FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/lua/lgc.c

     /*
     ** $Id: lgc.c,v 2.140.1.3 2014/09/01 16:55:08 roberto Exp $
     ** Garbage Collector
     ** See Copyright Notice in lua.h
     */
     
     #define lgc_c
     #define LUA_CORE
     
    #include <sys/lua/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"
    
    
    
    /*
    ** 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))
    
    /* maximum number of finalizers to call in each GC step */
    #define GCFINALIZENUM   4
    
    
    /*
    ** 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 plus the old bit and then
    ** sets only the current white bit
    */
    #define maskcolors      (~(bit2mask(BLACKBIT, OLDBIT) | WHITEBITS))
    #define makewhite(g,x)  \
     (gch(x)->marked = cast_byte((gch(x)->marked & maskcolors) | luaC_white(g)))
    
    #define white2gray(x)   resetbits(gch(x)->marked, WHITEBITS)
    #define black2gray(x)   resetbit(gch(x)->marked, BLACKBIT)
    
    
    #define isfinalized(x)          testbit(gch(x)->marked, FINALIZEDBIT)
    
    #define checkdeadkey(n) lua_assert(!ttisdeadkey(gkey(n)) || ttisnil(gval(n)))
    
    
    #define checkconsistency(obj)  \
      lua_longassert(!iscollectable(obj) || righttt(obj))
    
    
    #define markvalue(g,o) { checkconsistency(o); \
      if (valiswhite(o)) reallymarkobject(g,gcvalue(o)); }
    
    #define markobject(g,t) { if ((t) && iswhite(obj2gco(t))) \
                    reallymarkobject(g, obj2gco(t)); }
    
    static void reallymarkobject (global_State *g, GCObject *o);
    
    
    /*
    ** {======================================================
    ** Generic functions
    ** =======================================================
    */
    
    
    /*
    ** one after last element in a hash array
    */
    #define gnodelast(h)    gnode(h, cast(size_t, sizenode(h)))
    
    
    /*
    ** link table 'h' into list pointed by 'p'
    */
    #define linktable(h,p)  ((h)->gclist = *(p), *(p) = obj2gco(h))
    
   
   /*
   ** if key is not marked, mark its entry as dead (therefore removing it
   ** from the table)
   */
   static void removeentry (Node *n) {
     lua_assert(ttisnil(gval(n)));
     if (valiswhite(gkey(n)))
       setdeadvalue(gkey(n));  /* unused and unmarked key; remove it */
   }
   
   
   /*
   ** tells whether a key or value can be cleared from a weak
   ** table. Non-collectable objects are never removed from weak
   ** tables. Strings behave as `values', so are never removed too. for
   ** other objects: if really collected, cannot keep them; for objects
   ** being finalized, keep them in keys, but not in values
   */
   static int iscleared (global_State *g, const TValue *o) {
     if (!iscollectable(o)) return 0;
     else if (ttisstring(o)) {
       markobject(g, rawtsvalue(o));  /* strings are `values', so are never weak */
       return 0;
     }
     else return iswhite(gcvalue(o));
   }
   
   
   /*
   ** barrier that moves collector forward, that is, mark the white object
   ** being pointed by a black object.
   */
   void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v) {
     global_State *g = G(L);
     lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
     lua_assert(g->gcstate != GCSpause);
     lua_assert(gch(o)->tt != LUA_TTABLE);
     if (keepinvariantout(g))  /* must keep invariant? */
       reallymarkobject(g, v);  /* restore invariant */
     else {  /* sweep phase */
       lua_assert(issweepphase(g));
       makewhite(g, o);  /* mark main obj. as white to avoid other barriers */
     }
   }
   
   
   /*
   ** barrier that moves collector backward, that is, mark the black object
   ** pointing to a white object as gray again. (Current implementation
   ** only works for tables; access to 'gclist' is not uniform across
   ** different types.)
   */
   void luaC_barrierback_ (lua_State *L, GCObject *o) {
     global_State *g = G(L);
     lua_assert(isblack(o) && !isdead(g, o) && gch(o)->tt == LUA_TTABLE);
     black2gray(o);  /* make object gray (again) */
     gco2t(o)->gclist = g->grayagain;
     g->grayagain = o;
   }
   
