FM / pod

/usr/share/perl5/pod

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Edit: /usr/share/perl5/pod/perlintern.pod (26408B)

-*- buffer-read-only: t -*-

!!!!!!!   DO NOT EDIT THIS FILE   !!!!!!!
This file is built by autodoc.pl extracting documentation from the C source
files.

=head1 NAME

perlintern - autogenerated documentation of purely B<internal>
		 Perl functions

=head1 DESCRIPTION
X<internal Perl functions> X<interpreter functions>

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,
B<they are not for use in extensions>!

=head1 CV reference counts and CvOUTSIDE

=over 8

=item CvWEAKOUTSIDE
X<CvWEAKOUTSIDE>

Each CV has a pointer, C<CvOUTSIDE()>, to its lexically enclosing
CV (if any). Because pointers to anonymous sub prototypes are
stored in C<&> 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 C<CvOUTSIDE> in the I<one specific instance> that the parent
has a C<&> pad slot pointing back to us. In this case, we set the
C<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
C<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 $a is
executed, the C<eval '$x'> causes the chain of C<CvOUTSIDE>s to be followed,
and the freed BEGIN is accessed.

To avoid this, whenever a CV and its associated pad is freed, any
C<&> 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 C<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 C<$a> above).

One other thing to consider is that a CV may be merely undefined
rather than freed, eg C<undef &foo>. In this case, its refcount may
not have reached zero, but we still delete its pad and its C<CvROOT> etc.
Since various children may still have their C<CvOUTSIDE> pointing at this
undefined CV, we keep its own C<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)

=for hackers
Found in file cv.h

=back

=head1 Functions in file pad.h

=over 8

=item CX_CURPAD_SAVE
X<CX_CURPAD_SAVE>

Save the current pad in the given context block structure.

void	CX_CURPAD_SAVE(struct context)

=for hackers
Found in file pad.h

=item CX_CURPAD_SV
X<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)

=for hackers
Found in file pad.h

=item PAD_BASE_SV
X<PAD_BASE_SV>

Get the value from slot C<po> in the base (DEPTH=1) pad of a padlist

SV *	PAD_BASE_SV(PADLIST padlist, PADOFFSET po)

=for hackers
Found in file pad.h

=item PAD_CLONE_VARS
X<PAD_CLONE_VARS>

Clone the state variables associated with running and compiling pads.

void	PAD_CLONE_VARS(PerlInterpreter *proto_perl, CLONE_PARAMS* param)

=for hackers
Found in file pad.h

=item PAD_COMPNAME_FLAGS
X<PAD_COMPNAME_FLAGS>

Return the flags for the current compiling pad name
at offset C<po>. Assumes a valid slot entry.

U32	PAD_COMPNAME_FLAGS(PADOFFSET po)

=for hackers
Found in file pad.h

=item PAD_COMPNAME_GEN
X<PAD_COMPNAME_GEN>

The generation number of the name at offset C<po> in the current
compiling pad (lvalue). Note that C<SvUVX> is hijacked for this purpose.

STRLEN	PAD_COMPNAME_GEN(PADOFFSET po)

=for hackers
Found in file pad.h

=item PAD_COMPNAME_GEN_set
X<PAD_COMPNAME_GEN_set>

Sets the generation number of the name at offset C<po> in the current
ling pad (lvalue) to C<gen>.  Note that C<SvUV_set> is hijacked for this purpose.

STRLEN	PAD_COMPNAME_GEN_set(PADOFFSET po, int gen)

=for hackers
Found in file pad.h

=item PAD_COMPNAME_OURSTASH
X<PAD_COMPNAME_OURSTASH>

Return the stash associated with an C<our> variable.
Assumes the slot entry is a valid C<our> lexical.

HV *	PAD_COMPNAME_OURSTASH(PADOFFSET po)

=for hackers
Found in file pad.h

=item PAD_COMPNAME_PV
X<PAD_COMPNAME_PV>

Return the name of the current compiling pad name
at offset C<po>. Assumes a valid slot entry.

char *	PAD_COMPNAME_PV(PADOFFSET po)

=for hackers
Found in file pad.h

=item PAD_COMPNAME_TYPE
X<PAD_COMPNAME_TYPE>

Return the type (stash) of the current compiling pad name at offset
C<po>. Must be a valid name. Returns null if not typed.

HV *	PAD_COMPNAME_TYPE(PADOFFSET po)

=for hackers
Found in file pad.h

=item PAD_DUP
X<PAD_DUP>

Clone a padlist.

void	PAD_DUP(PADLIST dstpad, PADLIST srcpad, CLONE_PARAMS* param)

=for hackers
Found in file pad.h

=item PAD_RESTORE_LOCAL
X<PAD_RESTORE_LOCAL>

Restore the old pad saved into the local variable opad by PAD_SAVE_LOCAL()

void	PAD_RESTORE_LOCAL(PAD *opad)

=for hackers
Found in file pad.h

=item PAD_SAVE_LOCAL
X<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)

=for hackers
Found in file pad.h

=item PAD_SAVE_SETNULLPAD
X<PAD_SAVE_SETNULLPAD>

Save the current pad then set it to null.

