adjust some folder levels.

1 files changed, 1728 insertions, 0 deletions

diff --git a/src/3rdParty/lua/lgc.c b/src/3rdParty/lua/lgc.c
new file mode 100644
index 0000000..b360eed
--- /dev/null
+++ b/src/3rdParty/lua/lgc.c
@@ -0,0 +1,1728 @@
+/*
+** $Id: lgc.c $
+** Garbage Collector
+** See Copyright Notice in lua.h
+*/
+
+#define lgc_c
+#define LUA_CORE
+
+#include "lprefix.h"
+
+#include <stdio.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"
+
+
+/*
+** Maximum number of elements to sweep in each single step.
+** (Large enough to dissipate fixed overheads but small enough
+** to allow small steps for the collector.)
+*/
+#define GCSWEEPMAX      100
+
+/*
+** Maximum number of finalizers to call in each single step.
+*/
+#define GCFINMAX        10
+
+
+/*
+** Cost of calling one finalizer.
+*/
+#define GCFINALIZECOST  50
+
+
+/*
+** The equivalent, in bytes, of one unit of "work" (visiting a slot,
+** sweeping an object, etc.)
+*/
+#define WORK2MEM        sizeof(TValue)
+
+
+/*
+** macro to adjust 'pause': 'pause' is actually used like
+** 'pause / PAUSEADJ' (value chosen by tests)
+*/
+#define PAUSEADJ                100
+
+
+/* mask with all color bits */
+#define maskcolors      (bitmask(BLACKBIT) | WHITEBITS)
+
+/* mask with all GC bits */
+#define maskgcbits      (maskcolors | AGEBITS)
+
+
+/* macro to erase all color bits then set only the current white bit */
+#define makewhite(g,x)  \
+  (x->marked = cast_byte((x->marked & ~maskcolors) | luaC_white(g)))
+
+/* make an object gray (neither white nor black) */
+#define set2gray(x)     resetbits(x->marked, maskcolors)
+
+
+/* make an object black (coming from any color) */
+#define set2black(x)  \
+  (x->marked = cast_byte((x->marked & ~WHITEBITS) | bitmask(BLACKBIT)))
+
+
+#define valiswhite(x)   (iscollectable(x) && iswhite(gcvalue(x)))
+
+#define keyiswhite(n)   (keyiscollectable(n) && iswhite(gckey(n)))
+
+
+/*
+** Protected access to objects in values
+*/
+#define gcvalueN(o)     (iscollectable(o) ? gcvalue(o) : NULL)
+
+
+#define markvalue(g,o) { checkliveness(g->mainthread,o); \
+  if (valiswhite(o)) reallymarkobject(g,gcvalue(o)); }
+
+#define markkey(g, n)   { if keyiswhite(n) reallymarkobject(g,gckey(n)); }
+
+#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);
+static lu_mem atomic (lua_State *L);
+static void entersweep (lua_State *L);
+
+
+/*
+** {======================================================
+** Generic functions
+** =======================================================
+*/
+
+
+/*
+** one after last element in a hash array
+*/
+#define gnodelast(h)    gnode(h, cast_sizet(sizenode(h)))
+
+
+static GCObject **getgclist (GCObject *o) {
+  switch (o->tt) {
+    case LUA_VTABLE: return &gco2t(o)->gclist;
+    case LUA_VLCL: return &gco2lcl(o)->gclist;
+    case LUA_VCCL: return &gco2ccl(o)->gclist;
+    case LUA_VTHREAD: return &gco2th(o)->gclist;
+    case LUA_VPROTO: return &gco2p(o)->gclist;
+    case LUA_VUSERDATA: {
+      Udata *u = gco2u(o);
+      lua_assert(u->nuvalue > 0);
+      return &u->gclist;
+    }
+    default: lua_assert(0); return 0;
+  }
+}
+
+
+/*
+** Link a collectable object 'o' with a known type into the list 'p'.
+** (Must be a macro to access the 'gclist' field in different types.)
+*/
+#define linkgclist(o,p) linkgclist_(obj2gco(o), &(o)->gclist, &(p))
+
+static void linkgclist_ (GCObject *o, GCObject **pnext, GCObject **list) {
+  lua_assert(!isgray(o));  /* cannot be in a gray list */
+  *pnext = *list;
+  *list = o;
+  set2gray(o);  /* now it is */
+}
+
+
+/*
+** Link a generic collectable object 'o' into the list 'p'.
+*/
+#define linkobjgclist(o,p) linkgclist_(obj2gco(o), getgclist(o), &(p))
+
+
+
+/*
+** Clear keys for empty entries in tables. If entry is empty, mark its
+** entry as dead. This allows the collection of the key, but keeps its
+** entry in the table: its removal could break a chain and could break
+** a table traversal.  Other places never manipulate dead keys, because
+** its associated empty value is enough to signal that the entry is
+** logically empty.
+*/
+static void clearkey (Node *n) {
+  lua_assert(isempty(gval(n)));
+  if (keyiscollectable(n))
+    setdeadkey(n);  /* unused 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 GCObject *o) {
+  if (o == NULL) return 0;  /* non-collectable value */
+  else if (novariant(o->tt) == LUA_TSTRING) {
+    markobject(g, o);  /* strings are 'values', so are never weak */
+    return 0;
+  }
+  else return iswhite(o);
+}
+
+
+/*
+** Barrier that moves collector forward, that is, marks the white object
+** 'v' being pointed by the black object 'o'.  In the generational
+** mode, 'v' must also become old, if 'o' is old; however, it cannot
+** be changed directly to OLD, because it may still point to non-old
+** objects. So, it is marked as OLD0. In the next cycle it will become
+** OLD1, and in the next it will finally become OLD (regular old). By
+** then, any object it points to will also be old.  If called in the
+** incremental sweep phase, it clears the black object to white (sweep
+** it) to avoid other barrier calls for this same object. (That cannot
+** be done is generational mode, as its sweep does not distinguish
+** whites from deads.)
