3 perlintern - autogenerated documentation of purely B<internal>
8 This file is the autogenerated documentation of functions in the
9 Perl interpreter that are documented using Perl's internal documentation
10 format but are not marked as part of the Perl API. In other words,
11 B<they are not for use in extensions>!
14 =head1 CV reference counts and CvOUTSIDE
20 Each CV has a pointer, C<CvOUTSIDE()>, to its lexically enclosing
21 CV (if any). Because pointers to anonymous sub prototypes are
22 stored in C<&> pad slots, it is a possible to get a circular reference,
23 with the parent pointing to the child and vice-versa. To avoid the
24 ensuing memory leak, we do not increment the reference count of the CV
25 pointed to by C<CvOUTSIDE> in the I<one specific instance> that the parent
26 has a C<&> pad slot pointing back to us. In this case, we set the
27 C<CvWEAKOUTSIDE> flag in the child. This allows us to determine under what
28 circumstances we should decrement the refcount of the parent when freeing
31 There is a further complication with non-closure anonymous subs (ie those
32 that do not refer to any lexicals outside that sub). In this case, the
33 anonymous prototype is shared rather than being cloned. This has the
34 consequence that the parent may be freed while there are still active
37 BEGIN { $a = sub { eval '$x' } }
39 In this case, the BEGIN is freed immediately after execution since there
40 are no active references to it: the anon sub prototype has
41 C<CvWEAKOUTSIDE> set since it's not a closure, and $a points to the same
42 CV, so it doesn't contribute to BEGIN's refcount either. When $a is
43 executed, the C<eval '$x'> causes the chain of C<CvOUTSIDE>s to be followed,
44 and the freed BEGIN is accessed.
46 To avoid this, whenever a CV and its associated pad is freed, any
47 C<&> entries in the pad are explicitly removed from the pad, and if the
48 refcount of the pointed-to anon sub is still positive, then that
49 child's C<CvOUTSIDE> is set to point to its grandparent. This will only
50 occur in the single specific case of a non-closure anon prototype
51 having one or more active references (such as C<$a> above).
53 One other thing to consider is that a CV may be merely undefined
54 rather than freed, eg C<undef &foo>. In this case, its refcount may
55 not have reached zero, but we still delete its pad and its C<CvROOT> etc.
56 Since various children may still have their C<CvOUTSIDE> pointing at this
57 undefined CV, we keep its own C<CvOUTSIDE> for the time being, so that
58 the chain of lexical scopes is unbroken. For example, the following
62 sub tmp { sub { eval '$x' } }
67 bool CvWEAKOUTSIDE(CV *cv)
75 =head1 Functions in file pad.h
82 Save the current pad in the given context block structure.
84 void CX_CURPAD_SAVE(struct context)
91 Access the SV at offset po in the saved current pad in the given
92 context block structure (can be used as an lvalue).
94 SV * CX_CURPAD_SV(struct context, PADOFFSET po)
101 Get the value from slot C<po> in the base (DEPTH=1) pad of a padlist
103 SV * PAD_BASE_SV (PADLIST padlist, PADOFFSET po)
111 Clone the state variables associated with running and compiling pads.
113 void PAD_CLONE_VARS(PerlInterpreter *proto_perl \)
118 =item PAD_COMPNAME_FLAGS
120 Return the flags for the current compiling pad name
121 at offset C<po>. Assumes a valid slot entry.
123 U32 PAD_COMPNAME_FLAGS(PADOFFSET po)
128 =item PAD_COMPNAME_GEN
130 The generation number of the name at offset C<po> in the current
131 compiling pad (lvalue). Note that C<SvCUR> is hijacked for this purpose.
133 STRLEN PAD_COMPNAME_GEN(PADOFFSET po)
138 =item PAD_COMPNAME_GEN_set
140 Sets the generation number of the name at offset C<po> in the current
141 ling pad (lvalue) to C<gen>. Note that C<SvCUR_set> is hijacked for this purpose.
