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      1 /*	$NetBSD: lgc.h,v 1.10 2023/06/08 21:12:08 nikita Exp $	*/
      2 
      3 /*
      4 ** Id: lgc.h
      5 ** Garbage Collector
      6 ** See Copyright Notice in lua.h
      7 */
      8 
      9 #ifndef lgc_h
     10 #define lgc_h
     11 
     12 
     13 #include "lobject.h"
     14 #include "lstate.h"
     15 
     16 /*
     17 ** Collectable objects may have one of three colors: white, which means
     18 ** the object is not marked; gray, which means the object is marked, but
     19 ** its references may be not marked; and black, which means that the
     20 ** object and all its references are marked.  The main invariant of the
     21 ** garbage collector, while marking objects, is that a black object can
     22 ** never point to a white one. Moreover, any gray object must be in a
     23 ** "gray list" (gray, grayagain, weak, allweak, ephemeron) so that it
     24 ** can be visited again before finishing the collection cycle. (Open
     25 ** upvalues are an exception to this rule.)  These lists have no meaning
     26 ** when the invariant is not being enforced (e.g., sweep phase).
     27 */
     28 
     29 
     30 /*
     31 ** Possible states of the Garbage Collector
     32 */
     33 #define GCSpropagate	0
     34 #define GCSenteratomic	1
     35 #define GCSatomic	2
     36 #define GCSswpallgc	3
     37 #define GCSswpfinobj	4
     38 #define GCSswptobefnz	5
     39 #define GCSswpend	6
     40 #define GCScallfin	7
     41 #define GCSpause	8
     42 
     43 
     44 #define issweepphase(g)  \
     45 	(GCSswpallgc <= (g)->gcstate && (g)->gcstate <= GCSswpend)
     46 
     47 
     48 /*
     49 ** macro to tell when main invariant (white objects cannot point to black
     50 ** ones) must be kept. During a collection, the sweep
     51 ** phase may break the invariant, as objects turned white may point to
     52 ** still-black objects. The invariant is restored when sweep ends and
     53 ** all objects are white again.
     54 */
     55 
     56 #define keepinvariant(g)	((g)->gcstate <= GCSatomic)
     57 
     58 
     59 /*
     60 ** some useful bit tricks
     61 */
     62 #define resetbits(x,m)		((x) &= cast_byte(~(m)))
     63 #define setbits(x,m)		((x) |= (m))
     64 #define testbits(x,m)		((x) & (m))
     65 #define bitmask(b)		(1<<(b))
     66 #define bit2mask(b1,b2)		(bitmask(b1) | bitmask(b2))
     67 #define l_setbit(x,b)		setbits(x, bitmask(b))
     68 #define resetbit(x,b)		resetbits(x, bitmask(b))
     69 #define testbit(x,b)		testbits(x, bitmask(b))
     70 
     71 
     72 /*
     73 ** Layout for bit use in 'marked' field. First three bits are
     74 ** used for object "age" in generational mode. Last bit is used
     75 ** by tests.
     76 */
     77 #define WHITE0BIT	3  /* object is white (type 0) */
     78 #define WHITE1BIT	4  /* object is white (type 1) */
     79 #define BLACKBIT	5  /* object is black */
     80 #define FINALIZEDBIT	6  /* object has been marked for finalization */
     81 
     82 #define TESTBIT		7
     83 
     84 
     85 
     86 #define WHITEBITS	bit2mask(WHITE0BIT, WHITE1BIT)
     87 
     88 
     89 #define iswhite(x)      testbits((x)->marked, WHITEBITS)
     90 #define isblack(x)      testbit((x)->marked, BLACKBIT)
     91 #define isgray(x)  /* neither white nor black */  \
     92 	(!testbits((x)->marked, WHITEBITS | bitmask(BLACKBIT)))
     93 
     94 #define tofinalize(x)	testbit((x)->marked, FINALIZEDBIT)
     95 
     96 #define otherwhite(g)	((g)->currentwhite ^ WHITEBITS)
     97 #define isdeadm(ow,m)	((m) & (ow))
     98 #define isdead(g,v)	isdeadm(otherwhite(g), (v)->marked)
     99 
    100 #define changewhite(x)	((x)->marked ^= WHITEBITS)
    101 #define nw2black(x)  \
    102 	check_exp(!iswhite(x), l_setbit((x)->marked, BLACKBIT))
    103 
    104 #define luaC_white(g)	cast_byte((g)->currentwhite & WHITEBITS)
    105 
    106 
    107 /* object age in generational mode */
    108 #define G_NEW		0	/* created in current cycle */
    109 #define G_SURVIVAL	1	/* created in previous cycle */
    110 #define G_OLD0		2	/* marked old by frw. barrier in this cycle */
    111 #define G_OLD1		3	/* first full cycle as old */
    112 #define G_OLD		4	/* really old object (not to be visited) */
    113 #define G_TOUCHED1	5	/* old object touched this cycle */
    114 #define G_TOUCHED2	6	/* old object touched in previous cycle */
    115 
    116 #define AGEBITS		7  /* all age bits (111) */
    117 
    118 #define getage(o)	((o)->marked & AGEBITS)
    119 #define setage(o,a)  ((o)->marked = cast_byte(((o)->marked & (~AGEBITS)) | a))
    120 #define isold(o)	(getage(o) > G_SURVIVAL)
    121 
    122 #define changeage(o,f,t)  \
    123 	check_exp(getage(o) == (f), (o)->marked ^= ((f)^(t)))
    124 
    125 
    126 /* Default Values for GC parameters */
    127 #define LUAI_GENMAJORMUL         100
    128 #define LUAI_GENMINORMUL         20
    129 
    130 /* wait memory to double before starting new cycle */
    131 #define LUAI_GCPAUSE    200
    132 
    133 /*
    134 ** some gc parameters are stored divided by 4 to allow a maximum value
    135 ** up to 1023 in a 'lu_byte'.