+*/
+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 */
+    if (isold(o)) {
+      lua_assert(!isold(v));  /* white object could not be old */
+      setage(v, G_OLD0);  /* restore generational invariant */
+    }
+  }
+  else {  /* sweep phase */
+    lua_assert(issweepphase(g));
+    if (g->gckind == KGC_INC)  /* incremental mode? */
+      makewhite(g, o);  /* mark 'o' 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, GCObject *o) {
+  global_State *g = G(L);
+  lua_assert(isblack(o) && !isdead(g, o));
+  lua_assert((g->gckind == KGC_GEN) == (isold(o) && getage(o) != G_TOUCHED1));
+  if (getage(o) == G_TOUCHED2)  /* already in gray list? */
+    set2gray(o);  /* make it gray to become touched1 */
+  else  /* link it in 'grayagain' and paint it gray */
+    linkobjgclist(o, g->grayagain);
+  if (isold(o))  /* generational mode? */
+    setage(o, G_TOUCHED1);  /* touched in current cycle */
+}
+
+
+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! */
+  set2gray(o);  /* they will be gray forever */
+  setage(o, G_OLD);  /* and old 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 with no user values, strings, and closed
+** upvalues are visited and turned black here.  Open upvalues are
+** already indirectly linked through their respective threads in the
+** 'twups' list, so they don't go to the gray list; nevertheless, they
+** are kept gray to avoid barriers, as their values will be revisited
+** by the thread or by 'remarkupvals'.  Other objects are added to the
+** gray list to be visited (and turned black) later.  Both userdata and
+** upvalues can call this function recursively, but this recursion goes
+** for at most two levels: An upvalue cannot refer to another upvalue
+** (only closures can), and a userdata's metatable must be a table.
+*/
+static void reallymarkobject (global_State *g, GCObject *o) {
+  switch (o->tt) {
+    case LUA_VSHRSTR:
+    case LUA_VLNGSTR: {
+      set2black(o);  /* nothing to visit */
+      break;
+    }
+    case LUA_VUPVAL: {
+      UpVal *uv = gco2upv(o);
+      if (upisopen(uv))
+        set2gray(uv);  /* open upvalues are kept gray */
+      else
+        set2black(uv);  /* closed upvalues are visited here */
+      markvalue(g, uv->v);  /* mark its content */
+      break;
+    }
+    case LUA_VUSERDATA: {
+      Udata *u = gco2u(o);
+      if (u->nuvalue == 0) {  /* no user values? */
+        markobjectN(g, u->metatable);  /* mark its metatable */
+        set2black(u);  /* nothing else to mark */
+        break;
+      }
+      /* else... */
+    }  /* FALLTHROUGH */
+    case LUA_VLCL: case LUA_VCCL: case LUA_VTABLE:
+    case LUA_VTHREAD: case LUA_VPROTO: {
+      linkobjgclist(o, g->gray);  /* to be visited later */
+      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 lu_mem markbeingfnz (global_State *g) {
+  GCObject *o;
+  lu_mem count = 0;
+  for (o = g->tobefnz; o != NULL; o = o->next) {
+    count++;
+    markobject(g, o);
+  }
+  return count;
+}
+
+
+/*
+** For each non-marked thread, simulates a barrier between each open
+** upvalue and its value. (If the thread is collected, the value will be
+** assigned to the upvalue, but then it can be too late for the barrier
+** to act. The "barrier" does not need to check colors: A non-marked
+** thread must be young; upvalues cannot be older than their threads; so
+** any visited upvalue must be young too.) Also removes the thread from
+** the list, as it was already visited. Removes also threads with no
+** upvalues, as they have nothing to be checked. (If the thread gets an
+** upvalue later, it will be linked in the list again.)
+*/
+static int remarkupvals (global_State *g) {
+  lua_State *thread;
+  lua_State **p = &g->twups;
+  int work = 0;  /* estimate of how much work was done here */
+  while ((thread = *p) != NULL) {
+    work++;
+    if (!iswhite(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;
+      lua_assert(!isold(thread) || thread->openupval == NULL);
+      *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) {
+        lua_assert(getage(uv) <= getage(thread));
+        work++;
+        if (!iswhite(uv)) {  /* upvalue already visited? */
+          lua_assert(upisopen(uv) && isgray(uv));
+          markvalue(g, uv->v);  /* mark its value */
+        }
+      }
+    }
+  }
+  return work;
+}
+
+
+static void cleargraylists (global_State *g) {
+  g->gray = g->grayagain = NULL;
+  g->weak = g->allweak = g->ephemeron = NULL;
+}
+
+
+/*
+** mark root set and reset all gray lists, to start a new collection
+*/
+static void restartcollection (global_State *g) {
+  cleargraylists(g);
+  markobject(g, g->mainthread);
+  markvalue(g, &g->l_registry);
+  markmt(g);
+  markbeingfnz(g);  /* mark any finalizing object left from previous cycle */
+}
+
+/* }====================================================== */
+
+
+/*
+** {======================================================
+** Traverse functions
+** =======================================================
+*/
+
+
+/*
+** Check whether object 'o' should be kept in the 'grayagain' list for
+** post-processing by 'correctgraylist'. (It could put all old objects
+** in the list and leave all the work to 'correctgraylist', but it is
+** more efficient to avoid adding elements that will be removed.) Only
+** TOUCHED1 objects need to be in the list. TOUCHED2 doesn't need to go
+** back to a gray list, but then it must become OLD. (That is what
+** 'correctgraylist' does when it finds a TOUCHED2 object.)
+*/
+static void genlink (global_State *g, GCObject *o) {
+  lua_assert(isblack(o));
+  if (getage(o) == G_TOUCHED1) {  /* touched in this cycle? */
+    linkobjgclist(o, g->grayagain);  /* link it back in 'grayagain' */
+  }  /* everything else do not need to be linked back */
+  else if (getage(o) == G_TOUCHED2)
+    changeage(o, G_TOUCHED2, G_OLD);  /* advance age */
+}
+
+
+/*
+** 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->alimit > 0);
+  for (n = gnode(h, 0); n < limit; n++) {  /* traverse hash part */
+    if (isempty(gval(n)))  /* entry is empty? */
+      clearkey(n);  /* clear its key */
+    else {
+      lua_assert(!keyisnil(n));
+      markkey(g, n);
+      if (!hasclears && iscleared(g, gcvalueN(gval(n))))  /* a white value? */
+        hasclears = 1;  /* table will have to be cleared */
+    }
+  }
+  if (g->gcstate == GCSatomic && hasclears)
+    linkgclist(h, g->weak);  /* has to be cleared later */
+  else
+    linkgclist(h, g->grayagain);  /* must retraverse it in atomic phase */
+}
+
+
+/*
+** 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). In generational mode, some tables
+** must be kept in some gray list for post-processing; this is done
+** by 'genlink'.
