Lua2RTT/lua/lgc.c

/*
** $Id: lgc.c,v 2.38.1.1 2007/12/27 13:02:25 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"
#include "lrotable.h"

#define GCSTEPSIZE  1024u
#define GCSWEEPMAX  40
#define GCSWEEPCOST 10
#define GCFINALIZECOST  100


#define maskmarks   cast_byte(~(bitmask(BLACKBIT)|WHITEBITS))

#define makewhite(g,x)  \
   ((x)->gch.marked = cast_byte(((x)->gch.marked & maskmarks) | luaC_white(g)))

#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)    l_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 markobject(g,t) { if (iswhite(obj2gco(t))) \
        reallymarkobject(g, obj2gco(t)); }


#define setthreshold(g)  (g->GCthreshold = (g->estimate/100) * g->gcpause)


static void removeentry(Node *n)
{
    lua_assert(ttisnil(gval(n)));
    if (iscollectable(gkey(n)))
        setttype(gkey(n), LUA_TDEADKEY);  /* dead key; remove it */
}


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 && !luaR_isrotable(mt)) markobject(g, mt);
        markobject(g, gco2u(o)->env);
        return;
    }
    case LUA_TUPVAL:
    {
        UpVal *uv = gco2uv(o);
        markvalue(g, uv->v);
        if (uv->v == &uv->u.value)  /* closed? */
            gray2black(o);  /* open upvalues are never black */
        return;
    }
    case LUA_TFUNCTION:
    {
        gco2cl(o)->c.gclist = g->gray;
        g->gray = o;
        break;
    }
    case LUA_TTABLE:
    {
        gco2h(o)->gclist = g->gray;
        g->gray = o;
        break;
    }
    case LUA_TTHREAD:
    {
        gco2th(o)->gclist = g->gray;
        g->gray = o;
        break;
    }
    case LUA_TPROTO:
    {
        gco2p(o)->gclist = g->gray;
        g->gray = o;
        break;
    }
    default:
        lua_assert(0);
    }
}


static void marktmu(global_State *g)
{
    GCObject *u = g->tmudata;
    if (u)
    {
        do
        {
            u = u->gch.next;
            makewhite(g, u);  /* may be marked, if left from previous GC */
            reallymarkobject(g, u);
        }
        while (u != g->tmudata);
    }
}


/* move `dead' udata that need finalization to list `tmudata' */
size_t luaC_separateudata(lua_State *L, int all)
{
    global_State *g = G(L);
    size_t deadmem = 0;
    GCObject **p = &g->mainthread->next;
    GCObject *curr;
    while ((curr = *p) != NULL)
    {
        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));
            markfinalized(gco2u(curr));
            *p = curr->gch.next;
            /* link `curr' at the end of `tmudata' list */
            if (g->tmudata == NULL)  /* list is empty? */
                g->tmudata = curr->gch.next = curr;  /* creates a circular list */
            else
            {
                curr->gch.next = g->tmudata->gch.next;
                g->tmudata->gch.next = curr;
                g->tmudata = curr;
            }
        }
    }
    return deadmem;
}


static int traversetable(global_State *g, Table *h)
{
    int i;
    int weakkey = 0;
    int weakvalue = 0;
    const TValue *mode;
    if (h->metatable && !luaR_isrotable(h->metatable))
        markobject(g, h->metatable);
    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_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);
        lua_assert(ttype(gkey(n)) != LUA_TDEADKEY || ttisnil(gval(n)));
        if (ttisnil(gval(n)))
            removeentry(n);  /* remove empty entries */
        else
        {
            lua_assert(!ttisnil(gkey(n)));
            if (!weakkey) markvalue(g, gkey(n));
            if (!weakvalue) markvalue(g, gval(n));
        }
    }
    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)
{
    markobject(g, cl->c.env);
    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, cl->l.p);
        for (i = 0; i < cl->l.nupvalues; i++) /* mark its upvalues */
        {
            if (cl->l.upvals[i])
                markobject(g, cl->l.upvals[i]);
        }
    }
}


static void checkstacksizes(lua_State *L, StkId max)
{
    int ci_used = cast_int(L->ci - L->base_ci);  /* number of `ci' in use */
    int s_used = cast_int(max - L->stack);  /* part of stack in use */
    if (L->size_ci > LUAI_MAXCALLS)  /* handling overflow? */
        return;  /* do not touch the stacks */
    if (4 * ci_used < L->size_ci && 2 * BASIC_CI_SIZE < L->size_ci)
        luaD_reallocCI(L, L->size_ci / 2); /* still big enough... */
    condhardstacktests(luaD_reallocCI(L, ci_used + 1));
    if (4 * s_used < L->stacksize &&
            2 * (BASIC_STACK_SIZE + EXTRA_STACK) < L->stacksize)
        luaD_reallocstack(L, L->stacksize / 2); /* still big enough... */
    condhardstacktests(luaD_reallocstack(L, s_used));
}


