src/lj_gc.c

   1 /*
   2 ** Garbage collector.
   3 ** Copyright (C) 2005-2014 Mike Pall. See Copyright Notice in luajit.h
   4 **
   5 ** Major portions taken verbatim or adapted from the Lua interpreter.
   6 ** Copyright (C) 1994-2008 Lua.org, PUC-Rio. See Copyright Notice in lua.h
   7 */
   8
   9 #define lj_gc_c
  10 #define LUA_CORE
  11
  12 #include "lj_obj.h"
  13 #include "lj_gc.h"
  14 #include "lj_err.h"
  15 #include "lj_str.h"
  16 #include "lj_tab.h"
  17 #include "lj_func.h"
  18 #include "lj_udata.h"
  19 #include "lj_meta.h"
  20 #include "lj_state.h"
  21 #include "lj_frame.h"
  22 #if LJ_HASFFI
  23 #include "lj_ctype.h"
  24 #include "lj_cdata.h"
  25 #endif
  26 #include "lj_trace.h"
  27 #include "lj_vm.h"
  28
  29 #define GCSTEPSIZE      1024u
  30 #define GCSWEEPMAX      40
  31 #define GCSWEEPCOST     10
  32 #define GCFINALIZECOST  100
  33
  34 /* Macros to set GCobj colors and flags. */
  35 #define white2gray(x)           ((x)->gch.marked &= (uint8_t)~LJ_GC_WHITES)
  36 #define gray2black(x)           ((x)->gch.marked |= LJ_GC_BLACK)
  37 #define isfinalized(u)          ((u)->marked & LJ_GC_FINALIZED)
  38
  39 /* -- Mark phase ---------------------------------------------------------- */
  40
  41 /* Mark a TValue (if needed). */
  42 #define gc_marktv(g, tv) \
  43   { lua_assert(!tvisgcv(tv) || (~itype(tv) == gcval(tv)->gch.gct)); \
  44     if (tviswhite(tv)) gc_mark(g, gcV(tv)); }
  45
  46 /* Mark a GCobj (if needed). */
  47 #define gc_markobj(g, o) \
  48   { if (iswhite(obj2gco(o))) gc_mark(g, obj2gco(o)); }
  49
  50 /* Mark a string object. */
  51 #define gc_mark_str(s)          ((s)->marked &= (uint8_t)~LJ_GC_WHITES)
  52
  53 /* Mark a white GCobj. */
  54 static void gc_mark(global_State *g, GCobj *o)
  55 {
  56   int gct = o->gch.gct;
  57   lua_assert(iswhite(o) && !isdead(g, o));
  58   white2gray(o);
  59   if (LJ_UNLIKELY(gct == ~LJ_TUDATA)) {
  60     GCtab *mt = tabref(gco2ud(o)->metatable);
  61     gray2black(o);  /* Userdata are never gray. */
  62     if (mt) gc_markobj(g, mt);
  63     gc_markobj(g, tabref(gco2ud(o)->env));
  64   } else if (LJ_UNLIKELY(gct == ~LJ_TUPVAL)) {
  65     GCupval *uv = gco2uv(o);
  66     gc_marktv(g, uvval(uv));
  67     if (uv->closed)
  68       gray2black(o);  /* Closed upvalues are never gray. */
  69   } else if (gct != ~LJ_TSTR && gct != ~LJ_TCDATA) {
  70     lua_assert(gct == ~LJ_TFUNC || gct == ~LJ_TTAB ||
  71                gct == ~LJ_TTHREAD || gct == ~LJ_TPROTO);
  72     setgcrefr(o->gch.gclist, g->gc.gray);
  73     setgcref(g->gc.gray, o);
  74   }
  75 }
  76
  77 /* Mark GC roots. */
  78 static void gc_mark_gcroot(global_State *g)
  79 {
  80   ptrdiff_t i;
  81   for (i = 0; i < GCROOT_MAX; i++)
  82     if (gcref(g->gcroot[i]) != NULL)
  83       gc_markobj(g, gcref(g->gcroot[i]));
  84 }
  85
  86 /* Start a GC cycle and mark the root set. */
  87 static void gc_mark_start(global_State *g)
  88 {
  89   setgcrefnull(g->gc.gray);
  90   setgcrefnull(g->gc.grayagain);
  91   setgcrefnull(g->gc.weak);
  92   gc_markobj(g, mainthread(g));
  93   gc_markobj(g, tabref(mainthread(g)->env));
  94   gc_marktv(g, &g->registrytv);
  95   gc_mark_gcroot(g);
  96   g->gc.state = GCSpropagate;
  97 }
  98
  99 /* Mark open upvalues. */
 100 static void gc_mark_uv(global_State *g)
 101 {
 102   GCupval *uv;
 103   for (uv = uvnext(&g->uvhead); uv != &g->uvhead; uv = uvnext(uv)) {
 104     lua_assert(uvprev(uvnext(uv)) == uv && uvnext(uvprev(uv)) == uv);
 105     if (isgray(obj2gco(uv)))
 106       gc_marktv(g, uvval(uv));
 107   }
 108 }
 109
 110 /* Mark userdata in mmudata list. */
 111 static void gc_mark_mmudata(global_State *g)
 112 {
 113   GCobj *root = gcref(g->gc.mmudata);
 114   GCobj *u = root;
 115   if (u) {
 116     do {
 117       u = gcnext(u);
 118       makewhite(g, u);  /* Could be from previous GC. */
