RE: NSLINKMODULE_OPTION_PRIVATE a problem? (OS X require of a modulemultiple times)

["Jerome Vuarand" <jerome.vuarand@...>]

Sam Roberts wrote:
> On Mon, Apr 02, 2007 at 09:49:56PM +0300, Asko Kauppi wrote:
>> Lua uses NSLINKMODULE_OPTION_PRIVATE flag on OS X for its "require",
>> but this causes globals in a module required in two separate Lua
>> states NOT to have common globals. I faced this today, and the only
>> solution found was removing that flag from loadlib.c.
> 
> As a quick fix, have you tried using dlopen() instead? It is
> recommended on OS X (by Apple, see
> http://lua-users.org/wiki/BuildingLua).  
> 
> Still, I'm a little surprised that the bundle was loaded twice.
> 
> Could this be a bug? Isn't package supposed to load the bundle/so/dll
> only the first time the module is required, and the other times to
> use the previously opened shared library handle, find the luaopen_XX
> symbol using that handle, and call it again in the new state?   
> 
> The package module definitely keeps the load handle around, I don't
> see why it shouldn't use it! 

The problem comes from the fact that Asko use separate Lua states. If a
binary module is required in two independents Lua states, it's
initialization function must be called twice. Since binary modules may
not be reentrant and use globals to store "Lua-state"-specific
information, having it loaded twice with private static data allows to
avoid collisions in memory between the two instances of the module,
while the package system still ensure that all require in the same Lua
state will always return the same module table.

If you make the static data shared (by removing the aforementioned
flag), to allow communication between the two instances of the module,
you have to make sure all binary modules you load don't store
"Lua-state"-specific information in static variables. For example you
can't store registry indices in globals and share them between Lua
states, since each has its own registry.