static void traversestack(global_State *g, lua_State *l)
{
    StkId o, lim;
    CallInfo *ci;
    markvalue(g, gt(l));
    lim = l->top;
    if (l->stack == NULL) return; /* no stack to traverse */
    for (ci = l->base_ci; ci <= l->ci; ci++)
    {
        lua_assert(ci->top <= l->stack_last);
        if (lim < ci->top) lim = ci->top;
    }
    for (o = l->stack; o < l->top; o++)
        markvalue(g, o);
    for (; o <= lim; o++)
        setnilvalue(o);
    if (!isfixedstack(l)) /* if stack size is fixed, can't resize it. */
        checkstacksizes(l, lim);
}


/*
** traverse one gray object, turning it to black.
** Returns `quantity' traversed.
*/
static l_mem propagatemark(global_State *g)
{
    GCObject *o = g->gray;
    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 */
        return sizeof(Table) + sizeof(TValue) * h->sizearray +
               sizeof(Node) * sizenode(h);
    }
    case LUA_TFUNCTION:
    {
        Closure *cl = gco2cl(o);
        g->gray = cl->c.gclist;
        traverseclosure(g, cl);
        return (cl->c.isC) ? sizeCclosure(cl->c.nupvalues) :
               sizeLclosure(cl->l.nupvalues);
    }
    case LUA_TTHREAD:
    {
        lua_State *th = gco2th(o);
        g->gray = th->gclist;
        th->gclist = g->grayagain;
        g->grayagain = o;
        black2gray(o);
        traversestack(g, th);
        return sizeof(lua_State) + sizeof(TValue) * th->stacksize +
               sizeof(CallInfo) * th->size_ci;
    }
    case LUA_TPROTO:
    {
        Proto *p = gco2p(o);
        g->gray = p->gclist;
        traverseproto(g, p);
        return sizeof(Proto) + sizeof(Proto *) * p->sizep +
               sizeof(TValue) * p->sizek +
               sizeof(LocVar) * p->sizelocvars +
               sizeof(TString *) * p->sizeupvalues +
               (proto_is_readonly(p) ? 0 : sizeof(Instruction) * p->sizecode +
                sizeof(int) * p->sizelineinfo);
    }
    default:
        lua_assert(0);
        return 0;
    }
}


static size_t propagateall(global_State *g)
{
    size_t m = 0;
    while (g->gray) m += propagatemark(g);
    return m;
}


/*
** 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))));
}


/*
** 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(key2tval(n), 1) || iscleared(gval(n), 0)))
            {
                setnilvalue(gval(n));  /* remove value ... */
                removeentry(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:
        luaF_freeupval(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:
    {
        G(L)->strt.nuse--;
        luaM_freemem(L, o, sizestring(gco2ts(o)));
        break;
    }
    case LUA_TUSERDATA:
    {
        luaM_freemem(L, o, sizeudata(gco2u(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)
{
    GCObject *curr;
    global_State *g = G(L);
    int deadmask = otherwhite(g);
    while ((curr = *p) != NULL && count-- > 0)
    {
        if (curr->gch.tt == LUA_TTHREAD)  /* sweep open upvalues of each thread */
            sweepwholelist(L, &gco2th(curr)->openupval);
        if ((curr->gch.marked ^ WHITEBITS) & deadmask)    /* not dead? */
        {
            lua_assert(!isdead(g, curr) || testbit(curr->gch.marked, FIXEDBIT));
            makewhite(g, curr);  /* make it white (for next cycle) */
            p = &curr->gch.next;
        }
        else    /* must erase `curr' */
        {
            lua_assert(isdead(g, curr) || deadmask == bitmask(SFIXEDBIT));
            *p = curr->gch.next;
            freeobj(L, curr);
        }
    }
    return p;
}


static void checkSizes(lua_State *L)
{
    global_State *g = G(L);
    /* check size of string hash */
    if (g->strt.nuse < cast(lu_int32, g->strt.size / 4) &&
            g->strt.size > MINSTRTABSIZE * 2)
        luaS_resize(L, g->strt.size / 2); /* table is too big */
    /* it is not safe to re-size the buffer if it is in use. */
    if (luaZ_bufflen(&g->buff) > 0) return;
    /* 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->gch.next;  /* get first element */
    Udata *udata = rawgco2u(o);
    const TValue *tm;
    /* remove udata from `tmudata' */
    if (o == g->tmudata)  /* last element? */
        g->tmudata = NULL;
    else
        g->tmudata->gch.next = udata->uv.next;
    udata->uv.next = g->mainthread->next;  /* return it to `root' list */
    g->mainthread->next = o;
    makewhite(g, o);
    tm = fasttm(L, udata->uv.metatable, TM_GC);
    if (tm != NULL)
    {
        lu_byte oldah = L->allowhook;
        lu_mem oldt = g->GCthreshold;
        L->allowhook = 0;  /* stop debug hooks during GC tag method */
        g->GCthreshold = 2 * g->totalbytes; /* avoid GC steps */
        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 */
        g->GCthreshold = oldt;  /* restore threshold */
    }
}


