/*
** $Id: lgc.c,v 2.140 2013/03/16 21:10:18 roberto Exp $
** Garbage Collector
** See Copyright Notice in lua.h
*/
#include <string.h>
#define lgc_c
#define LUA_CORE
#include "lua.h"
#include "ldebug.h"
#include "ldo.h"
#include "lfunc.h"
#include "lgc.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "lstring.h"
#include "ltable.h"
#include "ltm.h"
/*
** cost of sweeping one element (the size of a small object divided
** by some adjust for the sweep speed)
*/
#define GCSWEEPCOST ((sizeof(TString) + 4) / 4)
/* maximum number of elements to sweep in each single step */
#define GCSWEEPMAX (cast_int((GCSTEPSIZE / GCSWEEPCOST) / 4))
/* maximum number of finalizers to call in each GC step */
#define GCFINALIZENUM 4
/*
** macro to adjust 'stepmul': 'stepmul' is actually used like
** 'stepmul / STEPMULADJ' (value chosen by tests)
*/
#define STEPMULADJ 200
/*
** macro to adjust 'pause': 'pause' is actually used like
** 'pause / PAUSEADJ' (value chosen by tests)
*/
#define PAUSEADJ 100
/*
** 'makewhite' erases all color bits plus the old bit and then
** sets only the current white bit
*/
#define maskcolors (~(bit2mask(BLACKBIT, OLDBIT) | WHITEBITS))
#define makewhite(g,x) \
(gch(x)->marked = cast_byte((gch(x)->marked & maskcolors) | luaC_white(g)))
#define white2gray(x) resetbits(gch(x)->marked, WHITEBITS)
#define black2gray(x) resetbit(gch(x)->marked, BLACKBIT)
#define isfinalized(x) testbit(gch(x)->marked, FINALIZEDBIT)
#define checkdeadkey(n) lua_assert(!ttisdeadkey(gkey(n)) || ttisnil(gval(n)))
#define checkconsistency(obj) \
lua_longassert(!iscollectable(obj) || righttt(obj))
#define markvalue(g,o) { checkconsistency(o); \
if (valiswhite(o)) reallymarkobject(g,gcvalue(o)); }
#define markobject(g,t) { if ((t) && iswhite(obj2gco(t))) \
reallymarkobject(g, obj2gco(t)); }
static void reallymarkobject(global_State *g, GCObject *o);
/*
** {======================================================
** Generic functions
** =======================================================
*/
/*
** one after last element in a hash array
*/
#define gnodelast(h) gnode(h, cast(size_t, sizenode(h)))
/*
** link table 'h' into list pointed by 'p'
*/
#define linktable(h,p) ((h)->gclist = *(p), *(p) = obj2gco(h))
/*
** if key is not marked, mark its entry as dead (therefore removing it
** from the table)
*/
static void removeentry(Node *n) {
lua_assert(ttisnil(gval(n)));
if (valiswhite(gkey(n)))
setdeadvalue(gkey(n)); /* unused and unmarked key; remove it */
}
/*
** tells whether a key or value can be cleared from a weak
** table. Non-collectable objects are never removed from weak
** tables. Strings behave as `values', so are never removed too. for
** other objects: if really collected, cannot keep them; for objects
** being finalized, keep them in keys, but not in values
*/
static int iscleared(global_State *g, const TValue *o) {
if (!iscollectable(o)) return 0;
else if (ttisstring(o)) {
markobject(g, rawtsvalue(o)); /* strings are `values', so are never weak */
return 0;
} else return iswhite(gcvalue(o));
}
/*
** barrier that moves collector forward, that is, mark the white object
** being pointed by a black object.
*/
void luaC_barrier_(lua_State *L, GCObject *o, GCObject *v) {
global_State *g = G(L);
lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
lua_assert(g->gcstate != GCSpause);
lua_assert(gch(o)->tt != LUA_TTABLE);
if (keepinvariantout(g)) /* must keep invariant? */
reallymarkobject(g, v); /* restore invariant */
else { /* sweep phase */
lua_assert(issweepphase(g));
makewhite(g, o); /* mark main obj. as white to avoid other barriers */
}
}
/*
** barrier that moves collector backward, that is, mark the black object
** pointing to a white object as gray again. (Current implementation
** only works for tables; access to 'gclist' is not uniform across
** different types.)
*/
void luaC_barrierback_(lua_State *L, GCObject *o) {
global_State *g = G(L);
lua_assert(isblack(o) && !isdead(g, o) && gch(o)->tt == LUA_TTABLE);
black2gray(o); /* make object gray (again) */
gco2t(o)->gclist = g->grayagain;
g->grayagain = o;
