29 Freitag, 29.März 2013
> Betreff: Re: Lua and preemptive scheduling for coroutines
> 
> It was thus said that the Great Leo Romanoff once stated:
>>  > 
>>  > I'm not sure if it can be done, but could you use the lock/unlock 
> macros to 
>>  > perform the yield?
>> 
>>  Can you elaborate a bit? Where I should use such macros? In the C code? Or 
> in Lua? 
>>  If it is in C, can I invoke such a C-function which does lock/unlock from 
> Lua?
>>  And how is it different from lua_yield that can be used in C?
> 
>   He's talking about two C macros in llimits.h which are there so you can
> add an implemention (in C).  They're there to make Lua thread safe (as in,
> multiple operating system threads can share the same Lua state).  What is
> being suggested is that at each point in the C code that comprises Lua hits
> a point that two independent threads could cause data corruption is
> protected via a lua_lock()/lua_unlock() pair (for instance, two threads
> sharing the same Lua state attemp to modify the same table).
> 
>   What you are trying to do is somewhat similar---doing an implicit 
> "yield" in the middle of an operation could lead to problems.  
> 
>   I don't know enough about the internals of Lua to say if this is a good or
> bad idea, but it would be something I would look into.  

OK. Thanks for clarifications.

>   -spc (I slowly coming to the idea that pre-emptive multitasking is no
>     longer a Good Thing(TM) but I still need to formulate my thoughts on  this)


In principle, I agree with this. But I'm also not sure that explicit cooperative multi-tasking is such a good thing. I think that cooperative implicit multi-tasking (with ability to control at the meta-level or higher-level how cooperation happens, e.g. by means of custom policies or something like this) is more bullet-proof.

-Leo