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_OURSTASH
140 Return the stash associated with an C<our> variable.
141 Assumes the slot entry is a valid C<our> lexical.
143 HV * PAD_COMPNAME_OURSTASH(PADOFFSET po)
148 =item PAD_COMPNAME_PV
150 Return the name of the current compiling pad name
151 at offset C<po>. Assumes a valid slot entry.
153 char * PAD_COMPNAME_PV(PADOFFSET po)
158 =item PAD_COMPNAME_TYPE
160 Return the type (stash) of the current compiling pad name at offset
161 C<po>. Must be a valid name. Returns null if not typed.
163 HV * PAD_COMPNAME_TYPE(PADOFFSET po)
172 void PAD_DUP(PADLIST dstpad, PADLIST srcpad, CLONE_PARAMS* param)
177 =item PAD_RESTORE_LOCAL
179 Restore the old pad saved into the local variable opad by PAD_SAVE_LOCAL()
181 void PAD_RESTORE_LOCAL(PAD *opad)
188 Save the current pad to the local variable opad, then make the
189 current pad equal to npad
191 void PAD_SAVE_LOCAL(PAD *opad, PAD *npad)
196 =item PAD_SAVE_SETNULLPAD
198 Save the current pad then set it to null.
200 void PAD_SAVE_SETNULLPAD()
207 Set the slot at offset C<po> in the current pad to C<sv>
209 SV * PAD_SETSV (PADOFFSET po, SV* sv)
216 Set the current pad to be pad C<n> in the padlist, saving
217 the previous current pad.
219 void PAD_SET_CUR (PADLIST padlist, I32 n)
224 =item PAD_SET_CUR_NOSAVE
226 like PAD_SET_CUR, but without the save
228 void PAD_SET_CUR_NOSAVE (PADLIST padlist, I32 n)
235 Get the value at offset C<po> in the current pad
237 void PAD_SV (PADOFFSET po)
244 Lightweight and lvalue version of C<PAD_SV>.
245 Get or set the value at offset C<po> in the current pad.
246 Unlike C<PAD_SV>, does not print diagnostics with -DX.
247 For internal use only.
249 SV * PAD_SVl (PADOFFSET po)
256 Clear the pointed to pad value on scope exit. (ie the runtime action of 'my')
258 void SAVECLEARSV (SV **svp)
265 save PL_comppad and PL_curpad
278 Save a pad slot (used to restore after an iteration)
280 XXX DAPM it would make more sense to make the arg a PADOFFSET
281 void SAVEPADSV (PADOFFSET po)
289 =head1 Functions in file pp_ctl.c
296 Locate the CV corresponding to the currently executing sub or eval.
297 If db_seqp is non_null, skip CVs that are in the DB package and populate
298 *db_seqp with the cop sequence number at the point that the DB:: code was
299 entered. (allows debuggers to eval in the scope of the breakpoint rather
300 than in in the scope of the debugger itself).
302 CV* find_runcv(U32 *db_seqp)
305 Found in file pp_ctl.c
310 =head1 Global Variables
316 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
317 boolean which indicates whether subs are being single-stepped.
318 Single-stepping is automatically turned on after every step. This is the C
319 variable which corresponds to Perl's $DB::single variable. See
325 Found in file intrpvar.h
329 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
330 the SV which holds the name of the sub being debugged. This is the C
331 variable which corresponds to Perl's $DB::sub variable. See
337 Found in file intrpvar.h
341 Trace variable used when Perl is run in debugging mode, with the B<-d>
342 switch. This is the C variable which corresponds to Perl's $DB::trace
343 variable. See C<PL_DBsingle>.
348 Found in file intrpvar.h
352 The C variable which corresponds to Perl's $^W warning variable.
357 Found in file intrpvar.h
361 The GV which was last used for a filehandle input operation. (C<< <FH> >>)
366 Found in file thrdvar.h
370 The output field separator - C<$,> in Perl space.
375 Found in file thrdvar.h
379 The input record separator - C<$/> in Perl space.
384 Found in file thrdvar.h
395 Returns C<TRUE> if given the name of a magical GV.
397 Currently only useful internally when determining if a GV should be
398 created even in rvalue contexts.