+*/
+static int traverseephemeron (global_State *g, Table *h, int inv) {
+  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" */
+  unsigned int i;
+  unsigned int asize = luaH_realasize(h);
+  unsigned int nsize = sizenode(h);
+  /* traverse array part */
+  for (i = 0; i < asize; i++) {
+    if (valiswhite(&h->array[i])) {
+      marked = 1;
+      reallymarkobject(g, gcvalue(&h->array[i]));
+    }
+  }
+  /* traverse hash part; if 'inv', traverse descending
+     (see 'convergeephemerons') */
+  for (i = 0; i < nsize; i++) {
+    Node *n = inv ? gnode(h, nsize - 1 - i) : gnode(h, i);
+    if (isempty(gval(n)))  /* entry is empty? */
+      clearkey(n);  /* clear its key */
+    else if (iscleared(g, gckeyN(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 */
+  else
+    genlink(g, obj2gco(h));  /* check whether collector still needs to see it */
+  return marked;
+}
+
+
+static void traversestrongtable (global_State *g, Table *h) {
+  Node *n, *limit = gnodelast(h);
+  unsigned int i;
+  unsigned int asize = luaH_realasize(h);
+  for (i = 0; i < asize; i++)  /* traverse array part */
+    markvalue(g, &h->array[i]);
+  for (n = gnode(h, 0); n < limit; n++) {  /* traverse hash part */
+    if (isempty(gval(n)))  /* entry is empty? */
+      clearkey(n);  /* clear its key */
+    else {
+      lua_assert(!keyisnil(n));
+      markkey(g, n);
+      markvalue(g, gval(n));
+    }
+  }
+  genlink(g, obj2gco(h));
+}
+
+
+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? */
+      (cast_void(weakkey = strchr(svalue(mode), 'k')),
+       cast_void(weakvalue = strchr(svalue(mode), 'v')),
+       (weakkey || weakvalue))) {  /* is really weak? */
+    if (!weakkey)  /* strong keys? */
+      traverseweakvalue(g, h);
+    else if (!weakvalue)  /* strong values? */
+      traverseephemeron(g, h, 0);
+    else  /* all weak */
+      linkgclist(h, g->allweak);  /* nothing to traverse now */
+  }
+  else  /* not weak */
+    traversestrongtable(g, h);
+  return 1 + h->alimit + 2 * allocsizenode(h);
+}
+
+
+static int traverseudata (global_State *g, Udata *u) {
+  int i;
+  markobjectN(g, u->metatable);  /* mark its metatable */
+  for (i = 0; i < u->nuvalue; i++)
+    markvalue(g, &u->uv[i].uv);
+  genlink(g, obj2gco(u));
+  return 1 + u->nuvalue;
+}
+
+
+/*
+** 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;
+  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 1 + f->sizek + f->sizeupvalues + f->sizep + f->sizelocvars;
+}
+
+
+static int traverseCclosure (global_State *g, CClosure *cl) {
+  int i;
+  for (i = 0; i < cl->nupvalues; i++)  /* mark its upvalues */
+    markvalue(g, &cl->upvalue[i]);
+  return 1 + cl->nupvalues;
+}
+
+/*
+** Traverse a Lua closure, marking its prototype and its upvalues.
+** (Both can be NULL while closure is being created.)
+*/
+static int traverseLclosure (global_State *g, LClosure *cl) {
+  int i;
+  markobjectN(g, cl->p);  /* mark its prototype */
+  for (i = 0; i < cl->nupvalues; i++) {  /* visit its upvalues */
+    UpVal *uv = cl->upvals[i];
+    markobjectN(g, uv);  /* mark upvalue */
+  }
+  return 1 + cl->nupvalues;
+}
+
+
+/*
+** Traverse a thread, marking the elements in the stack up to its top
+** and cleaning the rest of the stack in the final traversal. That
+** ensures that the entire stack have valid (non-dead) objects.
+** Threads have no barriers. In gen. mode, old threads must be visited
+** at every cycle, because they might point to young objects.  In inc.
+** mode, the thread can still be modified before the end of the cycle,
+** and therefore it must be visited again in the atomic phase. To ensure
+** these visits, threads must return to a gray list if they are not new
+** (which can only happen in generational mode) or if the traverse is in
+** the propagate phase (which can only happen in incremental mode).
+*/
+static int traversethread (global_State *g, lua_State *th) {
+  UpVal *uv;
+  StkId o = th->stack;
+  if (isold(th) || g->gcstate == GCSpropagate)
+    linkgclist(th, g->grayagain);  /* insert into 'grayagain' list */
+  if (o == NULL)
+    return 1;  /* stack not completely built yet */
+  lua_assert(g->gcstate == GCSatomic ||
+             th->openupval == NULL || isintwups(th));
+  for (; o < th->top; o++)  /* mark live elements in the stack */
+    markvalue(g, s2v(o));
+  for (uv = th->openupval; uv != NULL; uv = uv->u.open.next)
+    markobject(g, uv);  /* open upvalues cannot be collected */
+  if (g->gcstate == GCSatomic) {  /* final traversal? */
+    for (; o < th->stack_last + EXTRA_STACK; o++)
+      setnilvalue(s2v(o));  /* clear dead stack slice */
+    /* '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->gcemergency)
+    luaD_shrinkstack(th); /* do not change stack in emergency cycle */
+  return 1 + stacksize(th);
+}
+
+
+/*
+** traverse one gray object, turning it to black.
+*/
+static lu_mem propagatemark (global_State *g) {
+  GCObject *o = g->gray;
+  nw2black(o);
+  g->gray = *getgclist(o);  /* remove from 'gray' list */
+  switch (o->tt) {
+    case LUA_VTABLE: return traversetable(g, gco2t(o));
+    case LUA_VUSERDATA: return traverseudata(g, gco2u(o));
+    case LUA_VLCL: return traverseLclosure(g, gco2lcl(o));
+    case LUA_VCCL: return traverseCclosure(g, gco2ccl(o));
+    case LUA_VPROTO: return traverseproto(g, gco2p(o));
+    case LUA_VTHREAD: return traversethread(g, gco2th(o));
+    default: lua_assert(0); return 0;
+  }
+}
+
+
+static lu_mem propagateall (global_State *g) {
+  lu_mem tot = 0;
+  while (g->gray)
+    tot += propagatemark(g);
+  return tot;
+}
+
+
+/*
+** Traverse all ephemeron tables propagating marks from keys to values.
+** Repeat until it converges, that is, nothing new is marked. 'dir'
+** inverts the direction of the traversals, trying to speed up
+** convergence on chains in the same table.
