Re: Unpicking require

[Roberto Ierusalimschy <roberto@...>]

Serious?  This bug is there for more than 10 years, and you wait to
announce it one minute after we announce a new release candidate?

> Roberto Ierusalimschy wrote:
> 
> > dlclose is called when you close the Lua state, calling lua_close.
> > The package loadlib creates a table in the registry, where it puts
> > all C packages it loads. We can see this table with this code:
> > 
> >    print(debug.getregistry()._CLIBS)    -- for Lua 5.4
> > 
> > This table has a metamethod __gc that dlclose's all libraries in that
> > table. As the table is in the registry, it is never collected, so that
> > it is called only when we close the Lua state.
> > 
> > Because this table is created and marked before we can load any C
> > module, it will be collected after the collection of any object
> > created by any C module.
> 
> This seems not to be true when closing a state and a finalizer creates a new object with a finalizer and calls os.exit(0, true). The os.exit call will append the new finalizer to the list tobefnz which already contains the finalizer for the _CLIBS table. With this the finalizer will run with all the c libs closed. The following code will crash with a Segmentation fault due to the closed c lib.
> 
> local tl = require "testlib"
> 
> setmetatable({},{__gc=function()
>     -- Called when state is closed
>     setmetatable({},{__gc=function()
>         -- Called as last finalizer during os.exit(0, true)
>         -- Here _CLIBS finalizer was already called
>         tl.test()
>     end})
>     os.exit(0, true)
> end})
> 
> where testlib can be replaced with any c lib but here is the version used:
> 
> #include "lua.h"
> #include "lauxlib.h"
> 
> static int test(lua_State* L) {
>     return 0;
> }
> 
> static const struct luaL_Reg functions [] = {
>     {"test", test},
>     {NULL, NULL}
> };
> 
> int luaopen_testlib(lua_State *L) {
>     luaL_newlib(L, functions);
>     return 1;
> }
> 
> Regards,
> Xmilia


-- Roberto