Efficiently marking a Lua userdata or thread to prevent __gc?

[Graham Wakefield <lists@...>]

Hi,

I have Lua embedded in an application in which events resume  
lua_States. Some resources (userdata and Lua thread states) are  
shared between Lua and C++; these resources may need to be persistent  
even when no reference in Lua exists.

So far, I've been using the registry and/or library environment  
tables to keep active, hidden Lua references to these items. But I  
wondered if there was a more efficient method to add/remove  
references. In particular, what would be a good method to have  
reference counting (C++ references) to Lua userdata/threads? I guess  
I could store a reference count integer against the state/thread, but  
it seems long-winded...

I wondered if there is a lower-level way to interact with Lua's  
reference/gc system.

Thanks