+**
+*/
+static void convergeephemerons (global_State *g) {
+  int changed;
+  int dir = 0;
+  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) {  /* for each ephemeron table */
+      Table *h = gco2t(w);
+      next = h->gclist;  /* list is rebuilt during loop */
+      nw2black(h);  /* out of the list (for now) */
+      if (traverseephemeron(g, h, dir)) {  /* marked some value? */
+        propagateall(g);  /* propagate changes */
+        changed = 1;  /* will have to revisit all ephemeron tables */
+      }
+    }
+    dir = !dir;  /* invert direction next time */
+  } while (changed);  /* repeat until no more changes */
+}
+
+/* }====================================================== */
+
+
+/*
+** {======================================================
+** Sweep Functions
+** =======================================================
+*/
+
+
+/*
+** clear entries with unmarked keys from all weaktables in list 'l'
+*/
+static void clearbykeys (global_State *g, GCObject *l) {
+  for (; l; l = gco2t(l)->gclist) {
+    Table *h = gco2t(l);
+    Node *limit = gnodelast(h);
+    Node *n;
+    for (n = gnode(h, 0); n < limit; n++) {
+      if (iscleared(g, gckeyN(n)))  /* unmarked key? */
+        setempty(gval(n));  /* remove entry */
+      if (isempty(gval(n)))  /* is entry empty? */
+        clearkey(n);  /* clear its key */
+    }
+  }
+}
+
+
+/*
+** clear entries with unmarked values from all weaktables in list 'l' up
+** to element 'f'
+*/
+static void clearbyvalues (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;
+    unsigned int asize = luaH_realasize(h);
+    for (i = 0; i < asize; i++) {
+      TValue *o = &h->array[i];
+      if (iscleared(g, gcvalueN(o)))  /* value was collected? */
+        setempty(o);  /* remove entry */
+    }
+    for (n = gnode(h, 0); n < limit; n++) {
+      if (iscleared(g, gcvalueN(gval(n))))  /* unmarked value? */
+        setempty(gval(n));  /* remove entry */
+      if (isempty(gval(n)))  /* is entry empty? */
+        clearkey(n);  /* clear its key */
+    }
+  }
+}
+
+
+static void freeupval (lua_State *L, UpVal *uv) {
+  if (upisopen(uv))
+    luaF_unlinkupval(uv);
+  luaM_free(L, uv);
+}
+
+
+static void freeobj (lua_State *L, GCObject *o) {
+  switch (o->tt) {
+    case LUA_VPROTO:
+      luaF_freeproto(L, gco2p(o));
+      break;
+    case LUA_VUPVAL:
+      freeupval(L, gco2upv(o));
+      break;
+    case LUA_VLCL: {
+      LClosure *cl = gco2lcl(o);
+      luaM_freemem(L, cl, sizeLclosure(cl->nupvalues));
+      break;
+    }
+    case LUA_VCCL: {
+      CClosure *cl = gco2ccl(o);
+      luaM_freemem(L, cl, sizeCclosure(cl->nupvalues));
+      break;
+    }
+    case LUA_VTABLE:
+      luaH_free(L, gco2t(o));
+      break;
+    case LUA_VTHREAD:
+      luaE_freethread(L, gco2th(o));
+      break;
+    case LUA_VUSERDATA: {
+      Udata *u = gco2u(o);
+      luaM_freemem(L, o, sizeudata(u->nuvalue, u->len));
+      break;
+    }
+    case LUA_VSHRSTR: {
+      TString *ts = gco2ts(o);
+      luaS_remove(L, ts);  /* remove it from hash table */
+      luaM_freemem(L, ts, sizelstring(ts->shrlen));
+      break;
+    }
+    case LUA_VLNGSTR: {
+      TString *ts = gco2ts(o);
+      luaM_freemem(L, ts, sizelstring(ts->u.lnglen));
+      break;
+    }
+    default: lua_assert(0);
+  }
+}
+
+
+/*
+** sweep at most 'countin' 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. ('*countout' gets the number of elements traversed.)
+*/
+static GCObject **sweeplist (lua_State *L, GCObject **p, int countin,
+                             int *countout) {
+  global_State *g = G(L);
+  int ow = otherwhite(g);
+  int i;
+  int white = luaC_white(g);  /* current white */
+  for (i = 0; *p != NULL && i < countin; i++) {
+    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 & ~maskgcbits) | white);
+      p = &curr->next;  /* go to next element */
+    }
+  }
+  if (countout)
+    *countout = i;  /* number of elements traversed */
+  return (*p == NULL) ? NULL : p;
+}
+
+
+/*
+** sweep a list until a live object (or end of list)
+*/
+static GCObject **sweeptolive (lua_State *L, GCObject **p) {
+  GCObject **old = p;
+  do {
+    p = sweeplist(L, p, 1, NULL);
+  } while (p == old);
+  return p;
+}
+
+/* }====================================================== */
+
+
+/*
+** {======================================================
+** Finalization
+** =======================================================
+*/
+
+/*
+** If possible, shrink string table.
+*/
+static void checkSizes (lua_State *L, global_State *g) {
+  if (!g->gcemergency) {
+    if (g->strt.nuse < g->strt.size / 4) {  /* string table too big? */
+      l_mem olddebt = g->GCdebt;
+      luaS_resize(L, g->strt.size / 2);
+      g->GCestimate += g->GCdebt - olddebt;  /* correct estimate */
+    }
+  }
+}
+
+
+/*
+** Get the next udata to be finalized from the 'tobefnz' list, and
+** link it back into the 'allgc' list.
+*/
+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 */
+  else if (getage(o) == G_OLD1)
+    g->firstold1 = o;  /* it is the first OLD1 object in the list */
+  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) {
+  global_State *g = G(L);
+  const TValue *tm;
+  TValue v;
+  lua_assert(!g->gcemergency);
+  setgcovalue(L, &v, udata2finalize(g));
+  tm = luaT_gettmbyobj(L, &v, TM_GC);
+  if (!notm(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++, &v);  /* ... and its argument */
+    L->ci->callstatus |= CIST_FIN;  /* will run a finalizer */
+    status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
+    L->ci->callstatus &= ~CIST_FIN;  /* not running a finalizer anymore */
+    L->allowhook = oldah;  /* restore hooks */
+    g->gcrunning = running;  /* restore state */
+    if (l_unlikely(status != LUA_OK)) {  /* error while running __gc? */
+      luaE_warnerror(L, "__gc metamethod");
+      L->top--;  /* pops error object */
+    }
+  }
+}
+
+
+/*
+** Call a few finalizers
+*/
+static int runafewfinalizers (lua_State *L, int n) {
+  global_State *g = G(L);
+  int i;
+  for (i = 0; i < n && g->tobefnz; i++)
+    GCTM(L);  /* call one finalizer */
+  return i;
+}
+
+
+/*
+** call all pending finalizers
+*/
+static void callallpendingfinalizers (lua_State *L) {
+  global_State *g = G(L);
+  while (g->tobefnz)
+    GCTM(L);
+}
+
+
+/*
+** 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).
+** (Note that objects after 'finobjold1' cannot be white, so they
+** don't need to be traversed. In incremental mode, 'finobjold1' is NULL,
+** so the whole list is traversed.)
