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sv.c
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sv.c
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/* sv.c
*
* Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
* 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 by Larry Wall
* and others
*
* You may distribute under the terms of either the GNU General Public
* License or the Artistic License, as specified in the README file.
*
*/
/*
* 'I wonder what the Entish is for "yes" and "no",' he thought.
* --Pippin
*
* [p.480 of _The Lord of the Rings_, III/iv: "Treebeard"]
*/
/*
*
*
* This file contains the code that creates, manipulates and destroys
* scalar values (SVs). The other types (AV, HV, GV, etc.) reuse the
* structure of an SV, so their creation and destruction is handled
* here; higher-level functions are in av.c, hv.c, and so on. Opcode
* level functions (eg. substr, split, join) for each of the types are
* in the pp*.c files.
*/
#include "EXTERN.h"
#define PERL_IN_SV_C
#include "perl.h"
#include "regcomp.h"
#ifdef __VMS
# include <rms.h>
#endif
#ifdef __Lynx__
/* Missing proto on LynxOS */
char *gconvert(double, int, int, char *);
#endif
#ifdef USE_QUADMATH
# define SNPRINTF_G(nv, buffer, size, ndig) \
quadmath_snprintf(buffer, size, "%.*Qg", (int)ndig, (NV)(nv))
#else
# define SNPRINTF_G(nv, buffer, size, ndig) \
PERL_UNUSED_RESULT(Gconvert((NV)(nv), (int)ndig, 0, buffer))
#endif
#ifndef SV_COW_THRESHOLD
# define SV_COW_THRESHOLD 0 /* COW iff len > K */
#endif
#ifndef SV_COWBUF_THRESHOLD
# define SV_COWBUF_THRESHOLD 1250 /* COW iff len > K */
#endif
#ifndef SV_COW_MAX_WASTE_THRESHOLD
# define SV_COW_MAX_WASTE_THRESHOLD 80 /* COW iff (len - cur) < K */
#endif
#ifndef SV_COWBUF_WASTE_THRESHOLD
# define SV_COWBUF_WASTE_THRESHOLD 80 /* COW iff (len - cur) < K */
#endif
#ifndef SV_COW_MAX_WASTE_FACTOR_THRESHOLD
# define SV_COW_MAX_WASTE_FACTOR_THRESHOLD 2 /* COW iff len < (cur * K) */
#endif
#ifndef SV_COWBUF_WASTE_FACTOR_THRESHOLD
# define SV_COWBUF_WASTE_FACTOR_THRESHOLD 2 /* COW iff len < (cur * K) */
#endif
/* Work around compiler warnings about unsigned >= THRESHOLD when thres-
hold is 0. */
#if SV_COW_THRESHOLD
# define GE_COW_THRESHOLD(cur) ((cur) >= SV_COW_THRESHOLD)
#else
# define GE_COW_THRESHOLD(cur) 1
#endif
#if SV_COWBUF_THRESHOLD
# define GE_COWBUF_THRESHOLD(cur) ((cur) >= SV_COWBUF_THRESHOLD)
#else
# define GE_COWBUF_THRESHOLD(cur) 1
#endif
#if SV_COW_MAX_WASTE_THRESHOLD
# define GE_COW_MAX_WASTE_THRESHOLD(cur,len) (((len)-(cur)) < SV_COW_MAX_WASTE_THRESHOLD)
#else
# define GE_COW_MAX_WASTE_THRESHOLD(cur,len) 1
#endif
#if SV_COWBUF_WASTE_THRESHOLD
# define GE_COWBUF_WASTE_THRESHOLD(cur,len) (((len)-(cur)) < SV_COWBUF_WASTE_THRESHOLD)
#else
# define GE_COWBUF_WASTE_THRESHOLD(cur,len) 1
#endif
#if SV_COW_MAX_WASTE_FACTOR_THRESHOLD
# define GE_COW_MAX_WASTE_FACTOR_THRESHOLD(cur,len) ((len) < SV_COW_MAX_WASTE_FACTOR_THRESHOLD * (cur))
#else
# define GE_COW_MAX_WASTE_FACTOR_THRESHOLD(cur,len) 1
#endif
