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lua/lgc.c

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/*
** $Id: lgc.c,v 2.2 2003/12/12 18:29:34 roberto Exp roberto $
** Garbage Collector
** See Copyright Notice in lua.h
*/
#include <string.h>
#define lgc_c
#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"
#define GCSTEPSIZE (40*sizeof(TValue))
#define gray2black(x) setbit((x)->gch.marked, BLACKBIT)
#define maskmarks \
cast(lu_byte, ~(bitmask(BLACKBIT)|bit2mask(WHITE0BIT, WHITE1BIT)))
#define makewhite(g,x) \
((x)->gch.marked = ((x)->gch.marked & maskmarks) | g->currentwhite)
#define isgray(x) (!isblack(x) && !iswhite(x))
#define white2gray(x) reset2bits((x)->gch.marked, WHITE0BIT, WHITE1BIT)
#define black2gray(x) resetbit((x)->gch.marked, BLACKBIT)
#define stringmark(s) reset2bits((s)->tsv.marked, WHITE0BIT, WHITE1BIT)
#define isfinalized(u) testbit((u)->marked, FINALIZEDBIT)
#define markfinalized(u) setbit((u)->marked, FINALIZEDBIT)
#define KEYWEAK bitmask(KEYWEAKBIT)
#define VALUEWEAK bitmask(VALUEWEAKBIT)
#define markvalue(g,o) { checkconsistency(o); \
if (iscollectable(o) && iswhite(gcvalue(o))) reallymarkobject(g,gcvalue(o)); }
#define condmarkobject(g,o,c) { checkconsistency(o); \
if (iscollectable(o) && iswhite(gcvalue(o)) && (c)) \
reallymarkobject(g,gcvalue(o)); }
#define markobject(g,t) { if (iswhite(obj2gco(t))) \
reallymarkobject(g, obj2gco(t)); }
/*
** computes the size of a collectible object
*/
static size_t objsize (GCObject *o) {
switch (o->gch.tt) {
case LUA_TSTRING: {
TString *ts = rawgco2ts(o);
return sizestring(ts->tsv.len);
}
case LUA_TUSERDATA: {
Udata *u = rawgco2u(o);
return sizeudata(u->uv.len);
}
case LUA_TTABLE: {
Table *h = gco2h(o);
return sizeof(Table) + sizeof(TValue) * h->sizearray +
sizeof(Node) * sizenode(h);
}
case LUA_TUPVAL:
return sizeof(UpVal);
case LUA_TFUNCTION: {
Closure *cl = gco2cl(o);
return (cl->c.isC) ? sizeCclosure(cl->c.nupvalues) :
sizeLclosure(cl->l.nupvalues);
}
case LUA_TTHREAD: {
lua_State *th = gco2th(o);
return sizeof(lua_State) + sizeof(TValue) * th->stacksize +
sizeof(CallInfo) * th->size_ci;
}
case LUA_TPROTO: {
Proto *p = gco2p(o);
return sizeof(Proto) + sizeof(Instruction) * p->sizecode +
sizeof(Proto *) * p->sizep + sizeof(TValue) * p->sizek +
sizeof(int) * p->sizelineinfo + sizeof(LocVar) * p->sizelocvars +
sizeof(TString *) * p->sizeupvalues;
}
}
lua_assert(0);
return 0; /* to avoid warnings */
}
static void reallymarkobject (global_State *g, GCObject *o) {
lua_assert(iswhite(o) && !isdead(g, o));
white2gray(o);
switch (o->gch.tt) {
case LUA_TSTRING: {
return;
}
case LUA_TUSERDATA: {
Table *mt = gco2u(o)->metatable;
gray2black(o); /* udata are never gray */
if (mt) markobject(g, mt);
return;
}
case LUA_TFUNCTION: {
gco2cl(o)->c.gclist = g->gray;
break;
}
case LUA_TTABLE: {
gco2h(o)->gclist = g->gray;
break;
}
case LUA_TTHREAD: {
gco2th(o)->gclist = g->gray;
break;
}
case LUA_TPROTO: {
gco2p(o)->gclist = g->gray;
break;
}
case LUA_TUPVAL: {
gco2uv(o)->gclist = g->gray;
break;
}
default: lua_assert(0);
}
