lua/doxygen/lgc_8h_source.html

/*

** $Id: lgc.h $

** 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. (Open

** upvalues are an exception to this rule.)  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 GCSenteratomic  1

#define GCSatomic   2

#define GCSswpallgc 3

#define GCSswpfinobj    4

#define GCSswptobefnz   5

#define GCSswpend   6

#define GCScallfin  7

#define GCSpause    8


#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_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. First three bits are

** used for object "age" in generational mode. Last bit is used

** by tests.

*/

#define WHITE0BIT   3  /* object is white (type 0) */

#define WHITE1BIT   4  /* object is white (type 1) */

#define BLACKBIT    5  /* object is black */

#define FINALIZEDBIT    6  /* object has been marked for finalization */


#define TESTBIT     7


#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) & (ow))

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


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

#define nw2black(x)  \

    check_exp(!iswhite(x), l_setbit((x)->marked, BLACKBIT))


#define luaC_white(g)   cast_byte((g)->currentwhite & WHITEBITS)


/* object age in generational mode */

#define G_NEW       0   /* created in current cycle */

#define G_SURVIVAL  1   /* created in previous cycle */

#define G_OLD0      2   /* marked old by frw. barrier in this cycle */

#define G_OLD1      3   /* first full cycle as old */

#define G_OLD       4   /* really old object (not to be visited) */

#define G_TOUCHED1  5   /* old object touched this cycle */

#define G_TOUCHED2  6   /* old object touched in previous cycle */


#define AGEBITS     7  /* all age bits (111) */


#define getage(o)   ((o)->marked & AGEBITS)

#define setage(o,a)  ((o)->marked = cast_byte(((o)->marked & (~AGEBITS)) | a))

#define isold(o)    (getage(o) > G_SURVIVAL)


#define changeage(o,f,t)  \

    check_exp(getage(o) == (f), (o)->marked ^= ((f)^(t)))


/* Default Values for GC parameters */

#define LUAI_GENMAJORMUL         100

#define LUAI_GENMINORMUL         20


/* wait memory to double before starting new cycle */

#define LUAI_GCPAUSE    200


/*

** some gc parameters are stored divided by 4 to allow a maximum value

** up to 1023 in a 'lu_byte'.

*/

#define getgcparam(p)   ((p) * 4)

#define setgcparam(p,v) ((p) = (v) / 4)


#define LUAI_GCMUL      100


/* how much to allocate before next GC step (log2) */

#define LUAI_GCSTEPSIZE 13      /* 8 KB */


/*

** Check whether the declared GC mode is generational. While in

** generational mode, the collector can go temporarily to incremental

** mode to improve performance. This is signaled by 'g->lastatomic != 0'.

*/

#define isdecGCmodegen(g)   (g->gckind == KGC_GEN || g->lastatomic != 0)


/*

** 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))


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, GCObject *o);

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

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


#endif