+*/
+static void separatetobefnz (global_State *g, int all) {
+  GCObject *curr;
+  GCObject **p = &g->finobj;
+  GCObject **lastnext = findlast(&g->tobefnz);
+  while ((curr = *p) != g->finobjold1) {  /* traverse all finalizable objects */
+    lua_assert(tofinalize(curr));
+    if (!(iswhite(curr) || all))  /* not being collected? */
+      p = &curr->next;  /* don't bother with it */
+    else {
+      if (curr == g->finobjsur)  /* removing 'finobjsur'? */
+        g->finobjsur = curr->next;  /* correct it */
+      *p = curr->next;  /* remove 'curr' from 'finobj' list */
+      curr->next = *lastnext;  /* link at the end of 'tobefnz' list */
+      *lastnext = curr;
+      lastnext = &curr->next;
+    }
+  }
+}
+
+
+/*
+** If pointer 'p' points to 'o', move it to the next element.
+*/
+static void checkpointer (GCObject **p, GCObject *o) {
+  if (o == *p)
+    *p = o->next;
+}
+
+
+/*
+** Correct pointers to objects inside 'allgc' list when
+** object 'o' is being removed from the list.
+*/
+static void correctpointers (global_State *g, GCObject *o) {
+  checkpointer(&g->survival, o);
+  checkpointer(&g->old1, o);
+  checkpointer(&g->reallyold, o);
+  checkpointer(&g->firstold1, o);
+}
+
+
+/*
+** 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);  /* change 'sweepgc' */
+    }
+    else
+      correctpointers(g, o);
+    /* 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 */
+  }
+}
+
+/* }====================================================== */
+
+
+/*
+** {======================================================
+** Generational Collector
+** =======================================================
+*/
+
+static void setpause (global_State *g);
+
+
+/*
+** Sweep a list of objects to enter generational mode.  Deletes dead
+** objects and turns the non dead to old. All non-dead threads---which
+** are now old---must be in a gray list. Everything else is not in a
+** gray list. Open upvalues are also kept gray.
+*/
+static void sweep2old (lua_State *L, GCObject **p) {
+  GCObject *curr;
+  global_State *g = G(L);
+  while ((curr = *p) != NULL) {
+    if (iswhite(curr)) {  /* is 'curr' dead? */
+      lua_assert(isdead(g, curr));
+      *p = curr->next;  /* remove 'curr' from list */
+      freeobj(L, curr);  /* erase 'curr' */
+    }
+    else {  /* all surviving objects become old */
+      setage(curr, G_OLD);
+      if (curr->tt == LUA_VTHREAD) {  /* threads must be watched */
+        lua_State *th = gco2th(curr);
+        linkgclist(th, g->grayagain);  /* insert into 'grayagain' list */
+      }
+      else if (curr->tt == LUA_VUPVAL && upisopen(gco2upv(curr)))
+        set2gray(curr);  /* open upvalues are always gray */
+      else  /* everything else is black */
+        nw2black(curr);
+      p = &curr->next;  /* go to next element */
+    }
+  }
+}
+
+
+/*
+** Sweep for generational mode. Delete dead objects. (Because the
+** collection is not incremental, there are no "new white" objects
+** during the sweep. So, any white object must be dead.) For
+** non-dead objects, advance their ages and clear the color of
+** new objects. (Old objects keep their colors.)
+** The ages of G_TOUCHED1 and G_TOUCHED2 objects cannot be advanced
+** here, because these old-generation objects are usually not swept
+** here.  They will all be advanced in 'correctgraylist'. That function
+** will also remove objects turned white here from any gray list.
+*/
+static GCObject **sweepgen (lua_State *L, global_State *g, GCObject **p,
+                            GCObject *limit, GCObject **pfirstold1) {
+  static const lu_byte nextage[] = {
+    G_SURVIVAL,  /* from G_NEW */
+    G_OLD1,      /* from G_SURVIVAL */
+    G_OLD1,      /* from G_OLD0 */
+    G_OLD,       /* from G_OLD1 */
+    G_OLD,       /* from G_OLD (do not change) */
+    G_TOUCHED1,  /* from G_TOUCHED1 (do not change) */
+    G_TOUCHED2   /* from G_TOUCHED2 (do not change) */
+  };
+  int white = luaC_white(g);
+  GCObject *curr;
+  while ((curr = *p) != limit) {
+    if (iswhite(curr)) {  /* is 'curr' dead? */
+      lua_assert(!isold(curr) && isdead(g, curr));
+      *p = curr->next;  /* remove 'curr' from list */
+      freeobj(L, curr);  /* erase 'curr' */
+    }
+    else {  /* correct mark and age */
+      if (getage(curr) == G_NEW) {  /* new objects go back to white */
+        int marked = curr->marked & ~maskgcbits;  /* erase GC bits */
+        curr->marked = cast_byte(marked | G_SURVIVAL | white);
+      }
+      else {  /* all other objects will be old, and so keep their color */
+        setage(curr, nextage[getage(curr)]);
+        if (getage(curr) == G_OLD1 && *pfirstold1 == NULL)
+          *pfirstold1 = curr;  /* first OLD1 object in the list */
+      }
+      p = &curr->next;  /* go to next element */
+    }
+  }
+  return p;
+}
+
+
+/*
+** Traverse a list making all its elements white and clearing their
+** age. In incremental mode, all objects are 'new' all the time,
+** except for fixed strings (which are always old).
+*/
+static void whitelist (global_State *g, GCObject *p) {
+  int white = luaC_white(g);
+  for (; p != NULL; p = p->next)
+    p->marked = cast_byte((p->marked & ~maskgcbits) | white);
+}
+
+
+/*
+** Correct a list of gray objects. Return pointer to where rest of the
+** list should be linked.
+** Because this correction is done after sweeping, young objects might
+** be turned white and still be in the list. They are only removed.
+** 'TOUCHED1' objects are advanced to 'TOUCHED2' and remain on the list;
+** Non-white threads also remain on the list; 'TOUCHED2' objects become
+** regular old; they and anything else are removed from the list.
+*/
+static GCObject **correctgraylist (GCObject **p) {
+  GCObject *curr;
+  while ((curr = *p) != NULL) {
+    GCObject **next = getgclist(curr);
+    if (iswhite(curr))
+      goto remove;  /* remove all white objects */
+    else if (getage(curr) == G_TOUCHED1) {  /* touched in this cycle? */
+      lua_assert(isgray(curr));
+      nw2black(curr);  /* make it black, for next barrier */
+      changeage(curr, G_TOUCHED1, G_TOUCHED2);
+      goto remain;  /* keep it in the list and go to next element */
+    }
+    else if (curr->tt == LUA_VTHREAD) {
+      lua_assert(isgray(curr));
+      goto remain;  /* keep non-white threads on the list */
+    }
+    else {  /* everything else is removed */
+      lua_assert(isold(curr));  /* young objects should be white here */
+      if (getage(curr) == G_TOUCHED2)  /* advance from TOUCHED2... */
+        changeage(curr, G_TOUCHED2, G_OLD);  /* ... to OLD */
+      nw2black(curr);  /* make object black (to be removed) */
+      goto remove;
+    }
+    remove: *p = *next; continue;
+    remain: p = next; continue;
+  }
+  return p;
+}
+
+
+/*
+** Correct all gray lists, coalescing them into 'grayagain'.