400 C<flags> is not used at present but available for future extension to
401 allow selecting particular classes of magical variable.
403 Currently assumes that C<name> is NUL terminated (as well as len being valid).
404 This assumption is met by all callers within the perl core, which all pass
405 pointers returned by SvPV.
407 bool is_gv_magical(const char *name, STRLEN len, U32 flags)
412 =item is_gv_magical_sv
414 Returns C<TRUE> if given the name of a magical GV. Calls is_gv_magical.
416 bool is_gv_magical_sv(SV *name, U32 flags)
430 Function called by C<do_readline> to spawn a glob (or do the glob inside
431 perl on VMS). This code used to be inline, but now perl uses C<File::Glob>
432 this glob starter is only used by miniperl during the build process.
433 Moving it away shrinks pp_hot.c; shrinking pp_hot.c helps speed perl up.
435 PerlIO* start_glob(SV* pattern, IO *io)
443 =head1 Pad Data Structures
449 CV's can have CvPADLIST(cv) set to point to an AV.
451 For these purposes "forms" are a kind-of CV, eval""s are too (except they're
452 not callable at will and are always thrown away after the eval"" is done
453 executing). Require'd files are simply evals without any outer lexical
456 XSUBs don't have CvPADLIST set - dXSTARG fetches values from PL_curpad,
457 but that is really the callers pad (a slot of which is allocated by
460 The CvPADLIST AV has does not have AvREAL set, so REFCNT of component items
461 is managed "manual" (mostly in pad.c) rather than normal av.c rules.
462 The items in the AV are not SVs as for a normal AV, but other AVs:
464 0'th Entry of the CvPADLIST is an AV which represents the "names" or rather
465 the "static type information" for lexicals.
467 The CvDEPTH'th entry of CvPADLIST AV is an AV which is the stack frame at that
468 depth of recursion into the CV.
469 The 0'th slot of a frame AV is an AV which is @_.
470 other entries are storage for variables and op targets.
473 C<PL_comppad_name> is set to the names AV.
474 C<PL_comppad> is set to the frame AV for the frame CvDEPTH == 1.
475 C<PL_curpad> is set to the body of the frame AV (i.e. AvARRAY(PL_comppad)).
477 During execution, C<PL_comppad> and C<PL_curpad> refer to the live
478 frame of the currently executing sub.
480 Iterating over the names AV iterates over all possible pad
481 items. Pad slots that are SVs_PADTMP (targets/GVs/constants) end up having
482 &PL_sv_undef "names" (see pad_alloc()).
484 Only my/our variable (SVs_PADMY/SVs_PADOUR) slots get valid names.
485 The rest are op targets/GVs/constants which are statically allocated
486 or resolved at compile time. These don't have names by which they
487 can be looked up from Perl code at run time through eval"" like
488 my/our variables can be. Since they can't be looked up by "name"
489 but only by their index allocated at compile time (which is usually
490 in PL_op->op_targ), wasting a name SV for them doesn't make sense.
492 The SVs in the names AV have their PV being the name of the variable.
493 NV+1..IV inclusive is a range of cop_seq numbers for which the name is
494 valid. For typed lexicals name SV is SVt_PVMG and SvSTASH points at the
495 type. For C<our> lexicals, the type is SVt_PVGV, and GvSTASH points at the
496 stash of the associated global (so that duplicate C<our> delarations in the
497 same package can be detected). SvCUR is sometimes hijacked to
498 store the generation number during compilation.
