1 /*
2 ** $Id: lgc.h,v 2.58.1.1 2013/04/12 18:48:47 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
158