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PERLINTERN

Section: Perl Programmers Reference Guide (1)
Updated: 2017-08-16
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---

 

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!  

Compile-time scope hooks

BhkENTRY

NOTE: this function is experimental and may change or be removed without notice.

Return an entry from the BHK structure. "which" is a preprocessor token indicating which entry to return. If the appropriate flag is not set this will return "NULL". The type of the return value depends on which entry you ask for.

        void *  BhkENTRY(BHK *hk, which)

BhkFLAGS

NOTE: this function is experimental and may change or be removed without notice.

Return the BHK's flags.

        U32     BhkFLAGS(BHK *hk)

CALL_BLOCK_HOOKS

NOTE: this function is experimental and may change or be removed without notice.

Call all the registered block hooks for type "which". "which" is a preprocessing token; the type of "arg" depends on "which".

        void    CALL_BLOCK_HOOKS(which, arg)

 

Custom Operators

core_prototype

This function assigns the prototype of the named core function to "sv", or to a new mortal SV if "sv" is "NULL". It returns the modified "sv", or "NULL" if the core function has no prototype. "code" is a code as returned by "keyword()". It must not be equal to 0.

        SV *    core_prototype(SV *sv, const char *name,
                               const int code,
                               int * const opnum)

 

CV Manipulation Functions

docatch

Check for the cases 0 or 3 of cur_env.je_ret, only used inside an eval context.

0 is used as continue inside eval,

3 is used for a die caught by an inner eval - continue inner loop

See cop.h: je_mustcatch, when set at any runlevel to TRUE, means eval ops must establish a local jmpenv to handle exception traps.

        OP*     docatch(OP *o)

 

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, e.g.,

    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)

 

Embedding Functions

cv_dump

dump the contents of a CV

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

cv_forget_slab

When a CV has a reference count on its slab ("CvSLABBED"), it is responsible for making sure it is freed. (Hence, no two CVs should ever have a reference count on the same slab.) The CV only needs to reference the slab during compilation. Once it is compiled and "CvROOT" attached, it has finished its job, so it can forget the slab.

        void    cv_forget_slab(CV *cv)

do_dump_pad

Dump the contents of a padlist

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

pad_alloc_name

Allocates a place in the currently-compiling pad (via ``pad_alloc'' in perlapi) and then stores a name for that entry. "name" is adopted and becomes the name entry; it must already contain the name string. "typestash" and "ourstash" and the "padadd_STATE" flag get added to "name". None of the other processing of ``pad_add_name_pvn'' in perlapi is done. Returns the offset of the allocated pad slot.

        PADOFFSET pad_alloc_name(PADNAME *name, U32 flags,
                                 HV *typestash, HV *ourstash)

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(PADNAME *name, U32 flags,
                              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" is set to the innermost matched pad name or fake pad name; "out_flags" returns the flags normally associated with the "PARENT_FAKELEX_FLAGS" field of a fake pad name.

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 names in anon protoypes have to store in "xlow" the index into the parent pad.

        PADOFFSET pad_findlex(const char *namepv,
                              STRLEN namelen, U32 flags,
                              const CV* cv, U32 seq, int warn,
                              SV** out_capture,
                              PADNAME** out_name,
                              int *out_flags)

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()

padlist_dup

Duplicates a pad.

        PADLIST * padlist_dup(PADLIST *srcpad,
                              CLONE_PARAMS *param)

padname_dup

Duplicates a pad name.

        PADNAME * padname_dup(PADNAME *src, CLONE_PARAMS *param)

padnamelist_dup

Duplicates a pad name list.

        PADNAMELIST * padnamelist_dup(PADNAMELIST *srcpad,
                                      CLONE_PARAMS *param)

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_swipe

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

        void    pad_swipe(PADOFFSET po, bool refadjust)

 

GV Functions

gv_try_downgrade

NOTE: this function is experimental and may change or be removed without notice.

