Re: Lua callback in another thread

[Oleg Popov <dev-random@...>]

On Sat, Apr 23, 2016 at 05:18:59PM +0200, Laurent Faillie wrote:
> Hello,
> 
> Le 22/04/2016 08:52, Daurnimator a écrit :
> > Infact, sending a packet to a socket *is* actually the best option for
> > this sort of thing. On linux, you have a special fast kernel provided
> > file descriptor type 'eventfd' just for this purpose. In general, you
> > can fall back to using a pipe() or socketpair() and writing a single
> > byte so that the other end polls readable. 
> 
> My issue is not to signalize anything b/w thread, it's already done
> using eventfb and socket signaling :)
> My issue is to pass a function reference defined in the main thread to
> the newly created one w/o blocking the main one.

And... what are you going to do with that reference? Because references 
are just numbers, passing them through sockets is trivial, but they will 
be meaningless to another lua_State. If you are going to just pass the 
reference eventually back to the main thread, you may handle it as 
opaque number. But if you are going to call that function from the 
separate thread, you are in trouble. If both threads use the same state, 
then you MUST block. And if the state is different, then the only way to 
pass objects between states is to copy them, like LuaLanes does. The 
copying is difficult, slow and unreliable, and the copy of the function 
won't be able to modify the original state (all its upvalues will be 
copies of the originals, and _ENV will be that of the new lua_State).