lgc.c
(5.3.6)
/*
** $Id: lgc.c,v 2.215.1.2 2017/08/31 16:15:27 roberto Exp $
** Garbage Collector
** See Copyright Notice in lua.h
*/
#define lgc_c
#define LUA_CORE
#include "lprefix.h"
#include <string.h>
#include "lua.h"
#include "ldebug.h"
#include "ldo.h"
#include "lfunc.h"
#include "lgc.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "lstring.h"
#include "ltable.h"
#include "ltm.h"
/*
** internal state for collector while inside the atomic phase. The
** collector should never be in this state while running regular code.
*/
#define GCSinsideatomic (GCSpause + 1)
/*
** cost of sweeping one element (the size of a small object divided
** by some adjust for the sweep speed)
*/
#define GCSWEEPCOST ((sizeof(TString) + 4) / 4)
/* maximum number of elements to sweep in each single step */
#define GCSWEEPMAX (cast_int((GCSTEPSIZE / GCSWEEPCOST) / 4))
/* cost of calling one finalizer */
#define GCFINALIZECOST GCSWEEPCOST
/*
** macro to adjust 'stepmul': 'stepmul' is actually used like
** 'stepmul / STEPMULADJ' (value chosen by tests)
*/
#define STEPMULADJ 200
/*
** macro to adjust 'pause': 'pause' is actually used like
** 'pause / PAUSEADJ' (value chosen by tests)
*/
#define PAUSEADJ 100
/*
** 'makewhite' erases all color bits then sets only the current white
** bit
*/
#define maskcolors (~(bitmask(BLACKBIT) | WHITEBITS))
#define makewhite(g,x) \
(x->marked = cast_byte((x->marked & maskcolors) | luaC_white(g)))
#define white2gray(x) resetbits(x->marked, WHITEBITS)
#define black2gray(x) resetbit(x->marked, BLACKBIT)
#define valiswhite(x) (iscollectable(x) && iswhite(gcvalue(x)))
#define checkdeadkey(n) lua_assert(!ttisdeadkey(gkey(n)) || ttisnil(gval(n)))
#define checkconsistency(obj) \
lua_longassert(!iscollectable(obj) || righttt(obj))
#define markvalue(g,o) { checkconsistency(o); \
if (valiswhite(o)) reallymarkobject(g,gcvalue(o)); }
#define markobject(g,t) { if (iswhite(t)) reallymarkobject(g, obj2gco(t)); }
/*
** mark an object that can be NULL (either because it is really optional,
** or it was stripped as debug info, or inside an uncompleted structure)
*/
#define markobjectN(g,t) { if (t) markobject(g,t); }
static void reallymarkobject (global_State *g, GCObject *o);
/*
** {======================================================
** Generic functions
** =======================================================
*/
/*
** one after last element in a hash array
*/
#define gnodelast(h) gnode(h, cast(size_t, sizenode(h)))
/*
** link collectable object 'o' into list pointed by 'p'
*/
#define linkgclist(o,p) ((o)->gclist = (p), (p) = obj2gco(o))
/*
** If key is not marked, mark its entry as dead. This allows key to be
** collected, but keeps its entry in the table. A dead node is needed
** when Lua looks up for a key (it may be part of a chain) and when
** traversing a weak table (key might be removed from the table during
** traversal). Other places never manipulate dead keys, because its
** associated nil value is enough to signal that the entry is logically
** empty.
*/
static void removeentry (Node *n) {
lua_assert(ttisnil(gval(n)));
if (valiswhite(gkey(n)))
setdeadvalue(wgkey(n)); /* unused and unmarked key; remove it */
}
/*
** tells whether a key or value can be cleared from a weak
** table. Non-collectable objects are never removed from weak
** tables. Strings behave as 'values', so are never removed too. for
** other objects: if really collected, cannot keep them; for objects
** being finalized, keep them in keys, but not in values
*/
static int iscleared (global_State *g, const TValue *o) {
if (!iscollectable(o)) return 0;
else if (ttisstring(o)) {
markobject(g, tsvalue(o)); /* strings are 'values', so are never weak */
return 0;
}
else return iswhite(gcvalue(o));
