/*
	** $Id: lgc.c,v 2.210 2015/11/03 18:10:44 roberto Exp $
	** Garbage Collector
	** See Copyright Notice in lua.h
	*/
	
	#define lgc_c
	#define LUA_CORE
	
	#include "lprefix.h"
	
	
	#include <string.h>
	
	#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"
	
	
	/*
	** internal state for collector while inside the atomic phase. The
	** collector should never be in this state while running regular code.
	*/
	#define GCSinsideatomic		(GCSpause + 1)
	
	/*
	** cost of sweeping one element (the size of a small object divided
	** by some adjust for the sweep speed)
	*/
	#define GCSWEEPCOST	((sizeof(TString) + 4) / 4)
	
	/* maximum number of elements to sweep in each single step */
	#define GCSWEEPMAX	(cast_int((GCSTEPSIZE / GCSWEEPCOST) / 4))
	
	/* cost of calling one finalizer */
	#define GCFINALIZECOST	GCSWEEPCOST
	
	
	/*
	** macro to adjust 'stepmul': 'stepmul' is actually used like
	** 'stepmul / STEPMULADJ' (value chosen by tests)
	*/
	#define STEPMULADJ		200
	
	
	/*
	** macro to adjust 'pause': 'pause' is actually used like
	** 'pause / PAUSEADJ' (value chosen by tests)
	*/
	#define PAUSEADJ		100
	
	
	/*
	** 'makewhite' erases all color bits then sets only the current white
	** bit
	*/
	#define maskcolors	(~(bitmask(BLACKBIT) | WHITEBITS))
	#define makewhite(g,x)	\
	 (x->marked = cast_byte((x->marked & maskcolors) | luaC_white(g)))
	
	#define white2gray(x)	resetbits(x->marked, WHITEBITS)
	#define black2gray(x)	resetbit(x->marked, BLACKBIT)
	
	
	#define valiswhite(x)   (iscollectable(x) && iswhite(gcvalue(x)))
	
	#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 (iswhite(t)) reallymarkobject(g, obj2gco(t)); }
	
	/*
	** mark an object that can be NULL (either because it is really optional,
	** or it was stripped as debug info, or inside an uncompleted structure)
	*/
	#define markobjectN(g,t)	{ if (t) markobject(g,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 collectable object 'o' into list pointed by 'p'
	*/
	#define linkgclist(o,p)	((o)->gclist = (p), (p) = obj2gco(o))
	
	
	/*
	** If key is not marked, mark its entry as dead. This allows key to be
	** collected, but keeps its entry in the table.  A dead node is needed
	** when Lua looks up for a key (it may be part of a chain) and when
	** traversing a weak table (key might be removed from the table during
	** traversal). Other places never manipulate dead keys, because its
	** associated nil value is enough to signal that the entry is logically
	** empty.
	*/
	static void removeentry (Node *n) {
	  lua_assert(ttisnil(gval(n)));
	  if (valiswhite(gkey(n)))
	    setdeadvalue(wgkey(n));  /* unused and unmarked key; remove it */
	}
	
	
	/*
	** tells whether a key or value can be cleared from a weak
	** table. Non-collectable objects are never removed from weak
	** tables. Strings behave as 'values', so are never removed too. for
	** other objects: if really collected, cannot keep them; for objects
	** being finalized, keep them in keys, but not in values
	*/
	static int iscleared (global_State *g, const TValue *o) {
	  if (!iscollectable(o)) return 0;
	  else if (ttisstring(o)) {
	    markobject(g, tsvalue(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. (If in sweep phase, clear the black
	** object to white [sweep it] to avoid other barrier calls for this
	** same 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));
	  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.
	*/
	void luaC_barrierback_ (lua_State *L, Table *t) {
	  global_State *g = G(L);
	  lua_assert(isblack(t) && !isdead(g, t));
	  black2gray(t);  /* make table gray (again) */
	  linkgclist(t, g->grayagain);
	}
	
	
	/*
	** barrier for assignments to closed upvalues. Because upvalues are
	** shared among closures, it is impossible to know the color of all
	** closures pointing to it. So, we assume that the object being assigned
	** must be marked.
	*/
	void luaC_upvalbarrier_ (lua_State *L, UpVal *uv) {
	  global_State *g = G(L);
	  GCObject *o = gcvalue(uv->v);
	  lua_assert(!upisopen(uv));  /* ensured by macro luaC_upvalbarrier */
	  if (keepinvariant(g))
	    markobject(g, o);
	}
	
	
	void luaC_fix (lua_State *L, GCObject *o) {
	  global_State *g = G(L);
	  lua_assert(g->allgc == o);  /* object must be 1st in 'allgc' list! */
	  white2gray(o);  /* they will be gray forever */
	  g->allgc = o->next;  /* remove object from 'allgc' list */
	  o->next = g->fixedgc;  /* link it to 'fixedgc' list */
	  g->fixedgc = o;
	}
	
