B<they are not for use in extensions>!
+=head1 CV reference counts and CvOUTSIDE
+
+=over 8
+
+=item CvWEAKOUTSIDE
+
+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->();
+
+ bool CvWEAKOUTSIDE(CV *cv)
+
+=for hackers
+Found in file cv.h
+
+
+=back
+
=head1 Functions in file pad.h
=back
+=head1 Functions in file pp_ctl.c
+
+
+=over 8
+
+=item find_runcv
+
+Locate the CV corresponding to the currently executing sub or eval.
+If db_seqp is non_null, skip CVs that are in the DB package and populate
+*db_seqp with the cop sequence number at the point that the DB:: code was
+entered. (allows debuggers to eval in the scope of the breakpoint rather
+than in in the scope of the debuger itself).
+
+ CV* find_runcv(U32 *db_seqp)
+
+=for hackers
+Found in file pp_ctl.c
+
+
+=back
+
=head1 Global Variables
=over 8
store the generation number during compilation.
If SvFAKE is set on the name SV then slot in the frame AVs are
-a REFCNT'ed references to a lexical from "outside".
+a REFCNT'ed references to a lexical from "outside". In this case,
+the name SV does not have a cop_seq range, since it is in scope
+throughout.
If the 'name' is '&' the the corresponding entry in frame AV
is a CV representing a possible closure.
=item pad_findlex
Find a named lexical anywhere in a chain of nested pads. Add fake entries
-in the inner pads if its found in an outer one.
+in the inner pads if it's found in an outer one. innercv is the CV *inside*
+the chain of outer CVs to be searched. If newoff is non-null, this is a
+run-time cloning: don't add fake entries, just find the lexical and add a
+ref to it at newoff in the current pad.
-If flags == FINDLEX_NOSEARCH we don't bother searching outer contexts.
-
- PADOFFSET pad_findlex(char* name, PADOFFSET newoff, U32 seq, CV* startcv, I32 cx_ix, I32 saweval, U32 flags)
+ PADOFFSET pad_findlex(char* name, PADOFFSET newoff, CV* innercv)
=for hackers
Found in file pad.c
=item pad_fixup_inner_anons
For any anon CVs in the pad, change CvOUTSIDE of that CV from
-old_cv to new_cv if necessary.
+old_cv to new_cv if necessary. Needed when a newly-compiled CV has to be
+moved to a pre-existing CV struct.
void pad_fixup_inner_anons(PADLIST *padlist, CV *old_cv, CV *new_cv)
padnew_SAVE save old globals
padnew_SAVESUB also save extra stuff for start of sub
- PADLIST* pad_new(padnew_flags flags)
+ PADLIST* pad_new(int flags)
=for hackers
Found in file pad.c
If parts of it happen to be current, we null the relevant
PL_*pad* global vars so that we don't have any dangling references left.
We also repoint the CvOUTSIDE of any about-to-be-orphaned
-inner subs to outercv.
+inner subs to the outer of this cv.
+
+(This function should really be called pad_free, but the name was already
+taken)
- void pad_undef(CV* cv, CV* outercv)
+ void pad_undef(CV* cv)
=for hackers
Found in file pad.c
projects / p5sagit/p5-mst-13.2.git / blobdiff