}
/*
** barrier that moves collector forward, that is, mark the white object
** being pointed by a black object. (If in sweep phase, clear the black
** object to white [sweep it] to avoid other barrier calls for this
** same object.)
*/
void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v) {
global_State *g = G(L);
lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
if (keepinvariant(g)) /* must keep invariant? */
reallymarkobject(g, v); /* restore invariant */
else { /* sweep phase */
lua_assert(issweepphase(g));
makewhite(g, o); /* mark main obj. as white to avoid other barriers */
}
}
/*
** barrier that moves collector backward, that is, mark the black object
** pointing to a white object as gray again.
*/
void luaC_barrierback_ (lua_State *L, Table *t) {
global_State *g = G(L);
lua_assert(isblack(t) && !isdead(g, t));
black2gray(t); /* make table gray (again) */
linkgclist(t, g->grayagain);
}
/*
** barrier for assignments to closed upvalues. Because upvalues are
** shared among closures, it is impossible to know the color of all
** closures pointing to it. So, we assume that the object being assigned
** must be marked.
*/
void luaC_upvalbarrier_ (lua_State *L, UpVal *uv) {
global_State *g = G(L);
GCObject *o = gcvalue(uv->v);
lua_assert(!upisopen(uv)); /* ensured by macro luaC_upvalbarrier */
if (keepinvariant(g))
markobject(g, o);
}
void luaC_fix (lua_State *L, GCObject *o) {
global_State *g = G(L);
lua_assert(g->allgc == o); /* object must be 1st in 'allgc' list! */
white2gray(o); /* they will be gray forever */
g->allgc = o->next; /* remove object from 'allgc' list */
o->next = g->fixedgc; /* link it to 'fixedgc' list */
g->fixedgc = o;
}
/*
** create a new collectable object (with given type and size) and link
** it to 'allgc' list.
*/
GCObject *luaC_newobj (lua_State *L, int tt, size_t sz) {
global_State *g = G(L);
GCObject *o = cast(GCObject *, luaM_newobject(L, novariant(tt), sz));
o->marked = luaC_white(g);
o->tt = tt;
o->next = g->allgc;
g->allgc = o;
return o;
}
/* }====================================================== */
/*
** {======================================================
** Mark functions
** =======================================================
*/
/*
** mark an object. Userdata, strings, and closed upvalues are visited
** and turned black here. Other objects are marked gray and added
** to appropriate list to be visited (and turned black) later. (Open
** upvalues are already linked in 'headuv' list.)
*/
static void reallymarkobject (global_State *g, GCObject *o) {
reentry:
white2gray(o);
switch (o->tt) {
case LUA_TSHRSTR: {
gray2black(o);
g->GCmemtrav += sizelstring(gco2ts(o)->shrlen);
break;
}
case LUA_TLNGSTR: {
gray2black(o);
g->GCmemtrav += sizelstring(gco2ts(o)->u.lnglen);
break;
}
case LUA_TUSERDATA: {
TValue uvalue;
markobjectN(g, gco2u(o)->metatable); /* mark its metatable */
gray2black(o);
g->GCmemtrav += sizeudata(gco2u(o));
getuservalue(g->mainthread, gco2u(o), &uvalue);
if (valiswhite(&uvalue)) { /* markvalue(g, &uvalue); */
o = gcvalue(&uvalue);
goto reentry;
}
break;
}
case LUA_TLCL: {
linkgclist(gco2lcl(o), g->gray);
break;
}
case LUA_TCCL: {
linkgclist(gco2ccl(o), g->gray);
break;
}
case LUA_TTABLE: {
linkgclist(gco2t(o), g->gray);
break;
}
case LUA_TTHREAD: {
linkgclist(gco2th(o), g->gray);
break;
}
case LUA_TPROTO: {
linkgclist(gco2p(o), g->gray);
break;
}
default: lua_assert(0); break;
}
}
/*
** mark metamethods for basic types
*/
static void markmt (global_State *g) {
int i;
for (i=0; i < LUA_NUMTAGS; i++)
markobjectN(g, g->mt[i]);
}
/*
** mark all objects in list of being-finalized
*/
static void markbeingfnz (global_State *g) {
GCObject *o;
for (o = g->tobefnz; o != NULL; o = o->next)
markobject(g, o);
