lua/lgc.h

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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