lgc.h - external/github.com/lua/lua - Git at Google

 /*
 ** $Id: lgc.h $
 ** Garbage Collector
 ** See Copyright Notice in lua.h
 */

 #ifndef lgc_h
 #define lgc_h


 #include <stddef.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)


 /*
 ** In generational mode, objects are created 'new'. After surviving one
 ** cycle, they become 'survival'. Both 'new' and 'survival' can point
 ** to any other object, as they are traversed at the end of the cycle.
 ** We call them both 'young' objects.
 ** If a survival object survives another cycle, it becomes 'old1'.
 ** 'old1' objects can still point to survival objects (but not to
 ** new objects), so they still must be traversed. After another cycle
 ** (that, being old, 'old1' objects will "survive" no matter what)
 ** finally the 'old1' object becomes really 'old', and then they
 ** are no more traversed.
 **
 ** To keep its invariants, the generational mode uses the same barriers
 ** also used by the incremental mode. If a young object is caught in a
 ** foward barrier, it cannot become old immediately, because it can
 ** still point to other young objects. Instead, it becomes 'old0',
 ** which in the next cycle becomes 'old1'. So, 'old0' objects is
 ** old but can point to new and survival objects; 'old1' is old
 ** but cannot point to new objects; and 'old' cannot point to any
 ** young object.
 **
 ** If any old object ('old0', 'old1', 'old') is caught in a back
 ** barrier, it becomes 'touched1' and goes into a gray list, to be
 ** visited at the end of the cycle.  There it evolves to 'touched2',
 ** which can point to survivals but not to new objects. In yet another
 ** cycle then it becomes 'old' again.
 **
 ** The generational mode must also control the colors of objects,
 ** because of the barriers.  While the mutator is running, young objects
 ** are kept white. 'old', 'old1', and 'touched2' objects are kept black,
 ** as they cannot point to new objects; exceptions are threads and open
 ** upvalues, which age to 'old1' and 'old' but are kept gray. 'old0'
 ** objects may be gray or black, as in the incremental mode. 'touched1'
 ** objects are kept gray, as they must be visited again at the end of
 ** the cycle.
 */


 /* Default Values for GC parameters */

 /*
 ** Minor collections will shift to major ones after LUAI_MINORMAJOR%
 ** objects become old.
 */
 #define LUAI_MINORMAJOR         100

 /*
 ** Major collections will shift to minor ones after a collection
 ** collects at least LUAI_MAJORMINOR% of the new objects.
 */
 #define LUAI_MAJORMINOR         50

 /*
 ** A young (minor) collection will run after creating LUAI_GENMINORMUL%
 ** new objects.
 */
 #define LUAI_GENMINORMUL         25


 /* incremental */

 /* Number of objects must be LUAI_GCPAUSE% before starting new cycle */
 #define LUAI_GCPAUSE    200

 /* Step multiplier. (Roughly, the collector handles LUAI_GCMUL% objects
    for each new allocated object.) */
 #define LUAI_GCMUL      200

 /* How many objects to allocate before next GC step */
 #define LUAI_GCSTEPSIZE	250


 #define setgcparam(g,p,v)  (g->gcparams[LUA_GCP##p] = luaO_codeparam(v))
 #define applygcparam(g,p,x)  luaO_applyparam(g->gcparams[LUA_GCP##p], x)

 /*
 ** Control when GC is running:
 */
 #define GCSTPUSR	1  /* bit true when GC stopped by user */
 #define GCSTPGC		2  /* bit true when GC stopped by itself */
 #define GCSTPCLS	4  /* bit true when closing Lua state */
 #define gcrunning(g)	((g)->gcstp == 0)


 /*
 ** Does one step of collection when debt becomes zero. '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_objbarrier(L,p,o) (  \
 	(isblack(p) && iswhite(o)) ? \
 	luaC_barrier_(L,obj2gco(p),obj2gco(o)) : cast_void(0))

 #define luaC_barrier(L,p,v) (  \
 	iscollectable(v) ? luaC_objbarrier(L,p,gcvalue(v)) : cast_void(0))

 #define luaC_objbarrierback(L,p,o) (  \
 	(isblack(p) && iswhite(o)) ? luaC_barrierback_(L,p) : cast_void(0))

 #define luaC_barrierback(L,p,v) (  \
 	iscollectable(v) ? luaC_objbarrierback(L, p, gcvalue(v)) : 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 state, int fast);
 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 GCObject *luaC_newobjdt (lua_State *L, int tt, size_t sz,
                                                  size_t 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_checkfinalizer (lua_State *L, GCObject *o, Table *mt);
 LUAI_FUNC void luaC_changemode (lua_State *L, int newmode);