#if SV_COWBUF_WASTE_FACTOR_THRESHOLD
# define GE_COWBUF_WASTE_FACTOR_THRESHOLD(cur,len) ((len) < SV_COWBUF_WASTE_FACTOR_THRESHOLD * (cur))
#else
# define GE_COWBUF_WASTE_FACTOR_THRESHOLD(cur,len) 1
#endif
#define CHECK_COW_THRESHOLD(cur,len) (\
GE_COW_THRESHOLD((cur)) && \
GE_COW_MAX_WASTE_THRESHOLD((cur),(len)) && \
GE_COW_MAX_WASTE_FACTOR_THRESHOLD((cur),(len)) \
)
#define CHECK_COWBUF_THRESHOLD(cur,len) (\
GE_COWBUF_THRESHOLD((cur)) && \
GE_COWBUF_WASTE_THRESHOLD((cur),(len)) && \
GE_COWBUF_WASTE_FACTOR_THRESHOLD((cur),(len)) \
)
#ifdef PERL_UTF8_CACHE_ASSERT
/* if adding more checks watch out for the following tests:
* t/op/index.t t/op/length.t t/op/pat.t t/op/substr.t
* lib/utf8.t lib/Unicode/Collate/t/index.t
* --jhi
*/
# define ASSERT_UTF8_CACHE(cache) \
STMT_START { if (cache) { assert((cache)[0] <= (cache)[1]); \
assert((cache)[2] <= (cache)[3]); \
assert((cache)[3] <= (cache)[1]);} \
} STMT_END
#else
# define ASSERT_UTF8_CACHE(cache) NOOP
#endif
static const char S_destroy[] = "DESTROY";
#define S_destroy_len (sizeof(S_destroy)-1)
/* ============================================================================
=for apidoc_section $SV
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 internal function visit() scans the SV arenas list, and calls a specified
function for each SV it finds which is still live, I<i.e.> 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.
=head2 Arena allocator API Summary
Private API to rest of sv.c
new_SV(), del_SV(),
new_XPVNV(), del_XPVGV(),
etc
Public API:
sv_report_used(), sv_clean_objs(), sv_clean_all(), sv_free_arenas()
=cut
* ========================================================================= */
/*
* "A time to plant, and a time to uproot what was planted..."
*/
#ifdef PERL_MEM_LOG
# define MEM_LOG_NEW_SV(sv, file, line, func) \
Perl_mem_log_new_sv(sv, file, line, func)
# define MEM_LOG_DEL_SV(sv, file, line, func) \
Perl_mem_log_del_sv(sv, file, line, func)
#else
# define MEM_LOG_NEW_SV(sv, file, line, func) NOOP
# define MEM_LOG_DEL_SV(sv, file, line, func) NOOP
#endif
#ifdef DEBUG_LEAKING_SCALARS
# define FREE_SV_DEBUG_FILE(sv) STMT_START { \
if ((sv)->sv_debug_file) PerlMemShared_free((sv)->sv_debug_file); \
} STMT_END
# define DEBUG_SV_SERIAL(sv) \
DEBUG_m(PerlIO_printf(Perl_debug_log, "0x%" UVxf ": (%05ld) del_SV\n", \
PTR2UV(sv), (long)(sv)->sv_debug_serial))
#else
# define FREE_SV_DEBUG_FILE(sv)
# define DEBUG_SV_SERIAL(sv) NOOP
#endif
#ifdef PERL_POISON
# define SvARENA_CHAIN(sv) ((sv)->sv_u.svu_rv)
# define SvARENA_CHAIN_SET(sv,val) (sv)->sv_u.svu_rv = MUTABLE_SV((val))
/* Whilst I'd love to do this, it seems that things like to check on
unreferenced scalars
# define POISON_SV_HEAD(sv) PoisonNew(sv, 1, struct STRUCT_SV)
*/
# define POISON_SV_HEAD(sv) PoisonNew(&SvANY(sv), 1, void *), \
PoisonNew(&SvREFCNT(sv), 1, U32)
#else
# define SvARENA_CHAIN(sv) SvANY(sv)
# define SvARENA_CHAIN_SET(sv,val) SvANY(sv) = (void *)(val)
# define POISON_SV_HEAD(sv)
#endif
/* Mark an SV head as unused, and add to free list.
