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

                       void    PAD_CLONE_VARS(PerlInterpreter *proto_perl \)

       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* pattern, IO *io)

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

                       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_c3
               Returns the C3 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_c3(HV* stash, I32 level)

       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, I32 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();

                       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 v5.10.0                                     2007-12-18                                    PERLINTERN(1)