}
/*
** Mark all values stored in marked open upvalues from non-marked threads.
** (Values from marked threads were already marked when traversing the
** thread.) Remove from the list threads that no longer have upvalues and
** not-marked threads.
*/
static void remarkupvals (global_State *g) {
lua_State *thread;
lua_State **p = &g->twups;
while ((thread = *p) != NULL) {
lua_assert(!isblack(thread)); /* threads are never black */
if (isgray(thread) && thread->openupval != NULL)
p = &thread->twups; /* keep marked thread with upvalues in the list */
else { /* thread is not marked or without upvalues */
UpVal *uv;
*p = thread->twups; /* remove thread from the list */
thread->twups = thread; /* mark that it is out of list */
for (uv = thread->openupval; uv != NULL; uv = uv->u.open.next) {
if (uv->u.open.touched) {
markvalue(g, uv->v); /* remark upvalue's value */
uv->u.open.touched = 0;
}
}
}
}
}
/*
** mark root set and reset all gray lists, to start a new collection
*/
static void restartcollection (global_State *g) {
g->gray = g->grayagain = NULL;
g->weak = g->allweak = g->ephemeron = NULL;
markobject(g, g->mainthread);
markvalue(g, &g->l_registry);
markmt(g);
markbeingfnz(g); /* mark any finalizing object left from previous cycle */
}
/* }====================================================== */
/*
** {======================================================
** Traverse functions
** =======================================================
*/
/*
** Traverse a table with weak values and link it to proper list. During
** propagate phase, keep it in 'grayagain' list, to be revisited in the
** atomic phase. In the atomic phase, if table has any white value,
** put it in 'weak' list, to be cleared.
*/
static void traverseweakvalue (global_State *g, Table *h) {
Node *n, *limit = gnodelast(h);
/* if there is array part, assume it may have white values (it is not
worth traversing it now just to check) */
int hasclears = (h->sizearray > 0);
for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
checkdeadkey(n);
if (ttisnil(gval(n))) /* entry is empty? */
removeentry(n); /* remove it */
else {
lua_assert(!ttisnil(gkey(n)));
markvalue(g, gkey(n)); /* mark key */
if (!hasclears && iscleared(g, gval(n))) /* is there a white value? */
hasclears = 1; /* table will have to be cleared */
}
}
if (g->gcstate == GCSpropagate)
linkgclist(h, g->grayagain); /* must retraverse it in atomic phase */
else if (hasclears)
linkgclist(h, g->weak); /* has to be cleared later */
}
/*
** Traverse an ephemeron table and link it to proper list. Returns true
** iff any object was marked during this traversal (which implies that
** convergence has to continue). During propagation phase, keep table
** in 'grayagain' list, to be visited again in the atomic phase. In
** the atomic phase, if table has any white->white entry, it has to
** be revisited during ephemeron convergence (as that key may turn
** black). Otherwise, if it has any white key, table has to be cleared
** (in the atomic phase).
*/
static int traverseephemeron (global_State *g, Table *h) {
int marked = 0; /* true if an object is marked in this traversal */
int hasclears = 0; /* true if table has white keys */
int hasww = 0; /* true if table has entry "white-key -> white-value" */
Node *n, *limit = gnodelast(h);
unsigned int i;
/* traverse array part */
for (i = 0; i < h->sizearray; i++) {
if (valiswhite(&h->array[i])) {
marked = 1;
reallymarkobject(g, gcvalue(&h->array[i]));
}
}
/* traverse hash part */
for (n = gnode(h, 0); n < limit; n++) {
checkdeadkey(n);
if (ttisnil(gval(n))) /* entry is empty? */
removeentry(n); /* remove it */
else if (iscleared(g, gkey(n))) { /* key is not marked (yet)? */
hasclears = 1; /* table must be cleared */
if (valiswhite(gval(n))) /* value not marked yet? */
hasww = 1; /* white-white entry */
}
else if (valiswhite(gval(n))) { /* value not marked yet? */
marked = 1;
reallymarkobject(g, gcvalue(gval(n))); /* mark it now */
}
}
/* link table into proper list */
if (g->gcstate == GCSpropagate)
linkgclist(h, g->grayagain); /* must retraverse it in atomic phase */
else if (hasww) /* table has white->white entries? */