g->gray = o; /* finish list linking */
}
static void marktmu (global_State *g) {
GCObject *u;
for (u = g->tmudata; u; u = u->gch.next) {
makewhite(g, u); /* may be marked, if left from previous GC */
reallymarkobject(g, u);
}
}
/* move `dead' udata that need finalization to list `tmudata' */
size_t luaC_separateudata (lua_State *L, int all) {
size_t deadmem = 0;
GCObject **p = &G(L)->firstudata;
GCObject *curr;
GCObject *collected = NULL; /* to collect udata with gc event */
GCObject **lastcollected = &collected;
while ((curr = *p) != NULL) {
lua_assert(curr->gch.tt == LUA_TUSERDATA);
if (!(iswhite(curr) || all) || isfinalized(gco2u(curr)))
p = &curr->gch.next; /* don't bother with them */
else if (fasttm(L, gco2u(curr)->metatable, TM_GC) == NULL) {
markfinalized(gco2u(curr)); /* don't need finalization */
p = &curr->gch.next;
}
else { /* must call its gc method */
deadmem += sizeudata(gco2u(curr)->len);
markfinalized(gco2u(curr));
*p = curr->gch.next;
curr->gch.next = NULL; /* link `curr' at the end of `collected' list */
*lastcollected = curr;
lastcollected = &curr->gch.next;
}
}
/* insert collected udata with gc event into `tmudata' list */
*lastcollected = G(L)->tmudata;
G(L)->tmudata = collected;
return deadmem;
}
static int traversetable (global_State *g, Table *h) {
int i;
int weakkey = 0;
int weakvalue = 0;
const TValue *mode;
if (h->metatable)
markobject(g, h->metatable);
lua_assert(h->lsizenode || h->node == g->dummynode);
mode = gfasttm(g, h->metatable, TM_MODE);
if (mode && ttisstring(mode)) { /* is there a weak mode? */
weakkey = (strchr(svalue(mode), 'k') != NULL);
weakvalue = (strchr(svalue(mode), 'v') != NULL);
if (weakkey || weakvalue) { /* is really weak? */
h->marked &= ~(KEYWEAK | VALUEWEAK); /* clear bits */
h->marked |= cast(lu_byte, (weakkey << KEYWEAKBIT) |
(weakvalue << VALUEWEAKBIT));
h->gclist = g->weak; /* must be cleared after GC, ... */
g->weak = obj2gco(h); /* ... so put in the appropriate list */
}
}
if (weakkey && weakvalue) return 1;
if (!weakvalue) {
i = h->sizearray;
while (i--)
markvalue(g, &h->array[i]);
}
i = sizenode(h);
while (i--) {
Node *n = gnode(h, i);
if (!ttisnil(gval(n))) {
lua_assert(!ttisnil(gkey(n)));
condmarkobject(g, gkey(n), !weakkey);
condmarkobject(g, gval(n), !weakvalue);
}
}
return weakkey || weakvalue;
}
/*
** All marks are conditional because a GC may happen while the
** prototype is still being created
*/
static void traverseproto (global_State *g, Proto *f) {
int i;
if (f->source) stringmark(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 */
if (f->upvalues[i])
stringmark(f->upvalues[i]);
}
for (i=0; i<f->sizep; i++) { /* mark nested protos */
if (f->p[i])
markobject(g, f->p[i]);
}
for (i=0; i<f->sizelocvars; i++) { /* mark local-variable names */
if (f->locvars[i].varname)
stringmark(f->locvars[i].varname);
}
}
static void traverseclosure (global_State *g, Closure *cl) {
if (cl->c.isC) {
int i;
for (i=0; i<cl->c.nupvalues; i++) /* mark its upvalues */
markvalue(g, &cl->c.upvalue[i]);
}
else {
int i;
lua_assert(cl->l.nupvalues == cl->l.p->nups);