	
	/*
	** create a new collectable object (with given type and size) and link
	** it to 'allgc' list.
	*/
	GCObject *luaC_newobj (lua_State *L, int tt, size_t sz) {
	  global_State *g = G(L);
	  GCObject *o = cast(GCObject *, luaM_newobject(L, novariant(tt), sz));
	  o->marked = luaC_white(g);
	  o->tt = tt;
	  o->next = g->allgc;
	  g->allgc = o;
	  return o;
	}
	
	/* }====================================================== */
	
	
	
	/*
	** {======================================================
	** Mark functions
	** =======================================================
	*/
	
	
	/*
	** mark an object. Userdata, strings, and closed upvalues are visited
	** and turned black here. Other objects are marked gray and added
	** to appropriate list to be visited (and turned black) later. (Open
	** upvalues are already linked in 'headuv' list.)
	*/
	static void reallymarkobject (global_State *g, GCObject *o) {
	 reentry:
	  white2gray(o);
	  switch (o->tt) {
	    case LUA_TSHRSTR: {
	      gray2black(o);
	      g->GCmemtrav += sizelstring(gco2ts(o)->shrlen);
	      break;
	    }
	    case LUA_TLNGSTR: {
	      gray2black(o);
	      g->GCmemtrav += sizelstring(gco2ts(o)->u.lnglen);
	      break;
	    }
	    case LUA_TUSERDATA: {
	      TValue uvalue;
	      markobjectN(g, gco2u(o)->metatable);  /* mark its metatable */
	      gray2black(o);
	      g->GCmemtrav += sizeudata(gco2u(o));
	      getuservalue(g->mainthread, gco2u(o), &uvalue);
	      if (valiswhite(&uvalue)) {  /* markvalue(g, &uvalue); */
	        o = gcvalue(&uvalue);
	        goto reentry;
	      }
	      break;
	    }
	    case LUA_TLCL: {
	      linkgclist(gco2lcl(o), g->gray);
	      break;
	    }
	    case LUA_TCCL: {
	      linkgclist(gco2ccl(o), g->gray);
	      break;
	    }
	    case LUA_TTABLE: {
	      linkgclist(gco2t(o), g->gray);
	      break;
	    }
	    case LUA_TTHREAD: {
	      linkgclist(gco2th(o), g->gray);
	      break;
	    }
	    case LUA_TPROTO: {
	      linkgclist(gco2p(o), g->gray);
	      break;
	    }
	    default: lua_assert(0); break;
	  }
	}
	
	
	/*
	** mark metamethods for basic types
	*/
	static void markmt (global_State *g) {
	  int i;
	  for (i=0; i < LUA_NUMTAGS; i++)
	    markobjectN(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 = o->next)
	    markobject(g, o);
	}
	
	
	/*
	** Mark all values stored in marked open upvalues from non-marked threads.
	** (Values from marked threads were already marked when traversing the
	** thread.) Remove from the list threads that no longer have upvalues and
	** not-marked threads.
	*/
	static void remarkupvals (global_State *g) {
	  lua_State *thread;
	  lua_State **p = &g->twups;
	  while ((thread = *p) != NULL) {
	    lua_assert(!isblack(thread));  /* threads are never black */
	    if (isgray(thread) && thread->openupval != NULL)
	      p = &thread->twups;  /* keep marked thread with upvalues in the list */
	    else {  /* thread is not marked or without upvalues */
	      UpVal *uv;
	      *p = thread->twups;  /* remove thread from the list */
	      thread->twups = thread;  /* mark that it is out of list */
	      for (uv = thread->openupval; uv != NULL; uv = uv->u.open.next) {
	        if (uv->u.open.touched) {
	          markvalue(g, uv->v);  /* remark upvalue's value */
	          uv->u.open.touched = 0;
	        }
	      }
	    }
	  }
	}
	
	
	/*
	** mark root set and reset all gray lists, to start a new collection
	*/
	static void restartcollection (global_State *g) {
	  g->gray = g->grayagain = NULL;
	  g->weak = g->allweak = g->ephemeron = NULL;
	  markobject(g, g->mainthread);
	  markvalue(g, &g->l_registry);
	  markmt(g);
	  markbeingfnz(g);  /* mark any finalizing object left from previous cycle */
	}
	
	/* }====================================================== */
	
	
	/*
	** {======================================================
	** Traverse functions
	** =======================================================
	*/
	
	/*
	** Traverse a table with weak values and link it to proper list. During
	** propagate phase, keep it in 'grayagain' list, to be revisited in the
	** atomic phase. In the atomic phase, if table has any white value,
	** put it in 'weak' list, to be cleared.
	*/
	static void traverseweakvalue (global_State *g, Table *h) {
	  Node *n, *limit = gnodelast(h);
	  /* if there is array part, assume it may have white values (it is not
	     worth traversing it now just to check) */
	  int hasclears = (h->sizearray > 0);
	  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 */
	      if (!hasclears && iscleared(g, gval(n)))  /* is there a white value? */
	        hasclears = 1;  /* table will have to be cleared */
	    }
	  }
	  if (g->gcstate == GCSpropagate)
	    linkgclist(h, g->grayagain);  /* must retraverse it in atomic phase */
	  else if (hasclears)
	    linkgclist(h, g->weak);  /* has to be cleared later */
	}
	