   
   /*
   ** barrier for prototypes. When creating first closure (cache is
   ** NULL), use a forward barrier; this may be the only closure of the
   ** prototype (if it is a "regular" function, with a single instance)
   ** and the prototype may be big, so it is better to avoid traversing
   ** it again. Otherwise, use a backward barrier, to avoid marking all
   ** possible instances.
   */
   LUAI_FUNC void luaC_barrierproto_ (lua_State *L, Proto *p, Closure *c) {
     global_State *g = G(L);
     lua_assert(isblack(obj2gco(p)));
     if (p->cache == NULL) {  /* first time? */
       luaC_objbarrier(L, p, c);
     }
     else {  /* use a backward barrier */
       black2gray(obj2gco(p));  /* make prototype gray (again) */
       p->gclist = g->grayagain;
       g->grayagain = obj2gco(p);
     }
   }
   
   
   /*
   ** check color (and invariants) for an upvalue that was closed,
   ** i.e., moved into the 'allgc' list
   */
   void luaC_checkupvalcolor (global_State *g, UpVal *uv) {
     GCObject *o = obj2gco(uv);
     lua_assert(!isblack(o));  /* open upvalues are never black */
     if (isgray(o)) {
       if (keepinvariant(g)) {
         resetoldbit(o);  /* see MOVE OLD rule */
         gray2black(o);  /* it is being visited now */
         markvalue(g, uv->v);
       }
       else {
         lua_assert(issweepphase(g));
         makewhite(g, o);
       }
     }
   }
   
   
   /*
   ** create a new collectable object (with given type and size) and link
   ** it to '*list'. 'offset' tells how many bytes to allocate before the
   ** object itself (used only by states).
   */
   GCObject *luaC_newobj (lua_State *L, int tt, size_t sz, GCObject **list,
                          int offset) {
     global_State *g = G(L);
     char *raw = cast(char *, luaM_newobject(L, novariant(tt), sz));
     GCObject *o = obj2gco(raw + offset);
     if (list == NULL)
       list = &g->allgc;  /* standard list for collectable objects */
     gch(o)->marked = luaC_white(g);
     gch(o)->tt = tt;
     gch(o)->next = *list;
     *list = o;
     return o;
   }
   
   /* }====================================================== */
   
   
   
   /*
   ** {======================================================
   ** Mark functions
   ** =======================================================
   */
   
   
   /*
   ** mark an object. Userdata, 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) {
     lu_mem size;
     white2gray(o);
     switch (gch(o)->tt) {
       case LUA_TSHRSTR:
       case LUA_TLNGSTR: {
         size = sizestring(gco2ts(o));
         break;  /* nothing else to mark; make it black */
       }
       case LUA_TUSERDATA: {
         Table *mt = gco2u(o)->metatable;
         markobject(g, mt);
         markobject(g, gco2u(o)->env);
         size = sizeudata(gco2u(o));
         break;
       }
       case LUA_TUPVAL: {
         UpVal *uv = gco2uv(o);
         markvalue(g, uv->v);
         if (uv->v != &uv->u.value)  /* open? */
           return;  /* open upvalues remain gray */
         size = sizeof(UpVal);
         break;
       }
       case LUA_TLCL: {
         gco2lcl(o)->gclist = g->gray;
         g->gray = o;
         return;
       }
       case LUA_TCCL: {
         gco2ccl(o)->gclist = g->gray;
         g->gray = o;
         return;
       }
       case LUA_TTABLE: {
         linktable(gco2t(o), &g->gray);
         return;
       }
       case LUA_TTHREAD: {
         gco2th(o)->gclist = g->gray;
         g->gray = o;
         return;
       }
       case LUA_TPROTO: {
         gco2p(o)->gclist = g->gray;
         g->gray = o;
         return;
       }
       default: lua_assert(0); return;
     }
     gray2black(o);
     g->GCmemtrav += size;
   }
   
   
   /*
   ** mark metamethods for basic types
   */
   static void markmt (global_State *g) {
     int i;
     for (i=0; i < LUA_NUMTAGS; i++)
       markobject(g, g->mt[i]);
   }
   
   
   /*
   ** mark all objects in list of being-finalized
   */
   static void markbeingfnz (global_State *g) {
     GCObject *o;
     for (o = g->tobefnz; o != NULL; o = gch(o)->next) {
       makewhite(g, o);
       reallymarkobject(g, o);
     }
   }
   
   
   /*
   ** mark all values stored in marked open upvalues. (See comment in
   ** 'lstate.h'.)
   */
   static void remarkupvals (global_State *g) {
     UpVal *uv;
     for (uv = g->uvhead.u.l.next; uv != &g->uvhead; uv = uv->u.l.next) {
       if (isgray(obj2gco(uv)))
         markvalue(g, uv->v);
     }
   }
   
