Extract something from yesterdays effort - convert my mail on pad

data structures (incoporating Sarathy's corrections/clarifications)
into POD in cv.h which gets autodoc.pl'ed into pod/perlintern.pod.

p4raw-id: //depot/perlio@14595

3 files changed, 315 insertions, 137 deletions

diff --git a/cv.h b/cv.h
index 2c438be838..824517c199 100644
--- a/cv.h
+++ b/cv.h
@@ -136,3 +136,62 @@ Returns the stash of the CV.
 #define CvCONST(cv)		(CvFLAGS(cv) & CVf_CONST)
 #define CvCONST_on(cv)		(CvFLAGS(cv) |= CVf_CONST)
 #define CvCONST_off(cv)		(CvFLAGS(cv) &= ~CVf_CONST)
+
+/*
+=head1 Pad Data Structures
+
+=for apidoc m|AV *|CvPADLIST|CV *cv
+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 op.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 the the the names AV.
+C<PL_comppad> is set the the frame AV for the frame CvDEPTH == 1.
+C<PL_curpad> is set the body of the frame AV (i.e. AvARRAY(PL_comppad)).
+
+Itterating over the names AV itterates 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.
+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.
+
+If SvFAKE is set on the name SV then slot in the frame AVs are
+a REFCNT'ed references to a lexical from "outside".
+
+If the 'name' is '&' the 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.)
+
+=cut
+*/
+
diff --git a/pod/perlapi.pod b/pod/perlapi.pod
index d55b88a13a..dc52664ef7 100644
--- a/pod/perlapi.pod
+++ b/pod/perlapi.pod
@@ -1266,6 +1266,16 @@ argument more than once.
 =for hackers
 Found in file sv.h
 
+=item SvLOCK
+
+Arranges for a mutual exclusion lock to be obtained on sv if a suitable module
+has been loaded.
+
+	void	SvLOCK(SV* sv)
+
+=for hackers
+Found in file sv.h
+
 =item SvSETMAGIC
 
 Invokes C<mg_set> on an SV if it has 'set' magic.  This macro evaluates its
@@ -1285,6 +1295,15 @@ Like C<SvSetSV>, but does any set magic required afterwards.
 =for hackers
 Found in file sv.h
 
+=item SvSetMagicSV_nosteal
+
+Like C<SvSetMagicSV>, but does any set magic required afterwards.
+
+	void	SvSetMagicSV_nosteal(SV* dsv, SV* ssv)
+
+=for hackers
+Found in file sv.h
+
 =item SvSetSV
 
 Calls C<sv_setsv> if dsv is not the same as ssv.  May evaluate arguments
@@ -1305,6 +1324,16 @@ ssv. May evaluate arguments more than once.
 =for hackers
 Found in file sv.h
 
+=item SvSHARE
+
+Arranges for sv to be shared between threads if a suitable module
+has been loaded.
+
+	void	SvSHARE(SV* sv)
+
+=for hackers
+Found in file sv.h
+
 
 =back
 
@@ -1417,13 +1446,24 @@ Found in file util.c
 =item savepvn
 
 Copy a string to a safe spot.  The C<len> indicates number of bytes to
-copy.  This does not use an SV.
+copy. If pointer is NULL allocate space for a string of size specified.
+This does not use an SV.
 
 	char*	savepvn(const char* sv, I32 len)
 
 =for hackers
 Found in file util.c
 
+=item savesharedpv
+
+Copy a string to a safe spot in memory shared between threads.
+This does not use an SV.
+
+	char*	savesharedpv(const char* sv)
+
+=for hackers
+Found in file util.c
+
 =item StructCopy
 
 This is an architecture-independent macro to copy one structure to another.
@@ -1750,77 +1790,6 @@ Found in file op.c
 
 =back
 
-=head1 Shared SV Functions
-
-=over 8
-
-=item sharedsv_find
-
-Tries to find if a given SV has a shared backend, either by
-looking at magic, or by checking if it is tied again threads::shared.
-
-	shared_sv*	sharedsv_find(SV* sv)
-
-=for hackers
-Found in file sharedsv.c
-
-=item sharedsv_init
-
-Saves a space for keeping SVs wider than an interpreter,
-currently only stores a pointer to the first interpreter.
-
-	void	sharedsv_init()
-
-=for hackers
-Found in file sharedsv.c
-
-=item sharedsv_lock
-
-Recursive locks on a sharedsv.
-Locks are dynamically scoped at the level of the first lock.
-	void	sharedsv_lock(shared_sv* ssv)
-
-=for hackers
-Found in file sharedsv.c
-
-=item sharedsv_new
-
-Allocates a new shared sv struct, you must yourself create the SV/AV/HV.
-	shared_sv*	sharedsv_new()
-
-=for hackers
-Found in file sharedsv.c
-
-=item sharedsv_thrcnt_dec
-
-Decrements the threadcount of a shared sv. When a threads frontend is freed
-this function should be called.
-
-	void	sharedsv_thrcnt_dec(shared_sv* ssv)
-
-=for hackers
-Found in file sharedsv.c
-
-=item sharedsv_thrcnt_inc
-
-Increments the threadcount of a sharedsv.
-	void	sharedsv_thrcnt_inc(shared_sv* ssv)
-
-=for hackers
-Found in file sharedsv.c
-
-=item sharedsv_unlock
-
-Recursively unlocks a shared sv.
-
-	void	sharedsv_unlock(shared_sv* ssv)
-
-=for hackers
-Found in file sharedsv.c
-
-
-=back
-
 =head1 Stack Manipulation Macros
 
