From: Bob X <bobx@...>
Date: 2002-08-28T06:22:33+09:00
Subject: Re: Temporary VALUE Needs to Be Protected?

William Djaja Tjokroaminata wrote:
> Hi,
> 
> I am dealing with this puzzle.  We know that we need to protect a global
> variable using "rb_global_variable()" which simply calls
> "rb_gc_register_address()", so that it will not be swept by Ruby gc.
> 
> Now, regarding the temporary variable such as in
> 
>     static VALUE func (VALUE var1, ...)
>     {
>         VALUE var2;
>         ....
>         var2 = ....
>         ....
>     }
> 
> My feeling says that even var1 and var2 should also be protected as in
> 
>     static VALUE func (VALUE var1, ...)
>     {
>         VALUE var2;
> 
>         rb_gc_register_address (&var1);
>         rb_gc_register_address (&var2);
>         ....
>         (some codes)
>         ....
>         rb_gc_unregister_address (&var1)
>         rb_gc_unregister_address (&var2)
>         return Qnil;
>     }
> 
> because the "some codes" there may invoke rb_gc().  Is this really a good
> practice?
> 
> In my opinion, we have 3 options:
> 
> 1) Make sure that since a VALUE is assigned until it is disposed of no
> rb_gc() will occur.  I think this is very tricky, because even a function
> such as rb_scan_args() seems to be capable of invoking gc as it has some
> "rb_ary_new...()" there.
> 
> 2) Always do the pair rb_gc_un/register_address() for each temporary
> VALUE.  This will make the corresponding C code longer (more typing
> :) ).  However, this may be an acceptable solution.
> 
> 3) Have a separate Ruby heaps, where we can manually allocate and
> deallocate valid Ruby objects without intervention from the gc.  This will
> probably be the ideal solution, as it is the most efficient in terms of
> execution.
> 
> Opinion, anyone?
> 
> Regards,
> 
> Bill
If you wanted to protect them couldn't you use $SAFE? This is from a 
newbie wondering...

Bob