   
   /*
   ** mark root set and reset all gray lists, to start a new
   ** incremental (or full) collection
   */
   static void 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
   ** =======================================================
   */
   
   static void traverseweakvalue (global_State *g, Table *h) {
     Node *n, *limit = gnodelast(h);
     /* if there is array part, assume it may have white values (do not
        traverse it just to check) */
     int hasclears = (h->sizearray > 0);
     for (n = gnode(h, 0); n < limit; n++) {
       checkdeadkey(n);
       if (ttisnil(gval(n)))  /* entry is empty? */
         removeentry(n);  /* remove it */
       else {
         lua_assert(!ttisnil(gkey(n)));
         markvalue(g, gkey(n));  /* mark key */
         if (!hasclears && iscleared(g, gval(n)))  /* is there a white value? */
           hasclears = 1;  /* table will have to be cleared */
       }
     }
     if (hasclears)
       linktable(h, &g->weak);  /* has to be cleared later */
     else  /* no white values */
       linktable(h, &g->grayagain);  /* no need to clean */
   }
   
   
   static int traverseephemeron (global_State *g, Table *h) {
     int marked = 0;  /* true if an object is marked in this traversal */
     int hasclears = 0;  /* true if table has white keys */
     int prop = 0;  /* true if table has entry "white-key -> white-value" */
     Node *n, *limit = gnodelast(h);
     int i;
     /* traverse array part (numeric keys are 'strong') */
     for (i = 0; i < h->sizearray; i++) {
       if (valiswhite(&h->array[i])) {
         marked = 1;
         reallymarkobject(g, gcvalue(&h->array[i]));
       }
     }
     /* traverse hash part */
     for (n = gnode(h, 0); n < limit; n++) {
       checkdeadkey(n);
       if (ttisnil(gval(n)))  /* entry is empty? */
         removeentry(n);  /* remove it */
       else if (iscleared(g, gkey(n))) {  /* key is not marked (yet)? */
         hasclears = 1;  /* table must be cleared */
         if (valiswhite(gval(n)))  /* value not marked yet? */
           prop = 1;  /* must propagate again */
       }
       else if (valiswhite(gval(n))) {  /* value not marked yet? */
         marked = 1;
         reallymarkobject(g, gcvalue(gval(n)));  /* mark it now */
       }
     }
     if (g->gcstate != GCSatomic || prop)
       linktable(h, &g->ephemeron);  /* have to propagate again */
     else if (hasclears)  /* does table have white keys? */
       linktable(h, &g->allweak);  /* may have to clean white keys */
     else  /* no white keys */
       linktable(h, &g->grayagain);  /* no need to clean */
     return marked;
   }
   
   
   static void traversestrongtable (global_State *g, Table *h) {
     Node *n, *limit = gnodelast(h);
     int i;
     for (i = 0; i < h->sizearray; i++)  /* traverse array part */
       markvalue(g, &h->array[i]);
     for (n = gnode(h, 0); n < limit; n++) {  /* traverse hash part */
       checkdeadkey(n);
       if (ttisnil(gval(n)))  /* entry is empty? */
         removeentry(n);  /* remove it */
       else {
         lua_assert(!ttisnil(gkey(n)));
         markvalue(g, gkey(n));  /* mark key */
         markvalue(g, gval(n));  /* mark value */
       }
     }
   }
   
   
   static lu_mem traversetable (global_State *g, Table *h) {
     const char *weakkey, *weakvalue;
     const TValue *mode = gfasttm(g, h->metatable, TM_MODE);
     markobject(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(obj2gco(h));  /* keep table gray */
       if (!weakkey)  /* strong keys? */
         traverseweakvalue(g, h);
       else if (!weakvalue)  /* strong values? */
         traverseephemeron(g, h);
       else  /* all weak */
         linktable(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));
   }
   
   
   static int traverseproto (global_State *g, Proto *f) {
     int i;
     if (f->cache && iswhite(obj2gco(f->cache)))
       f->cache = NULL;  /* allow cache to be collected */
     markobject(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 */
       markobject(g, f->upvalues[i].name);
     for (i = 0; i < f->sizep; i++)  /* mark nested protos */
       markobject(g, f->p[i]);
     for (i = 0; i < f->sizelocvars; i++)  /* mark local-variable names */
       markobject(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);
   }
   
   static lu_mem traverseLclosure (global_State *g, LClosure *cl) {
     int i;
     markobject(g, cl->p);  /* mark its prototype */
     for (i = 0; i < cl->nupvalues; i++)  /* mark its upvalues */
       markobject(g, cl->upvals[i]);
     return sizeLclosure(cl->nupvalues);
   }
   