	
	/*
	** Traverse an ephemeron table and link it to proper list. Returns true
	** iff any object was marked during this traversal (which implies that
	** convergence has to continue). During propagation phase, keep table
	** in 'grayagain' list, to be visited again in the atomic phase. In
	** the atomic phase, if table has any white->white entry, it has to
	** be revisited during ephemeron convergence (as that key may turn
	** black). Otherwise, if it has any white key, table has to be cleared
	** (in the atomic phase).
	*/
	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 hasww = 0;  /* true if table has entry "white-key -> white-value" */
	  Node *n, *limit = gnodelast(h);
	  unsigned int i;
	  /* traverse array part */
	  for (i = 0; i < h->sizearray; i++) {
	    if (valiswhite(&h->array[i])) {
	      marked = 1;
	      reallymarkobject(g, gcvalue(&h->array[i]));
	    }
	  }
	  /* traverse hash part */
	  for (n = gnode(h, 0); n < limit; n++) {
	    checkdeadkey(n);
	    if (ttisnil(gval(n)))  /* entry is empty? */
	      removeentry(n);  /* remove it */
	    else if (iscleared(g, gkey(n))) {  /* key is not marked (yet)? */
	      hasclears = 1;  /* table must be cleared */
	      if (valiswhite(gval(n)))  /* value not marked yet? */
	        hasww = 1;  /* white-white entry */
	    }
	    else if (valiswhite(gval(n))) {  /* value not marked yet? */
	      marked = 1;
	      reallymarkobject(g, gcvalue(gval(n)));  /* mark it now */
	    }
	  }
	  /* link table into proper list */
	  if (g->gcstate == GCSpropagate)
	    linkgclist(h, g->grayagain);  /* must retraverse it in atomic phase */
	  else if (hasww)  /* table has white->white entries? */
	    linkgclist(h, g->ephemeron);  /* have to propagate again */
	  else if (hasclears)  /* table has white keys? */
	    linkgclist(h, g->allweak);  /* may have to clean white keys */
	  return marked;
	}
	
	
	static void traversestrongtable (global_State *g, Table *h) {
	  Node *n, *limit = gnodelast(h);
	  unsigned int i;
	  for (i = 0; i < h->sizearray; i++)  /* traverse array part */
	    markvalue(g, &h->array[i]);
	  for (n = gnode(h, 0); n < limit; n++) {  /* traverse hash part */
	    checkdeadkey(n);
	    if (ttisnil(gval(n)))  /* entry is empty? */
	      removeentry(n);  /* remove it */
	    else {
	      lua_assert(!ttisnil(gkey(n)));
	      markvalue(g, gkey(n));  /* mark key */
	      markvalue(g, gval(n));  /* mark value */
	    }
	  }
	}
	
	
	static lu_mem traversetable (global_State *g, Table *h) {
	  const char *weakkey, *weakvalue;
	  const TValue *mode = gfasttm(g, h->metatable, TM_MODE);

	  markobjectN(g, h->metatable);

	  if (mode && ttisstring(mode) &&  /* is there a weak mode? */
	      ((weakkey = strchr(svalue(mode), 'k')),
	       (weakvalue = strchr(svalue(mode), 'v')),
	       (weakkey || weakvalue))) {  /* is really weak? */
	    black2gray(h);  /* keep table gray */
	    if (!weakkey)  /* strong keys? */
	      traverseweakvalue(g, h);
	    else if (!weakvalue)  /* strong values? */
	      traverseephemeron(g, h);
	    else  /* all weak */
	      linkgclist(h, g->allweak);  /* nothing to traverse now */
	  }
	  else  /* not weak */
	    traversestrongtable(g, h);
	  return sizeof(Table) + sizeof(TValue) * h->sizearray +
	                         sizeof(Node) * cast(size_t, sizenode(h));
	}
	
	
	/*
	** Traverse a prototype. (While a prototype is being build, its
	** arrays can be larger than needed; the extra slots are filled with
	** NULL, so the use of 'markobjectN')
	*/
	static int traverseproto (global_State *g, Proto *f) {
	  int i;
	  if (f->cache && iswhite(f->cache))
	    f->cache = NULL;  /* allow cache to be collected */
	  markobjectN(g, f->source);
	  for (i = 0; i < f->sizek; i++)  /* mark literals */
	    markvalue(g, &f->k[i]);
	  for (i = 0; i < f->sizeupvalues; i++)  /* mark upvalue names */
	    markobjectN(g, f->upvalues[i].name);
	  for (i = 0; i < f->sizep; i++)  /* mark nested protos */
	    markobjectN(g, f->p[i]);
	  for (i = 0; i < f->sizelocvars; i++)  /* mark local-variable names */
	    markobjectN(g, f->locvars[i].varname);
	  return sizeof(Proto) + sizeof(Instruction) * f->sizecode +
	                         sizeof(Proto *) * f->sizep +
	                         sizeof(TValue) * f->sizek +
	                         sizeof(int) * f->sizelineinfo +
	                         sizeof(LocVar) * f->sizelocvars +
	                         sizeof(Upvaldesc) * f->sizeupvalues;
	}
	
	
	static lu_mem traverseCclosure (global_State *g, CClosure *cl) {
	  int i;
	  for (i = 0; i < cl->nupvalues; i++)  /* mark its upvalues */
	    markvalue(g, &cl->upvalue[i]);
	  return sizeCclosure(cl->nupvalues);
	}
	