}
/*
** barrier for prototypes. When creating first closure (cache is
** NULL), use a forward barrier; this may be the only closure of the
** prototype (if it is a "regular" function, with a single instance)
** and the prototype may be big, so it is better to avoid traversing
** it again. Otherwise, use a backward barrier, to avoid marking all
** possible instances.
*/
LUAI_FUNC void luaC_barrierproto_(lua_State *L, Proto *p, Closure *c) {
global_State *g = G(L);
lua_assert(isblack(obj2gco(p)));
if (p->cache == NULL) { /* first time? */
luaC_objbarrier(L, p, c);
} else { /* use a backward barrier */
black2gray(obj2gco(p)); /* make prototype gray (again) */
p->gclist = g->grayagain;
g->grayagain = obj2gco(p);
}
}
/*
** check color (and invariants) for an upvalue that was closed,
** i.e., moved into the 'allgc' list
*/
void luaC_checkupvalcolor(global_State *g, UpVal *uv) {
GCObject *o = obj2gco(uv);
lua_assert(!isblack(o)); /* open upvalues are never black */
if (isgray(o)) {
if (keepinvariant(g)) {
resetoldbit(o); /* see MOVE OLD rule */
gray2black(o); /* it is being visited now */
markvalue(g, uv->v);
} else {
lua_assert(issweepphase(g));
makewhite(g, o);
}
}
}
/*
** create a new collectable object (with given type and size) and link
** it to '*list'. 'offset' tells how many bytes to allocate before the
** object itself (used only by states).
*/
GCObject *luaC_newobj(lua_State *L, int tt, size_t sz, GCObject **list,
int offset) {
global_State *g = G(L);
char *raw = cast(char *, luaM_newobject(L, novariant(tt), sz));
GCObject *o = obj2gco(raw + offset);
if (list == NULL)
list = &g->allgc; /* standard list for collectable objects */
gch(o)->marked = luaC_white(g);
gch(o)->tt = tt;
gch(o)->next = *list;
*list = o;
return o;
}
/* }====================================================== */
/*
** {======================================================
** Mark functions
** =======================================================
*/
/*
** mark an object. Userdata, strings, and closed upvalues are visited
** and turned black here. Other objects are marked gray and added
** to appropriate list to be visited (and turned black) later. (Open
** upvalues are already linked in 'headuv' list.)
*/
static void reallymarkobject(global_State *g, GCObject *o) {
lu_mem size;
white2gray(o);
switch (gch(o)->tt) {
case LUA_TSHRSTR:
case LUA_TLNGSTR: {
size = sizestring(gco2ts(o));
break; /* nothing else to mark; make it black */
}
case LUA_TUSERDATA: {
Table *mt = gco2u(o)->metatable;
markobject(g, mt);
markobject(g, gco2u(o)->env);
size = sizeudata(gco2u(o));
break;
}
case LUA_TUPVAL: {
UpVal *uv = gco2uv(o);
markvalue(g, uv->v);
if (uv->v != &uv->u.value) /* open? */
return; /* open upvalues remain gray */
size = sizeof(UpVal);
break;
}
case LUA_TLCL: {
gco2lcl(o)->gclist = g->gray;
g->gray = o;
return;
}
case LUA_TCCL: {
gco2ccl(o)->gclist = g->gray;
g->gray = o;
return;
}
case LUA_TTABLE: {
linktable(gco2t(o), &g->gray);
return;
}
case LUA_TTHREAD: {
gco2th(o)->gclist = g->gray;
g->gray = o;
return;
}
case LUA_TPROTO: {
gco2p(o)->gclist = g->gray;
g->gray = o;
return;
}
default:
lua_assert(0);
return;
}
gray2black(o);
g->GCmemtrav += size;
}
/*
** mark metamethods for basic types
*/
static void markmt(global_State *g) {
int i;
for (i = 0; i < LUA_NUMTAGS; i++)
markobject(g, g->mt[i]);
}
/*
** mark all objects in list of being-finalized
*/
static void markbeingfnz(global_State *g) {
GCObject *o;
for (o = g->tobefnz; o != NULL; o = gch(o)->next) {
makewhite(g, o);
reallymarkobject(g, o);