 119       gc_mark(g, u);
 120     } while (u != root);
 121   }
 122 }
 123
 124 /* Separate userdata objects to be finalized to mmudata list. */
 125 size_t lj_gc_separateudata(global_State *g, int all)
 126 {
 127   size_t m = 0;
 128   GCRef *p = &mainthread(g)->nextgc;
 129   GCobj *o;
 130   while ((o = gcref(*p)) != NULL) {
 131     if (!(iswhite(o) || all) || isfinalized(gco2ud(o))) {
 132       p = &o->gch.nextgc;  /* Nothing to do. */
 133     } else if (!lj_meta_fastg(g, tabref(gco2ud(o)->metatable), MM_gc)) {
 134       markfinalized(o);  /* Done, as there's no __gc metamethod. */
 135       p = &o->gch.nextgc;
 136     } else {  /* Otherwise move userdata to be finalized to mmudata list. */
 137       m += sizeudata(gco2ud(o));
 138       markfinalized(o);
 139       *p = o->gch.nextgc;
 140       if (gcref(g->gc.mmudata)) {  /* Link to end of mmudata list. */
 141         GCobj *root = gcref(g->gc.mmudata);
 142         setgcrefr(o->gch.nextgc, root->gch.nextgc);
 143         setgcref(root->gch.nextgc, o);
 144         setgcref(g->gc.mmudata, o);
 145       } else {  /* Create circular list. */
 146         setgcref(o->gch.nextgc, o);
 147         setgcref(g->gc.mmudata, o);
 148       }
 149     }
 150   }
 151   return m;
 152 }
 153
 154 /* -- Propagation phase --------------------------------------------------- */
 155
 156 /* Traverse a table. */
 157 static int gc_traverse_tab(global_State *g, GCtab *t)
 158 {
 159   int weak = 0;
 160   cTValue *mode;
 161   GCtab *mt = tabref(t->metatable);
 162   if (mt)
 163     gc_markobj(g, mt);
 164   mode = lj_meta_fastg(g, mt, MM_mode);
 165   if (mode && tvisstr(mode)) {  /* Valid __mode field? */
 166     const char *modestr = strVdata(mode);
 167     int c;
 168     while ((c = *modestr++)) {
 169       if (c == 'k') weak |= LJ_GC_WEAKKEY;
 170       else if (c == 'v') weak |= LJ_GC_WEAKVAL;
 171       else if (c == 'K') weak = (int)(~0u & ~LJ_GC_WEAKVAL);
 172     }
 173     if (weak > 0) {  /* Weak tables are cleared in the atomic phase. */
 174       t->marked = (uint8_t)((t->marked & ~LJ_GC_WEAK) | weak);
 175       setgcrefr(t->gclist, g->gc.weak);
 176       setgcref(g->gc.weak, obj2gco(t));
 177     }
 178   }
 179   if (weak == LJ_GC_WEAK)  /* Nothing to mark if both keys/values are weak. */
 180     return 1;
 181   if (!(weak & LJ_GC_WEAKVAL)) {  /* Mark array part. */
 182     MSize i, asize = t->asize;
 183     for (i = 0; i < asize; i++)
 184       gc_marktv(g, arrayslot(t, i));
 185   }
 186   if (t->hmask > 0) {  /* Mark hash part. */
 187     Node *node = noderef(t->node);
 188     MSize i, hmask = t->hmask;
 189     for (i = 0; i <= hmask; i++) {
 190       Node *n = &node[i];
 191       if (!tvisnil(&n->val)) {  /* Mark non-empty slot. */
 192         lua_assert(!tvisnil(&n->key));
 193         if (!(weak & LJ_GC_WEAKKEY)) gc_marktv(g, &n->key);
 194         if (!(weak & LJ_GC_WEAKVAL)) gc_marktv(g, &n->val);
 195       }
 196     }
 197   }
 198   return weak;
 199 }
 200
 201 /* Traverse a function. */
 202 static void gc_traverse_func(global_State *g, GCfunc *fn)
 203 {
 204   gc_markobj(g, tabref(fn->c.env));
 205   if (isluafunc(fn)) {
 206     uint32_t i;
 207     lua_assert(fn->l.nupvalues <= funcproto(fn)->sizeuv);
 208     gc_markobj(g, funcproto(fn));
 209     for (i = 0; i < fn->l.nupvalues; i++)  /* Mark Lua function upvalues. */
 210       gc_markobj(g, &gcref(fn->l.uvptr[i])->uv);
 211   } else {
 212     uint32_t i;
 213     for (i = 0; i < fn->c.nupvalues; i++)  /* Mark C function upvalues. */
 214       gc_marktv(g, &fn->c.upvalue[i]);
 215   }
 216 }
 217
 218 #if LJ_HASJIT
 219 /* Mark a trace. */
 220 static void gc_marktrace(global_State *g, TraceNo traceno)
 221 {
 222   GCobj *o = obj2gco(traceref(G2J(g), traceno));
 223   lua_assert(traceno != G2J(g)->cur.traceno);