linkgclist(h, g->ephemeron); /* have to propagate again */
else if (hasclears) /* table has white keys? */
linkgclist(h, g->allweak); /* may have to clean white keys */
return marked;
}
static void traversestrongtable (global_State *g, Table *h) {
Node *n, *limit = gnodelast(h);
unsigned int i;
for (i = 0; i < h->sizearray; i++) /* traverse array part */
markvalue(g, &h->array[i]);
for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
checkdeadkey(n);
if (ttisnil(gval(n))) /* entry is empty? */
removeentry(n); /* remove it */
else {
lua_assert(!ttisnil(gkey(n)));
markvalue(g, gkey(n)); /* mark key */
markvalue(g, gval(n)); /* mark value */
}
}
}
static lu_mem traversetable (global_State *g, Table *h) {
const char *weakkey, *weakvalue;
const TValue *mode = gfasttm(g, h->metatable, TM_MODE);
markobjectN(g, h->metatable);
if (mode && ttisstring(mode) && /* is there a weak mode? */
((weakkey = strchr(svalue(mode), 'k')),
(weakvalue = strchr(svalue(mode), 'v')),
(weakkey || weakvalue))) { /* is really weak? */
black2gray(h); /* keep table gray */
if (!weakkey) /* strong keys? */
traverseweakvalue(g, h);
else if (!weakvalue) /* strong values? */
traverseephemeron(g, h);
else /* all weak */
linkgclist(h, g->allweak); /* nothing to traverse now */
}
else /* not weak */
traversestrongtable(g, h);
return sizeof(Table) + sizeof(TValue) * h->sizearray +
sizeof(Node) * cast(size_t, allocsizenode(h));
}
/*
** Traverse a prototype. (While a prototype is being build, its
** arrays can be larger than needed; the extra slots are filled with
** NULL, so the use of 'markobjectN')
*/
static int traverseproto (global_State *g, Proto *f) {
int i;
if (f->cache && iswhite(f->cache))
f->cache = NULL; /* allow cache to be collected */
markobjectN(g, f->source);
for (i = 0; i < f->sizek; i++) /* mark literals */
markvalue(g, &f->k[i]);
for (i = 0; i < f->sizeupvalues; i++) /* mark upvalue names */
markobjectN(g, f->upvalues[i].name);
for (i = 0; i < f->sizep; i++) /* mark nested protos */
markobjectN(g, f->p[i]);
for (i = 0; i < f->sizelocvars; i++) /* mark local-variable names */
markobjectN(g, f->locvars[i].varname);
return sizeof(Proto) + sizeof(Instruction) * f->sizecode +
sizeof(Proto *) * f->sizep +
sizeof(TValue) * f->sizek +
sizeof(int) * f->sizelineinfo +
sizeof(LocVar) * f->sizelocvars +
sizeof(Upvaldesc) * f->sizeupvalues;
}
static lu_mem traverseCclosure (global_State *g, CClosure *cl) {
int i;
for (i = 0; i < cl->nupvalues; i++) /* mark its upvalues */
markvalue(g, &cl->upvalue[i]);
return sizeCclosure(cl->nupvalues);
}
/*
** open upvalues point to values in a thread, so those values should
** be marked when the thread is traversed except in the atomic phase
** (because then the value cannot be changed by the thread and the
** thread may not be traversed again)
*/
static lu_mem traverseLclosure (global_State *g, LClosure *cl) {
int i;
markobjectN(g, cl->p); /* mark its prototype */
for (i = 0; i < cl->nupvalues; i++) { /* mark its upvalues */
UpVal *uv = cl->upvals[i];
if (uv != NULL) {
if (upisopen(uv) && g->gcstate != GCSinsideatomic)
uv->u.open.touched = 1; /* can be marked in 'remarkupvals' */
else
markvalue(g, uv->v);
}
}
return sizeLclosure(cl->nupvalues);
}
static lu_mem traversethread (global_State *g, lua_State *th) {
StkId o = th->stack;
if (o == NULL)
return 1; /* stack not completely built yet */
lua_assert(g->gcstate == GCSinsideatomic ||
th->openupval == NULL || isintwups(th));
for (; o < th->top; o++) /* mark live elements in the stack */
markvalue(g, o);
if (g->gcstate == GCSinsideatomic) { /* final traversal? */
StkId lim = th->stack + th->stacksize; /* real end of stack */
for (; o < lim; o++) /* clear not-marked stack slice */
setnilvalue(o);
/* 'remarkupvals' may have removed thread from 'twups' list */
if (!isintwups(th) && th->openupval != NULL) {
th->twups = g->twups; /* link it back to the list */
g->twups = th;
}
}
else if (g->gckind != KGC_EMERGENCY)
luaD_shrinkstack(th); /* do not change stack in emergency cycle */
return (sizeof(lua_State) + sizeof(TValue) * th->stacksize +
sizeof(CallInfo) * th->nci);