 #endif
	/*
	** $Id: lgc.h $
	** Garbage Collector
	** See Copyright Notice in lua.h
	*/

	#ifndef lgc_h
	#define lgc_h


	#include <stddef.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)


	/*
	** In generational mode, objects are created 'new'. After surviving one
	** cycle, they become 'survival'. Both 'new' and 'survival' can point
	** to any other object, as they are traversed at the end of the cycle.
	** We call them both 'young' objects.
	** If a survival object survives another cycle, it becomes 'old1'.
	** 'old1' objects can still point to survival objects (but not to
	** new objects), so they still must be traversed. After another cycle
	** (that, being old, 'old1' objects will "survive" no matter what)
	** finally the 'old1' object becomes really 'old', and then they
	** are no more traversed.
	**
	** To keep its invariants, the generational mode uses the same barriers
	** also used by the incremental mode. If a young object is caught in a
	** foward barrier, it cannot become old immediately, because it can
	** still point to other young objects. Instead, it becomes 'old0',
	** which in the next cycle becomes 'old1'. So, 'old0' objects is
	** old but can point to new and survival objects; 'old1' is old
	** but cannot point to new objects; and 'old' cannot point to any
	** young object.
	**
	** If any old object ('old0', 'old1', 'old') is caught in a back
	** barrier, it becomes 'touched1' and goes into a gray list, to be
	** visited at the end of the cycle. There it evolves to 'touched2',
	** which can point to survivals but not to new objects. In yet another
	** cycle then it becomes 'old' again.
	**
	** The generational mode must also control the colors of objects,
	** because of the barriers. While the mutator is running, young objects
	** are kept white. 'old', 'old1', and 'touched2' objects are kept black,
	** as they cannot point to new objects; exceptions are threads and open
	** upvalues, which age to 'old1' and 'old' but are kept gray. 'old0'
	** objects may be gray or black, as in the incremental mode. 'touched1'
	** objects are kept gray, as they must be visited again at the end of
	** the cycle.
	*/


	/* Default Values for GC parameters */

	/*
	** Minor collections will shift to major ones after LUAI_MINORMAJOR%
	** objects become old.
	*/
	#define LUAI_MINORMAJOR 100

	/*
	** Major collections will shift to minor ones after a collection
	** collects at least LUAI_MAJORMINOR% of the new objects.
	*/
	#define LUAI_MAJORMINOR 50

	/*
	** A young (minor) collection will run after creating LUAI_GENMINORMUL%
	** new objects.
	*/
	#define LUAI_GENMINORMUL 25


	/* incremental */

	/* Number of objects must be LUAI_GCPAUSE% before starting new cycle */
	#define LUAI_GCPAUSE 200

	/* Step multiplier. (Roughly, the collector handles LUAI_GCMUL% objects
	for each new allocated object.) */
	#define LUAI_GCMUL 200

	/* How many objects to allocate before next GC step */
	#define LUAI_GCSTEPSIZE 250


	#define setgcparam(g,p,v) (g->gcparams[LUA_GCP##p] = luaO_codeparam(v))
	#define applygcparam(g,p,x) luaO_applyparam(g->gcparams[LUA_GCP##p], x)

	/*
	** Control when GC is running:
	*/
	#define GCSTPUSR 1 /* bit true when GC stopped by user */
	#define GCSTPGC 2 /* bit true when GC stopped by itself */
	#define GCSTPCLS 4 /* bit true when closing Lua state */
	#define gcrunning(g) ((g)->gcstp == 0)


	/*
	** Does one step of collection when debt becomes zero. '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_objbarrier(L,p,o) ( \
	(isblack(p) && iswhite(o)) ? \
	luaC_barrier_(L,obj2gco(p),obj2gco(o)) : cast_void(0))

	#define luaC_barrier(L,p,v) ( \
	iscollectable(v) ? luaC_objbarrier(L,p,gcvalue(v)) : cast_void(0))

	#define luaC_objbarrierback(L,p,o) ( \
	(isblack(p) && iswhite(o)) ? luaC_barrierback_(L,p) : cast_void(0))

	#define luaC_barrierback(L,p,v) ( \
	iscollectable(v) ? luaC_objbarrierback(L, p, gcvalue(v)) : 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 state, int fast);
	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 GCObject luaC_newobjdt (lua_State L, int tt, size_t sz,
	size_t 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_checkfinalizer (lua_State L, GCObject o, Table *mt);
	LUAI_FUNC void luaC_changemode (lua_State *L, int newmode);


	#endif