 224   if (iswhite(o)) {
 225     white2gray(o);
 226     setgcrefr(o->gch.gclist, g->gc.gray);
 227     setgcref(g->gc.gray, o);
 228   }
 229 }
 230
 231 /* Traverse a trace. */
 232 static void gc_traverse_trace(global_State *g, GCtrace *T)
 233 {
 234   IRRef ref;
 235   if (T->traceno == 0) return;
 236   for (ref = T->nk; ref < REF_TRUE; ref++) {
 237     IRIns *ir = &T->ir[ref];
 238     if (ir->o == IR_KGC)
 239       gc_markobj(g, ir_kgc(ir));
 240   }
 241   if (T->link) gc_marktrace(g, T->link);
 242   if (T->nextroot) gc_marktrace(g, T->nextroot);
 243   if (T->nextside) gc_marktrace(g, T->nextside);
 244   gc_markobj(g, gcref(T->startpt));
 245 }
 246
 247 /* The current trace is a GC root while not anchored in the prototype (yet). */
 248 #define gc_traverse_curtrace(g) gc_traverse_trace(g, &G2J(g)->cur)
 249 #else
 250 #define gc_traverse_curtrace(g) UNUSED(g)
 251 #endif
 252
 253 /* Traverse a prototype. */
 254 static void gc_traverse_proto(global_State *g, GCproto *pt)
 255 {
 256   ptrdiff_t i;
 257   gc_mark_str(proto_chunkname(pt));
 258   for (i = -(ptrdiff_t)pt->sizekgc; i < 0; i++)  /* Mark collectable consts. */
 259     gc_markobj(g, proto_kgc(pt, i));
 260 #if LJ_HASJIT
 261   if (pt->trace) gc_marktrace(g, pt->trace);
 262 #endif
 263 }
 264
 265 /* Traverse the frame structure of a stack. */
 266 static MSize gc_traverse_frames(global_State *g, lua_State *th)
 267 {
 268   TValue *frame, *top = th->top-1, *bot = tvref(th->stack);
 269   /* Note: extra vararg frame not skipped, marks function twice (harmless). */
 270   for (frame = th->base-1; frame > bot; frame = frame_prev(frame)) {
 271     GCfunc *fn = frame_func(frame);
 272     TValue *ftop = frame;
 273     if (isluafunc(fn)) ftop += funcproto(fn)->framesize;
 274     if (ftop > top) top = ftop;
 275     gc_markobj(g, fn);  /* Need to mark hidden function (or L). */
 276   }
 277   top++;  /* Correct bias of -1 (frame == base-1). */
 278   if (top > tvref(th->maxstack)) top = tvref(th->maxstack);
 279   return (MSize)(top - bot);  /* Return minimum needed stack size. */
 280 }
 281
 282 /* Traverse a thread object. */
 283 static void gc_traverse_thread(global_State *g, lua_State *th)
 284 {
 285   TValue *o, *top = th->top;
 286   for (o = tvref(th->stack)+1; o < top; o++)
 287     gc_marktv(g, o);
 288   if (g->gc.state == GCSatomic) {
 289     top = tvref(th->stack) + th->stacksize;
 290     for (; o < top; o++)  /* Clear unmarked slots. */
 291       setnilV(o);
 292   }
 293   gc_markobj(g, tabref(th->env));
 294   lj_state_shrinkstack(th, gc_traverse_frames(g, th));
 295 }
 296
 297 /* Propagate one gray object. Traverse it and turn it black. */
 298 static size_t propagatemark(global_State *g)
 299 {
 300   GCobj *o = gcref(g->gc.gray);
 301   int gct = o->gch.gct;
 302   lua_assert(isgray(o));
 303   gray2black(o);
 304   setgcrefr(g->gc.gray, o->gch.gclist);  /* Remove from gray list. */
 305   if (LJ_LIKELY(gct == ~LJ_TTAB)) {
 306     GCtab *t = gco2tab(o);
 307     if (gc_traverse_tab(g, t) > 0)
 308       black2gray(o);  /* Keep weak tables gray. */
 309     return sizeof(GCtab) + sizeof(TValue) * t->asize +
 310                            sizeof(Node) * (t->hmask + 1);
 311   } else if (LJ_LIKELY(gct == ~LJ_TFUNC)) {
 312     GCfunc *fn = gco2func(o);
 313     gc_traverse_func(g, fn);
 314     return isluafunc(fn) ? sizeLfunc((MSize)fn->l.nupvalues) :
 315                            sizeCfunc((MSize)fn->c.nupvalues);
 316   } else if (LJ_LIKELY(gct == ~LJ_TPROTO)) {
 317     GCproto *pt = gco2pt(o);
 318     gc_traverse_proto(g, pt);
 319     return pt->sizept;
 320   } else if (LJ_LIKELY(gct == ~LJ_TTHREAD)) {
 321     lua_State *th = gco2th(o);
 322     setgcrefr(th->gclist, g->gc.grayagain);
 323     setgcref(g->gc.grayagain, o);
 324     black2gray(o);  /* Threads are never black. */