markobject(g, hvalue(&cl->l.g));
markobject(g, cl->l.p);
for (i=0; i<cl->l.nupvalues; i++) /* mark its upvalues */
markobject(g, cl->l.upvals[i]);
}
}
static void checkstacksizes (lua_State *L, StkId max) {
int used = L->ci - L->base_ci; /* number of `ci' in use */
if (4*used < L->size_ci && 2*BASIC_CI_SIZE < L->size_ci)
luaD_reallocCI(L, L->size_ci/2); /* still big enough... */
else condhardstacktests(luaD_reallocCI(L, L->size_ci));
used = max - L->stack; /* part of stack in use */
if (4*used < L->stacksize && 2*(BASIC_STACK_SIZE+EXTRA_STACK) < L->stacksize)
luaD_reallocstack(L, L->stacksize/2); /* still big enough... */
else condhardstacktests(luaD_reallocstack(L, L->stacksize));
}
static void traversestack (global_State *g, lua_State *L1) {
StkId o, lim;
CallInfo *ci;
markvalue(g, gt(L1));
lim = L1->top;
for (ci = L1->base_ci; ci <= L1->ci; ci++) {
lua_assert(ci->top <= L1->stack_last);
if (lim < ci->top) lim = ci->top;
}
for (o = L1->stack; o < L1->top; o++)
markvalue(g, o);
for (; o <= lim; o++)
setnilvalue(o);
checkstacksizes(L1, lim);
}
/*
** traverse a given `quantity' of gray objects,
** turning them to black. Returns extra `quantity' traversed.
*/
static l_mem propagatemarks (global_State *g, l_mem lim) {
GCObject *o;
while ((o = g->gray) != NULL) {
lua_assert(isgray(o));
gray2black(o);
switch (o->gch.tt) {
case LUA_TTABLE: {
Table *h = gco2h(o);
g->gray = h->gclist;
if (traversetable(g, h)) /* table is weak? */
black2gray(o); /* keep it gray */
break;
}
case LUA_TFUNCTION: {
Closure *cl = gco2cl(o);
g->gray = cl->c.gclist;
traverseclosure(g, cl);
break;
}
case LUA_TTHREAD: {
lua_State *th = gco2th(o);
g->gray = th->gclist;
th->gclist = g->grayagain;
g->grayagain = o;
black2gray(o);
traversestack(g, th);
break;
}
case LUA_TPROTO: {
Proto *p = gco2p(o);
g->gray = p->gclist;
traverseproto(g, p);
break;
}
case LUA_TUPVAL: {
UpVal *uv = gco2uv(o);
g->gray = uv->gclist;
if (uv->v != &uv->value) { /* open? */
uv->gclist = g->grayagain;
g->grayagain = o;
black2gray(o);
}
else
markvalue(g, &uv->value);
break;
}
default: lua_assert(0);
}
lim -= objsize(o);
if (lim <= 0) return lim;
}
return lim;
}
/*
** The next function 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 userdata
** being finalized, keep them in keys, but not in values
*/
static int iscleared (const TValue *o, int iskey) {
if (!iscollectable(o)) return 0;
if (ttisstring(o)) {
stringmark(rawtsvalue(o)); /* strings are `values', so are never weak */
return 0;
}
return iswhite(gcvalue(o)) ||
(ttisuserdata(o) && (!iskey && isfinalized(uvalue(o))));
}
static void removekey (Node *n) {
setnilvalue(gval(n)); /* remove corresponding value ... */
if (iscollectable(gkey(n)))
setttype(gkey(n), LUA_TNONE); /* dead key; remove it */
}
/*
** clear collected entries from weaktables
*/
static void cleartable (GCObject *l) {
while (l) {
Table *h = gco2h(l);
int i = h->sizearray;
lua_assert(testbit(h->marked, VALUEWEAKBIT) ||
testbit(h->marked, KEYWEAKBIT));
if (testbit(h->marked, VALUEWEAKBIT)) {
while (i--) {
TValue *o = &h->array[i];