}
}
/*
** mark all values stored in marked open upvalues. (See comment in
** 'lstate.h'.)
*/
static void remarkupvals(global_State *g) {
UpVal *uv;
for (uv = g->uvhead.u.l.next; uv != &g->uvhead; uv = uv->u.l.next) {
if (isgray(obj2gco(uv)))
markvalue(g, uv->v);
}
}
/*
** mark root set and reset all gray lists, to start a new
** incremental (or full) collection
*/
static void restartcollection(global_State *g) {
g->gray = g->grayagain = NULL;
g->weak = g->allweak = g->ephemeron = NULL;
markobject(g, g->mainthread);
markvalue(g, &g->l_registry);
markmt(g);
markbeingfnz(g); /* mark any finalizing object left from previous cycle */
}
/* }====================================================== */
/*
** {======================================================
** Traverse functions
** =======================================================
*/
static void traverseweakvalue(global_State *g, Table *h) {
Node *n, *limit = gnodelast(h);
/* if there is array part, assume it may have white values (do not
traverse it just to check) */
int hasclears = (h->sizearray > 0);
for (n = gnode(h, 0); n < limit; n++) {
checkdeadkey(n);
if (ttisnil(gval(n))) /* entry is empty? */
removeentry(n); /* remove it */
else {
lua_assert(!ttisnil(gkey(n)));
markvalue(g, gkey(n)); /* mark key */
if (!hasclears && iscleared(g, gval(n))) /* is there a white value? */
hasclears = 1; /* table will have to be cleared */
}
}
if (hasclears)
linktable(h, &g->weak); /* has to be cleared later */
else /* no white values */
linktable(h, &g->grayagain); /* no need to clean */
}
static int traverseephemeron(global_State *g, Table *h) {
int marked = 0; /* true if an object is marked in this traversal */
int hasclears = 0; /* true if table has white keys */
int prop = 0; /* true if table has entry "white-key -> white-value" */
Node *n, *limit = gnodelast(h);
int i;
/* traverse array part (numeric keys are 'strong') */
for (i = 0; i < h->sizearray; i++) {
if (valiswhite(&h->array[i])) {
marked = 1;
reallymarkobject(g, gcvalue(&h->array[i]));
}
}
/* traverse hash part */
for (n = gnode(h, 0); n < limit; n++) {
checkdeadkey(n);
if (ttisnil(gval(n))) /* entry is empty? */
removeentry(n); /* remove it */
else if (iscleared(g, gkey(n))) { /* key is not marked (yet)? */
hasclears = 1; /* table must be cleared */
if (valiswhite(gval(n))) /* value not marked yet? */
prop = 1; /* must propagate again */
} else if (valiswhite(gval(n))) { /* value not marked yet? */
marked = 1;
reallymarkobject(g, gcvalue(gval(n))); /* mark it now */
}
}
if (prop)
linktable(h, &g->ephemeron); /* have to propagate again */
else if (hasclears) /* does table have white keys? */
linktable(h, &g->allweak); /* may have to clean white keys */
else /* no white keys */
linktable(h, &g->grayagain); /* no need to clean */
return marked;
}
static void traversestrongtable(global_State *g, Table *h) {
Node *n, *limit = gnodelast(h);
int i;
for (i = 0; i < h->sizearray; i++) /* traverse array part */
markvalue(g, &h->array[i]);
for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
checkdeadkey(n);
if (ttisnil(gval(n))) /* entry is empty? */
removeentry(n); /* remove it */
else {
lua_assert(!ttisnil(gkey(n)));
markvalue(g, gkey(n)); /* mark key */
markvalue(g, gval(n)); /* mark value */
}
}
}
static lu_mem traversetable(global_State *g, Table *h) {
const char *weakkey, *weakvalue;
const TValue *mode = gfasttm(g, h->metatable, TM_MODE);
markobject(g, h->metatable);
if (mode && ttisstring(mode) && /* is there a weak mode? */
((weakkey = strchr(svalue(mode), 'k')),
(weakvalue = strchr(svalue(mode), 'v')),
(weakkey || weakvalue))) { /* is really weak? */
black2gray(obj2gco(h)); /* keep table gray */
if (!weakkey) /* strong keys? */
traverseweakvalue(g, h);
else if (!weakvalue) /* strong values? */
traverseephemeron(g, h);
else /* all weak */
linktable(h, &g->allweak); /* nothing to traverse now */
} else /* not weak */
traversestrongtable(g, h);
return sizeof(Table) + sizeof(TValue) * h->sizearray +
sizeof(Node) * cast(size_t, sizenode(h));
}
static int traverseproto(global_State *g, Proto *f) {
int i;
if (f->cache && iswhite(obj2gco(f->cache)))
f->cache = NULL; /* allow cache to be collected */
markobject(g, f->source);
for (i = 0; i < f->sizek; i++) /* mark literals */
markvalue(g, &f->k[i]);
for (i = 0; i < f->sizeupvalues; i++) /* mark upvalue names */
markobject(g, f->upvalues[i].name);
for (i = 0; i < f->sizep; i++) /* mark nested protos */
markobject(g, f->p[i]);
for (i = 0; i < f->sizelocvars; i++) /* mark local-variable names */
markobject(g, f->locvars[i].varname);
return sizeof(Proto) + sizeof(Instruction) * f->sizecode +
sizeof(Proto *) * f->sizep +
sizeof(TValue) * f->sizek +
sizeof(int) * f->sizelineinfo +
sizeof(LocVar) * f->sizelocvars +
sizeof(Upvaldesc) * f->sizeupvalues;
}
static lu_mem traverseCclosure(global_State *g, CClosure *cl) {
int i;
for (i = 0; i < cl->nupvalues; i++) /* mark its upvalues */
markvalue(g, &cl->upvalue[i]);
return sizeCclosure(cl->nupvalues);
}
static lu_mem traverseLclosure(global_State *g, LClosure *cl) {
int i;
markobject(g, cl->p); /* mark its prototype */
for (i = 0; i < cl->nupvalues; i++) /* mark its upvalues */
markobject(g, cl->upvals[i]);
return sizeLclosure(cl->nupvalues);
}
static lu_mem traversestack(global_State *g, lua_State *th) {
StkId o = th->stack;
if (o == NULL)
return 1; /* stack not completely built yet */
for (; o < th->top; o++)
markvalue(g, o);
if (g->gcstate == GCSatomic) { /* final traversal? */
StkId lim = th->stack + th->stacksize; /* real end of stack */
for (; o < lim; o++) /* clear not-marked stack slice */
setnilvalue(o);
}
return sizeof(lua_State) + sizeof(TValue) * th->stacksize;
