From: William Djaja Tjokroaminata <billtj@...>
Date: 2002-08-28T05:02:25+09:00
Subject: Temporary VALUE Needs to Be Protected?

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