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   1 /*
   2 ** $Id: lgc.h,v 2.58 2012/09/11 12:53:08 roberto Exp $
   3 ** Garbage Collector
   4 ** See Copyright Notice in lua.h
   5 */
   6
   7 #ifndef lgc_h
   8 #define lgc_h
   9
  10
  11 #include "lobject.h"
  12 #include "lstate.h"
  13
  14 /*
  15 ** Collectable objects may have one of three colors: white, which
  16 ** means the object is not marked; gray, which means the
  17 ** object is marked, but its references may be not marked; and
  18 ** black, which means that the object and all its references are marked.
  19 ** The main invariant of the garbage collector, while marking objects,
  20 ** is that a black object can never point to a white one. Moreover,
  21 ** any gray object must be in a "gray list" (gray, grayagain, weak,
  22 ** allweak, ephemeron) so that it can be visited again before finishing
  23 ** the collection cycle. These lists have no meaning when the invariant
  24 ** is not being enforced (e.g., sweep phase).
  25 */
  26
  27
  28
  29 /* how much to allocate before next GC step */
  30 #if !defined(GCSTEPSIZE)
  31 /* ~100 small strings */
  32 #define GCSTEPSIZE      (cast_int(100 * sizeof(TString)))
  33 #endif
  34
  35
  36 /*
  37 ** Possible states of the Garbage Collector
  38 */
  39 #define GCSpropagate    0
  40 #define GCSatomic       1
  41 #define GCSsweepstring  2
  42 #define GCSsweepudata   3
  43 #define GCSsweep        4
  44 #define GCSpause        5
  45
  46
  47 #define issweepphase(g)  \
  48         (GCSsweepstring <= (g)->gcstate && (g)->gcstate <= GCSsweep)
  49
  50 #define isgenerational(g)       ((g)->gckind == KGC_GEN)
  51
  52 /*
  53 ** macros to tell when main invariant (white objects cannot point to black
  54 ** ones) must be kept. During a non-generational collection, the sweep
  55 ** phase may break the invariant, as objects turned white may point to
  56 ** still-black objects. The invariant is restored when sweep ends and
  57 ** all objects are white again. During a generational collection, the
  58 ** invariant must be kept all times.
  59 */
  60
  61 #define keepinvariant(g)        (isgenerational(g) || g->gcstate <= GCSatomic)
  62
  63
  64 /*
  65 ** Outside the collector, the state in generational mode is kept in
  66 ** 'propagate', so 'keepinvariant' is always true.
  67 */
  68 #define keepinvariantout(g)  \
  69   check_exp(g->gcstate == GCSpropagate || !isgenerational(g),  \
  70             g->gcstate <= GCSatomic)
  71
  72
  73 /*
  74 ** some useful bit tricks
  75 */
  76 #define resetbits(x,m)          ((x) &= cast(lu_byte, ~(m)))
  77 #define setbits(x,m)            ((x) |= (m))
  78 #define testbits(x,m)           ((x) & (m))
  79 #define bitmask(b)              (1<<(b))
  80 #define bit2mask(b1,b2)         (bitmask(b1) | bitmask(b2))
  81 #define l_setbit(x,b)           setbits(x, bitmask(b))
  82 #define resetbit(x,b)           resetbits(x, bitmask(b))
  83 #define testbit(x,b)            testbits(x, bitmask(b))
  84
  85
  86 /* Layout for bit use in `marked' field: */
  87 #define WHITE0BIT       0  /* object is white (type 0) */
  88 #define WHITE1BIT       1  /* object is white (type 1) */