}
/*
** traverse one gray object, turning it to black (except for threads,
** which are always gray).
*/
static void propagatemark (global_State *g) {
lu_mem size;
GCObject *o = g->gray;
lua_assert(isgray(o));
gray2black(o);
switch (o->tt) {
case LUA_TTABLE: {
Table *h = gco2t(o);
g->gray = h->gclist; /* remove from 'gray' list */
size = traversetable(g, h);
break;
}
case LUA_TLCL: {
LClosure *cl = gco2lcl(o);
g->gray = cl->gclist; /* remove from 'gray' list */
size = traverseLclosure(g, cl);
break;
}
case LUA_TCCL: {
CClosure *cl = gco2ccl(o);
g->gray = cl->gclist; /* remove from 'gray' list */
size = traverseCclosure(g, cl);
break;
}
case LUA_TTHREAD: {
lua_State *th = gco2th(o);
g->gray = th->gclist; /* remove from 'gray' list */
linkgclist(th, g->grayagain); /* insert into 'grayagain' list */
black2gray(o);
size = traversethread(g, th);
break;
}
case LUA_TPROTO: {
Proto *p = gco2p(o);
g->gray = p->gclist; /* remove from 'gray' list */
size = traverseproto(g, p);
break;
}
default: lua_assert(0); return;
}
g->GCmemtrav += size;
}
static void propagateall (global_State *g) {
while (g->gray) propagatemark(g);
}
static void convergeephemerons (global_State *g) {
int changed;
do {
GCObject *w;
GCObject *next = g->ephemeron; /* get ephemeron list */
g->ephemeron = NULL; /* tables may return to this list when traversed */
changed = 0;
while ((w = next) != NULL) {
next = gco2t(w)->gclist;
if (traverseephemeron(g, gco2t(w))) { /* traverse marked some value? */
propagateall(g); /* propagate changes */
changed = 1; /* will have to revisit all ephemeron tables */
}
}
} while (changed);
}
/* }====================================================== */
/*
** {======================================================
** Sweep Functions
** =======================================================
*/
/*
** clear entries with unmarked keys from all weaktables in list 'l' up
** to element 'f'
*/
static void clearkeys (global_State *g, GCObject *l, GCObject *f) {
for (; l != f; l = gco2t(l)->gclist) {
Table *h = gco2t(l);
Node *n, *limit = gnodelast(h);
for (n = gnode(h, 0); n < limit; n++) {
if (!ttisnil(gval(n)) && (iscleared(g, gkey(n)))) {
setnilvalue(gval(n)); /* remove value ... */
}
if (ttisnil(gval(n))) /* is entry empty? */
removeentry(n); /* remove entry from table */
}
}
}
/*
** clear entries with unmarked values from all weaktables in list 'l' up
** to element 'f'
*/
static void clearvalues (global_State *g, GCObject *l, GCObject *f) {
for (; l != f; l = gco2t(l)->gclist) {
Table *h = gco2t(l);
Node *n, *limit = gnodelast(h);
unsigned int i;
for (i = 0; i < h->sizearray; i++) {
TValue *o = &h->array[i];
if (iscleared(g, o)) /* value was collected? */
setnilvalue(o); /* remove value */
}
for (n = gnode(h, 0); n < limit; n++) {
if (!ttisnil(gval(n)) && iscleared(g, gval(n))) {
setnilvalue(gval(n)); /* remove value ... */
removeentry(n); /* and remove entry from table */
}
}
}
}
void luaC_upvdeccount (lua_State *L, UpVal *uv) {
lua_assert(uv->refcount > 0);
uv->refcount--;
if (uv->refcount == 0 && !upisopen(uv))
luaM_free(L, uv);
}
static void freeLclosure (lua_State *L, LClosure *cl) {
int i;
for (i = 0; i < cl->nupvalues; i++) {
UpVal *uv = cl->upvals[i];
if (uv)