	/*
	** open upvalues point to values in a thread, so those values should
	** be marked when the thread is traversed except in the atomic phase
	** (because then the value cannot be changed by the thread and the
	** thread may not be traversed again)
	*/
	static lu_mem traverseLclosure (global_State *g, LClosure *cl) {
	  int i;
	  markobjectN(g, cl->p);  /* mark its prototype */
	  for (i = 0; i < cl->nupvalues; i++) {  /* mark its upvalues */
	    UpVal *uv = cl->upvals[i];
	    if (uv != NULL) {
	      if (upisopen(uv) && g->gcstate != GCSinsideatomic)
	        uv->u.open.touched = 1;  /* can be marked in 'remarkupvals' */
	      else
	        markvalue(g, uv->v);
	    }
	  }
	  return sizeLclosure(cl->nupvalues);
	}
	
	
	static lu_mem traversethread (global_State *g, lua_State *th) {
	  StkId o = th->stack;
	  if (o == NULL)
	    return 1;  /* stack not completely built yet */
	  lua_assert(g->gcstate == GCSinsideatomic ||
	             th->openupval == NULL || isintwups(th));
	  for (; o < th->top; o++)  /* mark live elements in the stack */
	    markvalue(g, o);
	  if (g->gcstate == GCSinsideatomic) {  /* final traversal? */
	    StkId lim = th->stack + th->stacksize;  /* real end of stack */
	    for (; o < lim; o++)  /* clear not-marked stack slice */
	      setnilvalue(o);
	    /* 'remarkupvals' may have removed thread from 'twups' list */ 
	    if (!isintwups(th) && th->openupval != NULL) {
	      th->twups = g->twups;  /* link it back to the list */
	      g->twups = th;
	    }
	  }
	  else if (g->gckind != KGC_EMERGENCY)
	    luaD_shrinkstack(th); /* do not change stack in emergency cycle */
	  return (sizeof(lua_State) + sizeof(TValue) * th->stacksize +
	          sizeof(CallInfo) * th->nci);
	}
	
	
	/*
	** traverse one gray object, turning it to black (except for threads,
	** which are always gray).
	*/
	static void propagatemark (global_State *g) {
	  lu_mem size;
	  GCObject *o = g->gray;
	  lua_assert(isgray(o));
	  gray2black(o);
	  switch (o->tt) {
	    case LUA_TTABLE: {
	      Table *h = gco2t(o);
	      g->gray = h->gclist;  /* remove from 'gray' list */
	      size = traversetable(g, h);
	      break;
	    }
	    case LUA_TLCL: {
	      LClosure *cl = gco2lcl(o);
	      g->gray = cl->gclist;  /* remove from 'gray' list */
	      size = traverseLclosure(g, cl);
	      break;
	    }
	    case LUA_TCCL: {
	      CClosure *cl = gco2ccl(o);
	      g->gray = cl->gclist;  /* remove from 'gray' list */
	      size = traverseCclosure(g, cl);
	      break;
	    }
	    case LUA_TTHREAD: {
	      lua_State *th = gco2th(o);
	      g->gray = th->gclist;  /* remove from 'gray' list */
	      linkgclist(th, g->grayagain);  /* insert into 'grayagain' list */
	      black2gray(o);
	      size = traversethread(g, th);
	      break;
	    }
	    case LUA_TPROTO: {
	      Proto *p = gco2p(o);
	      g->gray = p->gclist;  /* remove from 'gray' list */
	      size = traverseproto(g, p);
	      break;
	    }
	    default: lua_assert(0); return;
	  }
	  g->GCmemtrav += size;
	}
	
	
	static void propagateall (global_State *g) {
	  while (g->gray) propagatemark(g);
	}
	
	
	static void convergeephemerons (global_State *g) {
	  int changed;
	  do {
	    GCObject *w;
	    GCObject *next = g->ephemeron;  /* get ephemeron list */
	    g->ephemeron = NULL;  /* tables may return to this list when traversed */
	    changed = 0;
	    while ((w = next) != NULL) {
	      next = gco2t(w)->gclist;
	      if (traverseephemeron(g, gco2t(w))) {  /* traverse marked some value? */
	        propagateall(g);  /* propagate changes */
	        changed = 1;  /* will have to revisit all ephemeron tables */
	      }
	    }
	  } while (changed);
	}
	
	/* }====================================================== */
	
	
	/*
	** {======================================================
	** Sweep Functions
	** =======================================================
	*/
	