+*/
+static void correctgraylists (global_State *g) {
+  GCObject **list = correctgraylist(&g->grayagain);
+  *list = g->weak; g->weak = NULL;
+  list = correctgraylist(list);
+  *list = g->allweak; g->allweak = NULL;
+  list = correctgraylist(list);
+  *list = g->ephemeron; g->ephemeron = NULL;
+  correctgraylist(list);
+}
+
+
+/*
+** Mark black 'OLD1' objects when starting a new young collection.
+** Gray objects are already in some gray list, and so will be visited
+** in the atomic step.
+*/
+static void markold (global_State *g, GCObject *from, GCObject *to) {
+  GCObject *p;
+  for (p = from; p != to; p = p->next) {
+    if (getage(p) == G_OLD1) {
+      lua_assert(!iswhite(p));
+      changeage(p, G_OLD1, G_OLD);  /* now they are old */
+      if (isblack(p))
+        reallymarkobject(g, p);
+    }
+  }
+}
+
+
+/*
+** Finish a young-generation collection.
+*/
+static void finishgencycle (lua_State *L, global_State *g) {
+  correctgraylists(g);
+  checkSizes(L, g);
+  g->gcstate = GCSpropagate;  /* skip restart */
+  if (!g->gcemergency)
+    callallpendingfinalizers(L);
+}
+
+
+/*
+** Does a young collection. First, mark 'OLD1' objects. Then does the
+** atomic step. Then, sweep all lists and advance pointers. Finally,
+** finish the collection.
+*/
+static void youngcollection (lua_State *L, global_State *g) {
+  GCObject **psurvival;  /* to point to first non-dead survival object */
+  GCObject *dummy;  /* dummy out parameter to 'sweepgen' */
+  lua_assert(g->gcstate == GCSpropagate);
+  if (g->firstold1) {  /* are there regular OLD1 objects? */
+    markold(g, g->firstold1, g->reallyold);  /* mark them */
+    g->firstold1 = NULL;  /* no more OLD1 objects (for now) */
+  }
+  markold(g, g->finobj, g->finobjrold);
+  markold(g, g->tobefnz, NULL);
+  atomic(L);
+
+  /* sweep nursery and get a pointer to its last live element */
+  g->gcstate = GCSswpallgc;
+  psurvival = sweepgen(L, g, &g->allgc, g->survival, &g->firstold1);
+  /* sweep 'survival' */
+  sweepgen(L, g, psurvival, g->old1, &g->firstold1);
+  g->reallyold = g->old1;
+  g->old1 = *psurvival;  /* 'survival' survivals are old now */
+  g->survival = g->allgc;  /* all news are survivals */
+
+  /* repeat for 'finobj' lists */
+  dummy = NULL;  /* no 'firstold1' optimization for 'finobj' lists */
+  psurvival = sweepgen(L, g, &g->finobj, g->finobjsur, &dummy);
+  /* sweep 'survival' */
+  sweepgen(L, g, psurvival, g->finobjold1, &dummy);
+  g->finobjrold = g->finobjold1;
+  g->finobjold1 = *psurvival;  /* 'survival' survivals are old now */
+  g->finobjsur = g->finobj;  /* all news are survivals */
+
+  sweepgen(L, g, &g->tobefnz, NULL, &dummy);
+  finishgencycle(L, g);
+}
+
+
+/*
+** Clears all gray lists, sweeps objects, and prepare sublists to enter
+** generational mode. The sweeps remove dead objects and turn all
+** surviving objects to old. Threads go back to 'grayagain'; everything
+** else is turned black (not in any gray list).
+*/
+static void atomic2gen (lua_State *L, global_State *g) {
+  cleargraylists(g);
+  /* sweep all elements making them old */
+  g->gcstate = GCSswpallgc;
+  sweep2old(L, &g->allgc);
+  /* everything alive now is old */
+  g->reallyold = g->old1 = g->survival = g->allgc;
+  g->firstold1 = NULL;  /* there are no OLD1 objects anywhere */
+
+  /* repeat for 'finobj' lists */
+  sweep2old(L, &g->finobj);
+  g->finobjrold = g->finobjold1 = g->finobjsur = g->finobj;
+
+  sweep2old(L, &g->tobefnz);
+
+  g->gckind = KGC_GEN;
+  g->lastatomic = 0;
+  g->GCestimate = gettotalbytes(g);  /* base for memory control */
+  finishgencycle(L, g);
+}
+
+
+/*
+** Enter generational mode. Must go until the end of an atomic cycle
+** to ensure that all objects are correctly marked and weak tables
+** are cleared. Then, turn all objects into old and finishes the
+** collection.
+*/
+static lu_mem entergen (lua_State *L, global_State *g) {
+  lu_mem numobjs;
+  luaC_runtilstate(L, bitmask(GCSpause));  /* prepare to start a new cycle */
+  luaC_runtilstate(L, bitmask(GCSpropagate));  /* start new cycle */
+  numobjs = atomic(L);  /* propagates all and then do the atomic stuff */
+  atomic2gen(L, g);
+  return numobjs;
+}
+
+
+/*
+** Enter incremental mode. Turn all objects white, make all
+** intermediate lists point to NULL (to avoid invalid pointers),
+** and go to the pause state.
+*/
+static void enterinc (global_State *g) {
+  whitelist(g, g->allgc);
+  g->reallyold = g->old1 = g->survival = NULL;
+  whitelist(g, g->finobj);
+  whitelist(g, g->tobefnz);
+  g->finobjrold = g->finobjold1 = g->finobjsur = NULL;
+  g->gcstate = GCSpause;
+  g->gckind = KGC_INC;
+  g->lastatomic = 0;
+}
+
+
+/*
+** Change collector mode to 'newmode'.
+*/
+void luaC_changemode (lua_State *L, int newmode) {
+  global_State *g = G(L);
+  if (newmode != g->gckind) {
+    if (newmode == KGC_GEN)  /* entering generational mode? */
+      entergen(L, g);
+    else
+      enterinc(g);  /* entering incremental mode */
+  }
+  g->lastatomic = 0;
+}
+
+
+/*
+** Does a full collection in generational mode.
+*/
+static lu_mem fullgen (lua_State *L, global_State *g) {
+  enterinc(g);
+  return entergen(L, g);
+}
+
+
+/*
+** Set debt for the next minor collection, which will happen when
+** memory grows 'genminormul'%.