}
/*
** traverse one gray object, turning it to black (except for threads,
** which are always gray).
*/
static void propagatemark(global_State *g) {
lu_mem size;
GCObject *o = g->gray;
lua_assert(isgray(o));
gray2black(o);
switch (gch(o)->tt) {
case LUA_TTABLE: {
Table *h = gco2t(o);
g->gray = h->gclist; /* remove from 'gray' list */
size = traversetable(g, h);
break;
}
case LUA_TLCL: {
LClosure *cl = gco2lcl(o);
g->gray = cl->gclist; /* remove from 'gray' list */
size = traverseLclosure(g, cl);
break;
}
case LUA_TCCL: {
CClosure *cl = gco2ccl(o);
g->gray = cl->gclist; /* remove from 'gray' list */
size = traverseCclosure(g, cl);
break;
}
case LUA_TTHREAD: {
lua_State *th = gco2th(o);
g->gray = th->gclist; /* remove from 'gray' list */
th->gclist = g->grayagain;
g->grayagain = o; /* insert into 'grayagain' list */
black2gray(o);
size = traversestack(g, th);
break;
}
case LUA_TPROTO: {
Proto *p = gco2p(o);
g->gray = p->gclist; /* remove from 'gray' list */
size = traverseproto(g, p);
break;
}
default:
lua_assert(0);
return;
}
g->GCmemtrav += size;
}
static void propagateall(global_State *g) {
while (g->gray) propagatemark(g);
}
static void propagatelist(global_State *g, GCObject *l) {
lua_assert(g->gray == NULL); /* no grays left */
g->gray = l;
propagateall(g); /* traverse all elements from 'l' */
}
/*
** retraverse all gray lists. Because tables may be reinserted in other
** lists when traversed, traverse the original lists to avoid traversing
** twice the same table (which is not wrong, but inefficient)
*/
static void retraversegrays(global_State *g) {
GCObject *weak = g->weak; /* save original lists */
GCObject *grayagain = g->grayagain;
GCObject *ephemeron = g->ephemeron;
g->weak = g->grayagain = g->ephemeron = NULL;
propagateall(g); /* traverse main gray list */
propagatelist(g, grayagain);
propagatelist(g, weak);
propagatelist(g, ephemeron);
}
static void convergeephemerons(global_State *g) {
int changed;
do {
GCObject *w;
GCObject *next = g->ephemeron; /* get ephemeron list */
g->ephemeron = NULL; /* tables will return to this list when traversed */
changed = 0;
while ((w = next) != NULL) {
next = gco2t(w)->gclist;
if (traverseephemeron(g, gco2t(w))) { /* traverse marked some value? */
propagateall(g); /* propagate changes */
changed = 1; /* will have to revisit all ephemeron tables */
}
}
} while (changed);
}
/* }====================================================== */
/*
** {======================================================
** Sweep Functions
** =======================================================
*/
/*
** clear entries with unmarked keys from all weaktables in list 'l' up
** to element 'f'
*/
static void clearkeys(global_State *g, GCObject *l, GCObject *f) {
for (; l != f; l = gco2t(l)->gclist) {
Table *h = gco2t(l);
Node *n, *limit = gnodelast(h);
for (n = gnode(h, 0); n < limit; n++) {
if (!ttisnil(gval(n)) && (iscleared(g, gkey(n)))) {
setnilvalue(gval(n)); /* remove value ... */
removeentry(n); /* and remove entry from table */
}
}
}
}
/*
** clear entries with unmarked values from all weaktables in list 'l' up
** to element 'f'
*/
static void clearvalues(global_State *g, GCObject *l, GCObject *f) {
for (; l != f; l = gco2t(l)->gclist) {
Table *h = gco2t(l);
Node *n, *limit = gnodelast(h);
int i;
for (i = 0; i < h->sizearray; i++) {
TValue *o = &h->array[i];
if (iscleared(g, o)) /* value was collected? */
setnilvalue(o); /* remove value */
}
for (n = gnode(h, 0); n < limit; n++) {
if (!ttisnil(gval(n)) && iscleared(g, gval(n))) {
setnilvalue(gval(n)); /* remove value ... */
removeentry(n); /* and remove entry from table */
}
}
}
}
static void freeobj(lua_State *L, GCObject *o) {
switch (gch(o)->tt) {
case LUA_TPROTO:
luaF_freeproto(L, gco2p(o));
break;
case LUA_TLCL: {
luaM_freemem(L, o, sizeLclosure(gco2lcl(o)->nupvalues));
break;
}
case LUA_TCCL: {
luaM_freemem(L, o, sizeCclosure(gco2ccl(o)->nupvalues));
break;
}
case LUA_TUPVAL:
luaF_freeupval(L, gco2uv(o));
break;
case LUA_TTABLE:
luaH_free(L, gco2t(o));
break;
case LUA_TTHREAD:
luaE_freethread(L, gco2th(o));
break;
case LUA_TUSERDATA:
luaM_freemem(L, o, sizeudata(gco2u(o)));
break;
case LUA_TSHRSTR:
G(L)->strt.nuse--;
/* go through */
case LUA_TLNGSTR: {
luaM_freemem(L, o, sizestring(gco2ts(o)));
break;
}
default:
lua_assert(0);
}
}
#define sweepwholelist(L,p) sweeplist(L,p,MAX_LUMEM)
static GCObject **sweeplist(lua_State *L, GCObject **p, lu_mem count);
