mirror of
https://github.com/lua/lua
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257 lines
8.9 KiB
C
257 lines
8.9 KiB
C
/*
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** $Id: lgc.h $
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** Garbage Collector
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** See Copyright Notice in lua.h
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*/
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#ifndef lgc_h
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#define lgc_h
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#include <stddef.h>
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#include "lobject.h"
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#include "lstate.h"
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/*
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** Collectable objects may have one of three colors: white, which means
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** the object is not marked; gray, which means the object is marked, but
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** its references may be not marked; and black, which means that the
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** object and all its references are marked. The main invariant of the
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** garbage collector, while marking objects, is that a black object can
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** never point to a white one. Moreover, any gray object must be in a
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** "gray list" (gray, grayagain, weak, allweak, ephemeron) so that it
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** can be visited again before finishing the collection cycle. (Open
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** upvalues are an exception to this rule.) These lists have no meaning
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** when the invariant is not being enforced (e.g., sweep phase).
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*/
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/*
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** Possible states of the Garbage Collector
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*/
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#define GCSpropagate 0
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#define GCSenteratomic 1
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#define GCSatomic 2
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#define GCSswpallgc 3
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#define GCSswpfinobj 4
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#define GCSswptobefnz 5
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#define GCSswpend 6
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#define GCScallfin 7
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#define GCSpause 8
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#define issweepphase(g) \
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(GCSswpallgc <= (g)->gcstate && (g)->gcstate <= GCSswpend)
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/*
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** macro to tell when main invariant (white objects cannot point to black
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** ones) must be kept. During a collection, the sweep
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** phase may break the invariant, as objects turned white may point to
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** still-black objects. The invariant is restored when sweep ends and
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** all objects are white again.
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*/
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#define keepinvariant(g) ((g)->gcstate <= GCSatomic)
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/*
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** some useful bit tricks
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*/
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#define resetbits(x,m) ((x) &= cast_byte(~(m)))
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#define setbits(x,m) ((x) |= (m))
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#define testbits(x,m) ((x) & (m))
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#define bitmask(b) (1<<(b))
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#define bit2mask(b1,b2) (bitmask(b1) | bitmask(b2))
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#define l_setbit(x,b) setbits(x, bitmask(b))
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#define resetbit(x,b) resetbits(x, bitmask(b))
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#define testbit(x,b) testbits(x, bitmask(b))
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/*
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** Layout for bit use in 'marked' field. First three bits are
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** used for object "age" in generational mode. Last bit is used
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** by tests.
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*/
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#define WHITE0BIT 3 /* object is white (type 0) */
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#define WHITE1BIT 4 /* object is white (type 1) */
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#define BLACKBIT 5 /* object is black */
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#define FINALIZEDBIT 6 /* object has been marked for finalization */
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#define TESTBIT 7
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#define WHITEBITS bit2mask(WHITE0BIT, WHITE1BIT)
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#define iswhite(x) testbits((x)->marked, WHITEBITS)
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#define isblack(x) testbit((x)->marked, BLACKBIT)
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#define isgray(x) /* neither white nor black */ \
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(!testbits((x)->marked, WHITEBITS | bitmask(BLACKBIT)))
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#define tofinalize(x) testbit((x)->marked, FINALIZEDBIT)
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#define otherwhite(g) ((g)->currentwhite ^ WHITEBITS)
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#define isdeadm(ow,m) ((m) & (ow))
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#define isdead(g,v) isdeadm(otherwhite(g), (v)->marked)
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#define changewhite(x) ((x)->marked ^= WHITEBITS)
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#define nw2black(x) \
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check_exp(!iswhite(x), l_setbit((x)->marked, BLACKBIT))
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#define luaC_white(g) cast_byte((g)->currentwhite & WHITEBITS)
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/* object age in generational mode */
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#define G_NEW 0 /* created in current cycle */
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#define G_SURVIVAL 1 /* created in previous cycle */
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#define G_OLD0 2 /* marked old by frw. barrier in this cycle */
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#define G_OLD1 3 /* first full cycle as old */
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#define G_OLD 4 /* really old object (not to be visited) */
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#define G_TOUCHED1 5 /* old object touched this cycle */
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#define G_TOUCHED2 6 /* old object touched in previous cycle */
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#define AGEBITS 7 /* all age bits (111) */
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#define getage(o) ((o)->marked & AGEBITS)
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#define setage(o,a) ((o)->marked = cast_byte(((o)->marked & (~AGEBITS)) | a))
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#define isold(o) (getage(o) > G_SURVIVAL)
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#define changeage(o,f,t) \
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check_exp(getage(o) == (f), (o)->marked ^= ((f)^(t)))
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/*
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** In generational mode, objects are created 'new'. After surviving one
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** cycle, they become 'survival'. Both 'new' and 'survival' can point
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** to any other object, as they are traversed at the end of the cycle.
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** We call them both 'young' objects.
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** If a survival object survives another cycle, it becomes 'old1'.
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** 'old1' objects can still point to survival objects (but not to
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** new objects), so they still must be traversed. After another cycle
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** (that, being old, 'old1' objects will "survive" no matter what)
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** finally the 'old1' object becomes really 'old', and then they
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** are no more traversed.
