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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
	       "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 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 "SvUVX" 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 "SvUV_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)

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 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(const char *name, STRLEN len, U32 flags)

       is_gv_magical_sv
	       Returns "TRUE" if given the name of a magical GV. Calls
	       is_gv_magical.

		       bool    is_gv_magical_sv(SV *name, U32 flags)

Hash Manipulation Functions
       refcounted_he_chain_2hv
	       Generates and returns a "HV *" by walking up the tree starting
	       at the passed in "struct refcounted_he *".

		       HV *    refcounted_he_chain_2hv(const struct refcounted_he *c)

       refcounted_he_free
	       Decrements the reference count of the passed in "struct
	       refcounted_he *" by one. If the reference count reaches zero
	       the structure's memory is freed, and "refcounted_he_free"
	       iterates onto the parent node.

		       void    refcounted_he_free(struct refcounted_he *he)

       refcounted_he_new
	       Creates a new "struct refcounted_he". As key is copied, and
	       value is stored in a compact form, all references remain the
	       property of the caller.	The "struct refcounted_he" is returned
	       with a reference count of 1.

		       struct refcounted_he *  refcounted_he_new(struct refcounted_he *const parent, SV *const key, SV *const value)

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 *tmpglob, IO *io)

Magical Functions
       magic_clearhint
	       Triggered by a delete from %^H, records the key to
	       "PL_compiling.cop_hints_hash".

		       int     magic_clearhint(SV* sv, MAGIC* mg)

       magic_sethint
	       Triggered by a store to %^H, records the key/value pair to
	       "PL_compiling.cop_hints_hash".  It is assumed that hints aren't
	       storing anything that would need a deep copy.  Maybe we should
	       warn if we find a reference.

		       int     magic_sethint(SV* sv, MAGIC* mg)

       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)

MRO Functions
       mro_get_linear_isa_dfs
	       Returns the Depth-First Search linearization of @ISA the given
	       stash.  The return value is a read-only AV*.  "level" should be
	       0 (it is used internally in this function's recursion).

	       You are responsible for "SvREFCNT_inc()" on the return value if
	       you plan to store it anywhere semi-permanently (otherwise it
	       might be deleted out from under you the next time the cache is
	       invalidated).

		       AV*     mro_get_linear_isa_dfs(HV* stash, U32 level)

       mro_isa_changed_in
	       Takes the necessary steps (cache invalidations, mostly) when
	       the @ISA of the given package has changed.  Invoked by the
	       "setisa" magic, should not need to invoke directly.

		       void    mro_isa_changed_in(HV* stash)

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). 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 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 currently 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.  xlow+1..xhigh inclusive in the NV union 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 also SVt_PVMG, with the
	       SvOURSTASH slot pointing at the stash of the associated global
	       (so that duplicate "our" declarations in the same package can
	       be detected).  SvUVX is sometimes hijacked to store the
	       generation number during compilation.

	       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 xlow and xhigh to store a
	       cop_seq range, since it is in scope throughout. Instead xhigh
	       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, xlow contains the index
	       within the parent's pad where the lexical's value is stored, to
	       make cloning quicker.

	       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.)

	       Note that formats are treated as anon subs, and are cloned each
	       time write is called (if necessary).

	       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();

	       For state vars, SVf_PADSTALE is overloaded to mean 'not yet
	       initialised'

		       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 lexicals.

		       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 and associated PADMY SV in the current pad;
	       return the 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

	       If fake, it means we're cloning an existing entry

		       PADOFFSET       pad_add_name(const char *name, HV* typestash, HV* ourstash, bool clone, bool state)

       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' declaration

		       void    pad_check_dup(const char* name, bool is_our, const 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.

	       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.

	       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 xlow the index into the parent pad.

		       PADOFFSET       pad_findlex(const char *name, const CV* cv, U32 seq, int warn, SV** out_capture, SV** out_name_sv, int *out_flags)

       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(const 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)

       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 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)

Per-Interpreter 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 corresponds 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_DBsingle".

		       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

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
       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 reference or overload conversion.  You must use the
	       "SvNUM(sv)" macro to access this function.

		       SV*     sv_2num(SV* sv)

Unicode Support
       find_uninit_var
	       Find the name of the undefined variable (if any) that caused
	       the operator o to issue a "Use of uninitialized value" warning.
	       If match is true, only return a name if it's value matches
	       uninit_sv.  So roughly speaking, if a unary operator (such as
	       OP_COS) generates a warning, then following the direct child of
	       the op may yield an OP_PADSV or OP_GV that gives the name of
	       the undefined variable. On the other hand, with OP_ADD there
	       are two branches to follow, so we only print the variable name
	       if we get an exact match.

	       The name is returned as a mortal SV.

	       Assumes that PL_op is the op that originally triggered the
	       error, and that PL_comppad/PL_curpad points to the currently
	       executing pad.

		       SV*     find_uninit_var(OP* obase, SV* uninit_sv, bool top)

       report_uninit
	       Print appropriate "Use of uninitialized variable" warning

		       void    report_uninit(SV* uninit_sv)

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

SEE ALSO
       perlguts(1), perlapi(1)

perl v5.10.1			  2010-11-08			 PERLINTERN(1)
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