500 If SvFAKE is set on the name SV, then that slot in the frame AV is
501 a REFCNT'ed reference to a lexical from "outside". In this case,
502 the name SV does not use NVX and IVX to store a cop_seq range, since it is
503 in scope throughout. Instead IVX stores some flags containing info about
504 the real lexical (is it declared in an anon, and is it capable of being
505 instantiated multiple times?), and for fake ANONs, NVX contains the index
506 within the parent's pad where the lexical's value is stored, to make
509 If the 'name' is '&' the corresponding entry in frame AV
510 is a CV representing a possible closure.
511 (SvFAKE and name of '&' is not a meaningful combination currently but could
512 become so if C<my sub foo {}> is implemented.)
514 Note that formats are treated as anon subs, and are cloned each time
515 write is called (if necessary).
517 The flag SVf_PADSTALE is cleared on lexicals each time the my() is executed,
518 and set on scope exit. This allows the 'Variable $x is not available' warning
519 to be generated in evals, such as
521 { my $x = 1; sub f { eval '$x'} } f();
523 AV * CvPADLIST(CV *cv)
530 Clone a CV: make a new CV which points to the same code etc, but which
531 has a newly-created pad built by copying the prototype pad and capturing
534 CV* cv_clone(CV* proto)
541 dump the contents of a CV
543 void cv_dump(CV *cv, char *title)
550 Dump the contents of a padlist
552 void do_dump_pad(I32 level, PerlIO *file, PADLIST *padlist, int full)
559 "Introduce" my variables to visible status.
568 Add an anon code entry to the current compiling pad
570 PADOFFSET pad_add_anon(SV* sv, OPCODE op_type)
577 Create a new name and associated PADMY SV in the current pad; return the
579 If C<typestash> is valid, the name is for a typed lexical; set the
580 name's stash to that value.
581 If C<ourstash> is valid, it's an our lexical, set the name's
582 GvSTASH to that value
584 If fake, it means we're cloning an existing entry
586 PADOFFSET pad_add_name(char *name, HV* typestash, HV* ourstash, bool clone)
593 Allocate a new my or tmp pad entry. For a my, simply push a null SV onto
594 the end of PL_comppad, but for a tmp, scan the pad from PL_padix upwards
595 for a slot which has no name and and no active value.
597 PADOFFSET pad_alloc(I32 optype, U32 tmptype)
602 =item pad_block_start
604 Update the pad compilation state variables on entry to a new block
606 void pad_block_start(int full)
613 Check for duplicate declarations: report any of:
614 * a my in the current scope with the same name;
615 * an our (anywhere in the pad) with the same name and the same stash
617 C<is_our> indicates that the name to check is an 'our' declaration
619 void pad_check_dup(char* name, bool is_our, HV* ourstash)
626 Find a named lexical anywhere in a chain of nested pads. Add fake entries
627 in the inner pads if it's found in an outer one.
629 Returns the offset in the bottom pad of the lex or the fake lex.
630 cv is the CV in which to start the search, and seq is the current cop_seq
631 to match against. If warn is true, print appropriate warnings. The out_*
632 vars return values, and so are pointers to where the returned values
633 should be stored. out_capture, if non-null, requests that the innermost
634 instance of the lexical is captured; out_name_sv is set to the innermost
635 matched namesv or fake namesv; out_flags returns the flags normally
636 associated with the IVX field of a fake namesv.
638 Note that pad_findlex() is recursive; it recurses up the chain of CVs,
639 then comes back down, adding fake entries as it goes. It has to be this way
640 because fake namesvs in anon protoypes have to store in NVX the index into
643 PADOFFSET pad_findlex(char *name, CV* cv, U32 seq, int warn, SV** out_capture, SV** out_name_sv, int *out_flags)
650 Given a lexical name, try to find its offset, first in the current pad,
651 or failing that, in the pads of any lexically enclosing subs (including
652 the complications introduced by eval). If the name is found in an outer pad,
653 then a fake entry is added to the current pad.
654 Returns the offset in the current pad, or NOT_IN_PAD on failure.
656 PADOFFSET pad_findmy(char* name)
661 =item pad_fixup_inner_anons
663 For any anon CVs in the pad, change CvOUTSIDE of that CV from
664 old_cv to new_cv if necessary. Needed when a newly-compiled CV has to be
665 moved to a pre-existing CV struct.