143 STRLEN PAD_COMPNAME_GEN_set(PADOFFSET po, int gen)
148 =item PAD_COMPNAME_OURSTASH
150 Return the stash associated with an C<our> variable.
151 Assumes the slot entry is a valid C<our> lexical.
153 HV * PAD_COMPNAME_OURSTASH(PADOFFSET po)
158 =item PAD_COMPNAME_PV
160 Return the name of the current compiling pad name
161 at offset C<po>. Assumes a valid slot entry.
163 char * PAD_COMPNAME_PV(PADOFFSET po)
168 =item PAD_COMPNAME_TYPE
170 Return the type (stash) of the current compiling pad name at offset
171 C<po>. Must be a valid name. Returns null if not typed.
173 HV * PAD_COMPNAME_TYPE(PADOFFSET po)
182 void PAD_DUP(PADLIST dstpad, PADLIST srcpad, CLONE_PARAMS* param)
187 =item PAD_RESTORE_LOCAL
189 Restore the old pad saved into the local variable opad by PAD_SAVE_LOCAL()
191 void PAD_RESTORE_LOCAL(PAD *opad)
198 Save the current pad to the local variable opad, then make the
199 current pad equal to npad
201 void PAD_SAVE_LOCAL(PAD *opad, PAD *npad)
206 =item PAD_SAVE_SETNULLPAD
208 Save the current pad then set it to null.
210 void PAD_SAVE_SETNULLPAD()
217 Set the slot at offset C<po> in the current pad to C<sv>
219 SV * PAD_SETSV (PADOFFSET po, SV* sv)
226 Set the current pad to be pad C<n> in the padlist, saving
227 the previous current pad.
229 void PAD_SET_CUR (PADLIST padlist, I32 n)
234 =item PAD_SET_CUR_NOSAVE
236 like PAD_SET_CUR, but without the save
238 void PAD_SET_CUR_NOSAVE (PADLIST padlist, I32 n)
245 Get the value at offset C<po> in the current pad
247 void PAD_SV (PADOFFSET po)
254 Lightweight and lvalue version of C<PAD_SV>.
255 Get or set the value at offset C<po> in the current pad.
256 Unlike C<PAD_SV>, does not print diagnostics with -DX.
257 For internal use only.
259 SV * PAD_SVl (PADOFFSET po)
266 Clear the pointed to pad value on scope exit. (ie the runtime action of 'my')
268 void SAVECLEARSV (SV **svp)
275 save PL_comppad and PL_curpad
288 Save a pad slot (used to restore after an iteration)
290 XXX DAPM it would make more sense to make the arg a PADOFFSET
291 void SAVEPADSV (PADOFFSET po)
299 =head1 Functions in file pp_ctl.c
306 Locate the CV corresponding to the currently executing sub or eval.
307 If db_seqp is non_null, skip CVs that are in the DB package and populate
308 *db_seqp with the cop sequence number at the point that the DB:: code was
309 entered. (allows debuggers to eval in the scope of the breakpoint rather
310 than in in the scope of the debugger itself).
312 CV* find_runcv(U32 *db_seqp)
315 Found in file pp_ctl.c
320 =head1 Global Variables
326 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
327 boolean which indicates whether subs are being single-stepped.
328 Single-stepping is automatically turned on after every step. This is the C
329 variable which corresponds to Perl's $DB::single variable. See
335 Found in file intrpvar.h
339 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
340 the SV which holds the name of the sub being debugged. This is the C
341 variable which corresponds to Perl's $DB::sub variable. See
347 Found in file intrpvar.h
351 Trace variable used when Perl is run in debugging mode, with the B<-d>
352 switch. This is the C variable which corresponds to Perl's $DB::trace
353 variable. See C<PL_DBsingle>.