If the typeglob "gv" can be expressed more succinctly, by having something other than a real GV in its place in the stash, replace it with the optimised form. Basic requirements for this are that "gv" is a real typeglob, is sufficiently ordinary, and is only referenced from its package. This function is meant to be used when a GV has been looked up in part to see what was there, causing upgrading, but based on what was found it turns out that the real GV isn't required after all.

If "gv" is a completely empty typeglob, it is deleted from the stash.

If "gv" is a typeglob containing only a sufficiently-ordinary constant sub, the typeglob is replaced with a scalar-reference placeholder that more compactly represents the same thing.

        void    gv_try_downgrade(GV* gv)

 

Hash Manipulation Functions

hv_ename_add

Adds a name to a stash's internal list of effective names. See "hv_ename_delete".

This is called when a stash is assigned to a new location in the symbol table.

        void    hv_ename_add(HV *hv, const char *name, U32 len,
                             U32 flags)

hv_ename_delete

Removes a name from a stash's internal list of effective names. If this is the name returned by "HvENAME", then another name in the list will take its place ("HvENAME" will use it).

This is called when a stash is deleted from the symbol table.

        void    hv_ename_delete(HV *hv, const char *name,
                                U32 len, U32 flags)

refcounted_he_chain_2hv

Generates and returns a "HV *" representing the content of a "refcounted_he" chain. "flags" is currently unused and must be zero.

        HV *    refcounted_he_chain_2hv(
                    const struct refcounted_he *c, U32 flags
                )

refcounted_he_fetch_pv

Like ``refcounted_he_fetch_pvn'', but takes a nul-terminated string instead of a string/length pair.

        SV *    refcounted_he_fetch_pv(
                    const struct refcounted_he *chain,
                    const char *key, U32 hash, U32 flags
                )

refcounted_he_fetch_pvn

Search along a "refcounted_he" chain for an entry with the key specified by "keypv" and "keylen". If "flags" has the "REFCOUNTED_HE_KEY_UTF8" bit set, the key octets are interpreted as UTF-8, otherwise they are interpreted as Latin-1. "hash" is a precomputed hash of the key string, or zero if it has not been precomputed. Returns a mortal scalar representing the value associated with the key, or &PL_sv_placeholder if there is no value associated with the key.

        SV *    refcounted_he_fetch_pvn(
                    const struct refcounted_he *chain,
                    const char *keypv, STRLEN keylen, U32 hash,
                    U32 flags
                )

refcounted_he_fetch_pvs

Like ``refcounted_he_fetch_pvn'', but takes a "NUL"-terminated literal string instead of a string/length pair, and no precomputed hash.

        SV *    refcounted_he_fetch_pvs(
                    const struct refcounted_he *chain,
                    const char *key, U32 flags
                )

refcounted_he_fetch_sv

Like ``refcounted_he_fetch_pvn'', but takes a Perl scalar instead of a string/length pair.

        SV *    refcounted_he_fetch_sv(
                    const struct refcounted_he *chain, SV *key,
                    U32 hash, U32 flags
                )

refcounted_he_free

Decrements the reference count of a "refcounted_he" by one. If the reference count reaches zero the structure's memory is freed, which (recursively) causes a reduction of its parent "refcounted_he"'s reference count. It is safe to pass a null pointer to this function: no action occurs in this case.

        void    refcounted_he_free(struct refcounted_he *he)

refcounted_he_inc

Increment the reference count of a "refcounted_he". The pointer to the "refcounted_he" is also returned. It is safe to pass a null pointer to this function: no action occurs and a null pointer is returned.

        struct refcounted_he * refcounted_he_inc(
                                   struct refcounted_he *he
                               )

refcounted_he_new_pv

Like ``refcounted_he_new_pvn'', but takes a nul-terminated string instead of a string/length pair.

        struct refcounted_he * refcounted_he_new_pv(
                                   struct refcounted_he *parent,
                                   const char *key, U32 hash,
                                   SV *value, U32 flags
                               )

refcounted_he_new_pvn

Creates a new "refcounted_he". This consists of a single key/value pair and a reference to an existing "refcounted_he" chain (which may be empty), and thus forms a longer chain. When using the longer chain, the new key/value pair takes precedence over any entry for the same key further along the chain.