/*
** sweep the (open) upvalues of a thread and resize its stack and
** list of call-info structures.
*/
static void sweepthread(lua_State *L, lua_State *L1) {
if (L1->stack == NULL) return; /* stack not completely built yet */
sweepwholelist(L, &L1->openupval); /* sweep open upvalues */
luaE_freeCI(L1); /* free extra CallInfo slots */
/* should not change the stack during an emergency gc cycle */
if (G(L)->gckind != KGC_EMERGENCY)
luaD_shrinkstack(L1);
}
/*
** sweep at most 'count' elements from a list of GCObjects erasing dead
** objects, where a dead (not alive) object is one marked with the "old"
** (non current) white and not fixed.
** In non-generational mode, change all non-dead objects back to white,
** preparing for next collection cycle.
** In generational mode, keep black objects black, and also mark them as
** old; stop when hitting an old object, as all objects after that
** one will be old too.
** When object is a thread, sweep its list of open upvalues too.
*/
static GCObject **sweeplist(lua_State *L, GCObject **p, lu_mem count) {
global_State *g = G(L);
int ow = otherwhite(g);
int toclear, toset; /* bits to clear and to set in all live objects */
int tostop; /* stop sweep when this is true */
if (isgenerational(g)) { /* generational mode? */
toclear = ~0; /* clear nothing */
toset = bitmask(OLDBIT); /* set the old bit of all surviving objects */
tostop = bitmask(OLDBIT); /* do not sweep old generation */
} else { /* normal mode */
toclear = maskcolors; /* clear all color bits + old bit */
toset = luaC_white(g); /* make object white */
tostop = 0; /* do not stop */
}
while (*p != NULL && count-- > 0) {
GCObject *curr = *p;
int marked = gch(curr)->marked;
if (isdeadm(ow, marked)) { /* is 'curr' dead? */
*p = gch(curr)->next; /* remove 'curr' from list */
freeobj(L, curr); /* erase 'curr' */
} else {
if (testbits(marked, tostop))
return NULL; /* stop sweeping this list */
if (gch(curr)->tt == LUA_TTHREAD)
sweepthread(L, gco2th(curr)); /* sweep thread's upvalues */
/* update marks */
gch(curr)->marked = cast_byte((marked & toclear) | toset);
p = &gch(curr)->next; /* go to next element */
}
}
return (*p == NULL) ? NULL : p;
}
/*
** sweep a list until a live object (or end of list)
*/
static GCObject **sweeptolive(lua_State *L, GCObject **p, int *n) {
GCObject **old = p;
int i = 0;
do {
i++;
p = sweeplist(L, p, 1);
} while (p == old);
if (n) *n += i;
return p;
}
/* }====================================================== */
/*
** {======================================================
** Finalization
** =======================================================
*/
static void checkSizes(lua_State *L) {
global_State *g = G(L);
if (g->gckind != KGC_EMERGENCY) { /* do not change sizes in emergency */
int hs = g->strt.size / 2; /* half the size of the string table */
if (g->strt.nuse < cast(lu_int32, hs)) /* using less than that half? */
luaS_resize(L, hs); /* halve its size */
luaZ_freebuffer(L, &g->buff); /* free concatenation buffer */
}
}
static GCObject *udata2finalize(global_State *g) {
GCObject *o = g->tobefnz; /* get first element */
lua_assert(isfinalized(o));
g->tobefnz = gch(o)->next; /* remove it from 'tobefnz' list */
gch(o)->next = g->allgc; /* return it to 'allgc' list */
g->allgc = o;
resetbit(gch(o)->marked, SEPARATED); /* mark that it is not in 'tobefnz' */
lua_assert(!isold(o)); /* see MOVE OLD rule */
if (!keepinvariantout(g)) /* not keeping invariant? */
makewhite(g, o); /* "sweep" object */
return o;
}
static void dothecall(lua_State *L, void *ud) {
UNUSED(ud);
luaD_call(L, L->top - 2, 0, 0);
}
static void GCTM(lua_State *L, int propagateerrors) {
global_State *g = G(L);
const TValue *tm;
TValue v;
setgcovalue(L, &v, udata2finalize(g));
tm = luaT_gettmbyobj(L, &v, TM_GC);