	
	/*
	** clear entries with unmarked keys from all weaktables in list 'l' up
	** to element 'f'
	*/
	static void clearkeys (global_State *g, GCObject *l, GCObject *f) {
	  for (; l != f; l = gco2t(l)->gclist) {
	    Table *h = gco2t(l);
	    Node *n, *limit = gnodelast(h);
	    for (n = gnode(h, 0); n < limit; n++) {
	      if (!ttisnil(gval(n)) && (iscleared(g, gkey(n)))) {
	        setnilvalue(gval(n));  /* remove value ... */
	        removeentry(n);  /* and remove entry from table */
	      }
	    }
	  }
	}
	
	
	/*
	** clear entries with unmarked values from all weaktables in list 'l' up
	** to element 'f'
	*/
	static void clearvalues (global_State *g, GCObject *l, GCObject *f) {
	  for (; l != f; l = gco2t(l)->gclist) {
	    Table *h = gco2t(l);
	    Node *n, *limit = gnodelast(h);
	    unsigned int i;
	    for (i = 0; i < h->sizearray; i++) {
	      TValue *o = &h->array[i];
	      if (iscleared(g, o))  /* value was collected? */
	        setnilvalue(o);  /* remove value */
	    }
	    for (n = gnode(h, 0); n < limit; n++) {
	      if (!ttisnil(gval(n)) && iscleared(g, gval(n))) {
	        setnilvalue(gval(n));  /* remove value ... */
	        removeentry(n);  /* and remove entry from table */
	      }
	    }
	  }
	}
	
	
	void luaC_upvdeccount (lua_State *L, UpVal *uv) {
	  lua_assert(uv->refcount > 0);
	  uv->refcount--;
	  if (uv->refcount == 0 && !upisopen(uv))
	    luaM_free(L, uv);
	}
	
	
	static void freeLclosure (lua_State *L, LClosure *cl) {
	  int i;
	  for (i = 0; i < cl->nupvalues; i++) {
	    UpVal *uv = cl->upvals[i];
	    if (uv)
	      luaC_upvdeccount(L, uv);
	  }
	  luaM_freemem(L, cl, sizeLclosure(cl->nupvalues));
	}
	
	
	static void freeobj (lua_State *L, GCObject *o) {
	  switch (o->tt) {
	    case LUA_TPROTO: luaF_freeproto(L, gco2p(o)); break;
	    case LUA_TLCL: {
	      freeLclosure(L, gco2lcl(o));
	      break;
	    }
	    case LUA_TCCL: {
	      luaM_freemem(L, o, sizeCclosure(gco2ccl(o)->nupvalues));
	      break;
	    }
	    case LUA_TTABLE: luaH_free(L, gco2t(o)); break;
	    case LUA_TTHREAD: luaE_freethread(L, gco2th(o)); break;
	    case LUA_TUSERDATA: luaM_freemem(L, o, sizeudata(gco2u(o))); break;
	    case LUA_TSHRSTR:
	      luaS_remove(L, gco2ts(o));  /* remove it from hash table */
	      luaM_freemem(L, o, sizelstring(gco2ts(o)->shrlen));
	      break;
	    case LUA_TLNGSTR: {
	      luaM_freemem(L, o, sizelstring(gco2ts(o)->u.lnglen));
	      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 at most 'count' elements from a list of GCObjects erasing dead
	** objects, where a dead object is one marked with the old (non current)
	** white; change all non-dead objects back to white, preparing for next
	** collection cycle. Return where to continue the traversal or NULL if
	** list is finished.
	*/
	static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count) {
	  global_State *g = G(L);
	  int ow = otherwhite(g);
	  int white = luaC_white(g);  /* current white */
	  while (*p != NULL && count-- > 0) {
	    GCObject *curr = *p;
	    int marked = curr->marked;
	    if (isdeadm(ow, marked)) {  /* is 'curr' dead? */
	      *p = curr->next;  /* remove 'curr' from list */
	      freeobj(L, curr);  /* erase 'curr' */
	    }
	    else {  /* change mark to 'white' */
	      curr->marked = cast_byte((marked & maskcolors) | white);
	      p = &curr->next;  /* go to next element */
	    }
	  }
	  return (*p == NULL) ? NULL : p;
	}
	
	
	/*
	** sweep a list until a live object (or end of list)
	*/
	static GCObject **sweeptolive (lua_State *L, GCObject **p, int *n) {
	  GCObject **old = p;
	  int i = 0;
	  do {
	    i++;
	    p = sweeplist(L, p, 1);
	  } while (p == old);
	  if (n) *n += i;
	  return p;
	}
	
	/* }====================================================== */
	
	
	/*
	** {======================================================
	** Finalization
	** =======================================================
	*/
	
