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- Subject: Re: NSLINKMODULE_OPTION_PRIVATE a problem? (OS X require of a modulemultiple times)
- From: Asko Kauppi <askok@...>
- Date: Tue, 3 Apr 2007 13:08:26 +0300
Thanks for a good description of the issue.
So, I take it that the PRIVATE behaviour is expected, "by design" and
not by chance. It kind of does make sense, since privacy is always
good, and using separate states has been a marginal issue. WIth
multicore processors, this may change, though.
- is this behaviour consistent over architectures (Linux,
- is it documented, because it sure is an important point for
I may need to use named shared memory, or something, to actually get
the module instances know each other. Given that the PRIVATE
behaviour is there to stay. It may still be best to have it like
this, requiring people who want the instances to know each other to
take the extra steps. We may need a wiki page on this?
ps. in order to be at the same addresses, the variables need to be
global (not static) even if the PRIVATE flag is not there. This would
give a neat way of balancing between the two "modes" but maybe it's
too subtle, and a gcc upgrade would blow it off, some day? :)
Jerome Vuarand kirjoitti 2.4.2007 kello 23:10:
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
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.
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.