/*
** Call all GC tag methods
*/
void luaC_callGCTM(lua_State *L)
{
    while (G(L)->tmudata)
        GCTM(L);
}


void luaC_freeall(lua_State *L)
{
    global_State *g = G(L);
    int i;
    g->currentwhite = WHITEBITS | bitmask(SFIXEDBIT);  /* mask to collect all elements */
    sweepwholelist(L, &g->rootgc);
    for (i = 0; i < g->strt.size; i++)  /* free all string lists */
        sweepwholelist(L, &g->strt.hash[i]);
}


static void markmt(global_State *g)
{
    int i;
    for (i = 0; i < NUM_TAGS; i++)
        if (g->mt[i] && !luaR_isrotable(g->mt[i])) markobject(g, g->mt[i]);
}


/* mark root set */
static void markroot(lua_State *L)
{
    global_State *g = G(L);
    g->gray = NULL;
    g->grayagain = NULL;
    g->weak = NULL;
    markobject(g, g->mainthread);
    /* make global table be traversed before main stack */
    markvalue(g, gt(g->mainthread));
    markvalue(g, registry(L));
    markmt(g);
    g->gcstate = GCSpropagate;
}


static void remarkupvals(global_State *g)
{
    UpVal *uv;
    for (uv = g->uvhead.u.l.next; uv != &g->uvhead; uv = uv->u.l.next)
    {
        lua_assert(uv->u.l.next->u.l.prev == uv && uv->u.l.prev->u.l.next == uv);
        if (isgray(obj2gco(uv)))
            markvalue(g, uv->v);
    }
}


static void atomic(lua_State *L)
{
    global_State *g = G(L);
    size_t udsize;  /* total size of userdata to be finalized */
    /* remark occasional upvalues of (maybe) dead threads */
    remarkupvals(g);
    /* traverse objects cautch by write barrier and by 'remarkupvals' */
    propagateall(g);
    /* remark weak tables */
    g->gray = g->weak;
    g->weak = NULL;
    lua_assert(!iswhite(obj2gco(g->mainthread)));
    markobject(g, L);  /* mark running thread */
    markmt(g);  /* mark basic metatables (again) */
    propagateall(g);
    /* remark gray again */
    g->gray = g->grayagain;
    g->grayagain = NULL;
    propagateall(g);
    udsize = luaC_separateudata(L, 0);  /* separate userdata to be finalized */
    marktmu(g);  /* mark `preserved' userdata */
    udsize += propagateall(g);  /* remark, to propagate `preserveness' */
    cleartable(g->weak);  /* remove collected objects from weak tables */
    /* flip current white */
    g->currentwhite = cast_byte(otherwhite(g));
    g->sweepstrgc = 0;
    g->sweepgc = &g->rootgc;
    g->gcstate = GCSsweepstring;
    g->estimate = g->totalbytes - udsize;  /* first estimate */
}

static void sweepstrstep(global_State *g, lua_State *L)
{
    lu_mem old = g->totalbytes;
    sweepwholelist(L, &g->strt.hash[g->sweepstrgc++]);
    if (g->sweepstrgc >= g->strt.size)  /* nothing more to sweep? */
        g->gcstate = GCSsweep;  /* end sweep-string phase */
    lua_assert(old >= g->totalbytes);
    g->estimate -= old - g->totalbytes;
}


static l_mem singlestep(lua_State *L)
{
    global_State *g = G(L);
    /*lua_checkmemory(L);*/
    switch (g->gcstate)
    {
    case GCSpause:
    {
        markroot(L);  /* start a new collection */
        return 0;
    }
    case GCSpropagate:
    {
        if (g->gray)
            return propagatemark(g);
        else    /* no more `gray' objects */
        {
            atomic(L);  /* finish mark phase */
            return 0;
        }
    }
    case GCSsweepstring:
    {
        sweepstrstep(g, L);
        return GCSWEEPCOST;
    }
    case GCSsweep:
    {
        lu_mem old = g->totalbytes;
        g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
        if (*g->sweepgc == NULL)    /* nothing more to sweep? */
        {
            checkSizes(L);
            g->gcstate = GCSfinalize;  /* end sweep phase */
        }
        lua_assert(old >= g->totalbytes);
        g->estimate -= old - g->totalbytes;
        return GCSWEEPMAX * GCSWEEPCOST;
    }
    case GCSfinalize:
    {
        if (g->tmudata)
        {
            GCTM(L);
            if (g->estimate > GCFINALIZECOST)
                g->estimate -= GCFINALIZECOST;
            return GCFINALIZECOST;
        }
        else
        {
            g->gcstate = GCSpause;  /* end collection */
            g->gcdept = 0;
            return 0;
        }
    }
    default:
        lua_assert(0);
        return 0;
    }
}


