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
=for hackers
Found in file pad.h
+=item PAD_SET_CUR_NOSAVE
+
+like PAD_SET_CUR, but without the save
+
+ void PAD_SET_CUR_NOSAVE (PADLIST padlist, I32 n)
+
+=for hackers
+Found in file pad.h
+
=item PAD_SV
Get the value at offset C<po> in the current pad
=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
For these purposes "forms" are a kind-of CV, eval""s are too (except they're
not callable at will and are always thrown away after the eval"" is done
-executing).
+executing). Require'd files are simply evals without any outer lexical
+scope.
XSUBs don't have CvPADLIST set - dXSTARG fetches values from PL_curpad,
but that is really the callers pad (a slot of which is allocated by
other entries are storage for variables and op targets.
During compilation:
-C<PL_comppad_name> is set the the the names AV.
-C<PL_comppad> is set the the frame AV for the frame CvDEPTH == 1.
-C<PL_curpad> is set the body of the frame AV (i.e. AvARRAY(PL_comppad)).
+C<PL_comppad_name> is set to the names AV.
+C<PL_comppad> is set to the frame AV for the frame CvDEPTH == 1.
+C<PL_curpad> is set to the body of the frame AV (i.e. AvARRAY(PL_comppad)).
During execution, C<PL_comppad> and C<PL_curpad> refer to the live
frame of the currently executing sub.
same package can be detected). SvCUR is sometimes hijacked to
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".
+If SvFAKE is set on the name SV, then that slot in the frame AV is
+a REFCNT'ed reference to a lexical from "outside". In this case,
+the name SV does not use NVX and IVX to store a cop_seq range, since it is
+in scope throughout. Instead IVX stores some flags containing info about
+the real lexical (is it declared in an anon, and is it capable of being
+instantiated multiple times?), and for fake ANONs, NVX contains the index
+within the parent's pad where the lexical's value is stored, to make
+cloning quicker.
-If the 'name' is '&' the the corresponding entry in frame AV
+If the 'name' is '&' the corresponding entry in frame AV
is a CV representing a possible closure.
(SvFAKE and name of '&' is not a meaningful combination currently but could
become so if C<my sub foo {}> is implemented.)
+Note that formats are treated as anon subs, and are cloned each time
+write is called (if necessary).
+
AV * CvPADLIST(CV *cv)
=for hackers
=item pad_add_name
-Create a new name in the current pad at the specified offset.
+Create a new name and associated PADMY SV in the current pad; return the
+offset.
If C<typestash> is valid, the name is for a typed lexical; set the
name's stash to that value.
If C<ourstash> is valid, it's an our lexical, set the name's
GvSTASH to that value
-Also, if the name is @.. or %.., create a new array or hash for that slot
-
If fake, it means we're cloning an existing entry
PADOFFSET pad_add_name(char *name, HV* typestash, HV* ourstash, bool clone)
=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.
+
+Returns the offset in the bottom pad of the lex or the fake lex.
+cv is the CV in which to start the search, and seq is the current cop_seq
+to match against. If warn is true, print appropriate warnings. The out_*
+vars return values, and so are pointers to where the returned values
+should be stored. out_capture, if non-null, requests that the innermost
+instance of the lexical is captured; out_name_sv is set to the innermost
+matched namesv or fake namesv; out_flags returns the flags normally
+associated with the IVX field of a fake namesv.
-If flags == FINDLEX_NOSEARCH we don't bother searching outer contexts.
+Note that pad_findlex() is recursive; it recurses up the chain of CVs,
+then comes back down, adding fake entries as it goes. It has to be this way
+because fake namesvs in anon protoypes have to store in NVX the index into
+the parent pad.
- PADOFFSET pad_findlex(char* name, PADOFFSET newoff, U32 seq, CV* startcv, I32 cx_ix, I32 saweval, U32 flags)
+ PADOFFSET pad_findlex(char *name, CV* cv, U32 seq, int warn, SV** out_capture, SV** out_name_sv, int *out_flags)
=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
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