luaC_upvdeccount(L, uv);
}
luaM_freemem(L, cl, sizeLclosure(cl->nupvalues));
}
static void freeobj (lua_State *L, GCObject *o) {
switch (o->tt) {
case LUA_TPROTO: luaF_freeproto(L, gco2p(o)); break;
case LUA_TLCL: {
freeLclosure(L, gco2lcl(o));
break;
}
case LUA_TCCL: {
luaM_freemem(L, o, sizeCclosure(gco2ccl(o)->nupvalues));
break;
}
case LUA_TTABLE: luaH_free(L, gco2t(o)); break;
case LUA_TTHREAD: luaE_freethread(L, gco2th(o)); break;
case LUA_TUSERDATA: luaM_freemem(L, o, sizeudata(gco2u(o))); break;
case LUA_TSHRSTR:
luaS_remove(L, gco2ts(o)); /* remove it from hash table */
luaM_freemem(L, o, sizelstring(gco2ts(o)->shrlen));
break;
case LUA_TLNGSTR: {
luaM_freemem(L, o, sizelstring(gco2ts(o)->u.lnglen));
break;
}
default: lua_assert(0);
}
}
#define sweepwholelist(L,p) sweeplist(L,p,MAX_LUMEM)
static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count);
/*
** sweep at most 'count' elements from a list of GCObjects erasing dead
** objects, where a dead object is one marked with the old (non current)
** white; change all non-dead objects back to white, preparing for next
** collection cycle. Return where to continue the traversal or NULL if
** list is finished.
*/
static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count) {
global_State *g = G(L);
int ow = otherwhite(g);
int white = luaC_white(g); /* current white */
while (*p != NULL && count-- > 0) {
GCObject *curr = *p;
int marked = curr->marked;
if (isdeadm(ow, marked)) { /* is 'curr' dead? */
*p = curr->next; /* remove 'curr' from list */
freeobj(L, curr); /* erase 'curr' */
}
else { /* change mark to 'white' */
curr->marked = cast_byte((marked & maskcolors) | white);
p = &curr->next; /* go to next element */
}
}
return (*p == NULL) ? NULL : p;
}
/*
** sweep a list until a live object (or end of list)
*/
static GCObject **sweeptolive (lua_State *L, GCObject **p) {
GCObject **old = p;
do {
p = sweeplist(L, p, 1);
} while (p == old);
return p;
}
/* }====================================================== */
/*
** {======================================================
** Finalization
** =======================================================
*/
/*
** If possible, shrink string table
*/
static void checkSizes (lua_State *L, global_State *g) {
if (g->gckind != KGC_EMERGENCY) {
l_mem olddebt = g->GCdebt;
if (g->strt.nuse < g->strt.size / 4) /* string table too big? */
luaS_resize(L, g->strt.size / 2); /* shrink it a little */
g->GCestimate += g->GCdebt - olddebt; /* update estimate */
}
}
static GCObject *udata2finalize (global_State *g) {
GCObject *o = g->tobefnz; /* get first element */
lua_assert(tofinalize(o));
g->tobefnz = o->next; /* remove it from 'tobefnz' list */
o->next = g->allgc; /* return it to 'allgc' list */
g->allgc = o;
resetbit(o->marked, FINALIZEDBIT); /* object is "normal" again */
if (issweepphase(g))
makewhite(g, o); /* "sweep" object */
return o;
}
static void dothecall (lua_State *L, void *ud) {
UNUSED(ud);
luaD_callnoyield(L, L->top - 2, 0);
}
static void GCTM (lua_State *L, int propagateerrors) {
global_State *g = G(L);
const TValue *tm;
TValue v;
setgcovalue(L, &v, udata2finalize(g));
tm = luaT_gettmbyobj(L, &v, TM_GC);
if (tm != NULL && ttisfunction(tm)) { /* is there a finalizer? */