The new key is specified by "keypv" and "keylen". If "flags" has the "REFCOUNTED_HE_KEY_UTF8" bit set, the key octets are interpreted as UTF-8, otherwise they are interpreted as Latin-1. "hash" is a precomputed hash of the key string, or zero if it has not been precomputed.

"value" is the scalar value to store for this key. "value" is copied by this function, which thus does not take ownership of any reference to it, and later changes to the scalar will not be reflected in the value visible in the "refcounted_he". Complex types of scalar will not be stored with referential integrity, but will be coerced to strings. "value" may be either null or &PL_sv_placeholder to indicate that no value is to be associated with the key; this, as with any non-null value, takes precedence over the existence of a value for the key further along the chain.

"parent" points to the rest of the "refcounted_he" chain to be attached to the new "refcounted_he". This function takes ownership of one reference to "parent", and returns one reference to the new "refcounted_he".

        struct refcounted_he * refcounted_he_new_pvn(
                                   struct refcounted_he *parent,
                                   const char *keypv,
                                   STRLEN keylen, U32 hash,
                                   SV *value, U32 flags
                               )

refcounted_he_new_pvs

Like ``refcounted_he_new_pvn'', but takes a "NUL"-terminated literal string instead of a string/length pair, and no precomputed hash.

        struct refcounted_he * refcounted_he_new_pvs(
                                   struct refcounted_he *parent,
                                   const char *key, SV *value,
                                   U32 flags
                               )

refcounted_he_new_sv

Like ``refcounted_he_new_pvn'', but takes a Perl scalar instead of a string/length pair.

        struct refcounted_he * refcounted_he_new_sv(
                                   struct refcounted_he *parent,
                                   SV *key, U32 hash, SV *value,
                                   U32 flags
                               )

 

IO Functions

start_glob

NOTE: this function is experimental and may change or be removed without notice.

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, or when PERL_EXTERNAL_GLOB is defined. Moving it away shrinks pp_hot.c; shrinking pp_hot.c helps speed perl up.

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

 

Lexer interface

validate_proto

NOTE: this function is experimental and may change or be removed without notice.

This function performs syntax checking on a prototype, "proto". If "warn" is true, any illegal characters or mismatched brackets will trigger illegalproto warnings, declaring that they were detected in the prototype for "name".

The return value is "true" if this is a valid prototype, and "false" if it is not, regardless of whether "warn" was "true" or "false".

Note that "NULL" is a valid "proto" and will always return "true".

NOTE: the perl_ form of this function is deprecated.

        bool    validate_proto(SV *name, SV *proto, bool warn)

 

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_clearhints

Triggered by clearing "%^H", resets "PL_compiling.cop_hints_hash".

        int     magic_clearhints(SV* sv, MAGIC* mg)

magic_methcall

Invoke a magic method (like FETCH).

"sv" and "mg" are the tied thingy and the tie magic.

"meth" is the name of the method to call.

"argc" is the number of args (in addition to $self) to pass to the method.

The "flags" can be:

    G_DISCARD     invoke method with G_DISCARD flag and don't
                  return a value
    G_UNDEF_FILL  fill the stack with argc pointers to
                  PL_sv_undef

The arguments themselves are any values following the "flags" argument.

Returns the SV (if any) returned by the method, or "NULL" on failure.

        SV*     magic_methcall(SV *sv, const MAGIC *mg,
                               SV *meth, U32 flags, U32 argc,
                               ...)

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 (e.g., %ENV, $1, "tie") gets copied, value magic doesn't (e.g., "taint", "pos").

If "setmagic" is false then no set magic will be called on the new (empty) SV. This typically means that assignment will soon follow (e.g. 'local $x = $y'), and that will handle the magic.

        void    mg_localize(SV* sv, SV* nsv, bool setmagic)

 

Miscellaneous Functions

free_c_backtrace

Deallocates a backtrace received from get_c_bracktrace.

        void    free_c_backtrace(Perl_c_backtrace* bt)

get_c_backtrace

Collects the backtrace (aka ``stacktrace'') into a single linear malloced buffer, which the caller must "Perl_free_c_backtrace()".

