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PERLINTERN(1)          Perl Programmers Reference Guide          PERLINTERN(1)

       perlintern - autogenerated documentation of purely internal            Perl functions

       This file is the autogenerated documentation of functions in the Perl interpreter that are documented using
       Perl's internal documentation format but are not marked as part of the Perl API. In other words, they are not
       for use in extensions!

CV reference counts and CvOUTSIDE
               Each CV has a pointer, "CvOUTSIDE()", to its lexically enclosing CV (if any). Because pointers to
               anonymous sub prototypes are stored in "&" 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 "CvOUTSIDE" in the one specific instance that the
               parent has a "&" pad slot pointing back to us. In this case, we set the "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 (i.e. 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 "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 $a is executed, the "eval '$x'" causes
               the chain of "CvOUTSIDE"s to be followed, and the freed BEGIN is accessed.

               To avoid this, whenever a CV and its associated pad is freed, any "&" 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 "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 $a above).

               One other thing to consider is that a CV may be merely undefined rather than freed, eg "undef &foo". In
               this case, its refcount may not have reached zero, but we still delete its pad and its "CvROOT" etc.
               Since various children may still have their "CvOUTSIDE" pointing at this undefined CV, we keep its own
               "CvOUTSIDE" for the time being, so that the chain of lexical scopes is unbroken. For example, the fol-
               lowing should print 123:

                   my $x = 123;
                   sub tmp { sub { eval '$x' } }
                   my $a = tmp();
                   undef &tmp;
                   print  $a->();

                       bool    CvWEAKOUTSIDE(CV *cv)

Functions in file pad.h
               Save the current pad in the given context block structure.

                       void    CX_CURPAD_SAVE(struct context)

               Access the SV at offset po in the saved current pad in the given context block structure (can be used
               as an lvalue).

                       SV *    CX_CURPAD_SV(struct context, PADOFFSET po)

               Get the value from slot "po" in the base (DEPTH=1) pad of a padlist

                       SV *    PAD_BASE_SV(PADLIST padlist, PADOFFSET po)

               |CLONE_PARAMS* param Clone the state variables associated with running and compiling pads.

                       void    PAD_CLONE_VARS(PerlInterpreter *proto_perl \)

               Return the flags for the current compiling pad name at offset "po". Assumes a valid slot entry.

                       U32     PAD_COMPNAME_FLAGS(PADOFFSET po)

               The generation number of the name at offset "po" in the current compiling pad (lvalue). Note that
               "SvCUR" is hijacked for this purpose.

                       STRLEN  PAD_COMPNAME_GEN(PADOFFSET po)

               Sets the generation number of the name at offset "po" in the current ling pad (lvalue) to "gen".  Note
               that "SvCUR_set" is hijacked for this purpose.

                       STRLEN  PAD_COMPNAME_GEN_set(PADOFFSET po, int gen)

               Return the stash associated with an "our" variable.  Assumes the slot entry is a valid "our" lexical.

                       HV *    PAD_COMPNAME_OURSTASH(PADOFFSET po)

               Return the name of the current compiling pad name at offset "po". Assumes a valid slot entry.

                       char *  PAD_COMPNAME_PV(PADOFFSET po)

               Return the type (stash) of the current compiling pad name at offset "po". Must be a valid name. Returns
               null if not typed.

                       HV *    PAD_COMPNAME_TYPE(PADOFFSET po)

       PAD_DUP Clone a padlist.

                       void    PAD_DUP(PADLIST dstpad, PADLIST srcpad, CLONE_PARAMS* param)

               Restore the old pad saved into the local variable opad by PAD_SAVE_LOCAL()

                       void    PAD_RESTORE_LOCAL(PAD *opad)

               Save the current pad to the local variable opad, then make the current pad equal to npad

                       void    PAD_SAVE_LOCAL(PAD *opad, PAD *npad)

               Save the current pad then set it to null.

                       void    PAD_SAVE_SETNULLPAD()

               Set the slot at offset "po" in the current pad to "sv"

                       SV *    PAD_SETSV(PADOFFSET po, SV* sv)

               Set the current pad to be pad "n" in the padlist, saving the previous current pad. NB currently this
               macro expands to a string too long for some compilers, so it's best to replace it with


                       void    PAD_SET_CUR(PADLIST padlist, I32 n)

               like PAD_SET_CUR, but without the save

                       void    PAD_SET_CUR_NOSAVE(PADLIST padlist, I32 n)

       PAD_SV  Get the value at offset "po" in the current pad

                       void    PAD_SV(PADOFFSET po)

       PAD_SVl Lightweight and lvalue version of "PAD_SV".  Get or set the value at offset "po" in the current pad.
               Unlike "PAD_SV", does not print diagnostics with -DX.  For internal use only.