int status;
lu_byte oldah = L->allowhook;
int running = g->gcrunning;
L->allowhook = 0; /* stop debug hooks during GC metamethod */
g->gcrunning = 0; /* avoid GC steps */
setobj2s(L, L->top, tm); /* push finalizer... */
setobj2s(L, L->top + 1, &v); /* ... and its argument */
L->top += 2; /* and (next line) call the finalizer */
L->ci->callstatus |= CIST_FIN; /* will run a finalizer */
status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
L->ci->callstatus &= ~CIST_FIN; /* not running a finalizer anymore */
L->allowhook = oldah; /* restore hooks */
g->gcrunning = running; /* restore state */
if (status != LUA_OK && propagateerrors) { /* error while running __gc? */
if (status == LUA_ERRRUN) { /* is there an error object? */
const char *msg = (ttisstring(L->top - 1))
? svalue(L->top - 1)
: "no message";
luaO_pushfstring(L, "error in __gc metamethod (%s)", msg);
status = LUA_ERRGCMM; /* error in __gc metamethod */
}
luaD_throw(L, status); /* re-throw error */
}
}
}
/*
** call a few (up to 'g->gcfinnum') finalizers
*/
static int runafewfinalizers (lua_State *L) {
global_State *g = G(L);
unsigned int i;
lua_assert(!g->tobefnz || g->gcfinnum > 0);
for (i = 0; g->tobefnz && i < g->gcfinnum; i++)
GCTM(L, 1); /* call one finalizer */
g->gcfinnum = (!g->tobefnz) ? 0 /* nothing more to finalize? */
: g->gcfinnum * 2; /* else call a few more next time */
return i;
}
/*
** call all pending finalizers
*/
static void callallpendingfinalizers (lua_State *L) {
global_State *g = G(L);
while (g->tobefnz)
GCTM(L, 0);
}
/*
** find last 'next' field in list 'p' list (to add elements in its end)
*/
static GCObject **findlast (GCObject **p) {
while (*p != NULL)
p = &(*p)->next;
return p;
}
/*
** move all unreachable objects (or 'all' objects) that need
** finalization from list 'finobj' to list 'tobefnz' (to be finalized)
*/
static void separatetobefnz (global_State *g, int all) {
GCObject *curr;
GCObject **p = &g->finobj;
GCObject **lastnext = findlast(&g->tobefnz);
while ((curr = *p) != NULL) { /* traverse all finalizable objects */
lua_assert(tofinalize(curr));
if (!(iswhite(curr) || all)) /* not being collected? */
p = &curr->next; /* don't bother with it */
else {
*p = curr->next; /* remove 'curr' from 'finobj' list */
curr->next = *lastnext; /* link at the end of 'tobefnz' list */
*lastnext = curr;
lastnext = &curr->next;
}
}
}
/*
** if object 'o' has a finalizer, remove it from 'allgc' list (must
** search the list to find it) and link it in 'finobj' list.
*/
void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt) {
global_State *g = G(L);
if (tofinalize(o) || /* obj. is already marked... */
gfasttm(g, mt, TM_GC) == NULL) /* or has no finalizer? */
return; /* nothing to be done */
else { /* move 'o' to 'finobj' list */
GCObject **p;
if (issweepphase(g)) {
makewhite(g, o); /* "sweep" object 'o' */
if (g->sweepgc == &o->next) /* should not remove 'sweepgc' object */
g->sweepgc = sweeptolive(L, g->sweepgc); /* change 'sweepgc' */
}
/* search for pointer pointing to 'o' */
for (p = &g->allgc; *p != o; p = &(*p)->next) { /* empty */ }
*p = o->next; /* remove 'o' from 'allgc' list */
o->next = g->finobj; /* link it in 'finobj' list */
g->finobj = o;