    136 */
    137 #define getgcparam(p)	((p) * 4)
    138 #define setgcparam(p,v)	((p) = (v) / 4)
    139 
    140 #define LUAI_GCMUL      100
    141 
    142 /* how much to allocate before next GC step (log2) */
    143 #define LUAI_GCSTEPSIZE 13      /* 8 KB */
    144 
    145 
    146 /*
    147 ** Check whether the declared GC mode is generational. While in
    148 ** generational mode, the collector can go temporarily to incremental
    149 ** mode to improve performance. This is signaled by 'g->lastatomic != 0'.
    150 */
    151 #define isdecGCmodegen(g)	(g->gckind == KGC_GEN || g->lastatomic != 0)
    152 
    153 
    154 /*
    155 ** Control when GC is running:
    156 */
    157 #define GCSTPUSR	1  /* bit true when GC stopped by user */
    158 #define GCSTPGC		2  /* bit true when GC stopped by itself */
    159 #define GCSTPCLS	4  /* bit true when closing Lua state */
    160 #define gcrunning(g)	((g)->gcstp == 0)
    161 
    162 
    163 /*
    164 ** Does one step of collection when debt becomes positive. 'pre'/'pos'
    165 ** allows some adjustments to be done only when needed. macro
    166 ** 'condchangemem' is used only for heavy tests (forcing a full
    167 ** GC cycle on every opportunity)
    168 */
    169 #define luaC_condGC(L,pre,pos) \
    170 	{ if (G(L)->GCdebt > 0) { pre; luaC_step(L); pos;}; \
    171 	  condchangemem(L,pre,pos); }
    172 
    173 /* more often than not, 'pre'/'pos' are empty */
    174 #define luaC_checkGC(L)		luaC_condGC(L,(void)0,(void)0)
    175 
    176 
    177 #define luaC_objbarrier(L,p,o) (  \
    178 	(isblack(p) && iswhite(o)) ? \
    179 	luaC_barrier_(L,obj2gco(p),obj2gco(o)) : cast_void(0))
    180 
    181 #define luaC_barrier(L,p,v) (  \
    182 	iscollectable(v) ? luaC_objbarrier(L,p,gcvalue(v)) : cast_void(0))
    183 
    184 #define luaC_objbarrierback(L,p,o) (  \
    185 	(isblack(p) && iswhite(o)) ? luaC_barrierback_(L,p) : cast_void(0))
    186 
    187 #define luaC_barrierback(L,p,v) (  \
    188 	iscollectable(v) ? luaC_objbarrierback(L, p, gcvalue(v)) : cast_void(0))
    189 
    190 LUAI_FUNC void luaC_fix (lua_State *L, GCObject *o);
    191 LUAI_FUNC void luaC_freeallobjects (lua_State *L);
    192 LUAI_FUNC void luaC_step (lua_State *L);
    193 LUAI_FUNC void luaC_runtilstate (lua_State *L, int statesmask);
    194 LUAI_FUNC void luaC_fullgc (lua_State *L, int isemergency);
    195 LUAI_FUNC GCObject *luaC_newobj (lua_State *L, int tt, size_t sz);
    196 LUAI_FUNC GCObject *luaC_newobjdt (lua_State *L, int tt, size_t sz,
    197                                                  size_t offset);
    198 LUAI_FUNC void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v);
    199 LUAI_FUNC void luaC_barrierback_ (lua_State *L, GCObject *o);
    200 LUAI_FUNC void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt);
    201 LUAI_FUNC void luaC_changemode (lua_State *L, int newmode);
    202 
    203 
    204 #endif
    205