/* cv.h
*
* Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1999,
* 2000, 2001, 2002, 2003, 2004, by Larry Wall and others
*
* You may distribute under the terms of either the GNU General Public
* License or the Artistic License, as specified in the README file.
*
*/
* in sv.h */
struct xpvcv {
char * xcv_file;
#ifdef USE_5005THREADS
#endif /* USE_5005THREADS */
* compilation) in the lexically enclosing
* sub */
};
/*
=head1 Handy Values
=for apidoc AmU||Nullcv
Null CV pointer.
=head1 CV Manipulation Functions
=for apidoc Am|HV*|CvSTASH|CV* cv
Returns the stash of the CV.
=cut
*/
#ifdef USE_ITHREADS
#else
#endif
#ifdef USE_5005THREADS
#endif /* USE_5005THREADS */
* require, eval). Not to be confused
* with the GVf_UNIQUE flag associated
* with the :unique attribute */
(esp. useful for special XSUBs) */
#ifdef PERL_XSUB_OLDSTYLE
#endif
/* BEGIN|CHECK|INIT|END */
/*
=head1 CV reference counts and CvOUTSIDE
=for apidoc m|bool|CvWEAKOUTSIDE|CV *cv
Each CV has a pointer, C<CvOUTSIDE()>, to its lexically enclosing
CV (if any). Because pointers to anonymous sub prototypes are
stored in C<&> pad slots, it is a possible to get a circular reference,
with the parent pointing to the child and vice-versa. To avoid the
ensuing memory leak, we do not increment the reference count of the CV
pointed to by C<CvOUTSIDE> in the I<one specific instance> that the parent
has a C<&> pad slot pointing back to us. In this case, we set the
C<CvWEAKOUTSIDE> flag in the child. This allows us to determine under what
circumstances we should decrement the refcount of the parent when freeing
the child.
There is a further complication with non-closure anonymous subs (ie those
that do not refer to any lexicals outside that sub). In this case, the
anonymous prototype is shared rather than being cloned. This has the
consequence that the parent may be freed while there are still active
children, eg
BEGIN { $a = sub { eval '$x' } }
In this case, the BEGIN is freed immediately after execution since there
are no active references to it: the anon sub prototype has
C<CvWEAKOUTSIDE> set since it's not a closure, and $a points to the same
CV, so it doesn't contribute to BEGIN's refcount either. When $a is
executed, the C<eval '$x'> causes the chain of C<CvOUTSIDE>s to be followed,
and the freed BEGIN is accessed.
To avoid this, whenever a CV and its associated pad is freed, any
C<&> entries in the pad are explicitly removed from the pad, and if the
refcount of the pointed-to anon sub is still positive, then that
child's C<CvOUTSIDE> is set to point to its grandparent. This will only
occur in the single specific case of a non-closure anon prototype
having one or more active references (such as C<$a> above).
One other thing to consider is that a CV may be merely undefined
rather than freed, eg C<undef &foo>. In this case, its refcount may
not have reached zero, but we still delete its pad and its C<CvROOT> etc.
Since various children may still have their C<CvOUTSIDE> pointing at this
undefined CV, we keep its own C<CvOUTSIDE> for the time being, so that
the chain of lexical scopes is unbroken. For example, the following
should print 123:
my $x = 123;
sub tmp { sub { eval '$x' } }
my $a = tmp();
undef &tmp;
print $a->();
=cut
*/