Scans the frames back by "depth + skip", then drops the "skip" innermost, returning at most "depth" frames.

        Perl_c_backtrace* get_c_backtrace(int max_depth,
                                          int skip)

 

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)

mro_package_moved

Call this function to signal to a stash that it has been assigned to another spot in the stash hierarchy. "stash" is the stash that has been assigned. "oldstash" is the stash it replaces, if any. "gv" is the glob that is actually being assigned to.

This can also be called with a null first argument to indicate that "oldstash" has been deleted.

This function invalidates isa caches on the old stash, on all subpackages nested inside it, and on the subclasses of all those, including non-existent packages that have corresponding entries in "stash".

It also sets the effective names ("HvENAME") on all the stashes as appropriate.

If the "gv" is present and is not in the symbol table, then this function simply returns. This checked will be skipped if "flags & 1".

        void    mro_package_moved(HV * const stash,
                                  HV * const oldstash,
                                  const GV * const gv,
                                  U32 flags)

 

Optree Manipulation Functions

finalize_optree

This function finalizes the optree. Should be called directly after the complete optree is built. It does some additional checking which can't be done in the normal "ck_"xxx functions and makes the tree thread-safe.

        void    finalize_optree(OP* o)

 

Pad Data Structures

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).

        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".         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)

PadnameIsOUR

Whether this is an ``our'' variable.

        bool    PadnameIsOUR(PADNAME pn)

PadnameIsSTATE

Whether this is a ``state'' variable.

        bool    PadnameIsSTATE(PADNAME pn)

PadnameOURSTASH

The stash in which this ``our'' variable was declared.

        HV *    PadnameOURSTASH()

PadnameOUTER

Whether this entry belongs to an outer pad. Entries for which this is true are often referred to as 'fake'.

        bool    PadnameOUTER(PADNAME pn)

PadnameTYPE

The stash associated with a typed lexical. This returns the %Foo:: hash for "my Foo $bar".

        HV *    PadnameTYPE(PADNAME pn)

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

        SV *    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)

 

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_ofsgv

The glob containing the output field separator - "*," in Perl space.

        GV*     PL_ofsgv

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" in perlapi". (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-Body Allocation

sv_2num

NOTE: this function is experimental and may change or be removed without notice.

Return an SV with the numeric value of the source SV, doing any necessary reference or overload conversion. The caller is expected to have handled get-magic already.

        SV*     sv_2num(SV *const sv)

sv_copypv

Copies a stringified representation of the source SV into the destination SV. Automatically performs any necessary "mg_get" and coercion of numeric values into strings. Guaranteed to preserve "UTF8" flag even from overloaded objects. Similar in nature to "sv_2pv[_flags]" but operates directly on an SV instead of just the string. Mostly uses "sv_2pv_flags" to do its work, except when that would lose the UTF-8'ness of the PV.

        void    sv_copypv(SV *const dsv, SV *const ssv)

 

SV Manipulation Functions

An SV (or AV, HV, etc.) is allocated in two parts: the head (struct sv, av, hv...) contains type and reference count information, and for many types, a pointer to the body (struct xrv, xpv, xpviv...), which contains fields specific to each type. Some types store all they need in the head, so don't have a body.

In all but the most memory-paranoid configurations (ex: PURIFY), heads and bodies are allocated out of arenas, which by default are approximately 4K chunks of memory parcelled up into N heads or bodies. Sv-bodies are allocated by their sv-type, guaranteeing size consistency needed to allocate safely from arrays.

For SV-heads, the first slot in each arena is reserved, and holds a link to the next arena, some flags, and a note of the number of slots. Snaked through each arena chain is a linked list of free items; when this becomes empty, an extra arena is allocated and divided up into N items which are threaded into the free list.

SV-bodies are similar, but they use arena-sets by default, which separate the link and info from the arena itself, and reclaim the 1st slot in the arena. SV-bodies are further described later.

