lgc.h

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/*
** $Id: lgc.h,v 2.91.1.1 2017/04/19 17:39:34 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).
*/



/* how much to allocate before next GC step */
#if !defined(GCSTEPSIZE)
/* ~100 small strings */
#define GCSTEPSIZE  (cast_int(100 * sizeof(TString)))
#endif


/*
** Possible states of the Garbage Collector
*/
#define GCSpropagate    0
#define GCSatomic   1
#define GCSswpallgc 2
#define GCSswpfinobj    3
#define GCSswptobefnz   4
#define GCSswpend   5
#define GCScallfin  6
#define GCSpause    7


#define issweepphase(g)  \
    (GCSswpallgc <= (g)->gcstate && (g)->gcstate <= GCSswpend)


/*
** macro to tell when main invariant (white objects cannot point to black
** ones) must be kept. During a 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.
*/

#define keepinvariant(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 marked for finalization */
/* bit 7 is currently used by tests (luaL_checkmemory) */

#define WHITEBITS   bit2mask(WHITE0BIT, WHITE1BIT)


#define iswhite(x)      testbits((x)->marked, WHITEBITS)
#define isblack(x)      testbit((x)->marked, BLACKBIT)
#define isgray(x)  /* neither white nor black */  \
    (!testbits((x)->marked, WHITEBITS | bitmask(BLACKBIT)))

#define tofinalize(x)   testbit((x)->marked, FINALIZEDBIT)

#define otherwhite(g)   ((g)->currentwhite ^ WHITEBITS)
#define isdeadm(ow,m)   (!(((m) ^ WHITEBITS) & (ow)))
#define isdead(g,v) isdeadm(otherwhite(g), (v)->marked)

#define changewhite(x)  ((x)->marked ^= WHITEBITS)
#define gray2black(x)   l_setbit((x)->marked, BLACKBIT)

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


/*
** Does one step of collection when debt becomes positive. 'pre'/'pos'
** allows some adjustments to be done only when needed. macro
** 'condchangemem' is used only for heavy tests (forcing a full
** GC cycle on every opportunity)
*/
#define luaC_condGC(L,pre,pos) \
    { if (G(L)->GCdebt > 0) { pre; luaC_step(L); pos;}; \
      condchangemem(L,pre,pos); }

/* more often than not, 'pre'/'pos' are empty */
#define luaC_checkGC(L)     luaC_condGC(L,(void)0,(void)0)


#define luaC_barrier(L,p,v) (  \
    (iscollectable(v) && isblack(p) && iswhite(gcvalue(v))) ?  \
    luaC_barrier_(L,obj2gco(p),gcvalue(v)) : cast_void(0))

#define luaC_barrierback(L,p,v) (  \
    (iscollectable(v) && isblack(p) && iswhite(gcvalue(v))) ? \
    luaC_barrierback_(L,p) : cast_void(0))

#define luaC_objbarrier(L,p,o) (  \
    (isblack(p) && iswhite(o)) ? \
    luaC_barrier_(L,obj2gco(p),obj2gco(o)) : cast_void(0))

#define luaC_upvalbarrier(L,uv) ( \
    (iscollectable((uv)->v) && !upisopen(uv)) ? \
         luaC_upvalbarrier_(L,uv) : cast_void(0))

LUAI_FUNC void luaC_fix (lua_State *L, GCObject *o);
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);
LUAI_FUNC void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v);
LUAI_FUNC void luaC_barrierback_ (lua_State *L, Table *o);
LUAI_FUNC void luaC_upvalbarrier_ (lua_State *L, UpVal *uv);
LUAI_FUNC void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt);
LUAI_FUNC void luaC_upvdeccount (lua_State *L, UpVal *uv);


#endif