 325     gc_traverse_thread(g, th);
 326     return sizeof(lua_State) + sizeof(TValue) * th->stacksize;
 327   } else {
 328 #if LJ_HASJIT
 329     GCtrace *T = gco2trace(o);
 330     gc_traverse_trace(g, T);
 331     return ((sizeof(GCtrace)+7)&~7) + (T->nins-T->nk)*sizeof(IRIns) +
 332            T->nsnap*sizeof(SnapShot) + T->nsnapmap*sizeof(SnapEntry);
 333 #else
 334     lua_assert(0);
 335     return 0;
 336 #endif
 337   }
 338 }
 339
 340 /* Propagate all gray objects. */
 341 static size_t gc_propagate_gray(global_State *g)
 342 {
 343   size_t m = 0;
 344   while (gcref(g->gc.gray) != NULL)
 345     m += propagatemark(g);
 346   return m;
 347 }
 348
 349 /* -- Sweep phase --------------------------------------------------------- */
 350
 351 /* Try to shrink some common data structures. */
 352 static void gc_shrink(global_State *g, lua_State *L)
 353 {
 354   if (g->strnum <= (g->strmask >> 2) && g->strmask > LJ_MIN_STRTAB*2-1)
 355     lj_str_resize(L, g->strmask >> 1);  /* Shrink string table. */
 356   if (g->tmpbuf.sz > LJ_MIN_SBUF*2)
 357     lj_str_resizebuf(L, &g->tmpbuf, g->tmpbuf.sz >> 1);  /* Shrink temp buf. */
 358 }
 359
 360 /* Type of GC free functions. */
 361 typedef void (LJ_FASTCALL *GCFreeFunc)(global_State *g, GCobj *o);
 362
 363 /* GC free functions for LJ_TSTR .. LJ_TUDATA. ORDER LJ_T */
 364 static const GCFreeFunc gc_freefunc[] = {
 365   (GCFreeFunc)lj_str_free,
 366   (GCFreeFunc)lj_func_freeuv,
 367   (GCFreeFunc)lj_state_free,
 368   (GCFreeFunc)lj_func_freeproto,
 369   (GCFreeFunc)lj_func_free,
 370 #if LJ_HASJIT
 371   (GCFreeFunc)lj_trace_free,
 372 #else
 373   (GCFreeFunc)0,
 374 #endif
 375 #if LJ_HASFFI
 376   (GCFreeFunc)lj_cdata_free,
 377 #else
 378   (GCFreeFunc)0,
 379 #endif
 380   (GCFreeFunc)lj_tab_free,
 381   (GCFreeFunc)lj_udata_free
 382 };
 383
 384 /* Full sweep of a GC list. */
 385 #define gc_fullsweep(g, p)      gc_sweep(g, (p), LJ_MAX_MEM)
 386
 387 /* Partial sweep of a GC list. */
 388 static GCRef *gc_sweep(global_State *g, GCRef *p, uint32_t lim)
 389 {
 390   /* Mask with other white and LJ_GC_FIXED. Or LJ_GC_SFIXED on shutdown. */
 391   int ow = otherwhite(g);
 392   GCobj *o;
 393   while ((o = gcref(*p)) != NULL && lim-- > 0) {
 394     if (o->gch.gct == ~LJ_TTHREAD)  /* Need to sweep open upvalues, too. */
 395       gc_fullsweep(g, &gco2th(o)->openupval);
 396     if (((o->gch.marked ^ LJ_GC_WHITES) & ow)) {  /* Black or current white? */
 397       lua_assert(!isdead(g, o) || (o->gch.marked & LJ_GC_FIXED));
 398       makewhite(g, o);  /* Value is alive, change to the current white. */
 399       p = &o->gch.nextgc;
 400     } else {  /* Otherwise value is dead, free it. */
 401       lua_assert(isdead(g, o) || ow == LJ_GC_SFIXED);
 402       setgcrefr(*p, o->gch.nextgc);
 403       if (o == gcref(g->gc.root))
 404         setgcrefr(g->gc.root, o->gch.nextgc);  /* Adjust list anchor. */
 405       gc_freefunc[o->gch.gct - ~LJ_TSTR](g, o);
 406     }
 407   }
 408   return p;
 409 }
 410
 411 /* Check whether we can clear a key or a value slot from a table. */
 412 static int gc_mayclear(cTValue *o, int val)
 413 {
 414   if (tvisgcv(o)) {  /* Only collectable objects can be weak references. */
 415     if (tvisstr(o)) {  /* But strings cannot be used as weak references. */
 416       gc_mark_str(strV(o));  /* And need to be marked. */
 417       return 0;
 418     }
 419     if (iswhite(gcV(o)))
 420       return 1;  /* Object is about to be collected. */
 421     if (tvisudata(o) && val && isfinalized(udataV(o)))
 422       return 1;  /* Finalized userdata is dropped only from values. */
 423   }
 424   return 0;  /* Cannot clear. */
 425 }
 426
 427 /* Clear collected entries from weak tables. */
 428 static void gc_clearweak(GCobj *o)
 429 {
 430   while (o) {
 431     GCtab *t = gco2tab(o);