+*/
+static void setminordebt (global_State *g) {
+  luaE_setdebt(g, -(cast(l_mem, (gettotalbytes(g) / 100)) * g->genminormul));
+}
+
+
+/*
+** Does a major collection after last collection was a "bad collection".
+**
+** When the program is building a big structure, it allocates lots of
+** memory but generates very little garbage. In those scenarios,
+** the generational mode just wastes time doing small collections, and
+** major collections are frequently what we call a "bad collection", a
+** collection that frees too few objects. To avoid the cost of switching
+** between generational mode and the incremental mode needed for full
+** (major) collections, the collector tries to stay in incremental mode
+** after a bad collection, and to switch back to generational mode only
+** after a "good" collection (one that traverses less than 9/8 objects
+** of the previous one).
+** The collector must choose whether to stay in incremental mode or to
+** switch back to generational mode before sweeping. At this point, it
+** does not know the real memory in use, so it cannot use memory to
+** decide whether to return to generational mode. Instead, it uses the
+** number of objects traversed (returned by 'atomic') as a proxy. The
+** field 'g->lastatomic' keeps this count from the last collection.
+** ('g->lastatomic != 0' also means that the last collection was bad.)
+*/
+static void stepgenfull (lua_State *L, global_State *g) {
+  lu_mem newatomic;  /* count of traversed objects */
+  lu_mem lastatomic = g->lastatomic;  /* count from last collection */
+  if (g->gckind == KGC_GEN)  /* still in generational mode? */
+    enterinc(g);  /* enter incremental mode */
+  luaC_runtilstate(L, bitmask(GCSpropagate));  /* start new cycle */
+  newatomic = atomic(L);  /* mark everybody */
+  if (newatomic < lastatomic + (lastatomic >> 3)) {  /* good collection? */
+    atomic2gen(L, g);  /* return to generational mode */
+    setminordebt(g);
+  }
+  else {  /* another bad collection; stay in incremental mode */
+    g->GCestimate = gettotalbytes(g);  /* first estimate */;
+    entersweep(L);
+    luaC_runtilstate(L, bitmask(GCSpause));  /* finish collection */
+    setpause(g);
+    g->lastatomic = newatomic;
+  }
+}
+
+
+/*
+** Does a generational "step".
+** Usually, this means doing a minor collection and setting the debt to
+** make another collection when memory grows 'genminormul'% larger.
+**
+** However, there are exceptions.  If memory grows 'genmajormul'%
+** larger than it was at the end of the last major collection (kept
+** in 'g->GCestimate'), the function does a major collection. At the
+** end, it checks whether the major collection was able to free a
+** decent amount of memory (at least half the growth in memory since
+** previous major collection). If so, the collector keeps its state,
+** and the next collection will probably be minor again. Otherwise,
+** we have what we call a "bad collection". In that case, set the field
+** 'g->lastatomic' to signal that fact, so that the next collection will
+** go to 'stepgenfull'.
+**
+** 'GCdebt <= 0' means an explicit call to GC step with "size" zero;
+** in that case, do a minor collection.
+*/
+static void genstep (lua_State *L, global_State *g) {
+  if (g->lastatomic != 0)  /* last collection was a bad one? */
+    stepgenfull(L, g);  /* do a full step */
+  else {
+    lu_mem majorbase = g->GCestimate;  /* memory after last major collection */
+    lu_mem majorinc = (majorbase / 100) * getgcparam(g->genmajormul);
+    if (g->GCdebt > 0 && gettotalbytes(g) > majorbase + majorinc) {
+      lu_mem numobjs = fullgen(L, g);  /* do a major collection */
+      if (gettotalbytes(g) < majorbase + (majorinc / 2)) {
+        /* collected at least half of memory growth since last major
+           collection; keep doing minor collections */
+        setminordebt(g);
+      }
+      else {  /* bad collection */
+        g->lastatomic = numobjs;  /* signal that last collection was bad */
+        setpause(g);  /* do a long wait for next (major) collection */
+      }
+    }
+    else {  /* regular case; do a minor collection */
+      youngcollection(L, g);
+      setminordebt(g);
+      g->GCestimate = majorbase;  /* preserve base value */
+    }
+  }
+  lua_assert(isdecGCmodegen(g));
+}
+
+/* }====================================================== */
+
+
+/*
+** {======================================================
+** GC control
+** =======================================================
+*/
+
+
+/*
+** Set the "time" to wait before starting a new GC cycle; cycle will
+** start when memory use hits the threshold of ('estimate' * pause /
+** PAUSEADJ). (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;
+  int pause = getgcparam(g->gcpause);
+  l_mem estimate = g->GCestimate / PAUSEADJ;  /* adjust 'estimate' */
+  lua_assert(estimate > 0);
+  threshold = (pause < MAX_LMEM / estimate)  /* overflow? */
+            ? estimate * pause  /* no overflow */
+            : MAX_LMEM;  /* overflow; truncate to maximum */
+  debt = gettotalbytes(g) - threshold;
+  if (debt > 0) debt = 0;
+  luaE_setdebt(g, debt);
+}
+
+
+/*
+** Enter first sweep phase.
+** The call to 'sweeptolive' makes the 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.
+*/
+static void entersweep (lua_State *L) {
+  global_State *g = G(L);
+  g->gcstate = GCSswpallgc;
+  lua_assert(g->sweepgc == NULL);
+  g->sweepgc = sweeptolive(L, &g->allgc);
+}
+
+
+/*
+** Delete all objects in list 'p' until (but not including) object
+** 'limit'.
+*/
+static void deletelist (lua_State *L, GCObject *p, GCObject *limit) {
+  while (p != limit) {
+    GCObject *next = p->next;
+    freeobj(L, p);
+    p = next;
+  }
+}
+
+
+/*
+** Call all finalizers of the objects in the given Lua state, and
+** then free all objects, except for the main thread.