	/*
	** If possible, shrink string table
	*/
	static void checkSizes (lua_State *L, global_State *g) {
	  if (g->gckind != KGC_EMERGENCY) {
	    l_mem olddebt = g->GCdebt;
	    if (g->strt.nuse < g->strt.size / 4)  /* string table too big? */
	      luaS_resize(L, g->strt.size / 2);  /* shrink it a little */
	    g->GCestimate += g->GCdebt - olddebt;  /* update estimate */
	  }
	}
	
	
	static GCObject *udata2finalize (global_State *g) {
	  GCObject *o = g->tobefnz;  /* get first element */
	  lua_assert(tofinalize(o));
	  g->tobefnz = o->next;  /* remove it from 'tobefnz' list */
	  o->next = g->allgc;  /* return it to 'allgc' list */
	  g->allgc = o;
	  resetbit(o->marked, FINALIZEDBIT);  /* object is "normal" again */
	  if (issweepphase(g))
	    makewhite(g, o);  /* "sweep" object */
	  return o;
	}
	
	
	static void dothecall (lua_State *L, void *ud) {
	  UNUSED(ud);
	  luaD_callnoyield(L, L->top - 2, 0);
	}
	
	
	static void GCTM (lua_State *L, int propagateerrors) {
	  global_State *g = G(L);
	  const TValue *tm;
	  TValue v;
	  setgcovalue(L, &v, udata2finalize(g));
	  tm = luaT_gettmbyobj(L, &v, TM_GC);
	  if (tm != NULL && ttisfunction(tm)) {  /* is there a finalizer? */
	    int status;
	    lu_byte oldah = L->allowhook;
	    int running  = g->gcrunning;
	    L->allowhook = 0;  /* stop debug hooks during GC metamethod */
	    g->gcrunning = 0;  /* avoid GC steps */
	    setobj2s(L, L->top, tm);  /* push finalizer... */
	    setobj2s(L, L->top + 1, &v);  /* ... and its argument */
	    L->top += 2;  /* and (next line) call the finalizer */
	    status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
	    L->allowhook = oldah;  /* restore hooks */
	    g->gcrunning = running;  /* restore state */
	    if (status != LUA_OK && propagateerrors) {  /* error while running __gc? */
	      if (status == LUA_ERRRUN) {  /* is there an error object? */
	        const char *msg = (ttisstring(L->top - 1))
	                            ? svalue(L->top - 1)
	                            : "no message";
	        luaO_pushfstring(L, "error in __gc metamethod (%s)", msg);
	        status = LUA_ERRGCMM;  /* error in __gc metamethod */
	      }
	      luaD_throw(L, status);  /* re-throw error */
	    }
	  }
	}
	
	
	/*
	** call a few (up to 'g->gcfinnum') finalizers
	*/
	static int runafewfinalizers (lua_State *L) {
	  global_State *g = G(L);
	  unsigned int i;
	  lua_assert(!g->tobefnz || g->gcfinnum > 0);
	  for (i = 0; g->tobefnz && i < g->gcfinnum; i++)
	    GCTM(L, 1);  /* call one finalizer */
	  g->gcfinnum = (!g->tobefnz) ? 0  /* nothing more to finalize? */
	                    : g->gcfinnum * 2;  /* else call a few more next time */
	  return i;
	}
	
	
	/*
	** call all pending finalizers
	*/
	static void callallpendingfinalizers (lua_State *L, int propagateerrors) {
	  global_State *g = G(L);
	  while (g->tobefnz)
	    GCTM(L, propagateerrors);
	}
	
	
	/*
	** find last 'next' field in list 'p' list (to add elements in its end)
	*/
	static GCObject **findlast (GCObject **p) {
	  while (*p != NULL)
	    p = &(*p)->next;
	  return p;
	}
	
	
	/*
	** move all unreachable objects (or 'all' objects) that need
	** finalization from list 'finobj' to list 'tobefnz' (to be finalized)
	*/
	static void separatetobefnz (global_State *g, int all) {
	  GCObject *curr;
	  GCObject **p = &g->finobj;
	  GCObject **lastnext = findlast(&g->tobefnz);
	  while ((curr = *p) != NULL) {  /* traverse all finalizable objects */
	    lua_assert(tofinalize(curr));
	    if (!(iswhite(curr) || all))  /* not being collected? */
	      p = &curr->next;  /* don't bother with it */
	    else {
	      *p = curr->next;  /* remove 'curr' from 'finobj' list */
	      curr->next = *lastnext;  /* link at the end of 'tobefnz' list */
	      *lastnext = curr;
	      lastnext = &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 (tofinalize(o) ||                 /* obj. is already marked... */
	      gfasttm(g, mt, TM_GC) == NULL)   /* or has no finalizer? */
	    return;  /* nothing to be done */
	  else {  /* move 'o' to 'finobj' list */
	    GCObject **p;
	    if (issweepphase(g)) {
	      makewhite(g, o);  /* "sweep" object 'o' */
	      if (g->sweepgc == &o->next)  /* should not remove 'sweepgc' object */
	        g->sweepgc = sweeptolive(L, g->sweepgc, NULL);  /* change 'sweepgc' */
	    }
	    /* search for pointer pointing to 'o' */
	    for (p = &g->allgc; *p != o; p = &(*p)->next) { /* empty */ }
	    *p = o->next;  /* remove 'o' from 'allgc' list */
	    o->next = g->finobj;  /* link it in 'finobj' list */
	    g->finobj = o;
	    l_setbit(o->marked, FINALIZEDBIT);  /* mark it as such */
	  }
	}
	
	/* }====================================================== */
	
	
	
	/*
	** {======================================================
	** GC control
	** =======================================================
	*/
	