if (tm != NULL && ttisfunction(tm)) { /* is there a finalizer? */
int status;
lu_byte oldah = L->allowhook;
int running = g->gcrunning;
L->allowhook = 0; /* stop debug hooks during GC metamethod */
g->gcrunning = 0; /* avoid GC steps */
setobj2s(L, L->top, tm); /* push finalizer... */
setobj2s(L, L->top + 1, &v); /* ... and its argument */
L->top += 2; /* and (next line) call the finalizer */
status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
L->allowhook = oldah; /* restore hooks */
g->gcrunning = running; /* restore state */
if (status != LUA_OK && propagateerrors) { /* error while running __gc? */
if (status == LUA_ERRRUN) { /* is there an error object? */
const char *msg = (ttisstring(L->top - 1))
? svalue(L->top - 1)
: "no message";
luaO_pushfstring(L, "error in __gc metamethod (%s)", msg);
status = LUA_ERRGCMM; /* error in __gc metamethod */
}
luaD_throw(L, status); /* re-throw error */
}
}
}
/*
** move all unreachable objects (or 'all' objects) that need
** finalization from list 'finobj' to list 'tobefnz' (to be finalized)
*/
static void separatetobefnz(lua_State *L, int all) {
global_State *g = G(L);
GCObject **p = &g->finobj;
GCObject *curr;
GCObject **lastnext = &g->tobefnz;
/* find last 'next' field in 'tobefnz' list (to add elements in its end) */
while (*lastnext != NULL)
lastnext = &gch(*lastnext)->next;
while ((curr = *p) != NULL) { /* traverse all finalizable objects */
lua_assert(!isfinalized(curr));
lua_assert(testbit(gch(curr)->marked, SEPARATED));
if (!(iswhite(curr) || all)) /* not being collected? */
p = &gch(curr)->next; /* don't bother with it */
else {
l_setbit(gch(curr)->marked, FINALIZEDBIT); /* won't be finalized again */
*p = gch(curr)->next; /* remove 'curr' from 'finobj' list */
gch(curr)->next = *lastnext; /* link at the end of 'tobefnz' list */
*lastnext = curr;
lastnext = &gch(curr)->next;
}
}
}
/*
** if object 'o' has a finalizer, remove it from 'allgc' list (must
** search the list to find it) and link it in 'finobj' list.
*/
void luaC_checkfinalizer(lua_State *L, GCObject *o, Table *mt) {
global_State *g = G(L);
if (testbit(gch(o)->marked, SEPARATED) || /* obj. is already separated... */
isfinalized(o) || /* ... or is finalized... */
gfasttm(g, mt, TM_GC) == NULL) /* or has no finalizer? */
return; /* nothing to be done */
else { /* move 'o' to 'finobj' list */
GCObject **p;
GCheader *ho = gch(o);
if (g->sweepgc == &ho->next) { /* avoid removing current sweep object */
lua_assert(issweepphase(g));
g->sweepgc = sweeptolive(L, g->sweepgc, NULL);
}
/* search for pointer pointing to 'o' */
for (p = &g->allgc; *p != o; p = &gch(*p)->next) { /* empty */ }
*p = ho->next; /* remove 'o' from root list */
ho->next = g->finobj; /* link it in list 'finobj' */
g->finobj = o;
l_setbit(ho->marked, SEPARATED); /* mark it as such */
if (!keepinvariantout(g)) /* not keeping invariant? */
makewhite(g, o); /* "sweep" object */
else
resetoldbit(o); /* see MOVE OLD rule */
}
}
/* }====================================================== */
/*
** {======================================================
** GC control
** =======================================================
*/
/*
** set a reasonable "time" to wait before starting a new GC cycle;
** cycle will start when memory use hits threshold
*/
static void setpause(global_State *g, l_mem estimate) {
l_mem debt, threshold;
estimate = estimate / PAUSEADJ; /* adjust 'estimate' */
threshold = (g->gcpause < MAX_LMEM / estimate) /* overflow? */
? estimate * g->gcpause /* no overflow */
: MAX_LMEM; /* overflow; truncate to maximum */
debt = -cast(l_mem, threshold - gettotalbytes(g));
luaE_setdebt(g, debt);
}
#define sweepphases \
(bitmask(GCSsweepstring) | bitmask(GCSsweepudata) | bitmask(GCSsweep))