   
   static lu_mem traversestack (global_State *g, lua_State *th) {
     int n = 0;
     StkId o = th->stack;
     if (o == NULL)
       return 1;  /* stack not completely built yet */
     for (; o < th->top; o++)  /* mark live elements in the stack */
       markvalue(g, o);
     if (g->gcstate == GCSatomic) {  /* final traversal? */
       StkId lim = th->stack + th->stacksize;  /* real end of stack */
       for (; o < lim; o++)  /* clear not-marked stack slice */
         setnilvalue(o);
     }
     else {  /* count call infos to compute size */
       CallInfo *ci;
       for (ci = &th->base_ci; ci != th->ci; ci = ci->next)
         n++;
     }
     return sizeof(lua_State) + sizeof(TValue) * th->stacksize +
            sizeof(CallInfo) * n;
   }
   
   
   /*
   ** 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 (gch(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 */
         th->gclist = g->grayagain;
         g->grayagain = o;  /* insert into 'grayagain' list */
         black2gray(o);
         size = traversestack(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 propagatelist (global_State *g, GCObject *l) {
     lua_assert(g->gray == NULL);  /* no grays left */
     g->gray = l;
     propagateall(g);  /* traverse all elements from 'l' */
   }
   
   /*
   ** retraverse all gray lists. Because tables may be reinserted in other
   ** lists when traversed, traverse the original lists to avoid traversing
   ** twice the same table (which is not wrong, but inefficient)
   */
   static void retraversegrays (global_State *g) {
     GCObject *weak = g->weak;  /* save original lists */
     GCObject *grayagain = g->grayagain;
     GCObject *ephemeron = g->ephemeron;
     g->weak = g->grayagain = g->ephemeron = NULL;
     propagateall(g);  /* traverse main gray list */
     propagatelist(g, grayagain);
     propagatelist(g, weak);
     propagatelist(g, ephemeron);
   }
   
   
   static void convergeephemerons (global_State *g) {
     int changed;
     do {
       GCObject *w;
       GCObject *next = g->ephemeron;  /* get ephemeron list */
       g->ephemeron = NULL;  /* tables will return to this list when traversed */
       changed = 0;
       while ((w = next) != NULL) {
         next = gco2t(w)->gclist;
         if (traverseephemeron(g, gco2t(w))) {  /* traverse marked some value? */
           propagateall(g);  /* propagate changes */
           changed = 1;  /* will have to revisit all ephemeron tables */
         }
       }
     } while (changed);
   }
   
   /* }====================================================== */
   
   
   /*
   ** {======================================================
   ** Sweep Functions
   ** =======================================================
   */
   
   
   /*
   ** clear entries with unmarked keys from all weaktables in list 'l' up
   ** to element 'f'
   */
   static void clearkeys (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);
       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 */
         }
       }
     }
   }
   
   
   static void freeobj (lua_State *L, GCObject *o) {
     switch (gch(o)->tt) {
       case LUA_TPROTO: luaF_freeproto(L, gco2p(o)); break;
       case LUA_TLCL: {
         luaM_freemem(L, o, sizeLclosure(gco2lcl(o)->nupvalues));
         break;
       }
       case LUA_TCCL: {
         luaM_freemem(L, o, sizeCclosure(gco2ccl(o)->nupvalues));
         break;
       }
       case LUA_TUPVAL: luaF_freeupval(L, gco2uv(o)); break;
       case LUA_TTABLE: luaH_free(L, gco2t(o)); break;
       case LUA_TTHREAD: luaE_freethread(L, gco2th(o)); break;
       case LUA_TUSERDATA: luaM_freemem(L, o, sizeudata(gco2u(o))); break;
       case LUA_TSHRSTR:
         G(L)->strt.nuse--;
         zfs_fallthrough;
       case LUA_TLNGSTR: {
         luaM_freemem(L, o, sizestring(gco2ts(o)));
         break;
       }
       default: lua_assert(0);
     }
   }
   
   
   #define sweepwholelist(L,p)     sweeplist(L,p,MAX_LUMEM)
   static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count);
   
   
   /*
   ** sweep the (open) upvalues of a thread and resize its stack and
   ** list of call-info structures.
   */
   static void sweepthread (lua_State *L, lua_State *L1) {
     if (L1->stack == NULL) return;  /* stack not completely built yet */
     sweepwholelist(L, &L1->openupval);  /* sweep open upvalues */
     luaE_freeCI(L1);  /* free extra CallInfo slots */
     /* should not change the stack during an emergency gc cycle */
     if (G(L)->gckind != KGC_EMERGENCY)
       luaD_shrinkstack(L1);
   }
   