	
	/*
	** Set a reasonable "time" to wait before starting a new GC cycle; cycle
	** will start when memory use hits threshold. (Division by 'estimate'
	** should be OK: it cannot be zero (because Lua cannot even start with
	** less than PAUSEADJ bytes).
	*/
	static void setpause (global_State *g) {
	  l_mem threshold, debt;
	  l_mem estimate = g->GCestimate / PAUSEADJ;  /* adjust 'estimate' */
	  lua_assert(estimate > 0);
	  threshold = (g->gcpause < MAX_LMEM / estimate)  /* overflow? */
	            ? estimate * g->gcpause  /* no overflow */
	            : MAX_LMEM;  /* overflow; truncate to maximum */
	  debt = gettotalbytes(g) - threshold;
	  luaE_setdebt(g, debt);
	}
	
	
	/*
	** Enter first sweep phase.
	** The call to 'sweeptolive' makes pointer point to an object inside
	** the list (instead of to the header), so that the real sweep do not
	** need to skip objects created between "now" and the start of the real
	** sweep.
	** Returns how many objects it swept.
	*/
	static int entersweep (lua_State *L) {
	  global_State *g = G(L);
	  int n = 0;
	  g->gcstate = GCSswpallgc;
	  lua_assert(g->sweepgc == NULL);
	  g->sweepgc = sweeptolive(L, &g->allgc, &n);
	  return n;
	}
	
	
	void luaC_freeallobjects (lua_State *L) {
	  global_State *g = G(L);
	  separatetobefnz(g, 1);  /* separate all objects with finalizers */
	  lua_assert(g->finobj == NULL);
	  callallpendingfinalizers(L, 0);
	  lua_assert(g->tobefnz == NULL);
	  g->currentwhite = WHITEBITS; /* this "white" makes all objects look dead */
	  g->gckind = KGC_NORMAL;
	  sweepwholelist(L, &g->finobj);
	  sweepwholelist(L, &g->allgc);
	  sweepwholelist(L, &g->fixedgc);  /* collect fixed objects */
	  lua_assert(g->strt.nuse == 0);
	}
	
	
	static l_mem atomic (lua_State *L) {
	  global_State *g = G(L);
	  l_mem work;
	  GCObject *origweak, *origall;
	  GCObject *grayagain = g->grayagain;  /* save original list */
	  lua_assert(g->ephemeron == NULL && g->weak == NULL);
	  lua_assert(!iswhite(g->mainthread));
	  g->gcstate = GCSinsideatomic;
	  g->GCmemtrav = 0;  /* start counting work */
	  markobject(g, L);  /* mark running thread */
	  /* registry and global metatables may be changed by API */
	  markvalue(g, &g->l_registry);
	  markmt(g);  /* mark global metatables */
	  /* remark occasional upvalues of (maybe) dead threads */
	  remarkupvals(g);
	  propagateall(g);  /* propagate changes */
	  work = g->GCmemtrav;  /* stop counting (do not recount 'grayagain') */
	  g->gray = grayagain;
	  propagateall(g);  /* traverse 'grayagain' list */
	  g->GCmemtrav = 0;  /* restart counting */
	  convergeephemerons(g);
	  /* at this point, all strongly accessible objects are marked. */
	  /* Clear values from weak tables, before checking finalizers */
	  clearvalues(g, g->weak, NULL);
	  clearvalues(g, g->allweak, NULL);
	  origweak = g->weak; origall = g->allweak;
	  work += g->GCmemtrav;  /* stop counting (objects being finalized) */
	  separatetobefnz(g, 0);  /* separate objects to be finalized */
	  g->gcfinnum = 1;  /* there may be objects to be finalized */
	  markbeingfnz(g);  /* mark objects that will be finalized */
	  propagateall(g);  /* remark, to propagate 'resurrection' */
	  g->GCmemtrav = 0;  /* restart counting */
	  convergeephemerons(g);
	  /* at this point, all resurrected objects are marked. */
	  /* remove dead objects from weak tables */
	  clearkeys(g, g->ephemeron, NULL);  /* clear keys from all ephemeron tables */
	  clearkeys(g, g->allweak, NULL);  /* clear keys from all 'allweak' tables */
	  /* clear values from resurrected weak tables */
	  clearvalues(g, g->weak, origweak);
	  clearvalues(g, g->allweak, origall);
	  luaS_clearcache(g);
	  g->currentwhite = cast_byte(otherwhite(g));  /* flip current white */
	  work += g->GCmemtrav;  /* complete counting */
	  return work;  /* estimate of memory marked by 'atomic' */
	}
	
	
	static lu_mem sweepstep (lua_State *L, global_State *g,
	                         int nextstate, GCObject **nextlist) {
	  if (g->sweepgc) {
	    l_mem olddebt = g->GCdebt;
	    g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
	    g->GCestimate += g->GCdebt - olddebt;  /* update estimate */
	    if (g->sweepgc)  /* is there still something to sweep? */
	      return (GCSWEEPMAX * GCSWEEPCOST);
	  }
	  /* else enter next state */
	  g->gcstate = nextstate;
	  g->sweepgc = nextlist;
	  return 0;
	}
	