*
* If SVf_BREAK is set, skip adding it to the free list, as this SV had
* its refcount artificially decremented during global destruction, so
* there may be dangling pointers to it. The last thing we want in that
* case is for it to be reused. */
#define plant_SV(p) \
STMT_START { \
const U32 old_flags = SvFLAGS(p); \
MEM_LOG_DEL_SV(p, __FILE__, __LINE__, FUNCTION__); \
DEBUG_SV_SERIAL(p); \
FREE_SV_DEBUG_FILE(p); \
POISON_SV_HEAD(p); \
SvFLAGS(p) = SVTYPEMASK; \
if (!(old_flags & SVf_BREAK)) { \
SvARENA_CHAIN_SET(p, PL_sv_root); \
PL_sv_root = (p); \
} \
--PL_sv_count; \
} STMT_END
#define uproot_SV(p) \
STMT_START { \
(p) = PL_sv_root; \
PL_sv_root = MUTABLE_SV(SvARENA_CHAIN(p)); \
++PL_sv_count; \
} STMT_END
/* make some more SVs by adding another arena */
STATIC SV*
S_more_sv(pTHX)
{
SV* sv;
char *chunk; /* must use New here to match call to */
Newx(chunk,PERL_ARENA_SIZE,char); /* Safefree() in sv_free_arenas() */
sv_add_arena(chunk, PERL_ARENA_SIZE, 0);
uproot_SV(sv);
return sv;
}
/* new_SV(): return a new, empty SV head */
#ifdef DEBUG_LEAKING_SCALARS
/* provide a real function for a debugger to play with */
STATIC SV*
S_new_SV(pTHX_ const char *file, int line, const char *func)
{
SV* sv;
if (PL_sv_root)
uproot_SV(sv);
else
sv = S_more_sv(aTHX);
SvANY(sv) = 0;
SvREFCNT(sv) = 1;
SvFLAGS(sv) = 0;
sv->sv_debug_optype = PL_op ? PL_op->op_type : 0;
sv->sv_debug_line = (U16) (PL_parser && PL_parser->copline != NOLINE
? PL_parser->copline
: PL_curcop
? CopLINE(PL_curcop)
: 0
);
sv->sv_debug_inpad = 0;
sv->sv_debug_parent = NULL;
sv->sv_debug_file = PL_curcop ? savesharedpv(CopFILE(PL_curcop)): NULL;
sv->sv_debug_serial = PL_sv_serial++;
MEM_LOG_NEW_SV(sv, file, line, func);
DEBUG_m(PerlIO_printf(Perl_debug_log, "0x%" UVxf ": (%05ld) new_SV (from %s:%d [%s])\n",
PTR2UV(sv), (long)sv->sv_debug_serial, file, line, func));
return sv;
}
# define new_SV(p) (p)=S_new_SV(aTHX_ __FILE__, __LINE__, FUNCTION__)
#else
# define new_SV(p) \
STMT_START { \
if (PL_sv_root) \
uproot_SV(p); \
else \
(p) = S_more_sv(aTHX); \
SvANY(p) = 0; \
SvREFCNT(p) = 1; \
SvFLAGS(p) = 0; \
MEM_LOG_NEW_SV(p, __FILE__, __LINE__, FUNCTION__); \
} STMT_END
#endif
/* del_SV(): return an empty SV head to the free list */
#ifdef DEBUGGING
#define del_SV(p) \
STMT_START { \
if (DEBUG_D_TEST) \
del_sv(p); \
else \
plant_SV(p); \
} STMT_END
STATIC void
S_del_sv(pTHX_ SV *p)
{
PERL_ARGS_ASSERT_DEL_SV;
if (DEBUG_D_TEST) {
SV* sva;
bool ok = 0;
for (sva = PL_sv_arenaroot; sva; sva = MUTABLE_SV(SvANY(sva))) {
const SV * const sv = sva + 1;
const SV * const svend = &sva[SvREFCNT(sva)];
if (p >= sv && p < svend) {
ok = 1;
break;
}
}
if (!ok) {
Perl_ck_warner_d(aTHX_ packWARN(WARN_INTERNAL),
"Attempt to free non-arena SV: 0x%" UVxf
pTHX__FORMAT, PTR2UV(p) pTHX__VALUE);
return;
}
}
plant_SV(p);
}
#else /* ! DEBUGGING */
#define del_SV(p) plant_SV(p)
#endif /* DEBUGGING */
/*
=for apidoc_section $SV
=for apidoc 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.
