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/*

** $Id: lgc.c,v 2.116 2011/12/02 13:18:41 roberto Exp $

** Garbage Collector

** See Copyright Notice in lua.h

*/

#include 

#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"

/* how much to allocate before next GC step */

#define GCSTEPSIZE	1024

/* maximum number of elements to sweep in each single step */

#define GCSWEEPMAX	40

/* cost of sweeping one element */

#define GCSWEEPCOST	1

/* maximum number of finalizers to call in each GC step */

#define GCFINALIZENUM	4

/* cost of marking the root set */

#define GCROOTCOST	10

/* cost of atomic step */

#define GCATOMICCOST	1000

/* basic cost to traverse one object (to be added to the links the

   object may have) */

#define TRAVCOST	5

/*

** standard negative debt for GC; a reasonable "time" to wait before

** starting a new cycle

*/

#define stddebt(g)	(-cast(l_mem, gettotalbytes(g)/100) * g->gcpause)

/*

** '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 stringmark(s)	((void)((s) && resetbits((s)->tsv.marked, WHITEBITS)))

#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 (const TValue *o) {

  if (!iscollectable(o)) return 0;

  else if (ttisstring(o)) {

    stringmark(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(isgenerational(g) || g->gcstate != GCSpause);

  lua_assert(gch(o)->tt != LUA_TTABLE);

  if (keepinvariant(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);

  GCObject *o = obj2gco(cast(char *, luaM_newobject(L, tt, sz)) + 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 and closed upvalues are visited and turned

** black here. Strings remain gray (it is the same as making them

** black). 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) {

  lua_assert(iswhite(o) && !isdead(g, o));

  white2gray(o);

  switch (gch(o)->tt) {

    case LUA_TSTRING: {

      return;  /* for strings, gray is as good as black */

    }

    case LUA_TUSERDATA: {

      Table *mt = gco2u(o)->metatable;

      markobject(g, mt);

      markobject(g, gco2u(o)->env);

      gray2black(o);  /* all pointers marked */

      return;

    }

    case LUA_TUPVAL: {

      UpVal *uv = gco2uv(o);

      markvalue(g, uv->v);

      if (uv->v == &uv->u.value)  /* closed? (open upvalues remain gray) */

        gray2black(o);  /* make it black */

      return;

    }

    case LUA_TFUNCTION: {

      gco2cl(o)->c.gclist = g->gray;

      g->gray = o;

      break;

    }

    case LUA_TTABLE: {

      linktable(gco2t(o), &g->gray);

      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);

  }

}

/*

** 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 markroot (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(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(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 int traversetable (global_State *g, Table *h) {

  const TValue *mode = gfasttm(g, h->metatable, TM_MODE);

  markobject(g, h->metatable);

  if (mode && ttisstring(mode)) {  /* is there a weak mode? */

    int weakkey = (strchr(svalue(mode), 'k') != NULL);

    int weakvalue = (strchr(svalue(mode), 'v') != NULL);

    if (weakkey || weakvalue) {  /* is really weak? */

      black2gray(obj2gco(h));  /* keep table gray */

      if (!weakkey) {  /* strong keys? */

        traverseweakvalue(g, h);

        return TRAVCOST + sizenode(h);

      }

      else if (!weakvalue) {  /* strong values? */

        traverseephemeron(g, h);

        return TRAVCOST + h->sizearray + sizenode(h);

      }

      else {

        linktable(h, &g->allweak);  /* nothing to traverse now */

        return TRAVCOST;

      }

    }  /* else go through */

  }

  traversestrongtable(g, h);

  return TRAVCOST + h->sizearray + (2 * 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 */

  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 */

    stringmark(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 */

    stringmark(f->locvars[i].varname);

  return TRAVCOST + f->sizek + f->sizeupvalues + f->sizep + f->sizelocvars;

}

static int traverseclosure (global_State *g, Closure *cl) {

  if (cl->c.isC) {

    int i;

    for (i=0; ic.nupvalues; i++)  /* mark its upvalues */

      markvalue(g, &cl->c.upvalue[i]);

  }

  else {

    int i;

    lua_assert(cl->l.nupvalues == cl->l.p->sizeupvalues);

    markobject(g, cl->l.p);  /* mark its prototype */

    for (i=0; il.nupvalues; i++)  /* mark its upvalues */

      markobject(g, cl->l.upvals[i]);

  }

  return TRAVCOST + cl->c.nupvalues;