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**
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** To keep its invariants, the generational mode uses the same barriers
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** also used by the incremental mode. If a young object is caught in a
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** foward barrier, it cannot become old immediately, because it can
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** still point to other young objects. Instead, it becomes 'old0',
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** which in the next cycle becomes 'old1'. So, 'old0' objects is
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** old but can point to new and survival objects; 'old1' is old
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** but cannot point to new objects; and 'old' cannot point to any
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** young object.
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**
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** If any old object ('old0', 'old1', 'old') is caught in a back
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** barrier, it becomes 'touched1' and goes into a gray list, to be
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** visited at the end of the cycle. There it evolves to 'touched2',
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** which can point to survivals but not to new objects. In yet another
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** cycle then it becomes 'old' again.
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**
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** The generational mode must also control the colors of objects,
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** because of the barriers. While the mutator is running, young objects
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** are kept white. 'old', 'old1', and 'touched2' objects are kept black,
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** as they cannot point to new objects; exceptions are threads and open
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** upvalues, which age to 'old1' and 'old' but are kept gray. 'old0'
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** objects may be gray or black, as in the incremental mode. 'touched1'
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** objects are kept gray, as they must be visited again at the end of
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** the cycle.
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*/
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/* Default Values for GC parameters */
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/* generational */
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#define LUAI_GENMAJORMUL 100 /* major multiplier */
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#define LUAI_GENMINORMUL 20 /* minor multiplier */
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/* incremental */
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/* wait memory to double before starting new cycle */
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#define LUAI_GCPAUSE 200
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#define LUAI_GCMUL 300 /* step multiplier */
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/* how many objects to allocate before next GC step (log2) */
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#define LUAI_GCSTEPSIZE 8 /* 256 objects */
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/*
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** Control when GC is running:
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*/
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#define GCSTPUSR 1 /* bit true when GC stopped by user */
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#define GCSTPGC 2 /* bit true when GC stopped by itself */
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#define GCSTPCLS 4 /* bit true when closing Lua state */
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#define gcrunning(g) ((g)->gcstp == 0)
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/*
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** Macros to set and apply GC parameters. GC parameters are given in
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** percentage points, but are stored as lu_byte. To reduce their
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** values and avoid repeated divisions by 100, these macros store
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** the original parameter multiplied by 2^n and divided by 100.
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** To apply them, the value is divided by 2^n (a shift) and then
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** multiplied by the stored parameter, yielding
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** value / 2^n * (original parameter * 2^n / 100), or approximately
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** (value * original parameter / 100).
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**
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** For most parameters, which are typically larger than 100%, 2^n is
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** 16 (2^4), allowing maximum values up to ~1500%, with a granularity
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** of ~6%. For the minor multiplier, which is typically smaller,
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** 2^n is 64 (2^6) to allow more precision. In that case, the maximum
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** value is ~400%, with a granularity of ~1.5%.
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*/
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#define gcparamshift(p) \
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(offsetof(global_State, p) == offsetof(global_State, genminormul) ? 6 : 4)
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#define setgcparam(g,p,v) \
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(g->p = (cast_uint(v) << gcparamshift(p)) / 100u)
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#define applygcparam(g,p,v) (((v) >> gcparamshift(p)) * g->p)
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/*
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** Does one step of collection when debt becomes zero. 'pre'/'pos'
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** allows some adjustments to be done only when needed. macro
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** 'condchangemem' is used only for heavy tests (forcing a full
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** GC cycle on every opportunity)
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*/
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#define luaC_condGC(L,pre,pos) \
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{ if (G(L)->GCdebt <= 0) { pre; luaC_step(L); pos;}; \
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condchangemem(L,pre,pos); }
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/* more often than not, 'pre'/'pos' are empty */
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#define luaC_checkGC(L) luaC_condGC(L,(void)0,(void)0)
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#define luaC_objbarrier(L,p,o) ( \
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(isblack(p) && iswhite(o)) ? \
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luaC_barrier_(L,obj2gco(p),obj2gco(o)) : cast_void(0))
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#define luaC_barrier(L,p,v) ( \
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iscollectable(v) ? luaC_objbarrier(L,p,gcvalue(v)) : cast_void(0))
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#define luaC_objbarrierback(L,p,o) ( \
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(isblack(p) && iswhite(o)) ? luaC_barrierback_(L,p) : cast_void(0))
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#define luaC_barrierback(L,p,v) ( \
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iscollectable(v) ? luaC_objbarrierback(L, p, gcvalue(v)) : cast_void(0))
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LUAI_FUNC void luaC_fix (lua_State *L, GCObject *o);
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LUAI_FUNC void luaC_freeallobjects (lua_State *L);
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LUAI_FUNC void luaC_step (lua_State *L);
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LUAI_FUNC void luaC_runtilstate (lua_State *L, int statesmask);
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LUAI_FUNC void luaC_fullgc (lua_State *L, int isemergency);
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LUAI_FUNC GCObject *luaC_newobj (lua_State *L, int tt, size_t sz);
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LUAI_FUNC GCObject *luaC_newobjdt (lua_State *L, int tt, size_t sz,
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size_t offset);
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LUAI_FUNC void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v);
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LUAI_FUNC void luaC_barrierback_ (lua_State *L, GCObject *o);
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LUAI_FUNC void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt);
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LUAI_FUNC void luaC_changemode (lua_State *L, int newmode);
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#endif
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