358 Found in file intrpvar.h
362 The C variable which corresponds to Perl's $^W warning variable.
367 Found in file intrpvar.h
371 The GV which was last used for a filehandle input operation. (C<< <FH> >>)
376 Found in file thrdvar.h
380 The output field separator - C<$,> in Perl space.
385 Found in file thrdvar.h
389 The input record separator - C<$/> in Perl space.
394 Found in file thrdvar.h
405 Returns C<TRUE> if given the name of a magical GV.
407 Currently only useful internally when determining if a GV should be
408 created even in rvalue contexts.
410 C<flags> is not used at present but available for future extension to
411 allow selecting particular classes of magical variable.
413 Currently assumes that C<name> is NUL terminated (as well as len being valid).
414 This assumption is met by all callers within the perl core, which all pass
415 pointers returned by SvPV.
417 bool is_gv_magical(const char *name, STRLEN len, U32 flags)
422 =item is_gv_magical_sv
424 Returns C<TRUE> if given the name of a magical GV. Calls is_gv_magical.
426 bool is_gv_magical_sv(SV *name, U32 flags)
440 Function called by C<do_readline> to spawn a glob (or do the glob inside
441 perl on VMS). This code used to be inline, but now perl uses C<File::Glob>
442 this glob starter is only used by miniperl during the build process.
443 Moving it away shrinks pp_hot.c; shrinking pp_hot.c helps speed perl up.
445 PerlIO* start_glob(SV* pattern, IO *io)
453 =head1 Pad Data Structures
459 CV's can have CvPADLIST(cv) set to point to an AV.
461 For these purposes "forms" are a kind-of CV, eval""s are too (except they're
462 not callable at will and are always thrown away after the eval"" is done
463 executing). Require'd files are simply evals without any outer lexical
466 XSUBs don't have CvPADLIST set - dXSTARG fetches values from PL_curpad,
467 but that is really the callers pad (a slot of which is allocated by
470 The CvPADLIST AV has does not have AvREAL set, so REFCNT of component items
471 is managed "manual" (mostly in pad.c) rather than normal av.c rules.
472 The items in the AV are not SVs as for a normal AV, but other AVs:
474 0'th Entry of the CvPADLIST is an AV which represents the "names" or rather
475 the "static type information" for lexicals.
477 The CvDEPTH'th entry of CvPADLIST AV is an AV which is the stack frame at that
478 depth of recursion into the CV.
479 The 0'th slot of a frame AV is an AV which is @_.
480 other entries are storage for variables and op targets.
483 C<PL_comppad_name> is set to the names AV.
484 C<PL_comppad> is set to the frame AV for the frame CvDEPTH == 1.
485 C<PL_curpad> is set to the body of the frame AV (i.e. AvARRAY(PL_comppad)).
487 During execution, C<PL_comppad> and C<PL_curpad> refer to the live
488 frame of the currently executing sub.
490 Iterating over the names AV iterates over all possible pad
491 items. Pad slots that are SVs_PADTMP (targets/GVs/constants) end up having
492 &PL_sv_undef "names" (see pad_alloc()).
494 Only my/our variable (SVs_PADMY/SVs_PADOUR) slots get valid names.
495 The rest are op targets/GVs/constants which are statically allocated
496 or resolved at compile time. These don't have names by which they
497 can be looked up from Perl code at run time through eval"" like
498 my/our variables can be. Since they can't be looked up by "name"
499 but only by their index allocated at compile time (which is usually
500 in PL_op->op_targ), wasting a name SV for them doesn't make sense.
502 The SVs in the names AV have their PV being the name of the variable.
503 NV+1..IV inclusive is a range of cop_seq numbers for which the name is
504 valid. For typed lexicals name SV is SVt_PVMG and SvSTASH points at the
505 type. For C<our> lexicals, the type is SVt_PVGV, and GvSTASH points at the
506 stash of the associated global (so that duplicate C<our> delarations in the
507 same package can be detected). SvCUR is sometimes hijacked to
508 store the generation number during compilation.