667 void pad_fixup_inner_anons(PADLIST *padlist, CV *old_cv, CV *new_cv)
674 Free the SV at offet po in the current pad.
676 void pad_free(PADOFFSET po)
683 Cleanup at end of scope during compilation: set the max seq number for
684 lexicals in this scope and warn of any lexicals that never got introduced.
693 Create a new compiling padlist, saving and updating the various global
694 vars at the same time as creating the pad itself. The following flags
695 can be OR'ed together:
697 padnew_CLONE this pad is for a cloned CV
698 padnew_SAVE save old globals
699 padnew_SAVESUB also save extra stuff for start of sub
701 PADLIST* pad_new(int flags)
708 Push a new pad frame onto the padlist, unless there's already a pad at
709 this depth, in which case don't bother creating a new one. Then give
710 the new pad an @_ in slot zero.
712 void pad_push(PADLIST *padlist, int depth)
719 Mark all the current temporaries for reuse
728 Set the entry at offset po in the current pad to sv.
729 Use the macro PAD_SETSV() rather than calling this function directly.
731 void pad_setsv(PADOFFSET po, SV* sv)
738 Abandon the tmp in the current pad at offset po and replace with a
741 void pad_swipe(PADOFFSET po, bool refadjust)
748 Tidy up a pad after we've finished compiling it:
749 * remove most stuff from the pads of anonsub prototypes;
753 void pad_tidy(padtidy_type type)
760 Free the padlist associated with a CV.
761 If parts of it happen to be current, we null the relevant
762 PL_*pad* global vars so that we don't have any dangling references left.
763 We also repoint the CvOUTSIDE of any about-to-be-orphaned
764 inner subs to the outer of this cv.
766 (This function should really be called pad_free, but the name was already
769 void pad_undef(CV* cv)
777 =head1 Stack Manipulation Macros
783 Declare Just C<SP>. This is actually identical to C<dSP>, and declares
784 a local copy of perl's stack pointer, available via the C<SP> macro.
785 See C<SP>. (Available for backward source code compatibility with the
786 old (Perl 5.005) thread model.)
795 True if this op will be the return value of an lvalue subroutine
803 =head1 SV Manipulation Functions
807 =item find_uninit_var
809 Find the name of the undefined variable (if any) that caused the operator o
810 to issue a "Use of uninitialized value" warning.
811 If match is true, only return a name if it's value matches uninit_sv.
812 So roughly speaking, if a unary operator (such as OP_COS) generates a
813 warning, then following the direct child of the op may yield an
814 OP_PADSV or OP_GV that gives the name of the undefined variable. On the
815 other hand, with OP_ADD there are two branches to follow, so we only print
816 the variable name if we get an exact match.
818 The name is returned as a mortal SV.
820 Assumes that PL_op is the op that originally triggered the error, and that
821 PL_comppad/PL_curpad points to the currently executing pad.
823 SV* find_uninit_var(OP* obase, SV* uninit_sv, bool top)
830 Print appropriate "Use of uninitialized variable" warning
832 void report_uninit(SV* uninit_sv)
839 Given a chunk of memory, link it to the head of the list of arenas,
840 and split it into a list of free SVs.
842 void sv_add_arena(char* ptr, U32 size, U32 flags)
849 Decrement the refcnt of each remaining SV, possibly triggering a
850 cleanup. This function may have to be called multiple times to free
851 SVs which are in complex self-referential hierarchies.
860 Attempt to destroy all objects not yet freed
869 Deallocate the memory used by all arenas. Note that all the individual SV
870 heads and bodies within the arenas must already have been freed.
872 void sv_free_arenas()
882 The autodocumentation system was originally added to the Perl core by
883 Benjamin Stuhl. Documentation is by whoever was kind enough to
884 document their functions.
888 perlguts(1), perlapi(1)
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