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)