 432     lua_assert((t->marked & LJ_GC_WEAK));
 433     if ((t->marked & LJ_GC_WEAKVAL)) {
 434       MSize i, asize = t->asize;
 435       for (i = 0; i < asize; i++) {
 436         /* Clear array slot when value is about to be collected. */
 437         TValue *tv = arrayslot(t, i);
 438         if (gc_mayclear(tv, 1))
 439           setnilV(tv);
 440       }
 441     }
 442     if (t->hmask > 0) {
 443       Node *node = noderef(t->node);
 444       MSize i, hmask = t->hmask;
 445       for (i = 0; i <= hmask; i++) {
 446         Node *n = &node[i];
 447         /* Clear hash slot when key or value is about to be collected. */
 448         if (!tvisnil(&n->val) && (gc_mayclear(&n->key, 0) ||
 449                                   gc_mayclear(&n->val, 1)))
 450           setnilV(&n->val);
 451       }
 452     }
 453     o = gcref(t->gclist);
 454   }
 455 }
 456
 457 /* Call a userdata or cdata finalizer. */
 458 static void gc_call_finalizer(global_State *g, lua_State *L,
 459                               cTValue *mo, GCobj *o)
 460 {
 461   /* Save and restore lots of state around the __gc callback. */
 462   uint8_t oldh = hook_save(g);
 463   MSize oldt = g->gc.threshold;
 464   int errcode;
 465   TValue *top;
 466   lj_trace_abort(g);
 467   top = L->top;
 468   L->top = top+2;
 469   hook_entergc(g);  /* Disable hooks and new traces during __gc. */
 470   g->gc.threshold = LJ_MAX_MEM;  /* Prevent GC steps. */
 471   copyTV(L, top, mo);
 472   setgcV(L, top+1, o, ~o->gch.gct);
 473   errcode = lj_vm_pcall(L, top+1, 1+0, -1);  /* Stack: |mo|o| -> | */
 474   hook_restore(g, oldh);
 475   g->gc.threshold = oldt;  /* Restore GC threshold. */
 476   if (errcode)
 477     lj_err_throw(L, errcode);  /* Propagate errors. */
 478 }
 479
 480 /* Finalize one userdata or cdata object from the mmudata list. */
 481 static void gc_finalize(lua_State *L)
 482 {
 483   global_State *g = G(L);
 484   GCobj *o = gcnext(gcref(g->gc.mmudata));
 485   cTValue *mo;
 486   lua_assert(gcref(g->jit_L) == NULL);  /* Must not be called on trace. */
 487   /* Unchain from list of userdata to be finalized. */
 488   if (o == gcref(g->gc.mmudata))
 489     setgcrefnull(g->gc.mmudata);
 490   else
 491     setgcrefr(gcref(g->gc.mmudata)->gch.nextgc, o->gch.nextgc);
 492 #if LJ_HASFFI
 493   if (o->gch.gct == ~LJ_TCDATA) {
 494     TValue tmp, *tv;
 495     /* Add cdata back to the GC list and make it white. */
 496     setgcrefr(o->gch.nextgc, g->gc.root);
 497     setgcref(g->gc.root, o);
 498     makewhite(g, o);
 499     o->gch.marked &= (uint8_t)~LJ_GC_CDATA_FIN;
 500     /* Resolve finalizer. */
 501     setcdataV(L, &tmp, gco2cd(o));
 502     tv = lj_tab_set(L, ctype_ctsG(g)->finalizer, &tmp);
 503     if (!tvisnil(tv)) {
 504       g->gc.nocdatafin = 0;
 505       copyTV(L, &tmp, tv);
 506       setnilV(tv);  /* Clear entry in finalizer table. */
 507       gc_call_finalizer(g, L, &tmp, o);
 508     }
 509     return;
 510   }
 511 #endif
 512   /* Add userdata back to the main userdata list and make it white. */
 513   setgcrefr(o->gch.nextgc, mainthread(g)->nextgc);
 514   setgcref(mainthread(g)->nextgc, o);
 515   makewhite(g, o);
 516   /* Resolve the __gc metamethod. */
 517   mo = lj_meta_fastg(g, tabref(gco2ud(o)->metatable), MM_gc);
 518   if (mo)
 519     gc_call_finalizer(g, L, mo, o);
 520 }
 521
 522 /* Finalize all userdata objects from mmudata list. */
 523 void lj_gc_finalize_udata(lua_State *L)
 524 {
 525   while (gcref(G(L)->gc.mmudata) != NULL)
 526     gc_finalize(L);
 527 }
 528
 529 #if LJ_HASFFI
 530 /* Finalize all cdata objects from finalizer table. */
 531 void lj_gc_finalize_cdata(lua_State *L)
 532 {
 533   global_State *g = G(L);
 534   CTState *cts = ctype_ctsG(g);
 535   if (cts) {
 536     GCtab *t = cts->finalizer;
 537     Node *node = noderef(t->node);
 538     ptrdiff_t i;