                       SV *    PAD_SVl(PADOFFSET po)

               Clear the pointed to pad value on scope exit. (i.e. the runtime action of 'my')

                       void    SAVECLEARSV(SV **svp)

               save PL_comppad and PL_curpad

                       void    SAVECOMPPAD()

               Save a pad slot (used to restore after an iteration)

               XXX DAPM it would make more sense to make the arg a PADOFFSET      void SAVEPADSV(PADOFFSET po)

Functions in file pp_ctl.c
               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 the
               scope of the debugger itself).

                       CV*     find_runcv(U32 *db_seqp)

Global Variables
               When Perl is run in debugging mode, with the -d switch, this SV is a boolean which indicates whether
               subs are being single-stepped.  Single-stepping is automatically turned on after every step.  This is
               the C variable which corresponds to Perl's $DB::single variable.  See "PL_DBsub".

                       SV *    PL_DBsingle

               When Perl is run in debugging mode, with the -d switch, this GV contains the SV which holds the name of
               the sub being debugged.  This is the C variable which corresponds to Perl's $DB::sub variable.  See

                       GV *    PL_DBsub

               Trace variable used when Perl is run in debugging mode, with the -d switch.  This is the C variable
               which corresponds to Perl's $DB::trace variable.  See "PL_DBsingle".

                       SV *    PL_DBtrace

               The C variable which corresponds to Perl's $^W warning variable.

                       bool    PL_dowarn

               The GV which was last used for a filehandle input operation. ("<FH>")

                       GV*     PL_last_in_gv

               The output field separator - $, in Perl space.

                       SV*     PL_ofs_sv

       PL_rs   The input record separator - $/ in Perl space.

                       SV*     PL_rs

GV Functions
               Returns "TRUE" if given the name of a magical GV.

               Currently only useful internally when determining if a GV should be created even in rvalue contexts.

               "flags" is not used at present but available for future extension to allow selecting particular classes
               of magical variable.

               Currently assumes that "name" is NUL terminated (as well as len being valid).  This assumption is met
               by all callers within the perl core, which all pass pointers returned by SvPV.

                       bool    is_gv_magical(char *name, STRLEN len, U32 flags)

IO Functions
               Function called by "do_readline" to spawn a glob (or do the glob inside perl on VMS). This code used to
               be inline, but now perl uses "File::Glob" this glob starter is only used by miniperl during the build
               process.  Moving it away shrinks pp_hot.c; shrinking pp_hot.c helps speed perl up.

                       PerlIO* start_glob(SV* pattern, IO *io)

Pad Data Structures
               CV's can have CvPADLIST(cv) set to point to an AV.

               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).

               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 every entersub).

               The CvPADLIST AV has does not have AvREAL set, so REFCNT of component items is managed "manual" (mostly
               in pad.c) rather than normal av.c rules.  The items in the AV are not SVs as for a normal AV, but other

               0'th Entry of the CvPADLIST is an AV which represents the "names" or rather the "static type informa-
               tion" for lexicals.

               The CvDEPTH'th entry of CvPADLIST AV is an AV which is the stack frame at that depth of recursion into
               the CV.  The 0'th slot of a frame AV is an AV which is @_.  other entries are storage for variables and
               op targets.

               During compilation: "PL_comppad_name" is set to the names AV.  "PL_comppad" is set to the frame AV for
               the frame CvDEPTH == 1.  "PL_curpad" is set to the body of the frame AV (i.e. AvARRAY(PL_comppad)).

               During execution, "PL_comppad" and "PL_curpad" refer to the live frame of the currently executing sub.

               Iterating over the names AV iterates over all possible pad items. Pad slots that are SVs_PADTMP (tar-
               gets/GVs/constants) end up having &PL_sv_undef "names" (see pad_alloc()).

               Only my/our variable (SVs_PADMY/SVs_PADOUR) slots get valid names.  The rest are op
               targets/GVs/constants which are statically allocated or resolved at compile time.  These don't have
               names by which they can be looked up from Perl code at run time through eval"" like my/our variables
               can be.  Since they can't be looked up by "name" but only by their index allocated at compile time
               (which is usually in PL_op->op_targ), wasting a name SV for them doesn't make sense.

               The SVs in the names AV have their PV being the name of the variable.  NV+1..IV inclusive is a range of
               cop_seq numbers for which the name is valid.  For typed lexicals name SV is SVt_PVMG and SvSTASH points
               at the type.  For "our" lexicals, the type is SVt_PVGV, and GvSTASH points at the stash of the associ-
               ated global (so that duplicate "our" declarations in the same package can be detected).  SvCUR is some-
               times 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". In this case, the name SV does not have a cop_seq range, since it is in scope throughout.

               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 "my sub foo
               {}" is implemented.)

               The flag SVf_PADSTALE is cleared on lexicals each time the my() is executed, and set on scope exit.
               This allows the 'Variable $x is not available' warning to be generated in evals, such as

                   { my $x = 1; sub f { eval '$x'} } f();

                       AV *    CvPADLIST(CV *cv)

               Clone a CV: make a new CV which points to the same code etc, but which has a newly-created pad built by
               copying the prototype pad and capturing any outer lexicals.