void	PAD_SAVE_SETNULLPAD()

=for hackers
Found in file pad.h

=item PAD_SETSV
X<PAD_SETSV>

Set the slot at offset C<po> in the current pad to C<sv>

SV *	PAD_SETSV(PADOFFSET po, SV* sv)

=for hackers
Found in file pad.h

=item PAD_SET_CUR
X<PAD_SET_CUR>

Set the current pad to be pad C<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)

=for hackers
Found in file pad.h

=item PAD_SET_CUR_NOSAVE
X<PAD_SET_CUR_NOSAVE>

like PAD_SET_CUR, but without the save

void	PAD_SET_CUR_NOSAVE(PADLIST padlist, I32 n)

=for hackers
Found in file pad.h

=item PAD_SV
X<PAD_SV>

Get the value at offset C<po> in the current pad

void	PAD_SV(PADOFFSET po)

=for hackers
Found in file pad.h

=item PAD_SVl
X<PAD_SVl>

Lightweight and lvalue version of C<PAD_SV>.
Get or set the value at offset C<po> in the current pad.
Unlike C<PAD_SV>, does not print diagnostics with -DX.
For internal use only.

SV *	PAD_SVl(PADOFFSET po)

=for hackers
Found in file pad.h

=item SAVECLEARSV
X<SAVECLEARSV>

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

void	SAVECLEARSV(SV **svp)

=for hackers
Found in file pad.h

=item SAVECOMPPAD
X<SAVECOMPPAD>

save PL_comppad and PL_curpad

void	SAVECOMPPAD()

=for hackers
Found in file pad.h

=item SAVEPADSV
X<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)

=for hackers
Found in file pad.h

=back

=head1 GV Functions

=over 8

=item is_gv_magical
X<is_gv_magical>

Returns C<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.

C<flags> is not used at present but available for future extension to
allow selecting particular classes of magical variable.

Currently assumes that C<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)

=for hackers
Found in file gv.c

=item is_gv_magical_sv
X<is_gv_magical_sv>

Returns C<TRUE> if given the name of a magical GV. Calls is_gv_magical.

bool	is_gv_magical_sv(SV *name, U32 flags)

=for hackers
Found in file gv.c

=back

=head1 Hash Manipulation Functions

=over 8

=item refcounted_he_chain_2hv
X<refcounted_he_chain_2hv>

Generates and returns a C<HV *> by walking up the tree starting at the passed
in C<struct refcounted_he *>.

HV *	refcounted_he_chain_2hv(const struct refcounted_he *c)

=for hackers
Found in file hv.c

=item refcounted_he_free
X<refcounted_he_free>

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

void	refcounted_he_free(struct refcounted_he *he)

=for hackers
Found in file hv.c

=item refcounted_he_new
X<refcounted_he_new>

Creates a new C<struct refcounted_he>. As S<key> is copied, and value is
stored in a compact form, all references remain the property of the caller.
The C<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)

=for hackers
Found in file hv.c

=back

=head1 IO Functions

=over 8

=item start_glob
X<start_glob>

Function called by C<do_readline> to spawn a glob (or do the glob inside
perl on VMS). This code used to be inline, but now perl uses C<File::Glob>
this glob starter is only used by miniperl during the build process.
Moving it away shrinks pp_hot.c; shrinking pp_hot.c helps speed perl up.

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

=for hackers
Found in file doio.c

=back

=head1 Magical Functions

=over 8

=item magic_clearhint
X<magic_clearhint>

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

int	magic_clearhint(SV* sv, MAGIC* mg)

=for hackers
Found in file mg.c

=item magic_sethint
X<magic_sethint>

Triggered by a store to %^H, records the key/value pair to
C<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)

=for hackers
Found in file mg.c

=item mg_localize
X<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)

=for hackers
Found in file mg.c

=back

=head1 MRO Functions

=over 8

=item mro_get_linear_isa_dfs
X<mro_get_linear_isa_dfs>

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

You are responsible for C<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)

=for hackers
Found in file mro.c

=item mro_isa_changed_in
X<mro_isa_changed_in>

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

void	mro_isa_changed_in(HV* stash)

=for hackers
Found in file mro.c

=back

=head1 Pad Data Structures

=over 8

=item CvPADLIST
X<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:
C<PL_comppad_name> is set to the names AV.
C<PL_comppad> is set to the frame AV for the frame CvDEPTH == 1.
C<PL_curpad> is set to the body of the frame AV (i.e. AvARRAY(PL_comppad)).

During execution, C<PL_comppad> and C<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 C<our> lexicals, the type is also SVt_PVMG, with the
SvOURSTASH slot pointing at the stash of the associated global (so that
duplicate C<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 C<my sub foo {}> is implemented.)

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

The flag SVf_PADSTALE is cleared on lexicals each time the my() is executed,
and set on scope exit. This allows the 'Variable $x is not available' warning
to be generated in evals, such as

{ my $x = 1; sub f { eval '$x'} } f();

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

AV *	CvPADLIST(CV *cv)