 539     setgcrefnull(t->metatable);  /* Mark finalizer table as disabled. */
 540     for (i = (ptrdiff_t)t->hmask; i >= 0; i--)
 541       if (!tvisnil(&node[i].val) && tviscdata(&node[i].key)) {
 542         GCobj *o = gcV(&node[i].key);
 543         TValue tmp;
 544         makewhite(g, o);
 545         o->gch.marked &= (uint8_t)~LJ_GC_CDATA_FIN;
 546         copyTV(L, &tmp, &node[i].val);
 547         setnilV(&node[i].val);
 548         gc_call_finalizer(g, L, &tmp, o);
 549       }
 550   }
 551 }
 552 #endif
 553
 554 /* Free all remaining GC objects. */
 555 void lj_gc_freeall(global_State *g)
 556 {
 557   MSize i, strmask;
 558   /* Free everything, except super-fixed objects (the main thread). */
 559   g->gc.currentwhite = LJ_GC_WHITES | LJ_GC_SFIXED;
 560   gc_fullsweep(g, &g->gc.root);
 561   strmask = g->strmask;
 562   for (i = 0; i <= strmask; i++)  /* Free all string hash chains. */
 563     gc_fullsweep(g, &g->strhash[i]);
 564 }
 565
 566 /* -- Collector ----------------------------------------------------------- */
 567
 568 /* Atomic part of the GC cycle, transitioning from mark to sweep phase. */
 569 static void atomic(global_State *g, lua_State *L)
 570 {
 571   size_t udsize;
 572
 573   gc_mark_uv(g);  /* Need to remark open upvalues (the thread may be dead). */
 574   gc_propagate_gray(g);  /* Propagate any left-overs. */
 575
 576   setgcrefr(g->gc.gray, g->gc.weak);  /* Empty the list of weak tables. */
 577   setgcrefnull(g->gc.weak);
 578   lua_assert(!iswhite(obj2gco(mainthread(g))));
 579   gc_markobj(g, L);  /* Mark running thread. */
 580   gc_traverse_curtrace(g);  /* Traverse current trace. */
 581   gc_mark_gcroot(g);  /* Mark GC roots (again). */
 582   gc_propagate_gray(g);  /* Propagate all of the above. */
 583
 584   setgcrefr(g->gc.gray, g->gc.grayagain);  /* Empty the 2nd chance list. */
 585   setgcrefnull(g->gc.grayagain);
 586   gc_propagate_gray(g);  /* Propagate it. */
 587
 588   udsize = lj_gc_separateudata(g, 0);  /* Separate userdata to be finalized. */
 589   gc_mark_mmudata(g);  /* Mark them. */
 590   udsize += gc_propagate_gray(g);  /* And propagate the marks. */
 591
 592   /* All marking done, clear weak tables. */
 593   gc_clearweak(gcref(g->gc.weak));
 594
 595   /* Prepare for sweep phase. */
 596   g->gc.currentwhite = (uint8_t)otherwhite(g);  /* Flip current white. */
 597   g->strempty.marked = g->gc.currentwhite;
 598   setmref(g->gc.sweep, &g->gc.root);
 599   g->gc.estimate = g->gc.total - (MSize)udsize;  /* Initial estimate. */
 600 }
 601
 602 /* GC state machine. Returns a cost estimate for each step performed. */
 603 static size_t gc_onestep(lua_State *L)
 604 {
 605   global_State *g = G(L);
 606   switch (g->gc.state) {
 607   case GCSpause:
 608     gc_mark_start(g);  /* Start a new GC cycle by marking all GC roots. */
 609     return 0;
 610   case GCSpropagate:
 611     if (gcref(g->gc.gray) != NULL)
 612       return propagatemark(g);  /* Propagate one gray object. */
 613     g->gc.state = GCSatomic;  /* End of mark phase. */
 614     return 0;
 615   case GCSatomic:
 616     if (gcref(g->jit_L))  /* Don't run atomic phase on trace. */
 617       return LJ_MAX_MEM;
 618     atomic(g, L);
 619     g->gc.state = GCSsweepstring;  /* Start of sweep phase. */
 620     g->gc.sweepstr = 0;
 621     return 0;
 622   case GCSsweepstring: {
 623     MSize old = g->gc.total;
 624     gc_fullsweep(g, &g->strhash[g->gc.sweepstr++]);  /* Sweep one chain. */
 625     if (g->gc.sweepstr > g->strmask)
 626       g->gc.state = GCSsweep;  /* All string hash chains sweeped. */
 627     lua_assert(old >= g->gc.total);
 628     g->gc.estimate -= old - g->gc.total;
 629     return GCSWEEPCOST;
 630     }
 631   case GCSsweep: {
 632     MSize old = g->gc.total;
 633     setmref(g->gc.sweep, gc_sweep(g, mref(g->gc.sweep, GCRef), GCSWEEPMAX));
