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/*

** $Id: lgc.h,v 2.52 2011/10/03 17:54:25 roberto Exp $

** Garbage Collector

** See Copyright Notice in lua.h

*/

#ifndef lgc_h

#define lgc_h

#include "lobject.h"

#include "lstate.h"

/*

** Collectable objects may have one of three colors: white, which

** means the object is not marked; gray, which means the

** object is marked, but its references may be not marked; and

** black, which means that the object and all its references are marked.

** The main invariant of the garbage collector, while marking objects,

** is that a black object can never point to a white one. Moreover,

** any gray object must be in a "gray list" (gray, grayagain, weak,

** allweak, ephemeron) so that it can be visited again before finishing

** the collection cycle. These lists have no meaning when the invariant

** is not being enforced (e.g., sweep phase).

*/

/*

** Possible states of the Garbage Collector

*/

#define GCSpropagate	0

#define GCSatomic	1

#define GCSsweepstring	2

#define GCSsweepudata	3

#define GCSsweep	4

#define GCSpause	5

#define issweepphase(g)  \

	(GCSsweepstring <= (g)->gcstate && (g)->gcstate <= GCSsweep)

#define isgenerational(g)	((g)->gckind == KGC_GEN)

/*

** macro to tell when main invariant (white objects cannot point to black

** ones) must be kept. During a non-generational collection, the sweep

** phase may break the invariant, as objects turned white may point to

** still-black objects. The invariant is restored when sweep ends and

** all objects are white again. During a generational collection, the

** invariant must be kept all times.

*/

#define keepinvariant(g)  (isgenerational(g) || g->gcstate <= GCSatomic)

/*

** some useful bit tricks

*/

#define resetbits(x,m)		((x) &= cast(lu_byte, ~(m)))

#define setbits(x,m)		((x) |= (m))

#define testbits(x,m)		((x) & (m))

#define bitmask(b)		(1<<(b))

#define bit2mask(b1,b2)		(bitmask(b1) | bitmask(b2))

#define l_setbit(x,b)		setbits(x, bitmask(b))

#define resetbit(x,b)		resetbits(x, bitmask(b))

#define testbit(x,b)		testbits(x, bitmask(b))

/* Layout for bit use in `marked' field: */

#define WHITE0BIT	0  /* object is white (type 0) */

#define WHITE1BIT	1  /* object is white (type 1) */

#define BLACKBIT	2  /* object is black */

#define FINALIZEDBIT	3  /* object has been separated for finalization */

#define SEPARATED	4  /* object is in 'finobj' list or in 'tobefnz' */

#define FIXEDBIT	5  /* object is fixed (should not be collected) */

#define OLDBIT		6  /* object is old (only in generational mode) */

/* bit 7 is currently used by tests (luaL_checkmemory) */

#define WHITEBITS	bit2mask(WHITE0BIT, WHITE1BIT)

#define iswhite(x)      testbits((x)->gch.marked, WHITEBITS)

#define isblack(x)      testbit((x)->gch.marked, BLACKBIT)

#define isgray(x)  /* neither white nor black */  \

	(!testbits((x)->gch.marked, WHITEBITS | bitmask(BLACKBIT)))

#define isold(x)	testbit((x)->gch.marked, OLDBIT)

/* MOVE OLD rule: whenever an object is moved to the beginning of

   a GC list, its old bit must be cleared */

#define resetoldbit(o)	resetbit((o)->gch.marked, OLDBIT)

#define otherwhite(g)	(g->currentwhite ^ WHITEBITS)

#define isdeadm(ow,m)	(!(((m) ^ WHITEBITS) & (ow)))

#define isdead(g,v)	isdeadm(otherwhite(g), (v)->gch.marked)

#define changewhite(x)	((x)->gch.marked ^= WHITEBITS)

#define gray2black(x)	l_setbit((x)->gch.marked, BLACKBIT)

#define valiswhite(x)	(iscollectable(x) && iswhite(gcvalue(x)))

#define luaC_white(g)	cast(lu_byte, (g)->currentwhite & WHITEBITS)

#define luaC_condGC(L,c) \

	{if (G(L)->GCdebt > 0) {c;}; condchangemem(L);}

#define luaC_checkGC(L)		luaC_condGC(L, luaC_step(L);)

#define luaC_barrier(L,p,v) { if (valiswhite(v) && isblack(obj2gco(p)))  \

	luaC_barrier_(L,obj2gco(p),gcvalue(v)); }

#define luaC_barrierback(L,p,v) { if (valiswhite(v) && isblack(obj2gco(p)))  \

	luaC_barrierback_(L,p); }

#define luaC_objbarrier(L,p,o)  \

	{ if (iswhite(obj2gco(o)) && isblack(obj2gco(p))) \

		luaC_barrier_(L,obj2gco(p),obj2gco(o)); }

#define luaC_objbarrierback(L,p,o)  \

   { if (iswhite(obj2gco(o)) && isblack(obj2gco(p))) luaC_barrierback_(L,p); }

#define luaC_barrierproto(L,p,c) \

   { if (isblack(obj2gco(p))) luaC_barrierproto_(L,p,c); }

LUAI_FUNC void luaC_freeallobjects (lua_State *L);

LUAI_FUNC void luaC_step (lua_State *L);

LUAI_FUNC void luaC_forcestep (lua_State *L);

LUAI_FUNC void luaC_runtilstate (lua_State *L, int statesmask);

LUAI_FUNC void luaC_fullgc (lua_State *L, int isemergency);

LUAI_FUNC GCObject *luaC_newobj (lua_State *L, int tt, size_t sz,

                                 GCObject **list, int offset);

LUAI_FUNC void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v);

LUAI_FUNC void luaC_barrierback_ (lua_State *L, GCObject *o);

LUAI_FUNC void luaC_barrierproto_ (lua_State *L, Proto *p, Closure *c);

LUAI_FUNC void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt);

LUAI_FUNC void luaC_checkupvalcolor (global_State *g, UpVal *uv);

LUAI_FUNC void luaC_changemode (lua_State *L, int mode);

#endif