510 If SvFAKE is set on the name SV, then that slot in the frame AV is
511 a REFCNT'ed reference to a lexical from "outside". In this case,
512 the name SV does not use NVX and IVX to store a cop_seq range, since it is
513 in scope throughout. Instead IVX stores some flags containing info about
514 the real lexical (is it declared in an anon, and is it capable of being
515 instantiated multiple times?), and for fake ANONs, NVX contains the index
516 within the parent's pad where the lexical's value is stored, to make
519 If the 'name' is '&' the corresponding entry in frame AV
520 is a CV representing a possible closure.
521 (SvFAKE and name of '&' is not a meaningful combination currently but could
522 become so if C<my sub foo {}> is implemented.)
524 Note that formats are treated as anon subs, and are cloned each time
525 write is called (if necessary).
527 The flag SVf_PADSTALE is cleared on lexicals each time the my() is executed,
528 and set on scope exit. This allows the 'Variable $x is not available' warning
529 to be generated in evals, such as
531 { my $x = 1; sub f { eval '$x'} } f();
533 AV * CvPADLIST(CV *cv)
540 Clone a CV: make a new CV which points to the same code etc, but which
541 has a newly-created pad built by copying the prototype pad and capturing
544 CV* cv_clone(CV* proto)
551 dump the contents of a CV
553 void cv_dump(const CV *cv, const char *title)
560 Dump the contents of a padlist
562 void do_dump_pad(I32 level, PerlIO *file, PADLIST *padlist, int full)
569 "Introduce" my variables to visible status.
578 Add an anon code entry to the current compiling pad
580 PADOFFSET pad_add_anon(SV* sv, OPCODE op_type)
587 Create a new name and associated PADMY SV in the current pad; return the
589 If C<typestash> is valid, the name is for a typed lexical; set the
590 name's stash to that value.
591 If C<ourstash> is valid, it's an our lexical, set the name's
592 GvSTASH to that value
594 If fake, it means we're cloning an existing entry
596 PADOFFSET pad_add_name(const char *name, HV* typestash, HV* ourstash, bool clone)
603 Allocate a new my or tmp pad entry. For a my, simply push a null SV onto
604 the end of PL_comppad, but for a tmp, scan the pad from PL_padix upwards
605 for a slot which has no name and and no active value.
607 PADOFFSET pad_alloc(I32 optype, U32 tmptype)
612 =item pad_block_start
614 Update the pad compilation state variables on entry to a new block
616 void pad_block_start(int full)
623 Check for duplicate declarations: report any of:
624 * a my in the current scope with the same name;
625 * an our (anywhere in the pad) with the same name and the same stash
627 C<is_our> indicates that the name to check is an 'our' declaration
629 void pad_check_dup(const char* name, bool is_our, const HV* ourstash)
636 Find a named lexical anywhere in a chain of nested pads. Add fake entries
637 in the inner pads if it's found in an outer one.
639 Returns the offset in the bottom pad of the lex or the fake lex.
640 cv is the CV in which to start the search, and seq is the current cop_seq
641 to match against. If warn is true, print appropriate warnings. The out_*
642 vars return values, and so are pointers to where the returned values
643 should be stored. out_capture, if non-null, requests that the innermost
644 instance of the lexical is captured; out_name_sv is set to the innermost
645 matched namesv or fake namesv; out_flags returns the flags normally
646 associated with the IVX field of a fake namesv.
648 Note that pad_findlex() is recursive; it recurses up the chain of CVs,
649 then comes back down, adding fake entries as it goes. It has to be this way
650 because fake namesvs in anon protoypes have to store in NVX the index into
653 PADOFFSET pad_findlex(const char *name, const CV* cv, U32 seq, int warn, SV** out_capture, SV** out_name_sv, int *out_flags)
660 Given a lexical name, try to find its offset, first in the current pad,
661 or failing that, in the pads of any lexically enclosing subs (including
662 the complications introduced by eval). If the name is found in an outer pad,
663 then a fake entry is added to the current pad.
664 Returns the offset in the current pad, or NOT_IN_PAD on failure.
666 PADOFFSET pad_findmy(const char* name)
671 =item pad_fixup_inner_anons
673 For any anon CVs in the pad, change CvOUTSIDE of that CV from
674 old_cv to new_cv if necessary. Needed when a newly-compiled CV has to be
675 moved to a pre-existing CV struct.