}

static int traversestack (global_State *g, lua_State *L) {

  StkId o = L->stack;

  if (o == NULL)

    return 1;  /* stack not completely built yet */

  for (; o < L->top; o++)

    markvalue(g, o);

  if (g->gcstate == GCSatomic) {  /* final traversal? */

    StkId lim = L->stack + L->stacksize;  /* real end of stack */

    for (; o < lim; o++)  /* clear not-marked stack slice */

      setnilvalue(o);

  }

  return TRAVCOST + cast_int(o - L->stack);

}

/*

** traverse one gray object, turning it to black (except for threads,

** which are always gray).

** Returns number of values traversed.

*/

static int propagatemark (global_State *g) {

  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;

      return traversetable(g, h);

    }

    case LUA_TFUNCTION: {

      Closure *cl = gco2cl(o);

      g->gray = cl->c.gclist;

      return traverseclosure(g, cl);

    }

    case LUA_TTHREAD: {

      lua_State *th = gco2th(o);

      g->gray = th->gclist;

      th->gclist = g->grayagain;

      g->grayagain = o;

      black2gray(o);

      return traversestack(g, th);

    }

    case LUA_TPROTO: {

      Proto *p = gco2p(o);

      g->gray = p->gclist;

      return traverseproto(g, p);

    }

    default: lua_assert(0); return 0;

  }

}

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 (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(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 (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(o))  /* value was collected? */

        setnilvalue(o);  /* remove value */

    }

    for (n = gnode(h, 0); n < limit; n++) {

      if (!ttisnil(gval(n)) && iscleared(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_TFUNCTION: luaF_freeclosure(L, gco2cl(o)); 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_TSTRING: {

      G(L)->strt.nuse--;

      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 */

  l_mem debt = g->GCdebt;  /* current debt */

  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 (gch(curr)->tt == LUA_TTHREAD)

        sweepthread(L, gco2th(curr));  /* sweep thread's upvalues */

      if (testbits(marked, tostop)) {

        static GCObject *nullp = NULL;

        p = &nullp;  /* stop sweeping this list */

        break;

      }

      /* update marks */

      gch(curr)->marked = cast_byte((marked & toclear) | toset);

      p = &gch(curr)->next;  /* go to next element */

    }

  }

  luaE_setdebt(g, debt);  /* sweeping should not change debt */

  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 (!keepinvariant(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 msg.? */

        luaO_pushfstring(L, "error in __gc metamethod (%s)",

                                        lua_tostring(L, -1));

        status = LUA_ERRGCMM;  /* error in __gc metamethod */

      }

      luaD_throw(L, status);  /* re-send 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 (!(all || iswhite(curr)))  /* 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;

    for (p = &g->allgc; *p != o; p = &gch(*p)->next) ;

    *p = gch(o)->next;  /* remove 'o' from root list */

    gch(o)->next = g->finobj;  /* link it in list 'finobj' */

    g->finobj = o;

    l_setbit(gch(o)->marked, SEPARATED);  /* mark it as such */

    resetoldbit(o);  /* see MOVE OLD rule */

  }

}

/* }====================================================== */

/*

** {======================================================

** GC control

** =======================================================

*/

#define sweepphases  \

	(bitmask(GCSsweepstring) | bitmask(GCSsweepudata) | bitmask(GCSsweep))

/*

** 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->lastmajormem = 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->sweepstrgc = 0;

    g->gcstate = GCSsweepstring;

    g->gckind = KGC_NORMAL;

    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 void atomic (lua_State *L) {

  global_State *g = G(L);

  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);

  /* traverse objects caught by write barrier and by 'remarkupvals' */

  retraversegrays(g);

  convergeephemerons(g);

  /* at this point, all strongly accessible objects are marked. */

  /* clear values from weak tables, before checking finalizers */

  clearvalues(g->weak, NULL);

  clearvalues(g->allweak, NULL);

  origweak = g->weak; origall = g->allweak;

  separatetobefnz(L, 0);  /* separate objects to be finalized */

  markbeingfnz(g);  /* mark userdata that will be finalized */

  propagateall(g);  /* remark, to propagate `preserveness' */

  convergeephemerons(g);

