text: /*
  ** $Id: lgc.c,v 2.205 2015/03/25 13:42:19 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 (therefore removing it
  ** from the table)
  */
  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);
  }
  
  
  /*
  ** 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, free concatenation buffer and shrink string table
  */
  static void checkSizes(lua_State *L, global_State *g) {
  	if (g->gckind != KGC_EMERGENCY) {
  		l_mem olddebt = g->GCdebt;
  		luaZ_freebuffer(L, &g->buff);  /* free concatenation buffer */
  		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_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 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;
  	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);
  }
  
  /* }====================================================== */
  
  
  