 634     lua_assert(old >= g->gc.total);
 635     g->gc.estimate -= old - g->gc.total;
 636     if (gcref(*mref(g->gc.sweep, GCRef)) == NULL) {
 637       gc_shrink(g, L);
 638       if (gcref(g->gc.mmudata)) {  /* Need any finalizations? */
 639         g->gc.state = GCSfinalize;
 640 #if LJ_HASFFI
 641         g->gc.nocdatafin = 1;
 642 #endif
 643       } else {  /* Otherwise skip this phase to help the JIT. */
 644         g->gc.state = GCSpause;  /* End of GC cycle. */
 645         g->gc.debt = 0;
 646       }
 647     }
 648     return GCSWEEPMAX*GCSWEEPCOST;
 649     }
 650   case GCSfinalize:
 651     if (gcref(g->gc.mmudata) != NULL) {
 652       if (gcref(g->jit_L))  /* Don't call finalizers on trace. */
 653         return LJ_MAX_MEM;
 654       gc_finalize(L);  /* Finalize one userdata object. */
 655       if (g->gc.estimate > GCFINALIZECOST)
 656         g->gc.estimate -= GCFINALIZECOST;
 657       return GCFINALIZECOST;
 658     }
 659 #if LJ_HASFFI
 660     if (!g->gc.nocdatafin) lj_tab_rehash(L, ctype_ctsG(g)->finalizer);
 661 #endif
 662     g->gc.state = GCSpause;  /* End of GC cycle. */
 663     g->gc.debt = 0;
 664     return 0;
 665   default:
 666     lua_assert(0);
 667     return 0;
 668   }
 669 }
 670
 671 /* Perform a limited amount of incremental GC steps. */
 672 int LJ_FASTCALL lj_gc_step(lua_State *L)
 673 {
 674   global_State *g = G(L);
 675   MSize lim;
 676   int32_t ostate = g->vmstate;
 677   setvmstate(g, GC);
 678   lim = (GCSTEPSIZE/100) * g->gc.stepmul;
 679   if (lim == 0)
 680     lim = LJ_MAX_MEM;
 681   if (g->gc.total > g->gc.threshold)
 682     g->gc.debt += g->gc.total - g->gc.threshold;
 683   do {
 684     lim -= (MSize)gc_onestep(L);
 685     if (g->gc.state == GCSpause) {
 686       g->gc.threshold = (g->gc.estimate/100) * g->gc.pause;
 687       g->vmstate = ostate;
 688       return 1;  /* Finished a GC cycle. */
 689     }
 690   } while ((int32_t)lim > 0);
 691   if (g->gc.debt < GCSTEPSIZE) {
 692     g->gc.threshold = g->gc.total + GCSTEPSIZE;
 693     g->vmstate = ostate;
 694     return -1;
 695   } else {
 696     g->gc.debt -= GCSTEPSIZE;
 697     g->gc.threshold = g->gc.total;
 698     g->vmstate = ostate;
 699     return 0;
 700   }
 701 }
 702
 703 /* Ditto, but fix the stack top first. */
 704 void LJ_FASTCALL lj_gc_step_fixtop(lua_State *L)
 705 {
 706   if (curr_funcisL(L)) L->top = curr_topL(L);
 707   lj_gc_step(L);
 708 }
 709
 710 #if LJ_HASJIT
 711 /* Perform multiple GC steps. Called from JIT-compiled code. */
 712 int LJ_FASTCALL lj_gc_step_jit(global_State *g, MSize steps)
 713 {
 714   lua_State *L = gco2th(gcref(g->jit_L));
 715   L->base = mref(G(L)->jit_base, TValue);
 716   L->top = curr_topL(L);
 717   while (steps-- > 0 && lj_gc_step(L) == 0)
 718     ;
 719   /* Return 1 to force a trace exit. */
 720   return (G(L)->gc.state == GCSatomic || G(L)->gc.state == GCSfinalize);
 721 }
 722 #endif
 723
 724 /* Perform a full GC cycle. */
 725 void lj_gc_fullgc(lua_State *L)
 726 {
 727   global_State *g = G(L);
 728   int32_t ostate = g->vmstate;
 729   setvmstate(g, GC);
 730   if (g->gc.state <= GCSatomic) {  /* Caught somewhere in the middle. */
 731     setmref(g->gc.sweep, &g->gc.root);  /* Sweep everything (preserving it). */
 732     setgcrefnull(g->gc.gray);  /* Reset lists from partial propagation. */
 733     setgcrefnull(g->gc.grayagain);
 734     setgcrefnull(g->gc.weak);
 735     g->gc.state = GCSsweepstring;  /* Fast forward to the sweep phase. */
 736     g->gc.sweepstr = 0;
 737   }
 738   while (g->gc.state == GCSsweepstring || g->gc.state == GCSsweep)
 739     gc_onestep(L);  /* Finish sweep. */
 740   lua_assert(g->gc.state == GCSfinalize || g->gc.state == GCSpause);
 741   /* Now perform a full GC. */
 742   g->gc.state = GCSpause;
 743   do { gc_onestep(L); } while (g->gc.state != GCSpause);