=cut
*/
static void
S_sv_add_arena(pTHX_ char *const ptr, const U32 size, const U32 flags)
{
SV *const sva = MUTABLE_SV(ptr);
SV* sv;
SV* svend;
PERL_ARGS_ASSERT_SV_ADD_ARENA;
/* The first SV in an arena isn't an SV. */
SvANY(sva) = (void *) PL_sv_arenaroot; /* ptr to next arena */
SvREFCNT(sva) = size / sizeof(SV); /* number of SV slots */
SvFLAGS(sva) = flags; /* FAKE if not to be freed */
PL_sv_arenaroot = sva;
PL_sv_root = sva + 1;
svend = &sva[SvREFCNT(sva) - 1];
sv = sva + 1;
while (sv < svend) {
SvARENA_CHAIN_SET(sv, (sv + 1));
#ifdef DEBUGGING
SvREFCNT(sv) = 0;
#endif
/* Must always set typemask because it's always checked in on cleanup
when the arenas are walked looking for objects. */
SvFLAGS(sv) = SVTYPEMASK;
sv++;
}
SvARENA_CHAIN_SET(sv, 0);
#ifdef DEBUGGING
SvREFCNT(sv) = 0;
#endif
SvFLAGS(sv) = SVTYPEMASK;
}
/* visit(): call the named function for each non-free SV in the arenas
* whose flags field matches the flags/mask args. */
STATIC I32
S_visit(pTHX_ SVFUNC_t f, const U32 flags, const U32 mask)
{
SV* sva;
I32 visited = 0;
PERL_ARGS_ASSERT_VISIT;
for (sva = PL_sv_arenaroot; sva; sva = MUTABLE_SV(SvANY(sva))) {
const SV * const svend = &sva[SvREFCNT(sva)];
SV* sv;
for (sv = sva + 1; sv < svend; ++sv) {
if (SvTYPE(sv) != (svtype)SVTYPEMASK
&& (sv->sv_flags & mask) == flags
&& SvREFCNT(sv))
{
(*f)(aTHX_ sv);
++visited;
}
}
}
return visited;
}
#ifdef DEBUGGING
/* called by sv_report_used() for each live SV */
static void
do_report_used(pTHX_ SV *const sv)
{
if (SvTYPE(sv) != (svtype)SVTYPEMASK) {
PerlIO_printf(Perl_debug_log, "****\n");
sv_dump(sv);
}
}
#endif
/*
=for apidoc sv_report_used
Dump the contents of all SVs not yet freed (debugging aid).
=cut
*/
void
Perl_sv_report_used(pTHX)
{
#ifdef DEBUGGING
visit(do_report_used, 0, 0);
#else
PERL_UNUSED_CONTEXT;
#endif
}
/* called by sv_clean_objs() for each live SV */
static void
do_clean_objs(pTHX_ SV *const ref)
{
assert (SvROK(ref));
{
SV * const target = SvRV(ref);
if (SvOBJECT(target)) {
DEBUG_D((PerlIO_printf(Perl_debug_log, "Cleaning object ref:\n "), sv_dump(ref)));
if (SvWEAKREF(ref)) {
sv_del_backref(target, ref);
SvWEAKREF_off(ref);
SvRV_set(ref, NULL);
} else {
SvROK_off(ref);
SvRV_set(ref, NULL);
SvREFCNT_dec_NN(target);
}
}
}
}
/* clear any slots in a GV which hold objects - except IO;
* called by sv_clean_objs() for each live GV */
static void
do_clean_named_objs(pTHX_ SV *const sv)
{
SV *obj;
assert(SvTYPE(sv) == SVt_PVGV);
assert(isGV_with_GP(sv));
if (!GvGP(sv))
return;
/* freeing GP entries may indirectly free the current GV;
* hold onto it while we mess with the GP slots */
SvREFCNT_inc(sv);
if ( ((obj = GvSV(sv) )) && SvOBJECT(obj)) {
DEBUG_D((PerlIO_printf(Perl_debug_log,
"Cleaning named glob SV object:\n "), sv_dump(obj)));
GvSV(sv) = NULL;
SvREFCNT_dec_NN(obj);
}
if ( ((obj = MUTABLE_SV(GvAV(sv)) )) && SvOBJECT(obj)) {
DEBUG_D((PerlIO_printf(Perl_debug_log,
"Cleaning named glob AV object:\n "), sv_dump(obj)));
GvAV(sv) = NULL;
SvREFCNT_dec_NN(obj);
}
if ( ((obj = MUTABLE_SV(GvHV(sv)) )) && SvOBJECT(obj)) {
DEBUG_D((PerlIO_printf(Perl_debug_log,
"Cleaning named glob HV object:\n "), sv_dump(obj)));