/*
** enter first sweep phase (strings) and prepare pointers for other
** sweep phases. The calls to 'sweeptolive' make pointers point to an
** object inside the list (instead of to the header), so that the real
** sweep do not need to skip objects created between "now" and the start
** of the real sweep.
** Returns how many objects it swept.
*/
static int entersweep(lua_State *L) {
global_State *g = G(L);
int n = 0;
g->gcstate = GCSsweepstring;
lua_assert(g->sweepgc == NULL && g->sweepfin == NULL);
/* prepare to sweep strings, finalizable objects, and regular objects */
g->sweepstrgc = 0;
g->sweepfin = sweeptolive(L, &g->finobj, &n);
g->sweepgc = sweeptolive(L, &g->allgc, &n);
return n;
}
/*
** change GC mode
*/
void luaC_changemode(lua_State *L, int mode) {
global_State *g = G(L);
if (mode == g->gckind) return; /* nothing to change */
if (mode == KGC_GEN) { /* change to generational mode */
/* make sure gray lists are consistent */
luaC_runtilstate(L, bitmask(GCSpropagate));
g->GCestimate = gettotalbytes(g);
g->gckind = KGC_GEN;
} else { /* change to incremental mode */
/* sweep all objects to turn them back to white
(as white has not changed, nothing extra will be collected) */
g->gckind = KGC_NORMAL;
entersweep(L);
luaC_runtilstate(L, ~sweepphases);
}
}
/*
** call all pending finalizers
*/
static void callallpendingfinalizers(lua_State *L, int propagateerrors) {
global_State *g = G(L);
while (g->tobefnz) {
resetoldbit(g->tobefnz);
GCTM(L, propagateerrors);
}
}
void luaC_freeallobjects(lua_State *L) {
global_State *g = G(L);
int i;
separatetobefnz(L, 1); /* separate all objects with finalizers */
lua_assert(g->finobj == NULL);
callallpendingfinalizers(L, 0);
g->currentwhite = WHITEBITS; /* this "white" makes all objects look dead */
g->gckind = KGC_NORMAL;
sweepwholelist(L, &g->finobj); /* finalizers can create objs. in 'finobj' */
sweepwholelist(L, &g->allgc);
for (i = 0; i < g->strt.size; i++) /* free all string lists */
sweepwholelist(L, &g->strt.hash[i]);
lua_assert(g->strt.nuse == 0);
}
static l_mem atomic(lua_State *L) {
global_State *g = G(L);
l_mem work = -cast(l_mem, g->GCmemtrav); /* start counting work */
GCObject *origweak, *origall;
lua_assert(!iswhite(obj2gco(g->mainthread)));
markobject(g, L); /* mark running thread */
/* registry and global metatables may be changed by API */
markvalue(g, &g->l_registry);
markmt(g); /* mark basic metatables */
/* remark occasional upvalues of (maybe) dead threads */
remarkupvals(g);
propagateall(g); /* propagate changes */
work += g->GCmemtrav; /* stop counting (do not (re)count grays) */
/* traverse objects caught by write barrier and by 'remarkupvals' */
retraversegrays(g);
work -= g->GCmemtrav; /* restart counting */
convergeephemerons(g);
/* at this point, all strongly accessible objects are marked. */
/* clear values from weak tables, before checking finalizers */
clearvalues(g, g->weak, NULL);
clearvalues(g, g->allweak, NULL);
origweak = g->weak;
origall = g->allweak;
work += g->GCmemtrav; /* stop counting (objects being finalized) */
separatetobefnz(L, 0); /* separate objects to be finalized */
markbeingfnz(g); /* mark objects that will be finalized */
propagateall(g); /* remark, to propagate `preserveness' */
work -= g->GCmemtrav; /* restart counting */
convergeephemerons(g);
/* at this point, all resurrected objects are marked. */
/* remove dead objects from weak tables */
clearkeys(g, g->ephemeron, NULL); /* clear keys from all ephemeron tables */
clearkeys(g, g->allweak, NULL); /* clear keys from all allweak tables */
/* clear values from resurrected weak tables */
clearvalues(g, g->weak, origweak);
clearvalues(g, g->allweak, origall);
g->currentwhite = cast_byte(otherwhite(g)); /* flip current white */
work += g->GCmemtrav; /* complete counting */
return work; /* estimate of memory marked by 'atomic' */
}
static lu_mem singlestep(lua_State *L) {
global_State *g = G(L);
switch (g->gcstate) {
case GCSpause: {
/* start to count memory traversed */
g->GCmemtrav = g->strt.size * sizeof(GCObject *);
lua_assert(!isgenerational(g));
restartcollection(g);
g->gcstate = GCSpropagate;
return g->GCmemtrav;
}
case GCSpropagate: {
if (g->gray) {
lu_mem oldtrav = g->GCmemtrav;
propagatemark(g);
return g->GCmemtrav - oldtrav; /* memory traversed in this step */
} else { /* no more `gray' objects */
lu_mem work;
int sw;
g->gcstate = GCSatomic; /* finish mark phase */
g->GCestimate = g->GCmemtrav; /* save what was counted */;
