Finding the main thread?

[M Joonas Pihlaja <jpihlaja@...>]

Hi,

It appears to me that there's no way a user of the lua C API can find 
out what the main thread of a lua_State is.  The lua_pushthread() 
function helpfully says if the current thread is the main thread, but 
that's about the extent of what the manual has to say on the subject 
that I could find.

If it's not possible in Lua 5.1, could Lua 5.2 include this 
functionality please?  My use case is:  I'm wrapping a library which 
doesn't provide a "userdata" pointer for its callback functions.  To 
inform my C->Lua gateways of the lua_State they should look for their 
Lua counterparts in I'm using a global lua_State.  My problem is that 
if the user actually set the Lua function callback to call from within 
a coroutine instead of the main Lua state, and that coroutine goes 
away before the callback gateway is called, then *boom* I've got a 
stale lua_State pointer.

My alternate safe solution is to store the current lua_State in a 
global at every Lua -> C boundary, but that's a much more invasive 
change to my wrapper code unfortunately.

Joonas