if (iscleared(o, 0)) /* value was collected? */
setnilvalue(o); /* remove value */
}
}
i = sizenode(h);
while (i--) {
Node *n = gnode(h, i);
if (!ttisnil(gval(n)) && /* non-empty entry? */
(iscleared(gkey(n), 1) || iscleared(gval(n), 0)))
removekey(n); /* remove entry from table */
}
l = h->gclist;
}
}
static void freeobj (lua_State *L, GCObject *o) {
switch (o->gch.tt) {
case LUA_TPROTO: luaF_freeproto(L, gco2p(o)); break;
case LUA_TFUNCTION: luaF_freeclosure(L, gco2cl(o)); break;
case LUA_TUPVAL: luaM_freelem(L, gco2uv(o)); break;
case LUA_TTABLE: luaH_free(L, gco2h(o)); break;
case LUA_TTHREAD: {
lua_assert(gco2th(o) != L && gco2th(o) != G(L)->mainthread);
luaE_freethread(L, gco2th(o));
break;
}
case LUA_TSTRING: {
luaM_free(L, o, sizestring(gco2ts(o)->len));
break;
}
case LUA_TUSERDATA: {
luaM_free(L, o, sizeudata(gco2u(o)->len));
break;
}
default: lua_assert(0);
}
}
static void sweepupvalues (global_State *g, lua_State *L1) {
GCObject *curr;
for (curr = L1->openupval; curr != NULL; curr = curr->gch.next)
makewhite(g, curr);
}
static GCObject **sweeplist (lua_State *L, GCObject **p, int all,
l_mem *plim) {
GCObject *curr;
global_State *g = G(L);
l_mem lim = *plim;
int dead = otherwhite(g);
while ((curr = *p) != NULL) {
int mark = curr->gch.marked;
lim -= objsize(curr);
if (!all && (!(mark & dead) || testbit(mark, FIXEDBIT))) {
makewhite(g, curr);
if (curr->gch.tt == LUA_TTHREAD)
sweepupvalues(g, gco2th(curr));
p = &curr->gch.next;
}
else {
*p = curr->gch.next;
if (curr == g->rootgc) /* is the first element of the list? */
g->rootgc = curr->gch.next; /* adjust first */
freeobj(L, curr);
}
if (lim <= 0) break;
}
*plim = lim;
return p;
}
static l_mem sweepstrings (lua_State *L, int all, l_mem lim) {
int i;
global_State *g = G(L);
int dead = otherwhite(g);
for (i = g->sweepstrgc; i < g->strt.size; i++) { /* for each list */
GCObject *curr;
GCObject **p = &G(L)->strt.hash[i];
while ((curr = *p) != NULL) {
int mark = curr->gch.marked;
lu_mem size = sizestring(gco2ts(curr)->len);
if (!all && (!(mark & dead) || testbit(mark, FIXEDBIT))) {
makewhite(g, curr);
lua_assert(iswhite(curr) && !isdead(g, curr));
p = &curr->gch.next;
}
else {
g->strt.nuse--;
*p = curr->gch.next;
luaM_free(L, curr, size);
}
lim -= size;
}
if (lim <= 0) break;
}
g->sweepstrgc = i+1;
return lim;
}
static void checkSizes (lua_State *L) {
global_State *g = G(L);
/* check size of string hash */
if (g->strt.nuse < cast(lu_int32, G(L)->strt.size/4) &&
g->strt.size > MINSTRTABSIZE*2)
luaS_resize(L, g->strt.size/2); /* table is too big */
/* check size of buffer */
if (luaZ_sizebuffer(&g->buff) > LUA_MINBUFFER*2) { /* buffer too big? */
size_t newsize = luaZ_sizebuffer(&g->buff) / 2;
luaZ_resizebuffer(L, &g->buff, newsize);
}
}
static void GCTM (lua_State *L) {
global_State *g = G(L);
GCObject *o = g->tmudata;
Udata *udata = rawgco2u(o);
const TValue *tm;
g->tmudata = udata->uv.next; /* remove udata from `tmudata' */
udata->uv.next = g->firstudata->uv.next; /* return it to `root' list */
g->firstudata->uv.next = o;
makewhite(g, o);