   
   /*
   ** sweep at most 'count' elements from a list of GCObjects erasing dead
   ** objects, where a dead (not alive) object is one marked with the "old"
   ** (non current) white and not fixed.
   ** In non-generational mode, change all non-dead objects back to white,
   ** preparing for next collection cycle.
   ** In generational mode, keep black objects black, and also mark them as
   ** old; stop when hitting an old object, as all objects after that
   ** one will be old too.
   ** When object is a thread, sweep its list of open upvalues too.
   */
   static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count) {
     global_State *g = G(L);
     int ow = otherwhite(g);
     int toclear, toset;  /* bits to clear and to set in all live objects */
     int tostop;  /* stop sweep when this is true */
     if (isgenerational(g)) {  /* generational mode? */
       toclear = ~0;  /* clear nothing */
       toset = bitmask(OLDBIT);  /* set the old bit of all surviving objects */
       tostop = bitmask(OLDBIT);  /* do not sweep old generation */
     }
     else {  /* normal mode */
       toclear = maskcolors;  /* clear all color bits + old bit */
       toset = luaC_white(g);  /* make object white */
       tostop = 0;  /* do not stop */
     }
     while (*p != NULL && count-- > 0) {
       GCObject *curr = *p;
       int marked = gch(curr)->marked;
       if (isdeadm(ow, marked)) {  /* is 'curr' dead? */
         *p = gch(curr)->next;  /* remove 'curr' from list */
         freeobj(L, curr);  /* erase 'curr' */
       }
       else {
         if (testbits(marked, tostop))
           return NULL;  /* stop sweeping this list */
         if (gch(curr)->tt == LUA_TTHREAD)
           sweepthread(L, gco2th(curr));  /* sweep thread's upvalues */
         /* update marks */
         gch(curr)->marked = cast_byte((marked & toclear) | toset);
         p = &gch(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
   ** =======================================================
   */
   
   static void checkSizes (lua_State *L) {
     global_State *g = G(L);
     if (g->gckind != KGC_EMERGENCY) {  /* do not change sizes in emergency */
       int hs = g->strt.size / 2;  /* half the size of the string table */
       if (g->strt.nuse < cast(lu_int32, hs))  /* using less than that half? */
         luaS_resize(L, hs);  /* halve its size */
       luaZ_freebuffer(L, &g->buff);  /* free concatenation buffer */
     }
   }
   
   
   static GCObject *udata2finalize (global_State *g) {
     GCObject *o = g->tobefnz;  /* get first element */
     lua_assert(isfinalized(o));
     g->tobefnz = gch(o)->next;  /* remove it from 'tobefnz' list */
     gch(o)->next = g->allgc;  /* return it to 'allgc' list */
     g->allgc = o;
     resetbit(gch(o)->marked, SEPARATED);  /* mark that it is not in 'tobefnz' */
     lua_assert(!isold(o));  /* see MOVE OLD rule */
     if (!keepinvariantout(g))  /* not keeping invariant? */
       makewhite(g, o);  /* "sweep" object */
     return o;
   }
   
   
   static void dothecall (lua_State *L, void *ud) {
     UNUSED(ud);
     luaD_call(L, L->top - 2, 0, 0);
   }
   
   
   static void GCTM (lua_State *L, int propagateerrors) {
     global_State *g = G(L);
     const TValue *tm;
     TValue v;
     setgcovalue(L, &v, udata2finalize(g));
     tm = luaT_gettmbyobj(L, &v, TM_GC);
     if (tm != NULL && ttisfunction(tm)) {  /* is there a finalizer? */
       int status;
       lu_byte oldah = L->allowhook;
       int running  = g->gcrunning;
       L->allowhook = 0;  /* stop debug hooks during GC metamethod */
       g->gcrunning = 0;  /* avoid GC steps */
       setobj2s(L, L->top, tm);  /* push finalizer... */
       setobj2s(L, L->top + 1, &v);  /* ... and its argument */
       L->top += 2;  /* and (next line) call the finalizer */
       status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
       L->allowhook = oldah;  /* restore hooks */
       g->gcrunning = running;  /* restore state */
       if (status != LUA_OK && propagateerrors) {  /* error while running __gc? */
         if (status == LUA_ERRRUN) {  /* is there an error 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 */
       }
     }
   }
   