 =over 8
@@ -2899,21 +2868,21 @@ Like C<SvPV_nolen>, but converts sv to utf8 first if necessary.
 =for hackers
 Found in file sv.h
 
-=item SvPVX
+=item SvPVx
 
-Returns a pointer to the physical string in the SV.  The SV must contain a
-string.
+A version of C<SvPV> which guarantees to evaluate sv only once.
 
-	char*	SvPVX(SV* sv)
+	char*	SvPVx(SV* sv, STRLEN len)
 
 =for hackers
 Found in file sv.h
 
-=item SvPVx
+=item SvPVX
 
-A version of C<SvPV> which guarantees to evaluate sv only once.
+Returns a pointer to the physical string in the SV.  The SV must contain a
+string.
 
-	char*	SvPVx(SV* sv, STRLEN len)
+	char*	SvPVX(SV* sv)
 
 =for hackers
 Found in file sv.h
@@ -3011,16 +2980,6 @@ Dereferences an RV to return the SV.
 =for hackers
 Found in file sv.h
 
-=item SvSetMagicSV_nosteal
-
-Like C<SvSetMagicSV>, but does any set magic required afterwards.
-
-
-	void	SvSetMagicSV_nosteal(SV* dsv, SV* ssv)
-
-=for hackers
-Found in file sv.h
-
 =item SvSTASH
 
 Returns the stash of the SV.
@@ -3091,6 +3050,17 @@ Returns the type of the SV.  See C<svtype>.
 =for hackers
 Found in file sv.h
 
+=item SvUNLOCK
+
+Releases a mutual exclusion lock on sv if a suitable module
+has been loaded.
+
+
+	void	SvUNLOCK(SV* sv)
+
+=for hackers
+Found in file sv.h
+
 =item SvUOK
 
 Returns a boolean indicating whether the SV contains an unsigned integer.
@@ -3148,22 +3118,22 @@ for a version which guarantees to evaluate sv only once.
 =for hackers
 Found in file sv.h
 
-=item SvUVx
+=item SvUVX
 
-Coerces the given SV to an unsigned integer and returns it. Guarantees to
-evaluate sv only once. Use the more efficient C<SvUV> otherwise.
+Returns the raw value in the SV's UV slot, without checks or conversions.
+Only use when you are sure SvIOK is true. See also C<SvUV()>.
 
-	UV	SvUVx(SV* sv)
+	UV	SvUVX(SV* sv)
 
 =for hackers
 Found in file sv.h
 
-=item SvUVX
+=item SvUVx
 
-Returns the raw value in the SV's UV slot, without checks or conversions.
-Only use when you are sure SvIOK is true. See also C<SvUV()>.
+Coerces the given SV to an unsigned integer and returns it. Guarantees to
+evaluate sv only once. Use the more efficient C<SvUV> otherwise.
 
-	UV	SvUVX(SV* sv)
+	UV	SvUVx(SV* sv)
 
 =for hackers
 Found in file sv.h
@@ -3674,13 +3644,32 @@ Found in file sv.c
 Adds magic to an SV. First upgrades C<sv> to type C<SVt_PVMG> if necessary,
 then adds a new magic item of type C<how> to the head of the magic list.
 
-C<name> is assumed to contain an C<SV*> if C<(name && namelen == HEf_SVKEY)>
-
 	void	sv_magic(SV* sv, SV* obj, int how, const char* name, I32 namlen)
 
 =for hackers
 Found in file sv.c
 
+=item sv_magicext
+
+Adds magic to an SV, upgrading it if necessary. Applies the
+supplied vtable and returns pointer to the magic added.
+
+Note that sv_magicext will allow things that sv_magic will not.
+In particular you can add magic to SvREADONLY SVs and and more than
+one instance of the same 'how'
+
+I C<namelen> is greater then zero then a savepvn() I<copy> of C<name> is stored,
+if C<namelen> is zero then C<name> is stored as-is and - as another special
+case - if C<(name && namelen == HEf_SVKEY)> then C<name> is assumed to contain
+an C<SV*> and has its REFCNT incremented
+
+(This is now used as a subroutine by sv_magic.)
+
+	MAGIC *	sv_magicext(SV* sv, SV* obj, int how, MGVTBL *vtbl, const char* name, I32 namlen	)
+
+=for hackers
+Found in file sv.c
+
 =item sv_mortalcopy
 
 Creates a new SV which is a copy of the original SV (using C<sv_setsv>).
@@ -3715,6 +3704,39 @@ instead.
 =for hackers
 Found in file sv.c
 