  /* at this point, all resurrected objects are marked. */

  /* remove dead objects from weak tables */

  clearkeys(g->ephemeron, NULL);  /* clear keys from all ephemeron tables */

  clearkeys(g->allweak, NULL);  /* clear keys from all allweak tables */

  /* clear values from resurrected weak tables */

  clearvalues(g->weak, origweak);

  clearvalues(g->allweak, origall);

  g->sweepstrgc = 0;  /* prepare to sweep strings */

  g->gcstate = GCSsweepstring;

  g->currentwhite = cast_byte(otherwhite(g));  /* flip current white */

  /*lua_checkmemory(L);*/

}

static l_mem singlestep (lua_State *L) {

  global_State *g = G(L);

  switch (g->gcstate) {

    case GCSpause: {

      if (!isgenerational(g))

        markroot(g);  /* start a new collection */

      /* in any case, root must be marked */

      lua_assert(!iswhite(obj2gco(g->mainthread))

              && !iswhite(gcvalue(&g->l_registry)));

      g->gcstate = GCSpropagate;

      return GCROOTCOST;

    }

    case GCSpropagate: {

      if (g->gray)

        return propagatemark(g);

      else {  /* no more `gray' objects */

        g->gcstate = GCSatomic;  /* finish mark phase */

        atomic(L);

        return GCATOMICCOST;

      }

    }

    case GCSsweepstring: {

      if (g->sweepstrgc < g->strt.size) {

        sweepwholelist(L, &g->strt.hash[g->sweepstrgc++]);

        return GCSWEEPCOST;

      }

      else {  /* no more strings to sweep */

        g->sweepgc = &g->finobj;  /* prepare to sweep finalizable objects */

        g->gcstate = GCSsweepudata;

        return 0;

      }

    }

    case GCSsweepudata: {

      if (*g->sweepgc) {

        g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);

        return GCSWEEPMAX*GCSWEEPCOST;

      }

      else {

        g->sweepgc = &g->allgc;  /* go to next phase */

        g->gcstate = GCSsweep;

        return GCSWEEPCOST;

      }

    }

    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);

  if (g->lastmajormem == 0) {  /* signal for another major collection? */

    luaC_fullgc(L, 0);  /* perform a full regular collection */

    g->lastmajormem = gettotalbytes(g);  /* update control */

  }

  else {

    luaC_runtilstate(L, ~bitmask(GCSpause));  /* run complete cycle */

    luaC_runtilstate(L, bitmask(GCSpause));

    if (gettotalbytes(g) > g->lastmajormem/100 * g->gcmajorinc)

      g->lastmajormem = 0;  /* signal for a major collection */

  }

  luaE_setdebt(g, stddebt(g));

}

static void step (lua_State *L) {

  global_State *g = G(L);

  l_mem lim = g->gcstepmul;  /* how much to work */

  do {  /* always perform at least one single step */

    lim -= singlestep(L);

  } while (lim > 0 && g->gcstate != GCSpause);

  if (g->gcstate != GCSpause)

    luaE_setdebt(g, g->GCdebt - GCSTEPSIZE);

  else

    luaE_setdebt(g, stddebt(g));

}

/*

** performs a basic GC step even if the collector is stopped

*/

void luaC_forcestep (lua_State *L) {

  global_State *g = G(L);

  int i;

  if (isgenerational(g)) generationalcollection(L);

  else step(L);

  for (i = 0; i < GCFINALIZENUM && g->tobefnz; i++)

    GCTM(L, 1);  /* Call a few pending finalizers */

}

/*

** performs a basic GC step only if collector is running

*/

void luaC_step (lua_State *L) {

  if (G(L)->gcrunning) luaC_forcestep(L);

}

/*

** 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 */

    callallpendingfinalizers(L, 1);

  if (keepinvariant(g)) {  /* marking phase? */

    /* must sweep all objects to turn them back to white

       (as white has not changed, nothing will be collected) */

    g->sweepstrgc = 0;

    g->gcstate = GCSsweepstring;

  }

  g->gckind = isemergency ? KGC_EMERGENCY : KGC_NORMAL;

  /* finish any pending sweep phase to start a new cycle */

  luaC_runtilstate(L, bitmask(GCSpause));

  /* run entire collector */

  luaC_runtilstate(L, ~bitmask(GCSpause));

  luaC_runtilstate(L, bitmask(GCSpause));

  if (origkind == KGC_GEN) {  /* generational mode? */

    /* generational mode must always start in propagate phase */

    luaC_runtilstate(L, bitmask(GCSpropagate));

  }

  g->gckind = origkind;

  luaE_setdebt(g, stddebt(g));

  if (!isemergency)   /* do not run finalizers during emergency GC */

    callallpendingfinalizers(L, 1);

}

/* }====================================================== */