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/*

** $Id: lgc.c,v 2.38 2006/05/24 14:34:06 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"

#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) 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)

    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 */

      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;

  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);

  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(Instruction) * p->sizecode +

                             sizeof(Proto *) * p->sizep +

                             sizeof(TValue) * p->sizek + 

                             sizeof(int) * p->sizelineinfo +

                             sizeof(LocVar) * p->sizelocvars +

                             sizeof(TString *) * p->sizeupvalues;

    }

    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;

      if (curr == g->rootgc)  /* is the first element of the list? */

        g->rootgc = curr->gch.next;  /* adjust first */

      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 */

  /* 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]) 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 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: {

      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;

      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);

  l_mem lim = (GCSTEPSIZE/100) * g->gcstepmul;

  if (lim == 0)

    lim = (MAX_LUMEM-1)/2;  /* no limit */

  g->gcdept += g->totalbytes - g->GCthreshold;

  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);

  }

}

void luaC_fullgc (lua_State *L) {

  global_State *g = G(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);

}

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_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);

    }

  }

}