+=item sv_nolocking
+
+Dummy routine which "locks" an SV when there is no locking module present.
+Exists to avoid test for a NULL function pointer and because it could potentially warn under
+some level of strict-ness.
+
+	void	sv_nolocking(SV *)
+
+=for hackers
+Found in file util.c
+
+=item sv_nosharing
+
+Dummy routine which "shares" an SV when there is no sharing module present.
+Exists to avoid test for a NULL function pointer and because it could potentially warn under
+some level of strict-ness.
+
+	void	sv_nosharing(SV *)
+
+=for hackers
+Found in file util.c
+
+=item sv_nounlocking
+
+Dummy routine which "unlocks" an SV when there is no locking module present.
+Exists to avoid test for a NULL function pointer and because it could potentially warn under
+some level of strict-ness.
+
+	void	sv_nounlocking(SV *)
+
+=for hackers
+Found in file util.c
+
 =item sv_nv
 
 A private implementation of the C<SvNVx> macro for compilers which can't
@@ -4477,7 +4499,7 @@ length len, the displayable version being at most pvlim bytes long
 (if longer, the rest is truncated and "..." will be appended).
 
 The flags argument can have UNI_DISPLAY_ISPRINT set to display
-isprint()able characters as themselves, UNI_DISPLAY_BACKSLASH
+isPRINT()able characters as themselves, UNI_DISPLAY_BACKSLASH
 to display the \\[nrfta\\] as the backslashed versions (like '\n')
 (UNI_DISPLAY_BACKSLASH is preferred over UNI_DISPLAY_ISPRINT for \\).
 UNI_DISPLAY_QQ (and its alias UNI_DISPLAY_REGEX) have both
diff --git a/pod/perlintern.pod b/pod/perlintern.pod
index 544b87887f..c9cb5e7698 100644
--- a/pod/perlintern.pod
+++ b/pod/perlintern.pod
@@ -10,41 +10,10 @@ 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>!
 
-=over 8
-
-=item djSP
-
-Declare Just C<SP>. This is actually identical to C<dSP>, and declares
-a local copy of perl's stack pointer, available via the C<SP> macro.
-See C<SP>.  (Available for backward source code compatibility with the
-old (Perl 5.005) thread model.)
 
-		djSP;
-
-=for hackers
-Found in file pp.h
-
-=item 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.
-
-	bool	is_gv_magical(char *name, STRLEN len, U32 flags)
-
-=for hackers
-Found in file gv.c
-
-=item LVRET
-
-True if this op will be the return value of an lvalue subroutine
+=head1 Global Variables
 
-=for hackers
-Found in file pp.h
+=over 8
 
 =item PL_DBsingle
 
@@ -118,14 +87,34 @@ The input record separator - C<$/> in Perl space.
 =for hackers
 Found in file thrdvar.h
 
-=item report_uninit
 
-Print appropriate "Use of uninitialized variable" warning
+=back
 
-	void	report_uninit()
+=head1 GV Functions
+
+=over 8
+
+=item 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.
+
+	bool	is_gv_magical(char *name, STRLEN len, U32 flags)
 
 =for hackers
-Found in file sv.c
+Found in file gv.c
+
+
+=back
+
+=head1 IO Functions
+
+=over 8
 
 =item start_glob
 
@@ -139,6 +128,113 @@ Moving it away shrinks pp_hot.c; shrinking pp_hot.c helps speed perl up.
 =for hackers
 Found in file doio.c
 
+
+=back
+
+=head1 Pad Data Structures
+
+=over 8
+
+=item 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 op.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 the the the names AV.
+C<PL_comppad> is set the the frame AV for the frame CvDEPTH == 1.
+C<PL_curpad> is set the body of the frame AV (i.e. AvARRAY(PL_comppad)).
+
+Itterating over the names AV itterates 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.
+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.
+
+If SvFAKE is set on the name SV then slot in the frame AVs are
+a REFCNT'ed references to a lexical from "outside".
+
+If the 'name' is '&' the 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.)
+
+	AV *	CvPADLIST(CV *cv)
+
+=for hackers
+Found in file cv.h
+
+
+=back
+
+=head1 Stack Manipulation Macros
+
+=over 8
+
+=item djSP
+
+Declare Just C<SP>. This is actually identical to C<dSP>, and declares
+a local copy of perl's stack pointer, available via the C<SP> macro.
+See C<SP>.  (Available for backward source code compatibility with the
+old (Perl 5.005) thread model.)
+
+		djSP;
+
+=for hackers
+Found in file pp.h
+
+=item LVRET
+
+True if this op will be the return value of an lvalue subroutine
+
+=for hackers
+Found in file pp.h
+
+
+=back
+
+=head1 SV Manipulation Functions
+
+=over 8
+
+=item report_uninit
+
+Print appropriate "Use of uninitialized variable" warning
+
+	void	report_uninit()
+
+=for hackers
+Found in file sv.c
+
 =item sv_add_arena
 
 Given a chunk of memory, link it to the head of the list of arenas,
@@ -179,6 +275,7 @@ heads and bodies within the arenas must already have been freed.
 =for hackers
 Found in file sv.c
 
+
 =back
 
 =head1 AUTHORS