677 void pad_fixup_inner_anons(PADLIST *padlist, CV *old_cv, CV *new_cv)
684 Free the SV at offet po in the current pad.
686 void pad_free(PADOFFSET po)
693 Cleanup at end of scope during compilation: set the max seq number for
694 lexicals in this scope and warn of any lexicals that never got introduced.
703 Create a new compiling padlist, saving and updating the various global
704 vars at the same time as creating the pad itself. The following flags
705 can be OR'ed together:
707 padnew_CLONE this pad is for a cloned CV
708 padnew_SAVE save old globals
709 padnew_SAVESUB also save extra stuff for start of sub
711 PADLIST* pad_new(int flags)
718 Push a new pad frame onto the padlist, unless there's already a pad at
719 this depth, in which case don't bother creating a new one. Then give
720 the new pad an @_ in slot zero.
722 void pad_push(PADLIST *padlist, int depth)
729 Mark all the current temporaries for reuse
738 Set the entry at offset po in the current pad to sv.
739 Use the macro PAD_SETSV() rather than calling this function directly.
741 void pad_setsv(PADOFFSET po, SV* sv)
748 Abandon the tmp in the current pad at offset po and replace with a
751 void pad_swipe(PADOFFSET po, bool refadjust)
758 Tidy up a pad after we've finished compiling it:
759 * remove most stuff from the pads of anonsub prototypes;
763 void pad_tidy(padtidy_type type)
770 Free the padlist associated with a CV.
771 If parts of it happen to be current, we null the relevant
772 PL_*pad* global vars so that we don't have any dangling references left.
773 We also repoint the CvOUTSIDE of any about-to-be-orphaned
774 inner subs to the outer of this cv.
776 (This function should really be called pad_free, but the name was already
779 void pad_undef(CV* cv)
787 =head1 Stack Manipulation Macros
793 Declare Just C<SP>. This is actually identical to C<dSP>, and declares
794 a local copy of perl's stack pointer, available via the C<SP> macro.
795 See C<SP>. (Available for backward source code compatibility with the
796 old (Perl 5.005) thread model.)
805 True if this op will be the return value of an lvalue subroutine
813 =head1 SV Manipulation Functions
817 =item find_uninit_var
819 Find the name of the undefined variable (if any) that caused the operator o
820 to issue a "Use of uninitialized value" warning.
821 If match is true, only return a name if it's value matches uninit_sv.
822 So roughly speaking, if a unary operator (such as OP_COS) generates a
823 warning, then following the direct child of the op may yield an
824 OP_PADSV or OP_GV that gives the name of the undefined variable. On the
825 other hand, with OP_ADD there are two branches to follow, so we only print
826 the variable name if we get an exact match.
828 The name is returned as a mortal SV.
830 Assumes that PL_op is the op that originally triggered the error, and that
831 PL_comppad/PL_curpad points to the currently executing pad.
833 SV* find_uninit_var(OP* obase, SV* uninit_sv, bool top)
840 Print appropriate "Use of uninitialized variable" warning
842 void report_uninit(SV* uninit_sv)
849 Given a chunk of memory, link it to the head of the list of arenas,
850 and split it into a list of free SVs.
852 void sv_add_arena(char* ptr, U32 size, U32 flags)
859 Decrement the refcnt of each remaining SV, possibly triggering a
860 cleanup. This function may have to be called multiple times to free
861 SVs which are in complex self-referential hierarchies.
870 Attempt to destroy all objects not yet freed
879 Deallocate the memory used by all arenas. Note that all the individual SV
880 heads and bodies within the arenas must already have been freed.
882 void sv_free_arenas()
892 The autodocumentation system was originally added to the Perl core by
893 Benjamin Stuhl. Documentation is by whoever was kind enough to
894 document their functions.
898 perlguts(1), perlapi(1)
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