                       CV*     cv_clone(CV* proto)

       cv_dump dump the contents of a CV

                       void    cv_dump(const CV *cv, const char *title)

               Dump the contents of a padlist

                       void    do_dump_pad(I32 level, PerlIO *file, PADLIST *padlist, int full)

               "Introduce" my variables to visible status.

                       U32     intro_my()

               Add an anon code entry to the current compiling pad

                       PADOFFSET       pad_add_anon(SV* sv, OPCODE op_type)

               Create a new name in the current pad at the specified offset.  If "typestash" is valid, the name is for
               a typed lexical; set the name's stash to that value.  If "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)

               Allocate a new my or tmp pad entry. For a my, simply push a null SV onto the end of PL_comppad, but for
               a tmp, scan the pad from PL_padix upwards for a slot which has no name and no active value.

                       PADOFFSET       pad_alloc(I32 optype, U32 tmptype)

               Update the pad compilation state variables on entry to a new block

                       void    pad_block_start(int full)

               Check for duplicate declarations: report any of:
                    * a my in the current scope with the same name;
                    * an our (anywhere in the pad) with the same name and the same stash
                      as "ourstash" "is_our" indicates that the name to check is an 'our' declaration

                       void    pad_check_dup(char* name, bool is_our, HV* ourstash)

               Find a named lexical anywhere in a chain of nested pads. Add fake entries 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.

                       PADOFFSET       pad_findlex(const char* name, PADOFFSET newoff, const CV* innercv)

               Given a lexical name, try to find its offset, first in the current pad, or failing that, in the pads of
               any lexically enclosing subs (including the complications introduced by eval). If the name is found in
               an outer pad, then a fake entry is added to the current pad.  Returns the offset in the current pad, or
               NOT_IN_PAD on failure.

                       PADOFFSET       pad_findmy(char* name)

               For any anon CVs in the pad, change CvOUTSIDE of that CV from 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)

               Free the SV at offset po in the current pad.

                       void    pad_free(PADOFFSET po)

               Cleanup at end of scope during compilation: set the max seq number for lexicals in this scope and warn
               of any lexicals that never got introduced.

                       void    pad_leavemy()

       pad_new Create a new compiling padlist, saving and updating the various global vars at the same time as creat-
               ing the pad itself. The following flags can be OR'ed together:

                   padnew_CLONE        this pad is for a cloned CV
                   padnew_SAVE         save old globals
                   padnew_SAVESUB      also save extra stuff for start of sub

                       PADLIST*        pad_new(int flags)

               Push a new pad frame onto the padlist, unless there's already a pad at this depth, in which case don't
               bother creating a new one.  If has_args is true, give the new pad an @_ in slot zero.

                       void    pad_push(PADLIST *padlist, int depth, int has_args)

               Mark all the current temporaries for reuse

                       void    pad_reset()

               Set the entry at offset po in the current pad to sv.  Use the macro PAD_SETSV() rather than calling
               this function directly.

                       void    pad_setsv(PADOFFSET po, SV* sv)

               Abandon the tmp in the current pad at offset po and replace with a new one.

                       void    pad_swipe(PADOFFSET po, bool refadjust)

               Tidy up a pad after we've finished compiling it:
                   * remove most stuff from the pads of anonsub prototypes;
                   * give it a @_;
                   * mark tmps as such.

                       void    pad_tidy(padtidy_type type)

               Free the padlist associated with a CV.  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 the outer of this cv.

               (This function should really be called pad_free, but the name was already taken)

                       void    pad_undef(CV* cv)

Stack Manipulation Macros
       djSP    Declare Just "SP". This is actually identical to "dSP", and declares a local copy of perl's stack
               pointer, available via the "SP" macro.  See "SP".  (Available for backward source code compatibility
               with the old (Perl 5.005) thread model.)


       LVRET   True if this op will be the return value of an lvalue subroutine

SV Manipulation Functions
               Print appropriate "Use of uninitialized variable" warning

                       void    report_uninit()

               Given a chunk of memory, link it to the head of the list of arenas, and split it into a list of free

                       void    sv_add_arena(char* ptr, U32 size, U32 flags)

               Decrement the refcnt of each remaining SV, possibly triggering a cleanup. This function may have to be
               called multiple times to free SVs which are in complex self-referential hierarchies.

                       I32     sv_clean_all()

               Attempt to destroy all objects not yet freed

                       void    sv_clean_objs()

               Deallocate the memory used by all arenas. Note that all the individual SV heads and bodies within the
               arenas must already have been freed.

                       void    sv_free_arenas()

       The autodocumentation system was originally added to the Perl core by Benjamin Stuhl. Documentation is by who-
       ever was kind enough to document their functions.

       perlguts(1), perlapi(1)

perl v5.8.8                       2006-01-07                     PERLINTERN(1)