perlintern



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 enclos-
               ing 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 incre-
               ment 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 cir-
               cumstances we should decrement the refcount of the parent when
               freeing the child.

               There is a further complication with non-closure anonymous subs
               (ie 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 proto-
               type has "CvWEAKOUTSIDE" set since it’s not a closure, and $a
               points to the same CV, so it doesn’t contribute to BEGIN’s ref-
               count 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 posi-
               tive, 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 ref-
               erences (such as $a above).

               One other thing to consider is that a CV may be merely unde-
               fined 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 lexi-
               cal 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 "SvCUR" is hijacked for this
               purpose.

                       STRLEN  PAD_COMPNAME_GEN(PADOFFSET po)

       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.

                       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. (ie 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)


Functions in file pp_ctl.c

       find_runcv
               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 in the scope
               of the debugger itself).

                       CV*     find_runcv(U32 *db_seqp)


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 sin-
               gle-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 vari-
               able.

                       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 exten-
               sion to allow selecting particular classes of magical variable.

                       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)


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. AvAR-
               RAY(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 stati-
               cally 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
               associated global (so that duplicate "our" delarations in the
               same package can be detected).  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 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)

       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 proto-
               type pad and capturing any outer lexicals.

                       CV*     cv_clone(CV* proto)

       cv_dump dump the contents of a CV

                       void    cv_dump(CV *cv, 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 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)

       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 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(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 current pad.

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

       pad_findmy
               Given a lexical name, try to find its offset, first in the cur-
               rent pad, or failing that, in the pads of any lexically enclos-
               ing 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 offet 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.  If has_args is true, 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 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.)

                               djSP;

       LVRET   True if this op will be the return value of an lvalue subrou-
               tine


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()


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 v5.8.6                       2004-11-05                     PERLINTERN(1)

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