GvHV(sv) = NULL;
SvREFCNT_dec_NN(obj);
}
if ( ((obj = MUTABLE_SV(GvCV(sv)) )) && SvOBJECT(obj)) {
DEBUG_D((PerlIO_printf(Perl_debug_log,
"Cleaning named glob CV object:\n "), sv_dump(obj)));
GvCV_set(sv, NULL);
SvREFCNT_dec_NN(obj);
}
SvREFCNT_dec_NN(sv); /* undo the inc above */
}
/* clear any IO slots in a GV which hold objects (except stderr, defout);
* called by sv_clean_objs() for each live GV */
static void
do_clean_named_io_objs(pTHX_ SV *const sv)
{
SV *obj;
assert(SvTYPE(sv) == SVt_PVGV);
assert(isGV_with_GP(sv));
if (!GvGP(sv) || sv == (SV*)PL_stderrgv || sv == (SV*)PL_defoutgv)
return;
SvREFCNT_inc(sv);
if ( ((obj = MUTABLE_SV(GvIO(sv)) )) && SvOBJECT(obj)) {
DEBUG_D((PerlIO_printf(Perl_debug_log,
"Cleaning named glob IO object:\n "), sv_dump(obj)));
GvIOp(sv) = NULL;
SvREFCNT_dec_NN(obj);
}
SvREFCNT_dec_NN(sv); /* undo the inc above */
}
/* Void wrapper to pass to visit() */
static void
do_curse(pTHX_ SV * const sv) {
if ((PL_stderrgv && GvGP(PL_stderrgv) && (SV*)GvIO(PL_stderrgv) == sv)
|| (PL_defoutgv && GvGP(PL_defoutgv) && (SV*)GvIO(PL_defoutgv) == sv))
return;
(void)curse(sv, 0);
}
/*
=for apidoc sv_clean_objs
Attempt to destroy all objects not yet freed.
=cut
*/
void
Perl_sv_clean_objs(pTHX)
{
GV *olddef, *olderr;
PL_in_clean_objs = TRUE;
visit(do_clean_objs, SVf_ROK, SVf_ROK);
/* Some barnacles may yet remain, clinging to typeglobs.
* Run the non-IO destructors first: they may want to output
* error messages, close files etc */
visit(do_clean_named_objs, SVt_PVGV|SVpgv_GP, SVTYPEMASK|SVp_POK|SVpgv_GP);
visit(do_clean_named_io_objs, SVt_PVGV|SVpgv_GP, SVTYPEMASK|SVp_POK|SVpgv_GP);
/* And if there are some very tenacious barnacles clinging to arrays,
closures, or what have you.... */
visit(do_curse, SVs_OBJECT, SVs_OBJECT);
olddef = PL_defoutgv;
PL_defoutgv = NULL; /* disable skip of PL_defoutgv */
if (olddef && isGV_with_GP(olddef))
do_clean_named_io_objs(aTHX_ MUTABLE_SV(olddef));
olderr = PL_stderrgv;
PL_stderrgv = NULL; /* disable skip of PL_stderrgv */
if (olderr && isGV_with_GP(olderr))
do_clean_named_io_objs(aTHX_ MUTABLE_SV(olderr));
SvREFCNT_dec(olddef);
PL_in_clean_objs = FALSE;
}
/* called by sv_clean_all() for each live SV */
static void
do_clean_all(pTHX_ SV *const sv)
{
if (sv == (const SV *) PL_fdpid || sv == (const SV *)PL_strtab) {
/* don't clean pid table and strtab */
return;
}
DEBUG_D((PerlIO_printf(Perl_debug_log, "Cleaning loops: SV at 0x%" UVxf "\n", PTR2UV(sv)) ));
SvFLAGS(sv) |= SVf_BREAK;
SvREFCNT_dec_NN(sv);
}
/*
=for apidoc 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.
=cut
*/
I32
Perl_sv_clean_all(pTHX)
{
I32 cleaned;
PL_in_clean_all = TRUE;
cleaned = visit(do_clean_all, 0,0);
return cleaned;
}
/*
ARENASETS: a meta-arena implementation which separates arena-info
into struct arena_set, which contains an array of struct
arena_descs, each holding info for a single arena. By separating
the meta-info from the arena, we recover the 1st slot, formerly
borrowed for list management. The arena_set is about the size of an
arena, avoiding the needless malloc overhead of a naive linked-list.