   
   /*
   ** move all unreachable objects (or 'all' objects) that need
   ** finalization from list 'finobj' to list 'tobefnz' (to be finalized)
   */
   static void separatetobefnz (lua_State *L, int all) {
     global_State *g = G(L);
     GCObject **p = &g->finobj;
     GCObject *curr;
     GCObject **lastnext = &g->tobefnz;
     /* find last 'next' field in 'tobefnz' list (to add elements in its end) */
     while (*lastnext != NULL)
       lastnext = &gch(*lastnext)->next;
     while ((curr = *p) != NULL) {  /* traverse all finalizable objects */
       lua_assert(!isfinalized(curr));
       lua_assert(testbit(gch(curr)->marked, SEPARATED));
       if (!(iswhite(curr) || all))  /* not being collected? */
         p = &gch(curr)->next;  /* don't bother with it */
       else {
         l_setbit(gch(curr)->marked, FINALIZEDBIT); /* won't be finalized again */
         *p = gch(curr)->next;  /* remove 'curr' from 'finobj' list */
         gch(curr)->next = *lastnext;  /* link at the end of 'tobefnz' list */
         *lastnext = curr;
         lastnext = &gch(curr)->next;
       }
     }
   }
   
   
   /*
   ** if object 'o' has a finalizer, remove it from 'allgc' list (must
   ** search the list to find it) and link it in 'finobj' list.
   */
   void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt) {
     global_State *g = G(L);
     if (testbit(gch(o)->marked, SEPARATED) || /* obj. is already separated... */
         isfinalized(o) ||                           /* ... or is finalized... */
         gfasttm(g, mt, TM_GC) == NULL)                /* or has no finalizer? */
       return;  /* nothing to be done */
     else {  /* move 'o' to 'finobj' list */
       GCObject **p;
       GCheader *ho = gch(o);
       if (g->sweepgc == &ho->next) {  /* avoid removing current sweep object */
         lua_assert(issweepphase(g));
         g->sweepgc = sweeptolive(L, g->sweepgc, NULL);
       }
       /* search for pointer pointing to 'o' */
       for (p = &g->allgc; *p != o; p = &gch(*p)->next) { /* empty */ }
       *p = ho->next;  /* remove 'o' from root list */
       ho->next = g->finobj;  /* link it in list 'finobj' */
       g->finobj = o;
       l_setbit(ho->marked, SEPARATED);  /* mark it as such */
       if (!keepinvariantout(g))  /* not keeping invariant? */
         makewhite(g, o);  /* "sweep" object */
       else
         resetoldbit(o);  /* see MOVE OLD rule */
     }
   }
   
   /* }====================================================== */
   
   
   /*
   ** {======================================================
   ** GC control
   ** =======================================================
   */
   
   
   /*
   ** set a reasonable "time" to wait before starting a new GC cycle;
   ** cycle will start when memory use hits threshold
   */
   static void setpause (global_State *g, l_mem estimate) {
     l_mem debt, threshold;
     estimate = estimate / PAUSEADJ;  /* adjust 'estimate' */
     threshold = (g->gcpause < MAX_LMEM / estimate)  /* overflow? */
               ? estimate * g->gcpause  /* no overflow */
               : MAX_LMEM;  /* overflow; truncate to maximum */
     debt = -cast(l_mem, threshold - gettotalbytes(g));
     luaE_setdebt(g, debt);
   }
   
   
   #define sweepphases  \
           (bitmask(GCSsweepstring) | bitmask(GCSsweepudata) | bitmask(GCSsweep))
   
   
   /*
   ** enter first sweep phase (strings) and prepare pointers for other
   ** sweep phases.  The calls to 'sweeptolive' make pointers 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 = GCSsweepstring;
     lua_assert(g->sweepgc == NULL && g->sweepfin == NULL);
     /* prepare to sweep strings, finalizable objects, and regular objects */
     g->sweepstrgc = 0;
     g->sweepfin = sweeptolive(L, &g->finobj, &n);
     g->sweepgc = sweeptolive(L, &g->allgc, &n);
     return n;
   }
   
   
   /*
   ** change GC mode
   */
   void luaC_changemode (lua_State *L, int mode) {
     global_State *g = G(L);
     if (mode == g->gckind) return;  /* nothing to change */
     if (mode == KGC_GEN) {  /* change to generational mode */
       /* make sure gray lists are consistent */
       luaC_runtilstate(L, bitmask(GCSpropagate));
       g->GCestimate = gettotalbytes(g);
       g->gckind = KGC_GEN;
     }
     else {  /* change to incremental mode */
       /* sweep all objects to turn them back to white
          (as white has not changed, nothing extra will be collected) */
       g->gckind = KGC_NORMAL;
       entersweep(L);
       luaC_runtilstate(L, ~sweepphases);
     }
   }
   
