lua/lgc.h

/*
** $Id: lgc.h,v 2.37 2010/05/06 18:17:22 roberto Exp roberto $
** 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 brak 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)


#define gcstopped(g)	((g)->GCdebt == MIN_LMEM)
#define stopgc(g)	((g)->GCdebt = MIN_LMEM)


/*
** 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))
#define set2bits(x,b1,b2)	setbits(x, (bit2mask(b1, b2)))
#define reset2bits(x,b1,b2)	resetbits(x, (bit2mask(b1, b2)))



/* 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  /* for userdata: has been finalized */
#define SEPARATED	4  /*  "    ": it's in 'udgc' list or in 'tobefnz' */
#define FIXEDBIT	5  /* object is fixed (should not be collected) */
#define OLDBIT		6  /* object is old (only in generational mode) */

#define WHITEBITS	bit2mask(WHITE0BIT, WHITE1BIT)


#define iswhite(x)      testbits((x)->gch.marked, WHITEBITS)
#define isblack(x)      testbit((x)->gch.marked, BLACKBIT)
#define isgray(x)	(!isblack(x) && !iswhite(x))

#define isold(x)	testbit((x)->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_checkGC(L) {condchangemem(L); if (G(L)->GCdebt > 0) luaC_step(L);}


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

#define luaC_barriert(L,t,v) { if (valiswhite(v) && isblack(obj2gco(t)))  \
	luaC_barrierback(L,t); }

#define luaC_objbarrier(L,p,o)  \
	{ if (iswhite(obj2gco(o)) && isblack(obj2gco(p))) \
		luaC_barrierf(L,obj2gco(p),obj2gco(o)); }

#define luaC_objbarriert(L,t,o)  \
   { if (iswhite(obj2gco(o)) && isblack(obj2gco(t))) luaC_barrierback(L,t); }

LUAI_FUNC void luaC_separateudata (lua_State *L, int all);
LUAI_FUNC void luaC_freeallobjects (lua_State *L);
LUAI_FUNC void luaC_step (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_barrierf (lua_State *L, GCObject *o, GCObject *v);
LUAI_FUNC void luaC_barrierback (lua_State *L, Table *t);
LUAI_FUNC void luaC_checkfinalizer (lua_State *L, Udata *u);
LUAI_FUNC void luaC_checkupvalcolor (global_State *g, UpVal *uv);
LUAI_FUNC void luaC_changemode (lua_State *L, int mode);

#endif