The cost is 1 arena-set malloc per ~320 arena-mallocs, + the unused
memory in the last arena-set (1/2 on average). In trade, we get
back the 1st slot in each arena (ie 1.7% of a CV-arena, less for
smaller types). The recovery of the wasted space allows use of
small arenas for large, rare body types, by changing array* fields
in body_details_by_type[] below.
*/
struct arena_desc {
char *arena; /* the raw storage, allocated aligned */
size_t size; /* its size ~4k typ */
svtype utype; /* bodytype stored in arena */
};
struct arena_set;
/* Get the maximum number of elements in set[] such that struct arena_set
will fit within PERL_ARENA_SIZE, which is probably just under 4K, and
therefore likely to be 1 aligned memory page. */
#define ARENAS_PER_SET ((PERL_ARENA_SIZE - sizeof(struct arena_set*) \
- 2 * sizeof(int)) / sizeof (struct arena_desc))
struct arena_set {
struct arena_set* next;
unsigned int set_size; /* ie ARENAS_PER_SET */
unsigned int curr; /* index of next available arena-desc */
struct arena_desc set[ARENAS_PER_SET];
};
/*
=for apidoc 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.
=cut
*/
void
Perl_sv_free_arenas(pTHX)
{
SV* sva;
SV* svanext;
unsigned int i;
/* Free arenas here, but be careful about fake ones. (We assume
contiguity of the fake ones with the corresponding real ones.) */
for (sva = PL_sv_arenaroot; sva; sva = svanext) {
svanext = MUTABLE_SV(SvANY(sva));
while (svanext && SvFAKE(svanext))
svanext = MUTABLE_SV(SvANY(svanext));
if (!SvFAKE(sva))
Safefree(sva);
}
{
struct arena_set *aroot = (struct arena_set*) PL_body_arenas;
while (aroot) {
struct arena_set *current = aroot;
i = aroot->curr;
while (i--) {
assert(aroot->set[i].arena);
Safefree(aroot->set[i].arena);
}
aroot = aroot->next;
Safefree(current);
}
}
PL_body_arenas = 0;
i = PERL_ARENA_ROOTS_SIZE;
while (i--)
PL_body_roots[i] = 0;
PL_sv_arenaroot = 0;
PL_sv_root = 0;
}
/*
Here are mid-level routines that manage the allocation of bodies out
of the various arenas. There are 4 kinds of arenas:
1. SV-head arenas, which are discussed and handled above
2. regular body arenas
3. arenas for reduced-size bodies
4. Hash-Entry arenas
Arena types 2 & 3 are chained by body-type off an array of
arena-root pointers, which is indexed by svtype. Some of the
larger/less used body types are malloced singly, since a large
unused block of them is wasteful. Also, several svtypes dont have
bodies; the data fits into the sv-head itself. The arena-root
pointer thus has a few unused root-pointers (which may be hijacked
later for arena type 4)
3 differs from 2 as an optimization; some body types have several
unused fields in the front of the structure (which are kept in-place
for consistency). These bodies can be allocated in smaller chunks,
because the leading fields arent accessed. Pointers to such bodies
are decremented to point at the unused 'ghost' memory, knowing that
the pointers are used with offsets to the real memory.
Allocation of SV-bodies is similar to SV-heads, differing as follows;
the allocation mechanism is used for many body types, so is somewhat
more complicated, it uses arena-sets, and has no need for still-live
SV detection.
At the outermost level, (new|del)_X*V macros return bodies of the
appropriate type. These macros call either (new|del)_body_type or
(new|del)_body_allocated macro pairs, depending on specifics of the
type. Most body types use the former pair, the latter pair is used to
allocate body types with "ghost fields".
"ghost fields" are fields that are unused in certain types, and
consequently don't need to actually exist. They are declared because
they're part of a "base type", which allows use of functions as
methods. The simplest examples are AVs and HVs, 2 aggregate types
which don't use the fields which support SCALAR semantics.
For these types, the arenas are carved up into appropriately sized
chunks, we thus avoid wasted memory for those unaccessed members.
When bodies are allocated, we adjust the pointer back in memory by the
size of the part not allocated, so it's as if we allocated the full
structure. (But things will all go boom if you write to the part that
is "not there", because you'll be overwriting the last members of the
preceding structure in memory.)