	
	static lu_mem singlestep (lua_State *L) {
	  global_State *g = G(L);
	  switch (g->gcstate) {
	    case GCSpause: {
	      g->GCmemtrav = g->strt.size * sizeof(GCObject*);
	      restartcollection(g);
	      g->gcstate = GCSpropagate;
	      return g->GCmemtrav;
	    }
	    case GCSpropagate: {
	      g->GCmemtrav = 0;
	      lua_assert(g->gray);
	      propagatemark(g);
	       if (g->gray == NULL)  /* no more gray objects? */
	        g->gcstate = GCSatomic;  /* finish propagate phase */
	      return g->GCmemtrav;  /* memory traversed in this step */
	    }
	    case GCSatomic: {
	      lu_mem work;
	      int sw;
	      propagateall(g);  /* make sure gray list is empty */
	      work = atomic(L);  /* work is what was traversed by 'atomic' */
	      sw = entersweep(L);
	      g->GCestimate = gettotalbytes(g);  /* first estimate */;
	      return work + sw * GCSWEEPCOST;
	    }
	    case GCSswpallgc: {  /* sweep "regular" objects */
	      return sweepstep(L, g, GCSswpfinobj, &g->finobj);
	    }
	    case GCSswpfinobj: {  /* sweep objects with finalizers */
	      return sweepstep(L, g, GCSswptobefnz, &g->tobefnz);
	    }
	    case GCSswptobefnz: {  /* sweep objects to be finalized */
	      return sweepstep(L, g, GCSswpend, NULL);
	    }
	    case GCSswpend: {  /* finish sweeps */
	      makewhite(g, g->mainthread);  /* sweep main thread */
	      checkSizes(L, g);
	      g->gcstate = GCScallfin;
	      return 0;
	    }
	    case GCScallfin: {  /* call remaining finalizers */
	      if (g->tobefnz && g->gckind != KGC_EMERGENCY) {
	        int n = runafewfinalizers(L);
	        return (n * GCFINALIZECOST);
	      }
	      else {  /* emergency mode or no more finalizers */
	        g->gcstate = GCSpause;  /* finish collection */
	        return 0;
	      }
	    }
	    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);
	}
	
	
	/*
	** get GC debt and convert it from Kb to 'work units' (avoid zero debt
	** and overflows)
	*/
	static l_mem getdebt (global_State *g) {
	  l_mem debt = g->GCdebt;
	  int stepmul = g->gcstepmul;
	  if (debt <= 0) return 0;  /* minimal debt */
	  else {
	    debt = (debt / STEPMULADJ) + 1;
	    debt = (debt < MAX_LMEM / stepmul) ? debt * stepmul : MAX_LMEM;
	    return debt;
	  }
	}
	
	/*
	** performs a basic GC step when collector is running
	*/
	void luaC_step (lua_State *L) {
	  global_State *g = G(L);
	  l_mem debt = getdebt(g);  /* GC deficit (be paid now) */
	  if (!g->gcrunning) {  /* not running? */
	    luaE_setdebt(g, -GCSTEPSIZE * 10);  /* avoid being called too often */
	    return;
	  }
	  do {  /* repeat until pause or enough "credit" (negative debt) */
	    lu_mem work = singlestep(L);  /* perform one single step */
	    debt -= work;
	  } while (debt > -GCSTEPSIZE && g->gcstate != GCSpause);
	  if (g->gcstate == GCSpause)
	    setpause(g);  /* pause until next cycle */
	  else {
	    debt = (debt / g->gcstepmul) * STEPMULADJ;  /* convert 'work units' to Kb */
	    luaE_setdebt(g, debt);
	    runafewfinalizers(L);
	  }
	}
	
	
	/*
	** Performs a full GC cycle; if 'isemergency', set a flag to avoid
	** some operations which could change the interpreter state in some
	** unexpected ways (running finalizers and shrinking some structures).
	** Before running the collection, check 'keepinvariant'; if it is true,
	** there may be some objects marked as black, so the collector has
	** to sweep all objects to turn them back to white (as white has not
	** changed, nothing will be collected).
	*/
	void luaC_fullgc (lua_State *L, int isemergency) {
	  global_State *g = G(L);
	  lua_assert(g->gckind == KGC_NORMAL);
	  if (isemergency) g->gckind = KGC_EMERGENCY;  /* set flag */
	  if (keepinvariant(g)) {  /* black objects? */
	    entersweep(L); /* sweep everything to turn them back to white */
	  }
	  /* finish any pending sweep phase to start a new cycle */
	  luaC_runtilstate(L, bitmask(GCSpause));
	  luaC_runtilstate(L, ~bitmask(GCSpause));  /* start new collection */
	  luaC_runtilstate(L, bitmask(GCScallfin));  /* run up to finalizers */
	  /* estimate must be correct after a full GC cycle */
	  lua_assert(g->GCestimate == gettotalbytes(g));
	  luaC_runtilstate(L, bitmask(GCSpause));  /* finish collection */
	  g->gckind = KGC_NORMAL;
	  setpause(g);
	}
	
	/* }====================================================== */