   
   /*
   ** call all pending finalizers
   */
   static void callallpendingfinalizers (lua_State *L, int propagateerrors) {
     global_State *g = G(L);
     while (g->tobefnz) {
       resetoldbit(g->tobefnz);
       GCTM(L, propagateerrors);
     }
   }
   
   
   void luaC_freeallobjects (lua_State *L) {
     global_State *g = G(L);
     int i;
     separatetobefnz(L, 1);  /* separate all objects with finalizers */
     lua_assert(g->finobj == NULL);
     callallpendingfinalizers(L, 0);
     g->currentwhite = WHITEBITS; /* this "white" makes all objects look dead */
     g->gckind = KGC_NORMAL;
     sweepwholelist(L, &g->finobj);  /* finalizers can create objs. in 'finobj' */
     sweepwholelist(L, &g->allgc);
     for (i = 0; i < g->strt.size; i++)  /* free all string lists */
       sweepwholelist(L, &g->strt.hash[i]);
     lua_assert(g->strt.nuse == 0);
   }
   
   
   static l_mem atomic (lua_State *L) {
     global_State *g = G(L);
     l_mem work = -cast(l_mem, g->GCmemtrav);  /* start counting work */
    GCObject *origweak, *origall;
    lua_assert(!iswhite(obj2gco(g->mainthread)));
    markobject(g, L);  /* mark running thread */
    /* registry and global metatables may be changed by API */
    markvalue(g, &g->l_registry);
    markmt(g);  /* mark basic metatables */
    /* remark occasional upvalues of (maybe) dead threads */
    remarkupvals(g);
    propagateall(g);  /* propagate changes */
    work += g->GCmemtrav;  /* stop counting (do not (re)count grays) */
    /* traverse objects caught by write barrier and by 'remarkupvals' */
    retraversegrays(g);
    work -= g->GCmemtrav;  /* 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(L, 0);  /* separate objects to be finalized */
    markbeingfnz(g);  /* mark objects that will be finalized */
    propagateall(g);  /* remark, to propagate `preserveness' */
    work -= g->GCmemtrav;  /* 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);
    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 singlestep (lua_State *L) {
    global_State *g = G(L);
    switch (g->gcstate) {
      case GCSpause: {
        /* start to count memory traversed */
        g->GCmemtrav = g->strt.size * sizeof(GCObject*);
        lua_assert(!isgenerational(g));
        restartcollection(g);
        g->gcstate = GCSpropagate;
        return g->GCmemtrav;
      }
      case GCSpropagate: {
        if (g->gray) {
          lu_mem oldtrav = g->GCmemtrav;
          propagatemark(g);
          return g->GCmemtrav - oldtrav;  /* memory traversed in this step */
        }
        else {  /* no more `gray' objects */
          lu_mem work;
          int sw;
          g->gcstate = GCSatomic;  /* finish mark phase */
          g->GCestimate = g->GCmemtrav;  /* save what was counted */
          work = atomic(L);  /* add what was traversed by 'atomic' */
          g->GCestimate += work;  /* estimate of total memory traversed */
          sw = entersweep(L);
          return work + sw * GCSWEEPCOST;
        }
      }
      case GCSsweepstring: {
        int i;
        for (i = 0; i < GCSWEEPMAX && g->sweepstrgc + i < g->strt.size; i++)
          sweepwholelist(L, &g->strt.hash[g->sweepstrgc + i]);
        g->sweepstrgc += i;
        if (g->sweepstrgc >= g->strt.size)  /* no more strings to sweep? */
          g->gcstate = GCSsweepudata;
        return i * GCSWEEPCOST;
      }
      case GCSsweepudata: {
        if (g->sweepfin) {
          g->sweepfin = sweeplist(L, g->sweepfin, GCSWEEPMAX);
          return GCSWEEPMAX*GCSWEEPCOST;
        }
        else {
          g->gcstate = GCSsweep;
          return 0;
        }
      }
      case GCSsweep: {
        if (g->sweepgc) {
          g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
          return GCSWEEPMAX*GCSWEEPCOST;
        }
        else {
          /* sweep main thread */
          GCObject *mt = obj2gco(g->mainthread);
          sweeplist(L, &mt, 1);
          checkSizes(L);
          g->gcstate = GCSpause;  /* finish collection */
          return GCSWEEPCOST;
        }
      }
      default: lua_assert(0); return 0;
    }
  }
  