  89 #define BLACKBIT        2  /* object is black */
  90 #define FINALIZEDBIT    3  /* object has been separated for finalization */
  91 #define SEPARATED       4  /* object is in 'finobj' list or in 'tobefnz' */
  92 #define FIXEDBIT        5  /* object is fixed (should not be collected) */
  93 #define OLDBIT          6  /* object is old (only in generational mode) */
  94 /* bit 7 is currently used by tests (luaL_checkmemory) */
  95
  96 #define WHITEBITS       bit2mask(WHITE0BIT, WHITE1BIT)
  97
  98
  99 #define iswhite(x)      testbits((x)->gch.marked, WHITEBITS)
 100 #define isblack(x)      testbit((x)->gch.marked, BLACKBIT)
 101 #define isgray(x)  /* neither white nor black */  \
 102         (!testbits((x)->gch.marked, WHITEBITS | bitmask(BLACKBIT)))
 103
 104 #define isold(x)        testbit((x)->gch.marked, OLDBIT)
 105
 106 /* MOVE OLD rule: whenever an object is moved to the beginning of
 107    a GC list, its old bit must be cleared */
 108 #define resetoldbit(o)  resetbit((o)->gch.marked, OLDBIT)
 109
 110 #define otherwhite(g)   (g->currentwhite ^ WHITEBITS)
 111 #define isdeadm(ow,m)   (!(((m) ^ WHITEBITS) & (ow)))
 112 #define isdead(g,v)     isdeadm(otherwhite(g), (v)->gch.marked)
 113
 114 #define changewhite(x)  ((x)->gch.marked ^= WHITEBITS)
 115 #define gray2black(x)   l_setbit((x)->gch.marked, BLACKBIT)
 116
 117 #define valiswhite(x)   (iscollectable(x) && iswhite(gcvalue(x)))
 118
 119 #define luaC_white(g)   cast(lu_byte, (g)->currentwhite & WHITEBITS)
 120
 121
 122 #define luaC_condGC(L,c) \
 123         {if (G(L)->GCdebt > 0) {c;}; condchangemem(L);}
 124 #define luaC_checkGC(L)         luaC_condGC(L, luaC_step(L);)
 125
 126
 127 #define luaC_barrier(L,p,v) { if (valiswhite(v) && isblack(obj2gco(p)))  \
 128         luaC_barrier_(L,obj2gco(p),gcvalue(v)); }
 129
 130 #define luaC_barrierback(L,p,v) { if (valiswhite(v) && isblack(obj2gco(p)))  \
 131         luaC_barrierback_(L,p); }
 132
 133 #define luaC_objbarrier(L,p,o)  \
 134         { if (iswhite(obj2gco(o)) && isblack(obj2gco(p))) \
 135                 luaC_barrier_(L,obj2gco(p),obj2gco(o)); }
 136
 137 #define luaC_objbarrierback(L,p,o)  \
 138    { if (iswhite(obj2gco(o)) && isblack(obj2gco(p))) luaC_barrierback_(L,p); }
 139
 140 #define luaC_barrierproto(L,p,c) \
 141    { if (isblack(obj2gco(p))) luaC_barrierproto_(L,p,c); }
 142
 143 LUAI_FUNC void luaC_freeallobjects (lua_State *L);
 144 LUAI_FUNC void luaC_step (lua_State *L);
 145 LUAI_FUNC void luaC_forcestep (lua_State *L);
 146 LUAI_FUNC void luaC_runtilstate (lua_State *L, int statesmask);
 147 LUAI_FUNC void luaC_fullgc (lua_State *L, int isemergency);
 148 LUAI_FUNC GCObject *luaC_newobj (lua_State *L, int tt, size_t sz,
 149                                  GCObject **list, int offset);
 150 LUAI_FUNC void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v);
 151 LUAI_FUNC void luaC_barrierback_ (lua_State *L, GCObject *o);
 152 LUAI_FUNC void luaC_barrierproto_ (lua_State *L, Proto *p, Closure *c);
 153 LUAI_FUNC void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt);
 154 LUAI_FUNC void luaC_checkupvalcolor (global_State *g, UpVal *uv);
 155 LUAI_FUNC void luaC_changemode (lua_State *L, int mode);
 156
 157 #endif