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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!

Compile-time scope hooks

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.

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

        void *  BhkENTRY(BHK *hk, which)
Return the BHK's flags.

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

        U32     BhkFLAGS(BHK *hk)
Call all the registered block hooks for type which. which is a preprocessing token; the type of arg depends on which.

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

        void    CALL_BLOCK_HOOKS(which, arg)

CV reference counts and CvOUTSIDE

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)

Embedding Functions

dump the contents of a CV 

        void    cv_dump(CV *cv, const char *title)
Dump the contents of a padlist 

        void    do_dump_pad(I32 level, PerlIO *file,
                            PADLIST *padlist, int full)
"Introduce" my variables to visible status. 

        U32     intro_my()
Duplicates a pad. 

        AV *    padlist_dup(AV *srcpad, CLONE_PARAMS *param)
Allocates a place in the currently-compiling pad (via "pad_alloc" in perlapi) and then stores a name for that entry. namesv is adopted and becomes the name entry; it must already contain the name string and be sufficiently upgraded. typestash and ourstash and the "padadd_STATE" flag get added to namesv. 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(SV *namesv, U32 flags,
                                 HV *typestash, HV *ourstash)
Update the pad compilation state variables on entry to a new block 

        void    pad_block_start(int full)
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 C<ourstash>

"is_our" indicates that the name to check is an 'our' declaration.

        void    pad_check_dup(SV *name, U32 flags,
                              const HV *ourstash)
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 *namepv,
                              STRLEN namelen, U32 flags,
                              const CV* cv, U32 seq, int warn,
                              SV** out_capture,
                              SV** out_name_sv, int *out_flags)
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)
Free the SV at offset po in the current pad. 

        void    pad_free(PADOFFSET po)
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()
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)
Mark all the current temporaries for reuse 

        void    pad_reset()
Abandon the tmp in the current pad at offset po and replace with a new one. 

        void    pad_swipe(PADOFFSET po, bool refadjust)

Functions in file op.c

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 be negative and unequal to -KEY_CORE. 

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

Functions in file pp_ctl.c

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)

GV Functions

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.

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

        void    gv_try_downgrade(GV* gv)

Hash Manipulation Functions

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)
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)
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
                )
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
                )
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
                )
Like "refcounted_he_fetch_pvn", but takes a 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
                )
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
                )
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)
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
                               )
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
                               )
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
                               )
Like "refcounted_he_new_pvn", but takes a 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
                               )
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

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.

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

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

Magical Functions

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

        int     magic_clearhint(SV* sv, MAGIC* mg)
Triggered by clearing %^H, resets "PL_compiling.cop_hints_hash". 

        int     magic_clearhints(SV* sv, MAGIC* mg)
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,
                               const char *meth, U32 flags,
                               U32 argc, ...)
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)
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).

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)

MRO Functions

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)
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)
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

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

Save the current pad in the given context block structure. 

        void    CX_CURPAD_SAVE(struct context)
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)
Get the value from slot "po" in the base (DEPTH=1) pad of a padlist 

        SV *    PAD_BASE_SV(PADLIST padlist, PADOFFSET po)
Clone the state variables associated with running and compiling pads. 

        void    PAD_CLONE_VARS(PerlInterpreter *proto_perl,
                               CLONE_PARAMS* param)
Return the flags for the current compiling pad name at offset "po". Assumes a valid slot entry. 

        U32     PAD_COMPNAME_FLAGS(PADOFFSET po)
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)
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)
Return the stash associated with an "our" variable. Assumes the slot entry is a valid "our" lexical. 

        HV *    PAD_COMPNAME_OURSTASH(PADOFFSET po)
Return the name of the current compiling pad name at offset "po". Assumes a valid slot entry. 

        char *  PAD_COMPNAME_PV(PADOFFSET po)
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)
When PERL_MAD is enabled, this is a small no-op function that gets called at the start of each pad-related function. It can be breakpointed to track all pad operations. The parameter is a string indicating the type of pad operation being performed.

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

        void    pad_peg(const char *s)
Restore the old pad saved into the local variable opad by PAD_SAVE_LOCAL() 

        void    PAD_RESTORE_LOCAL(PAD *opad)
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)
Save the current pad then set it to null. 

        void    PAD_SAVE_SETNULLPAD()
Set the slot at offset "po" in the current pad to "sv" 

        SV *    PAD_SETSV(PADOFFSET po, SV* sv)
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)
like PAD_SET_CUR, but without the save 

        void    PAD_SET_CUR_NOSAVE(PADLIST padlist, I32 n)
Get the value at offset "po" in the current pad 

        void    PAD_SV(PADOFFSET po)
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)
Clear the pointed to pad value on scope exit. (i.e. the runtime action of 'my') 

        void    SAVECLEARSV(SV **svp)
save PL_comppad and PL_curpad 

        void    SAVECOMPPAD()
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

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

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

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

        GV*     PL_ofsgv
The input record separator - $/ in Perl space. 

        SV*     PL_rs

Stack Manipulation Macros

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

SV Manipulation Functions

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)
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()
Attempt to destroy all objects not yet freed. 

        void    sv_clean_objs()
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

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.

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

        SV*     sv_2num(SV *const sv)
Returns a SV describing what the SV passed in is a reference to. 

        SV*     sv_ref(SV *dst, const SV *const sv,
                       const int ob)

Unicode Support

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.

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.

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

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

_add_range_to_invlist
_core_swash_init
_invlist_array_init
_invlist_contents
_invlist_intersection
_invlist_intersection_maybe_complement_2nd
_invlist_invert
_invlist_invert_prop
_invlist_populate_swatch
_invlist_subtract
_invlist_union
_invlist_union_maybe_complement_2nd
_is_utf8__perl_idstart
_new_invlist
_swash_inversion_hash
_swash_to_invlist
_to_fold_latin1
_to_upper_title_latin1

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

2021-02-02 perl v5.16.3