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- Subject: Re: More about packaging (fwd)
- From: Edgar Toernig <froese@...>
- Date: Sun, 6 Jun 2004 00:06:30 +0200
> > If the current scheme is to be modified:
> > 1) Unloadlib support please. (For Win32 - FreeLibrary())
> This will require some support in C. Probably the best way
> to do this would be to have a GC method associated with the
> namespace table.
IMHO, that would be too fragile - a script could crash the application.
What about the method outlined below?
|[ http://lua-users.org/lists/lua-l/2002-03/msg00199.html ]
| I meant real garbage collection. If there's no reference to the dynamic
| binary it should be unloaded. Because the only thing it can export are
| functions that's not that difficult.
| At the start you only have the startfunc. All future pushcclosure with
| a function from that binary has to be from startfunc or from some function
| created by it. And so on.
| So, if one could keep track of a "function creation history" you can
| detect when a dynamic binary is no longer in use. Luckily that's easy *g*
| You just keep a reference to the binary in the upvalues:
| - the change to Lua's core: lua_pushcclosure always appends the last
| upvalue of the currently active cclosure to the new cclosure (or nil
| if there is no active cclosure).
| - loadlib creates a userdata containing the handle for that binary.
| A GC call of the userdata will unload the binary.
| - loadlib attaches that userdata as the single upvalue for the created
| cclosure of startfunc. (Needs a special pushcclosure or a magic
| nupvalue so that lua_pushcclosure will not do its append stuff.)
| That's all. Automatic garbage collection of dynamic loaded binaries.
PS: Btw, what happens under Windows when an application tries to load a dll
multiple times? Is it allowed? How many FreeLibrary-calls are needed?
Does each instance gets its own data/bss segment?
 loadlib"io" f=io.open"foo" io=nil GC() print(f:read"*a")