From: Paul Brannan <pbrannan@...>
Date: 2002-10-22T23:04:28+09:00
Subject: Re: rb_gc_register_address problem

On Tue, Oct 22, 2002 at 10:02:50AM +0900, nobu.nokada@softhome.net wrote:
> At Tue, 22 Oct 2002 03:54:24 +0900,
> Paul Brannan wrote:
> > We ran into a problem today with the garbage collector (caused by our
> > own bug).  We had a function that did something like this:
> >   std::vector<char *> foo;
> >   void func(int argc, VALUE * argv, VALUE self) {
> >     foo.push_back(STR2CSTR(argv[0]));
> >     rb_global_variable(&argv[0]);
> >   }
> 
> If this "func" will be called from ruby as a method, you don't
> need to call rb_global_variable() here.

foo is global, so the call is necessary, so that the string object will
still be valid after func() returns.

> > So my question is: why does rb_gc_register_address() store VALUE*'s
> > instead of VALUE's?  I suppose that if it stored a VALUE, then it would
> > be possible to register an object as a global but not keep a reference
> > to that object; this may not be desirable.  In our case, though, we just
> > wanted the string to remain valid.
> 
> And introduce memory bugs?  Just store the VALUE in a local
> variable instead.

What memory bugs would be introduced?

(My goal here isn't to get the interpreter to change, but to understand
why it is written the way it is).

Paul