+*/
+void luaC_freeallobjects (lua_State *L) {
+  global_State *g = G(L);
+  luaC_changemode(L, KGC_INC);
+  separatetobefnz(g, 1);  /* separate all objects with finalizers */
+  lua_assert(g->finobj == NULL);
+  callallpendingfinalizers(L);
+  deletelist(L, g->allgc, obj2gco(g->mainthread));
+  deletelist(L, g->finobj, NULL);
+  deletelist(L, g->fixedgc, NULL);  /* collect fixed objects */
+  lua_assert(g->strt.nuse == 0);
+}
+
+
+static lu_mem atomic (lua_State *L) {
+  global_State *g = G(L);
+  lu_mem work = 0;
+  GCObject *origweak, *origall;
+  GCObject *grayagain = g->grayagain;  /* save original list */
+  g->grayagain = NULL;
+  lua_assert(g->ephemeron == NULL && g->weak == NULL);
+  lua_assert(!iswhite(g->mainthread));
+  g->gcstate = GCSatomic;
+  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 */
+  work += propagateall(g);  /* empties 'gray' list */
+  /* remark occasional upvalues of (maybe) dead threads */
+  work += remarkupvals(g);
+  work += propagateall(g);  /* propagate changes */
+  g->gray = grayagain;
+  work += propagateall(g);  /* traverse 'grayagain' list */
+  convergeephemerons(g);
+  /* at this point, all strongly accessible objects are marked. */
+  /* Clear values from weak tables, before checking finalizers */
+  clearbyvalues(g, g->weak, NULL);
+  clearbyvalues(g, g->allweak, NULL);
+  origweak = g->weak; origall = g->allweak;
+  separatetobefnz(g, 0);  /* separate objects to be finalized */
+  work += markbeingfnz(g);  /* mark objects that will be finalized */
+  work += propagateall(g);  /* remark, to propagate 'resurrection' */
+  convergeephemerons(g);
+  /* at this point, all resurrected objects are marked. */
+  /* remove dead objects from weak tables */
+  clearbykeys(g, g->ephemeron);  /* clear keys from all ephemeron tables */
+  clearbykeys(g, g->allweak);  /* clear keys from all 'allweak' tables */
+  /* clear values from resurrected weak tables */
+  clearbyvalues(g, g->weak, origweak);
+  clearbyvalues(g, g->allweak, origall);
+  luaS_clearcache(g);
+  g->currentwhite = cast_byte(otherwhite(g));  /* flip current white */
+  lua_assert(g->gray == NULL);
+  return work;  /* estimate of slots marked by 'atomic' */
+}
+
+
+static int sweepstep (lua_State *L, global_State *g,
+                      int nextstate, GCObject **nextlist) {
+  if (g->sweepgc) {
+    l_mem olddebt = g->GCdebt;
+    int count;
+    g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX, &count);
+    g->GCestimate += g->GCdebt - olddebt;  /* update estimate */
+    return count;
+  }
+  else {  /* enter next state */
+    g->gcstate = nextstate;
+    g->sweepgc = nextlist;
+    return 0;  /* no work done */
+  }
+}
+
+
+static lu_mem singlestep (lua_State *L) {
+  global_State *g = G(L);
+  lu_mem work;
+  lua_assert(!g->gcstopem);  /* collector is not reentrant */
+  g->gcstopem = 1;  /* no emergency collections while collecting */
+  switch (g->gcstate) {
+    case GCSpause: {
+      restartcollection(g);
+      g->gcstate = GCSpropagate;
+      work = 1;
+      break;
+    }
+    case GCSpropagate: {
+      if (g->gray == NULL) {  /* no more gray objects? */
+        g->gcstate = GCSenteratomic;  /* finish propagate phase */
+        work = 0;
+      }
+      else
+        work = propagatemark(g);  /* traverse one gray object */
+      break;
+    }
+    case GCSenteratomic: {
+      work = atomic(L);  /* work is what was traversed by 'atomic' */
+      entersweep(L);
+      g->GCestimate = gettotalbytes(g);  /* first estimate */;
+      break;
+    }
+    case GCSswpallgc: {  /* sweep "regular" objects */
+      work = sweepstep(L, g, GCSswpfinobj, &g->finobj);
+      break;
+    }
+    case GCSswpfinobj: {  /* sweep objects with finalizers */
+      work = sweepstep(L, g, GCSswptobefnz, &g->tobefnz);
+      break;
+    }
+    case GCSswptobefnz: {  /* sweep objects to be finalized */
+      work = sweepstep(L, g, GCSswpend, NULL);
+      break;
+    }
+    case GCSswpend: {  /* finish sweeps */
+      checkSizes(L, g);
+      g->gcstate = GCScallfin;
+      work = 0;
+      break;
+    }
+    case GCScallfin: {  /* call remaining finalizers */
+      if (g->tobefnz && !g->gcemergency) {
+        g->gcstopem = 0;  /* ok collections during finalizers */
+        work = runafewfinalizers(L, GCFINMAX) * GCFINALIZECOST;
+      }
+      else {  /* emergency mode or no more finalizers */
+        g->gcstate = GCSpause;  /* finish collection */
+        work = 0;
+      }
+      break;
+    }
+    default: lua_assert(0); return 0;
+  }
+  g->gcstopem = 0;
+  return work;
+}
+
+
+/*
+** 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);
+}
+
+
+/*
+** Performs a basic incremental step. The debt and step size are
+** converted from bytes to "units of work"; then the function loops
+** running single steps until adding that many units of work or
+** finishing a cycle (pause state). Finally, it sets the debt that
+** controls when next step will be performed.
+*/
+static void incstep (lua_State *L, global_State *g) {
+  int stepmul = (getgcparam(g->gcstepmul) | 1);  /* avoid division by 0 */
+  l_mem debt = (g->GCdebt / WORK2MEM) * stepmul;
+  l_mem stepsize = (g->gcstepsize <= log2maxs(l_mem))
+                 ? ((cast(l_mem, 1) << g->gcstepsize) / WORK2MEM) * stepmul
+                 : MAX_LMEM;  /* overflow; keep maximum value */
+  do {  /* repeat until pause or enough "credit" (negative debt) */
+    lu_mem work = singlestep(L);  /* perform one single step */
+    debt -= work;
+  } while (debt > -stepsize && g->gcstate != GCSpause);
+  if (g->gcstate == GCSpause)
+    setpause(g);  /* pause until next cycle */
+  else {
+    debt = (debt / stepmul) * WORK2MEM;  /* convert 'work units' to bytes */
+    luaE_setdebt(g, debt);
+  }
+}
+
+/*
+** performs a basic GC step if collector is running
+*/
+void luaC_step (lua_State *L) {
+  global_State *g = G(L);
+  lua_assert(!g->gcemergency);
+  if (g->gcrunning) {  /* running? */
+    if(isdecGCmodegen(g))
+      genstep(L, g);
+    else
+      incstep(L, g);
+  }
+}
+
+
+/*
+** Perform a full collection in incremental mode.
+** 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).
+*/
+static void fullinc (lua_State *L, global_State *g) {
+  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(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 */
+  setpause(g);
+}
+
+
+/*
+** 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).
+*/
+void luaC_fullgc (lua_State *L, int isemergency) {
+  global_State *g = G(L);
+  lua_assert(!g->gcemergency);
+  g->gcemergency = isemergency;  /* set flag */
+  if (g->gckind == KGC_INC)
+    fullinc(L, g);
+  else
+    fullgen(L, g);
+  g->gcemergency = 0;
+}
+
+/* }====================================================== */
+
+