Lua Library and Mutexas

[Phil Birkelbach <phil@...>]

I have an application that spawns several threads, each thread runs a  
Lua script (each with it's own lua_State).  Each script calls some  
extension functions that abstract a database / communication library  
that is NOT thread safe.  Yesterday I went about adding mutex lock /  
unlock code around every call to this API from my C code that is  
called from the scripts.  This seemed like the best answer until I got  
to a function in the API that is basically an iterator.  This function  
calls a callback function to deal with compound data types in the  
API.  This callback function calls Lua library functions, like  
lua_pushstring(), lua_rawset(), lua_rawget(), etc.  There are no  
lua_error() calls in here.  I'm worried about these functions raising  
errors, longjmp'ing back to the script and leaving my mutex locked,  
which will deadlock the application.

I thought about writing a wrapper function that I can call from  
lua_cpcall() but the way I read the documentation the stack that is  
passed to the C function in lua_cpcall() only has the lightuserdata  
that was passed.  I also need the Lua stack that was passed to the  
original function.

Thanks

Phil