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

NAME
       perlintern - autogenerated documentation of purely internal	      Perl functions

DESCRIPTION
       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
       CvWEAKOUTSIDE
	       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 "CvWEAK-
	       OUTSIDE" 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 proto-
	       type 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 "CvOUT-
	       SIDE"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 following 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
       CX_CURPAD_SAVE
	       Save the current pad in the given context block structure.

		       void    CX_CURPAD_SAVE(struct context)

       CX_CURPAD_SV
	       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)

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

		       SV *    PAD_BASE_SV(PADLIST padlist, PADOFFSET po)

       PAD_CLONE_VARS
	       Clone the state variables associated with running and compiling pads.

		       void    PAD_CLONE_VARS(PerlInterpreter *proto_perl, CLONE_PARAMS* param)

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

		       U32     PAD_COMPNAME_FLAGS(PADOFFSET po)

       PAD_COMPNAME_GEN
	       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)

       PAD_COMPNAME_GEN_set
	       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)

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

		       HV *    PAD_COMPNAME_OURSTASH(PADOFFSET po)

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

		       char *  PAD_COMPNAME_PV(PADOFFSET po)

       PAD_COMPNAME_TYPE
	       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)

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

		       void    PAD_RESTORE_LOCAL(PAD *opad)

       PAD_SAVE_LOCAL
	       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)

       PAD_SAVE_SETNULLPAD
	       Save the current pad then set it to null.

		       void    PAD_SAVE_SETNULLPAD()

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

		       SV *    PAD_SETSV(PADOFFSET po, SV* sv)

       PAD_SET_CUR
	       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

		   SAVECOMPPAD();
		   PAD_SET_CUR_NOSAVE(padlist,n);

		       void    PAD_SET_CUR(PADLIST padlist, I32 n)

       PAD_SET_CUR_NOSAVE
	       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)

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

		       void    SAVECLEARSV(SV **svp)

       SAVECOMPPAD
	       save PL_comppad and PL_curpad

		       void    SAVECOMPPAD()

       SAVEPADSV
	       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)

Global Variables
       PL_DBsingle
	       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

       PL_DBsub
	       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 cor-
	       responds to Perl's $DB::sub variable.  See "PL_DBsingle".

		       GV *    PL_DBsub

       PL_DBtrace
	       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_DBsin-
	       gle".

		       SV *    PL_DBtrace

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

		       bool    PL_dowarn

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

		       GV*     PL_last_in_gv

       PL_ofs_sv
	       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
       is_gv_magical
	       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 select-
	       ing 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 point-
	       ers returned by SvPV.

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

IO Functions
       start_glob
	       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)

Magical Functions
       mg_localize
	       Copy some of the magic from an existing SV to new localized version of that SV.
	       Container magic (eg %ENV, $1, tie) gets copied, value magic doesn't (eg taint,
	       pos).

		       void    mg_localize(SV* sv, SV* nsv)

Pad Data Structures
       CvPADLIST
	       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 AVs:

	       0'th Entry of the CvPADLIST is an AV which represents the "names" or rather the
	       "static type information" 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 cur-
	       rently executing sub.

	       Iterating over the names AV iterates over all possible pad items. Pad slots that
	       are SVs_PADTMP (targets/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 SvOURSTASH points at the stash of the associated global
	       (so that duplicate "our" declarations in the same package can be detected)(In
	       5.8.x and earlier SvOURSTASH is an alias for GvSTASH).  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 refer-
	       ences 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 cur-
	       rently 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)

       cv_clone
	       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 lexi-
	       cals.

		       CV*     cv_clone(CV* proto)

       cv_dump dump the contents of a CV

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

       do_dump_pad
	       Dump the contents of a padlist

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

       intro_my
	       "Introduce" my variables to visible status.

		       U32     intro_my()

       pad_add_anon
	       Add an anon code entry to the current compiling pad

		       PADOFFSET       pad_add_anon(SV* sv, OPCODE op_type)

       pad_add_name
	       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 SvOURSTASH 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)

       pad_alloc
	       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)

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

		       void    pad_block_start(int full)

       pad_check_dup
	       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' decla-
	       ration

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

       pad_findlex
	       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 cur-
	       rent pad.

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

       pad_findmy
	       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)

       pad_fixup_inner_anons
	       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)

       pad_free
	       Free the SV at offset po in the current pad.

		       void    pad_free(PADOFFSET po)

       pad_leavemy
	       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 creating 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)

       pad_push
	       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.  Then give the new pad an @_ in
	       slot zero.

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

       pad_reset
	       Mark all the current temporaries for reuse

		       void    pad_reset()

       pad_setsv
	       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)

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

		       void    pad_swipe(PADOFFSET po, bool refadjust)

       pad_tidy
	       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)

       pad_undef
	       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 refer-
	       ences 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.)

			       djSP;

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

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

		       void    report_uninit()

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

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

       sv_clean_all
	       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()

       sv_clean_objs
	       Attempt to destroy all objects not yet freed

		       void    sv_clean_objs()

       sv_free_arenas
	       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()

SV-Body Allocation
       sv_2num Return an SV with the numeric value of the source SV, doing any necessary refer-
	       ence or overload conversion.  You must use the "SvNUM(sv)" macro to access this
	       function.

		       SV*     sv_2num(SV* sv)

AUTHORS
       The autodocumentation system was originally added to the Perl core by Benjamin Stuhl. Doc-
       umentation is by whoever was kind enough to document their functions.

SEE ALSO
       perlguts(1), perlapi(1)

perl v5.8.9				    2007-11-17				    PERLINTERN(1)
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