void luaC_step(lua_State *L)
{
    global_State *g = G(L);
    if (is_block_gc(L)) return;
    set_block_gc(L);
    l_mem lim = (GCSTEPSIZE / 100) * g->gcstepmul;
    if (lim == 0)
        lim = (MAX_LUMEM - 1) / 2; /* no limit */
    g->gcdept += g->totalbytes - g->GCthreshold;
    if (g->estimate > g->totalbytes)
        g->estimate = g->totalbytes;
    do
    {
        lim -= singlestep(L);
        if (g->gcstate == GCSpause)
            break;
    }
    while (lim > 0);
    if (g->gcstate != GCSpause)
    {
        if (g->gcdept < GCSTEPSIZE)
            g->GCthreshold = g->totalbytes + GCSTEPSIZE;  /* - lim/g->gcstepmul;*/
        else
        {
            g->gcdept -= GCSTEPSIZE;
            g->GCthreshold = g->totalbytes;
        }
    }
    else
    {
        lua_assert(g->totalbytes >= g->estimate);
        setthreshold(g);
    }
    unset_block_gc(L);
}

int luaC_sweepstrgc(lua_State *L)
{
    global_State *g = G(L);
    if (g->gcstate == GCSsweepstring)
    {
        sweepstrstep(g, L);
        return (g->gcstate == GCSsweepstring) ? 1 : 0;
    }
    return 0;
}

void luaC_fullgc(lua_State *L)
{
    global_State *g = G(L);
    if (is_block_gc(L)) return;
    set_block_gc(L);
    if (g->gcstate <= GCSpropagate)
    {
        /* reset sweep marks to sweep all elements (returning them to white) */
        g->sweepstrgc = 0;
        g->sweepgc = &g->rootgc;
        /* reset other collector lists */
        g->gray = NULL;
        g->grayagain = NULL;
        g->weak = NULL;
        g->gcstate = GCSsweepstring;
    }
    lua_assert(g->gcstate != GCSpause && g->gcstate != GCSpropagate);
    /* finish any pending sweep phase */
    while (g->gcstate != GCSfinalize)
    {
        lua_assert(g->gcstate == GCSsweepstring || g->gcstate == GCSsweep);
        singlestep(L);
    }
    markroot(L);
    while (g->gcstate != GCSpause)
    {
        singlestep(L);
    }
    setthreshold(g);
    unset_block_gc(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));
    lua_assert(g->gcstate != GCSfinalize && g->gcstate != GCSpause);
    lua_assert(ttype(&o->gch) != LUA_TTABLE);
    /* must keep invariant? */
    if (g->gcstate == GCSpropagate)
        reallymarkobject(g, v);  /* restore invariant */
    else  /* don't mind */
        makewhite(g, o);  /* mark as white just to avoid other barriers */
}


void luaC_barrierback(lua_State *L, Table *t)
{
    global_State *g = G(L);
    GCObject *o = obj2gco(t);
    lua_assert(isblack(o) && !isdead(g, o));
    lua_assert(g->gcstate != GCSfinalize && g->gcstate != GCSpause);
    black2gray(o);  /* make table gray (again) */
    t->gclist = g->grayagain;
    g->grayagain = o;
}


void luaC_marknew(lua_State *L, GCObject *o)
{
    global_State *g = G(L);
    o->gch.marked = luaC_white(g);
    if (g->gcstate == GCSpropagate)
        reallymarkobject(g, o);  /* mark new objects as gray during propagate state. */
}


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;
}


void luaC_linkupval(lua_State *L, UpVal *uv)
{
    global_State *g = G(L);
    GCObject *o = obj2gco(uv);
    o->gch.next = g->rootgc;  /* link upvalue into `rootgc' list */
    g->rootgc = o;
    if (isgray(o))
    {
        if (g->gcstate == GCSpropagate)
        {
            gray2black(o);  /* closed upvalues need barrier */
            luaC_barrier(L, uv, uv->v);
        }
        else    /* sweep phase: sweep it (turning it into white) */
        {
            makewhite(g, o);
            lua_assert(g->gcstate != GCSfinalize && g->gcstate != GCSpause);
        }
    }
}