The following global variables are associated with arenas:

 PL_sv_arenaroot     pointer to list of SV arenas
 PL_sv_root          pointer to list of free SV structures

 PL_body_arenas      head of linked-list of body arenas
 PL_body_roots[]     array of pointers to list of free bodies of svtype
                     arrays are indexed by the svtype needed

A few special SV heads are not allocated from an arena, but are instead directly created in the interpreter structure, eg PL_sv_undef. The size of arenas can be changed from the default by setting PERL_ARENA_SIZE appropriately at compile time.

The SV arena serves the secondary purpose of allowing still-live SVs to be located and destroyed during final cleanup.

At the lowest level, the macros new_SV() and del_SV() grab and free an SV head. (If debugging with -DD, del_SV() calls the function S_del_sv() to return the SV to the free list with error checking.) new_SV() calls more_sv() / sv_add_arena() to add an extra arena if the free list is empty. SVs in the free list have their SvTYPE field set to all ones.

At the time of very final cleanup, sv_free_arenas() is called from perl_destruct() to physically free all the arenas allocated since the start of the interpreter.

The function visit() scans the SV arenas list, and calls a specified function for each SV it finds which is still live - ie which has an SvTYPE other than all 1's, and a non-zero SvREFCNT. visit() is used by the following functions (specified as [function that calls visit()] / [function called by visit() for each SV]):

    sv_report_used() / do_report_used()
                        dump all remaining SVs (debugging aid)

    sv_clean_objs() / do_clean_objs(),do_clean_named_objs(),
                      do_clean_named_io_objs(),do_curse()
                        Attempt to free all objects pointed to by RVs,
                        try to do the same for all objects indir-
                        ectly referenced by typeglobs too, and
                        then do a final sweep, cursing any
                        objects that remain.  Called once from
                        perl_destruct(), prior to calling sv_clean_all()
                        below.

    sv_clean_all() / do_clean_all()
                        SvREFCNT_dec(sv) each remaining SV, possibly
                        triggering an sv_free(). It also sets the
                        SVf_BREAK flag on the SV to indicate that the
                        refcnt has been artificially lowered, and thus
                        stopping sv_free() from giving spurious warnings
                        about SVs which unexpectedly have a refcnt
                        of zero.  called repeatedly from perl_destruct()
                        until there are no SVs left.

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 *const ptr, const U32 size,
                             const 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()

SvTHINKFIRST

A quick flag check to see whether an "sv" should be passed to "sv_force_normal" to be ``downgraded'' before "SvIVX" or "SvPVX" can be modified directly.

For example, if your scalar is a reference and you want to modify the "SvIVX" slot, you can't just do "SvROK_off", as that will leak the referent.

This is used internally by various sv-modifying functions, such as "sv_setsv", "sv_setiv" and "sv_pvn_force".

One case that this does not handle is a gv without SvFAKE set. After

    if (SvTHINKFIRST(gv)) sv_force_normal(gv);

it will still be a gv.

"SvTHINKFIRST" sometimes produces false positives. In those cases "sv_force_normal" does nothing.

        U32     SvTHINKFIRST(SV *sv)

 

Unicode Support

find_uninit_var

NOTE: this function is experimental and may change or be removed without notice.

Find the name of the undefined variable (if any) that caused the operator to issue a ``Use of uninitialized value'' warning. If match is true, only return a name if its 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. "desc_p" points to a string pointer holding the description of the op. This may be updated if needed.

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(const OP *const obase,
                                const SV *const uninit_sv,
                                bool match, const char **desc_p)

report_uninit

Print appropriate ``Use of uninitialized variable'' warning.

        void    report_uninit(const SV *uninit_sv)

 

Undocumented functions

The following functions are currently undocumented. If you use one of them, you may wish to consider creating and submitting documentation for it.

