Re: atexit in modules

[Mike Gran]

> 2008/11/14 Mike Gran :
> >
> > So I'm back to the idea of creating a module-level variable that exists 
> > while 
> > the module is in memory, and then calling library_end() when that variable 
> > is 
> > GC'd.  But I can make it more schemey by using guardians and after-gc-hook 
> > as 
> >you suggested.
> 


> But are modules ever unloaded?  I thought not.

Everything I said above is nonsense.  I tried four things, and the last one 
works fine.

Here's a review.  I had a scheme module that wrapped a C library that required 
calls to a library_init() and library_end() function pair that allocated and 
freed global data.  

Idea 1 was to wrap as library_init() as a scheme function that gets called when 
the scheme module is loaded, and then wrap library_end() as a scheme function 
that gets called when the module is unloaded.  But, modules are never unloaded.

Idea 2 was to wrap library_init() as above, and then wrap library_end() as a 
scheme function that gets called when Guile exits.  But, there is no such hook 
as far as I know for non-REPL Guile scripts.

Idea 3 was some nonsense idea that I could catch a module variable as it was 
being garbage collected and use this as the trigger to call library_end().  
Ignore everything I said about that.

Idea 4: So ultimately I went with this.  The C function library_init() gets 
called in init_foo() in the call to (load-extension "libfoo.so" "init_foo").  
The C function library_end() gets registered using the libc atexit() during the 
same call to init_foo().  That works fine.

-Mike Gran