tm = fasttm(L, udata->uv.metatable, TM_GC);
if (tm != NULL) {
lu_byte oldah = L->allowhook;
L->allowhook = 0; /* stop debug hooks during GC tag method */
setobj2s(L, L->top, tm);
setuvalue(L, L->top+1, udata);
L->top += 2;
luaD_call(L, L->top - 2, 0);
L->allowhook = oldah; /* restore hooks */
}
}
/*
** Call all GC tag methods
*/
void luaC_callGCTM (lua_State *L) {
while (G(L)->tmudata)
GCTM(L);
}
void luaC_sweepall (lua_State *L) {
l_mem dummy = MAXLMEM;
G(L)->sweepstrgc = 0;
sweepstrings(L, 1, dummy);
sweeplist(L, &G(L)->rootgc, 1, &dummy);
}
/* mark root set */
static void markroot (lua_State *L) {
global_State *g = G(L);
lua_assert(g->gray == NULL);
g->grayagain = NULL;
g->weak = NULL;
makewhite(g, obj2gco(g->mainthread));
markobject(g, g->mainthread);
markvalue(g, registry(L));
markobject(g, L); /* mark running thread */
g->gcstate = GCSpropagate;
}
static void atomic (lua_State *L) {
global_State *g = G(L);
lua_assert(g->gray == NULL);
/* remark weak tables */
g->gray = g->weak;
g->weak = NULL;
propagatemarks(g, MAXLMEM);
/* remark gray again */
g->gray = g->grayagain;
g->grayagain = NULL;
propagatemarks(g, MAXLMEM);
luaC_separateudata(L, 0); /* separate userdata to be preserved */
marktmu(g); /* mark `preserved' userdata */
propagatemarks(g, MAXLMEM); /* remark, to propagate `preserveness' */
cleartable(g->weak); /* remove collected objects from weak tables */
/* flip current white */
g->currentwhite = otherwhite(g);
g->sweepgc = &g->rootgc;
g->sweepstrgc = 0;
g->gcstate = GCSsweepstring;
}
void luaC_step (lua_State *L) {
global_State *g = G(L);
l_mem lim = (g->nblocks - (g->GCthreshold - GCSTEPSIZE)) * 2;
luaC_checkall(L);
switch (g->gcstate) {
case GCSpropagate: {
if (g->gray)
lim = propagatemarks(g, lim);
else { /* no more `gray' objects */
atomic(L); /* finish mark phase */
lim = 0;
}
break;
}
case GCSsweepstring: {
lim = sweepstrings(L, 0, lim);
if (g->sweepstrgc >= g->strt.size) { /* nothing more to sweep? */
g->sweepstrgc = 0;
g->gcstate = GCSsweep; /* end sweep-string phase */
}
break;
}
case GCSsweep: {
g->sweepgc = sweeplist(L, g->sweepgc, 0, &lim);
if (*g->sweepgc == NULL) { /* nothing more to sweep? */
checkSizes(L);
sweepupvalues(g, g->mainthread);
g->gcstate = GCSfinalize; /* end sweep phase */
}
break;
}
case GCSfinalize: {
if (g->tmudata) {
GCTM(L);
lim = 0;
}
else /* no more `udata' to finalize */
markroot(L); /* may restart collection */
break;
}
default: lua_assert(0);
}
g->GCthreshold = g->nblocks + GCSTEPSIZE - lim/2;
luaC_checkall(L);
}
void luaC_barrierf (lua_State *L, GCObject *o, GCObject *v) {
global_State *g = G(L);
lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
if (g->gcstate != GCSpropagate) /* sweeping phases? */
black2gray(o); /* just mark as gray to avoid other barriers */
else /* breaking invariant! */
reallymarkobject(g, v); /* restore it */
}
void luaC_link (lua_State *L, GCObject *o, lu_byte tt) {
global_State *g = G(L);
o->gch.next = g->rootgc;
g->rootgc = o;
o->gch.marked = luaC_white(g);
o->gch.tt = tt;
}
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