PerlIO_restore_errno

PerlIO_save_errno

Slab_Alloc

Slab_Free

Slab_to_ro

Slab_to_rw

_add_range_to_invlist

_core_swash_init

_get_encoding

_get_swash_invlist

_invlistEQ

_invlist_array_init

_invlist_contains_cp

_invlist_dump

_invlist_intersection

_invlist_intersection_maybe_complement_2nd

_invlist_invert

_invlist_len

_invlist_populate_swatch

_invlist_search

_invlist_subtract

_invlist_union

_invlist_union_maybe_complement_2nd

_load_PL_utf8_foldclosures

_new_invlist

_setup_canned_invlist

_swash_inversion_hash

_swash_to_invlist

_to_fold_latin1

_to_upper_title_latin1

_warn_problematic_locale

add_cp_to_invlist

alloc_maybe_populate_EXACT

allocmy

amagic_is_enabled

apply

av_extend_guts

av_reify

bind_match

boot_core_PerlIO

boot_core_UNIVERSAL

boot_core_mro

cando

check_utf8_print

ck_anoncode

ck_backtick

ck_bitop

ck_cmp

ck_concat

ck_defined

ck_delete

ck_each

ck_entersub_args_core

ck_eof

ck_eval

ck_exec

ck_exists

ck_ftst

ck_fun

ck_glob

ck_grep

ck_index

ck_join

ck_length

ck_lfun

ck_listiob

ck_match

ck_method

ck_null

ck_open

ck_prototype

ck_readline

ck_refassign

ck_repeat

ck_require

ck_return

ck_rfun

ck_rvconst

ck_sassign

ck_select

ck_shift

ck_smartmatch

ck_sort

ck_spair

ck_split

ck_stringify

ck_subr

ck_substr

ck_svconst

ck_tell

ck_trunc

closest_cop

compute_EXACTish

coresub_op

create_eval_scope

croak_no_mem

croak_popstack

current_re_engine

custom_op_get_field

cv_ckproto_len_flags

cv_clone_into

cv_const_sv_or_av

cv_undef_flags

cvgv_from_hek

cvgv_set

cvstash_set

deb_stack_all

defelem_target

delete_eval_scope

delimcpy_no_escape

die_unwind

do_aexec

do_aexec5

do_eof

do_exec

do_exec3

do_execfree

do_ipcctl

do_ipcget

do_msgrcv

do_msgsnd

do_ncmp

do_open6

do_open_raw

do_print

do_readline

do_seek

do_semop

do_shmio

do_sysseek

do_tell

do_trans

do_vecget

do_vecset

do_vop

dofile

drand48_init_r

drand48_r

dtrace_probe_call

dtrace_probe_load

dtrace_probe_op

dtrace_probe_phase

dump_all_perl

dump_packsubs_perl

dump_sub_perl

dump_sv_child

emulate_cop_io

feature_is_enabled

find_lexical_cv

find_runcv_where

find_script

form_short_octal_warning

free_tied_hv_pool

get_and_check_backslash_N_name

get_db_sub

get_debug_opts

get_hash_seed

get_invlist_iter_addr

get_invlist_offset_addr

get_invlist_previous_index_addr

get_no_modify

get_opargs

get_re_arg

getenv_len

grok_atoUV

grok_bslash_c

grok_bslash_o

grok_bslash_x

gv_fetchmeth_internal

gv_override

gv_setref

gv_stashpvn_internal

gv_stashsvpvn_cached

handle_named_backref

hfree_next_entry

hv_backreferences_p

hv_kill_backrefs

hv_placeholders_p

hv_undef_flags

init_argv_symbols

init_constants

init_dbargs

init_debugger

invert

invlist_array

invlist_clear

invlist_clone

invlist_highest

invlist_is_iterating

invlist_iterfinish

invlist_iterinit

invlist_max

invlist_previous_index

invlist_set_len

invlist_set_previous_index

invlist_trim

io_close

isGCB

is_utf8_common

isinfnansv

jmaybe

keyword

keyword_plugin_standard

list

localize

magic_clear_all_env

magic_cleararylen_p

magic_clearenv

magic_clearisa

magic_clearpack

magic_clearsig

magic_copycallchecker