We calculate the correction using the STRUCT_OFFSET macro on the first
member present. If the allocated structure is smaller (no initial NV
actually allocated) then the net effect is to subtract the size of the NV
from the pointer, to return a new pointer as if an initial NV were actually
allocated. (We were using structures named *_allocated for this, but
this turned out to be a subtle bug, because a structure without an NV
could have a lower alignment constraint, but the compiler is allowed to
optimised accesses based on the alignment constraint of the actual pointer
to the full structure, for example, using a single 64 bit load instruction
because it "knows" that two adjacent 32 bit members will be 8-byte aligned.)
This is the same trick as was used for NV and IV bodies. Ironically it
doesn't need to be used for NV bodies any more, because NV is now at
the start of the structure. IV bodies, and also in some builds NV bodies,
don't need it either, because they are no longer allocated.
In turn, the new_body_* allocators call S_new_body(), which invokes
new_body_inline macro, which takes a lock, and takes a body off the
linked list at PL_body_roots[sv_type], calling Perl_more_bodies() if
necessary to refresh an empty list. Then the lock is released, and
the body is returned.
Perl_more_bodies allocates a new arena, and carves it up into an array of N
bodies, which it strings into a linked list. It looks up arena-size
and body-size from the body_details table described below, thus
supporting the multiple body-types.
If PURIFY is defined, or PERL_ARENA_SIZE=0, arenas are not used, and
the (new|del)_X*V macros are mapped directly to malloc/free.
For each sv-type, struct body_details bodies_by_type[] carries
parameters which control these aspects of SV handling:
Arena_size determines whether arenas are used for this body type, and if
so, how big they are. PURIFY or PERL_ARENA_SIZE=0 set this field to
zero, forcing individual mallocs and frees.
Body_size determines how big a body is, and therefore how many fit into
each arena. Offset carries the body-pointer adjustment needed for
"ghost fields", and is used in *_allocated macros.
But its main purpose is to parameterize info needed in
Perl_sv_upgrade(). The info here dramatically simplifies the function
vs the implementation in 5.8.8, making it table-driven. All fields
are used for this, except for arena_size.
For the sv-types that have no bodies, arenas are not used, so those
PL_body_roots[sv_type] are unused, and can be overloaded. In
something of a special case, SVt_NULL is borrowed for HE arenas;
PL_body_roots[HE_SVSLOT=SVt_NULL] is filled by S_more_he, but the
bodies_by_type[SVt_NULL] slot is not used, as the table is not
available in hv.c.
*/
struct body_details {
U8 body_size; /* Size to allocate */
U8 copy; /* Size of structure to copy (may be shorter) */
U8 offset; /* Size of unalloced ghost fields to first alloced field*/
PERL_BITFIELD8 type : 4; /* We have space for a sanity check. */
PERL_BITFIELD8 cant_upgrade : 1;/* Cannot upgrade this type */
PERL_BITFIELD8 zero_nv : 1; /* zero the NV when upgrading from this */
PERL_BITFIELD8 arena : 1; /* Allocated from an arena */
U32 arena_size; /* Size of arena to allocate */
};
#define ALIGNED_TYPE_NAME(name) name##_aligned
#define ALIGNED_TYPE(name) \
typedef union { \
name align_me; \
NV nv; \
IV iv; \
} ALIGNED_TYPE_NAME(name)
ALIGNED_TYPE(regexp);
ALIGNED_TYPE(XPVGV);
ALIGNED_TYPE(XPVLV);
ALIGNED_TYPE(XPVAV);
ALIGNED_TYPE(XPVHV);
ALIGNED_TYPE(XPVCV);
ALIGNED_TYPE(XPVFM);
ALIGNED_TYPE(XPVIO);
#define HADNV FALSE
#define NONV TRUE
#ifdef PURIFY
/* With -DPURFIY we allocate everything directly, and don't use arenas.
This seems a rather elegant way to simplify some of the code below. */
#define HASARENA FALSE
#else
#define HASARENA TRUE
#endif
#define NOARENA FALSE
/* Size the arenas to exactly fit a given number of bodies. A count
of 0 fits the max number bodies into a PERL_ARENA_SIZE.block,
simplifying the default. If count > 0, the arena is sized to fit
only that many bodies, allowing arenas to be used for large, rare
bodies (XPVFM, XPVIO) without undue waste. The arena size is
limited by PERL_ARENA_SIZE, so we can safely oversize the
declarations.