work = atomic(L); /* add what was traversed by 'atomic' */
g->GCestimate += work; /* estimate of total memory traversed */
sw = entersweep(L);
return work + sw * GCSWEEPCOST;
}
}
case GCSsweepstring: {
int i;
for (i = 0; i < GCSWEEPMAX && g->sweepstrgc + i < g->strt.size; i++)
sweepwholelist(L, &g->strt.hash[g->sweepstrgc + i]);
g->sweepstrgc += i;
if (g->sweepstrgc >= g->strt.size) /* no more strings to sweep? */
g->gcstate = GCSsweepudata;
return i * GCSWEEPCOST;
}
case GCSsweepudata: {
if (g->sweepfin) {
g->sweepfin = sweeplist(L, g->sweepfin, GCSWEEPMAX);
return GCSWEEPMAX * GCSWEEPCOST;
} else {
g->gcstate = GCSsweep;
return 0;
}
}
case GCSsweep: {
if (g->sweepgc) {
g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
return GCSWEEPMAX * GCSWEEPCOST;
} else {
/* sweep main thread */
GCObject *mt = obj2gco(g->mainthread);
sweeplist(L, &mt, 1);
checkSizes(L);
g->gcstate = GCSpause; /* finish collection */
return GCSWEEPCOST;
}
}
default:
lua_assert(0);
return 0;
}
}
/*
** advances the garbage collector until it reaches a state allowed
** by 'statemask'
*/
void luaC_runtilstate(lua_State *L, int statesmask) {
global_State *g = G(L);
while (!testbit(statesmask, g->gcstate))
singlestep(L);
}
static void generationalcollection(lua_State *L) {
global_State *g = G(L);
lua_assert(g->gcstate == GCSpropagate);
if (g->GCestimate == 0) { /* signal for another major collection? */
luaC_fullgc(L, 0); /* perform a full regular collection */
g->GCestimate = gettotalbytes(g); /* update control */
} else {
lu_mem estimate = g->GCestimate;
luaC_runtilstate(L, bitmask(GCSpause)); /* run complete (minor) cycle */
g->gcstate = GCSpropagate; /* skip restart */
if (gettotalbytes(g) > (estimate / 100) * g->gcmajorinc)
g->GCestimate = 0; /* signal for a major collection */
else
g->GCestimate = estimate; /* keep estimate from last major coll. */
}
setpause(g, gettotalbytes(g));
lua_assert(g->gcstate == GCSpropagate);
}
static void incstep(lua_State *L) {
global_State *g = G(L);
l_mem debt = g->GCdebt;
int stepmul = g->gcstepmul;
if (stepmul < 40) stepmul = 40; /* avoid ridiculous low values (and 0) */
/* convert debt from Kb to 'work units' (avoid zero debt and overflows) */
debt = (debt / STEPMULADJ) + 1;
debt = (debt < MAX_LMEM / stepmul) ? debt * stepmul : MAX_LMEM;
do { /* always perform at least one single step */
lu_mem work = singlestep(L); /* do some work */
debt -= work;
} while (debt > -GCSTEPSIZE && g->gcstate != GCSpause);
if (g->gcstate == GCSpause)
setpause(g, g->GCestimate); /* pause until next cycle */
else {
debt = (debt / stepmul) * STEPMULADJ; /* convert 'work units' to Kb */
luaE_setdebt(g, debt);
}
}
/*
** performs a basic GC step
*/
void luaC_forcestep(lua_State *L) {
global_State *g = G(L);
int i;
if (isgenerational(g)) generationalcollection(L);
else incstep(L);
/* run a few finalizers (or all of them at the end of a collect cycle) */
for (i = 0; g->tobefnz && (i < GCFINALIZENUM || g->gcstate == GCSpause); i++)
GCTM(L, 1); /* call one finalizer */
}
/*
** performs a basic GC step only if collector is running
*/
void luaC_step(lua_State *L) {
global_State *g = G(L);
if (g->gcrunning) luaC_forcestep(L);
else luaE_setdebt(g, -GCSTEPSIZE); /* avoid being called too often */
}
/*
** performs a full GC cycle; if "isemergency", does not call
** finalizers (which could change stack positions)
*/
void luaC_fullgc(lua_State *L, int isemergency) {
global_State *g = G(L);
int origkind = g->gckind;
lua_assert(origkind != KGC_EMERGENCY);
if (isemergency) /* do not run finalizers during emergency GC */
g->gckind = KGC_EMERGENCY;
else {
g->gckind = KGC_NORMAL;
callallpendingfinalizers(L, 1);
}
if (keepinvariant(g)) { /* may there be some black objects? */
/* must sweep all objects to turn them back to white
(as white has not changed, nothing will be collected) */
entersweep(L);
}
/* finish any pending sweep phase to start a new cycle */
luaC_runtilstate(L, bitmask(GCSpause));
luaC_runtilstate(L, ~bitmask(GCSpause)); /* start new collection */
luaC_runtilstate(L, bitmask(GCSpause)); /* run entire collection */
if (origkind == KGC_GEN) { /* generational mode? */
/* generational mode must be kept in propagate phase */
luaC_runtilstate(L, bitmask(GCSpropagate));
}
g->gckind = origkind;
setpause(g, gettotalbytes(g));
if (!isemergency) /* do not run finalizers during emergency GC */
callallpendingfinalizers(L, 1);
}
/* }====================================================== */