magic_existspack

magic_freearylen_p

magic_freeovrld

magic_get

magic_getarylen

magic_getdebugvar

magic_getdefelem

magic_getnkeys

magic_getpack

magic_getpos

magic_getsig

magic_getsubstr

magic_gettaint

magic_getuvar

magic_getvec

magic_killbackrefs

magic_nextpack

magic_regdata_cnt

magic_regdatum_get

magic_regdatum_set

magic_scalarpack

magic_set

magic_set_all_env

magic_setarylen

magic_setcollxfrm

magic_setdbline

magic_setdebugvar

magic_setdefelem

magic_setenv

magic_setisa

magic_setlvref

magic_setmglob

magic_setnkeys

magic_setpack

magic_setpos

magic_setregexp

magic_setsig

magic_setsubstr

magic_settaint

magic_setutf8

magic_setuvar

magic_setvec

magic_sizepack

magic_wipepack

malloc_good_size

malloced_size

mem_collxfrm

mem_log_alloc

mem_log_free

mem_log_realloc

mg_find_mglob

mode_from_discipline

more_bodies

mro_meta_dup

mro_meta_init

multideref_stringify

my_attrs

my_clearenv

my_lstat_flags

my_stat_flags

my_unexec

newATTRSUB_x

newGP

newMETHOP_internal

newSTUB

newSVavdefelem

newXS_deffile

newXS_len_flags

new_warnings_bitfield

nextargv

noperl_die

oopsAV

oopsHV

op_clear

op_integerize

op_lvalue_flags

op_refcnt_dec

op_refcnt_inc

op_relocate_sv

op_std_init

op_unscope

opmethod_stash

opslab_force_free

opslab_free

opslab_free_nopad

package

package_version

pad_add_weakref

padlist_store

padname_free

padnamelist_free

parse_subsignature

parse_unicode_opts

parser_free

parser_free_nexttoke_ops

path_is_searchable

peep

pmruntime

populate_isa

ptr_hash

qerror

re_exec_indentf

re_indentf

re_op_compile

re_printf

reg_named_buff

reg_named_buff_iter

reg_numbered_buff_fetch

reg_numbered_buff_length

reg_numbered_buff_store

reg_qr_package

reg_skipcomment

reg_temp_copy

regcurly

regprop

report_evil_fh

report_redefined_cv

report_wrongway_fh

rpeep

rsignal_restore

rsignal_save

rxres_save

same_dirent

save_strlen

sawparens

scalar

scalarvoid

set_caret_X

set_padlist

should_warn_nl

sighandler

softref2xv

ssc_add_range

ssc_clear_locale

ssc_cp_and

ssc_intersection

ssc_union

sub_crush_depth

sv_add_backref

sv_buf_to_ro

sv_del_backref

sv_free2

sv_kill_backrefs

sv_len_utf8_nomg

sv_magicext_mglob

sv_mortalcopy_flags

sv_only_taint_gmagic

sv_or_pv_pos_u2b

sv_resetpvn

sv_sethek

sv_setsv_cow

sv_unglob

tied_method

tmps_grow_p

translate_substr_offsets

try_amagic_bin

try_amagic_un

unshare_hek

utilize

varname

vivify_defelem

vivify_ref

wait4pid

was_lvalue_sub

watch

win32_croak_not_implemented

write_to_stderr

xs_boot_epilog

xs_handshake

yyerror

yyerror_pv

yyerror_pvn

yylex

yyparse

yyunlex

 

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, perlapi

---

 

Index

NAME

DESCRIPTION

Compile-time scope hooks

Custom Operators

CV Manipulation Functions

CV reference counts and CvOUTSIDE

Embedding Functions

GV Functions

Hash Manipulation Functions

IO Functions

Lexer interface

Magical Functions

Miscellaneous Functions

MRO Functions

Optree Manipulation Functions

Pad Data Structures

Per-Interpreter Variables

Stack Manipulation Macros

SV-Body Allocation

SV Manipulation Functions

Unicode Support

Undocumented functions

AUTHORS

SEE ALSO