*/
#define FIT_ARENA0(body_size) \
((size_t)(PERL_ARENA_SIZE / body_size) * body_size)
#define FIT_ARENAn(count,body_size) \
( count * body_size <= PERL_ARENA_SIZE) \
? count * body_size \
: FIT_ARENA0 (body_size)
#define FIT_ARENA(count,body_size) \
(U32)(count \
? FIT_ARENAn (count, body_size) \
: FIT_ARENA0 (body_size))
/* Calculate the length to copy. Specifically work out the length less any
final padding the compiler needed to add. See the comment in sv_upgrade
for why copying the padding proved to be a bug. */
#define copy_length(type, last_member) \
STRUCT_OFFSET(type, last_member) \
+ sizeof (((type*)SvANY((const SV *)0))->last_member)
static const struct body_details bodies_by_type[] = {
/* HEs use this offset for their arena. */
{ 0, 0, 0, SVt_NULL, FALSE, NONV, NOARENA, 0 },
/* IVs are in the head, so the allocation size is 0. */
{ 0,
sizeof(IV), /* This is used to copy out the IV body. */
STRUCT_OFFSET(XPVIV, xiv_iv), SVt_IV, FALSE, NONV,
NOARENA /* IVS don't need an arena */, 0
},
#if NVSIZE <= IVSIZE
{ 0, sizeof(NV),
STRUCT_OFFSET(XPVNV, xnv_u),
SVt_NV, FALSE, HADNV, NOARENA, 0 },
#else
{ sizeof(NV), sizeof(NV),
STRUCT_OFFSET(XPVNV, xnv_u),
SVt_NV, FALSE, HADNV, HASARENA, FIT_ARENA(0, sizeof(NV)) },
#endif
{ sizeof(XPV) - STRUCT_OFFSET(XPV, xpv_cur),
copy_length(XPV, xpv_len) - STRUCT_OFFSET(XPV, xpv_cur),
+ STRUCT_OFFSET(XPV, xpv_cur),
SVt_PV, FALSE, NONV, HASARENA,
FIT_ARENA(0, sizeof(XPV) - STRUCT_OFFSET(XPV, xpv_cur)) },
{ sizeof(XINVLIST) - STRUCT_OFFSET(XPV, xpv_cur),
copy_length(XINVLIST, is_offset) - STRUCT_OFFSET(XPV, xpv_cur),
+ STRUCT_OFFSET(XPV, xpv_cur),
SVt_INVLIST, TRUE, NONV, HASARENA,
FIT_ARENA(0, sizeof(XINVLIST) - STRUCT_OFFSET(XPV, xpv_cur)) },
{ sizeof(XPVIV) - STRUCT_OFFSET(XPV, xpv_cur),
copy_length(XPVIV, xiv_u) - STRUCT_OFFSET(XPV, xpv_cur),
+ STRUCT_OFFSET(XPV, xpv_cur),
SVt_PVIV, FALSE, NONV, HASARENA,
FIT_ARENA(0, sizeof(XPVIV) - STRUCT_OFFSET(XPV, xpv_cur)) },
{ sizeof(XPVNV) - STRUCT_OFFSET(XPV, xpv_cur),
copy_length(XPVNV, xnv_u) - STRUCT_OFFSET(XPV, xpv_cur),
+ STRUCT_OFFSET(XPV, xpv_cur),
SVt_PVNV, FALSE, HADNV, HASARENA,
FIT_ARENA(0, sizeof(XPVNV) - STRUCT_OFFSET(XPV, xpv_cur)) },
{ sizeof(XPVMG), copy_length(XPVMG, xnv_u), 0, SVt_PVMG, FALSE, HADNV,
HASARENA, FIT_ARENA(0, sizeof(XPVMG)) },
{ sizeof(ALIGNED_TYPE_NAME(regexp)),
sizeof(regexp),
0,
SVt_REGEXP, TRUE, NONV, HASARENA,
FIT_ARENA(0, sizeof(ALIGNED_TYPE_NAME(regexp)))
},
{ sizeof(ALIGNED_TYPE_NAME(XPVGV)), sizeof(XPVGV), 0, SVt_PVGV, TRUE, HADNV,
HASARENA, FIT_ARENA(0, sizeof(ALIGNED_TYPE_NAME(XPVGV))) },
{ sizeof(ALIGNED_TYPE_NAME(XPVLV)), sizeof(XPVLV), 0, SVt_PVLV, TRUE, HADNV,