 744   g->gc.threshold = (g->gc.estimate/100) * g->gc.pause;
 745   g->vmstate = ostate;
 746 }
 747
 748 /* -- Write barriers ------------------------------------------------------ */
 749
 750 /* Move the GC propagation frontier forward. */
 751 void lj_gc_barrierf(global_State *g, GCobj *o, GCobj *v)
 752 {
 753   lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
 754   lua_assert(g->gc.state != GCSfinalize && g->gc.state != GCSpause);
 755   lua_assert(o->gch.gct != ~LJ_TTAB);
 756   /* Preserve invariant during propagation. Otherwise it doesn't matter. */
 757   if (g->gc.state == GCSpropagate || g->gc.state == GCSatomic)
 758     gc_mark(g, v);  /* Move frontier forward. */
 759   else
 760     makewhite(g, o);  /* Make it white to avoid the following barrier. */
 761 }
 762
 763 /* Specialized barrier for closed upvalue. Pass &uv->tv. */
 764 void LJ_FASTCALL lj_gc_barrieruv(global_State *g, TValue *tv)
 765 {
 766 #define TV2MARKED(x) \
 767   (*((uint8_t *)(x) - offsetof(GCupval, tv) + offsetof(GCupval, marked)))
 768   if (g->gc.state == GCSpropagate || g->gc.state == GCSatomic)
 769     gc_mark(g, gcV(tv));
 770   else
 771     TV2MARKED(tv) = (TV2MARKED(tv) & (uint8_t)~LJ_GC_COLORS) | curwhite(g);
 772 #undef TV2MARKED
 773 }
 774
 775 /* Close upvalue. Also needs a write barrier. */
 776 void lj_gc_closeuv(global_State *g, GCupval *uv)
 777 {
 778   GCobj *o = obj2gco(uv);
 779   /* Copy stack slot to upvalue itself and point to the copy. */
 780   copyTV(mainthread(g), &uv->tv, uvval(uv));
 781   setmref(uv->v, &uv->tv);
 782   uv->closed = 1;
 783   setgcrefr(o->gch.nextgc, g->gc.root);
 784   setgcref(g->gc.root, o);
 785   if (isgray(o)) {  /* A closed upvalue is never gray, so fix this. */
 786     if (g->gc.state == GCSpropagate || g->gc.state == GCSatomic) {
 787       gray2black(o);  /* Make it black and preserve invariant. */
 788       if (tviswhite(&uv->tv))
 789         lj_gc_barrierf(g, o, gcV(&uv->tv));
 790     } else {
 791       makewhite(g, o);  /* Make it white, i.e. sweep the upvalue. */
 792       lua_assert(g->gc.state != GCSfinalize && g->gc.state != GCSpause);
 793     }
 794   }
 795 }
 796
 797 #if LJ_HASJIT
 798 /* Mark a trace if it's saved during the propagation phase. */
 799 void lj_gc_barriertrace(global_State *g, uint32_t traceno)
 800 {
 801   if (g->gc.state == GCSpropagate || g->gc.state == GCSatomic)
 802     gc_marktrace(g, traceno);
 803 }
 804 #endif
 805
 806 /* -- Allocator ----------------------------------------------------------- */
 807
 808 /* Call pluggable memory allocator to allocate or resize a fragment. */
 809 void *lj_mem_realloc(lua_State *L, void *p, MSize osz, MSize nsz)
 810 {
 811   global_State *g = G(L);
 812   lua_assert((osz == 0) == (p == NULL));
 813   p = g->allocf(g->allocd, p, osz, nsz);
 814   if (p == NULL && nsz > 0)
 815     lj_err_mem(L);
 816   lua_assert((nsz == 0) == (p == NULL));
 817   lua_assert(checkptr32(p));
 818   g->gc.total = (g->gc.total - osz) + nsz;
 819   return p;
 820 }
 821
 822 /* Allocate new GC object and link it to the root set. */
 823 void * LJ_FASTCALL lj_mem_newgco(lua_State *L, MSize size)
 824 {
 825   global_State *g = G(L);
 826   GCobj *o = (GCobj *)g->allocf(g->allocd, NULL, 0, size);
 827   if (o == NULL)
 828     lj_err_mem(L);
 829   lua_assert(checkptr32(o));
 830   g->gc.total += size;
 831   setgcrefr(o->gch.nextgc, g->gc.root);
 832   setgcref(g->gc.root, o);
 833   newwhite(g, o);
 834   return o;
 835 }
 836
 837 /* Resize growable vector. */
 838 void *lj_mem_grow(lua_State *L, void *p, MSize *szp, MSize lim, MSize esz)
 839 {
 840   MSize sz = (*szp) << 1;
 841   if (sz < LJ_MIN_VECSZ)
 842     sz = LJ_MIN_VECSZ;
 843   if (sz > lim)
 844     sz = lim;
 845   p = lj_mem_realloc(L, p, (*szp)*esz, sz*esz);
 846   *szp = sz;
 847   return p;
 848 }
 849