  
  /*
  ** advances the garbage collector until it reaches a state allowed
  ** by 'statemask'
  */
  void luaC_runtilstate (lua_State *L, int statesmask) {
    global_State *g = G(L);
    while (!testbit(statesmask, g->gcstate))
      singlestep(L);
  }
  
  
  static void generationalcollection (lua_State *L) {
    global_State *g = G(L);
    lua_assert(g->gcstate == GCSpropagate);
    if (g->GCestimate == 0) {  /* signal for another major collection? */
      luaC_fullgc(L, 0);  /* perform a full regular collection */
      g->GCestimate = gettotalbytes(g);  /* update control */
    }
    else {
      lu_mem estimate = g->GCestimate;
      luaC_runtilstate(L, bitmask(GCSpause));  /* run complete (minor) cycle */
      g->gcstate = GCSpropagate;  /* skip restart */
      if (gettotalbytes(g) > (estimate / 100) * g->gcmajorinc)
        g->GCestimate = 0;  /* signal for a major collection */
      else
        g->GCestimate = estimate;  /* keep estimate from last major coll. */
  
    }
    setpause(g, gettotalbytes(g));
    lua_assert(g->gcstate == GCSpropagate);
  }
  
  
  static void incstep (lua_State *L) {
    global_State *g = G(L);
    l_mem debt = g->GCdebt;
    int stepmul = g->gcstepmul;
    if (stepmul < 40) stepmul = 40;  /* avoid ridiculous low values (and 0) */
    /* convert debt from Kb to 'work units' (avoid zero debt and overflows) */
    debt = (debt / STEPMULADJ) + 1;
    debt = (debt < MAX_LMEM / stepmul) ? debt * stepmul : MAX_LMEM;
    do {  /* always perform at least one single step */
      lu_mem work = singlestep(L);  /* do some work */
      debt -= work;
    } while (debt > -GCSTEPSIZE && g->gcstate != GCSpause);
    if (g->gcstate == GCSpause)
      setpause(g, g->GCestimate);  /* pause until next cycle */
    else {
      debt = (debt / stepmul) * STEPMULADJ;  /* convert 'work units' to Kb */
      luaE_setdebt(g, debt);
    }
  }
  
  
  /*
  ** performs a basic GC step
  */
  void luaC_forcestep (lua_State *L) {
    global_State *g = G(L);
    int i;
    if (isgenerational(g)) generationalcollection(L);
    else incstep(L);
    /* run a few finalizers (or all of them at the end of a collect cycle) */
    for (i = 0; g->tobefnz && (i < GCFINALIZENUM || g->gcstate == GCSpause); i++)
      GCTM(L, 1);  /* call one finalizer */
  }
  
  
  /*
  ** performs a basic GC step only if collector is running
  */
  void luaC_step (lua_State *L) {
    global_State *g = G(L);
    if (g->gcrunning) luaC_forcestep(L);
    else luaE_setdebt(g, -GCSTEPSIZE);  /* avoid being called too often */
  }
  
  
  
  /*
  ** performs a full GC cycle; if "isemergency", does not call
  ** finalizers (which could change stack positions)
  */
  void luaC_fullgc (lua_State *L, int isemergency) {
    global_State *g = G(L);
    int origkind = g->gckind;
    lua_assert(origkind != KGC_EMERGENCY);
    if (isemergency)  /* do not run finalizers during emergency GC */
      g->gckind = KGC_EMERGENCY;
    else {
      g->gckind = KGC_NORMAL;
      callallpendingfinalizers(L, 1);
    }
    if (keepinvariant(g)) {  /* may there be some black objects? */
      /* must sweep all objects to turn them back to white
         (as white has not changed, nothing will be collected) */
      entersweep(L);
    }
    /* 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(GCSpause));  /* run entire collection */
    if (origkind == KGC_GEN) {  /* generational mode? */
      /* generational mode must be kept in propagate phase */
      luaC_runtilstate(L, bitmask(GCSpropagate));
    }
    g->gckind = origkind;
    setpause(g, gettotalbytes(g));
    if (!isemergency)   /* do not run finalizers during emergency GC */
      callallpendingfinalizers(L, 1);
  }
  
  /* }====================================================== */

Cache object: 2a889b6873957882dc20d3fcb850978a