l_setbit(o->marked, FINALIZEDBIT); /* mark it as such */
}
}
/* }====================================================== */
/*
** {======================================================
** GC control
** =======================================================
*/
/*
** Set a reasonable "time" to wait before starting a new GC cycle; cycle
** will start when memory use hits threshold. (Division by 'estimate'
** should be OK: it cannot be zero (because Lua cannot even start with
** less than PAUSEADJ bytes).
*/
static void setpause (global_State *g) {
l_mem threshold, debt;
l_mem estimate = g->GCestimate / PAUSEADJ; /* adjust 'estimate' */
lua_assert(estimate > 0);
threshold = (g->gcpause < MAX_LMEM / estimate) /* overflow? */
? estimate * g->gcpause /* no overflow */
: MAX_LMEM; /* overflow; truncate to maximum */
debt = gettotalbytes(g) - threshold;
luaE_setdebt(g, debt);
}
/*
** Enter first sweep phase.
** The call to 'sweeplist' tries to make pointer point to an object
** inside the list (instead of to the header), so that the real sweep do
** not need to skip objects created between "now" and the start of the
** real sweep.
*/
static void entersweep (lua_State *L) {
global_State *g = G(L);
g->gcstate = GCSswpallgc;
lua_assert(g->sweepgc == NULL);
g->sweepgc = sweeplist(L, &g->allgc, 1);
}
void luaC_freeallobjects (lua_State *L) {
global_State *g = G(L);
separatetobefnz(g, 1); /* separate all objects with finalizers */
lua_assert(g->finobj == NULL);
callallpendingfinalizers(L);
lua_assert(g->tobefnz == NULL);
g->currentwhite = WHITEBITS; /* this "white" makes all objects look dead */
g->gckind = KGC_NORMAL;
sweepwholelist(L, &g->finobj);
sweepwholelist(L, &g->allgc);
sweepwholelist(L, &g->fixedgc); /* collect fixed objects */
lua_assert(g->strt.nuse == 0);
}
static l_mem atomic (lua_State *L) {
global_State *g = G(L);
l_mem work;
GCObject *origweak, *origall;
GCObject *grayagain = g->grayagain; /* save original list */
lua_assert(g->ephemeron == NULL && g->weak == NULL);
lua_assert(!iswhite(g->mainthread));
g->gcstate = GCSinsideatomic;
g->GCmemtrav = 0; /* start counting work */
markobject(g, L); /* mark running thread */
/* registry and global metatables may be changed by API */
markvalue(g, &g->l_registry);
markmt(g); /* mark global metatables */
/* remark occasional upvalues of (maybe) dead threads */
remarkupvals(g);
propagateall(g); /* propagate changes */
work = g->GCmemtrav; /* stop counting (do not recount 'grayagain') */
g->gray = grayagain;
propagateall(g); /* traverse 'grayagain' list */
g->GCmemtrav = 0; /* restart counting */
convergeephemerons(g);
/* at this point, all strongly accessible objects are marked. */
/* Clear values from weak tables, before checking finalizers */
clearvalues(g, g->weak, NULL);
clearvalues(g, g->allweak, NULL);
origweak = g->weak; origall = g->allweak;
work += g->GCmemtrav; /* stop counting (objects being finalized) */
separatetobefnz(g, 0); /* separate objects to be finalized */
g->gcfinnum = 1; /* there may be objects to be finalized */
markbeingfnz(g); /* mark objects that will be finalized */
propagateall(g); /* remark, to propagate 'resurrection' */
g->GCmemtrav = 0; /* restart counting */
convergeephemerons(g);
/* at this point, all resurrected objects are marked. */
/* remove dead objects from weak tables */
clearkeys(g, g->ephemeron, NULL); /* clear keys from all ephemeron tables */
clearkeys(g, g->allweak, NULL); /* clear keys from all 'allweak' tables */
/* clear values from resurrected weak tables */
clearvalues(g, g->weak, origweak);
clearvalues(g, g->allweak, origall);
luaS_clearcache(g);
g->currentwhite = cast_byte(otherwhite(g)); /* flip current white */
work += g->GCmemtrav; /* complete counting */
return work; /* estimate of memory marked by 'atomic' */
}
static lu_mem sweepstep (lua_State *L, global_State *g,
int nextstate, GCObject **nextlist) {
if (g->sweepgc) {
l_mem olddebt = g->GCdebt;
g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
g->GCestimate += g->GCdebt - olddebt; /* update estimate */
if (g->sweepgc) /* is there still something to sweep? */
return (GCSWEEPMAX * GCSWEEPCOST);
}
/* else enter next state */
g->gcstate = nextstate;
g->sweepgc = nextlist;
return 0;
}
static lu_mem singlestep (lua_State *L) {
global_State *g = G(L);
switch (g->gcstate) {
case GCSpause: {
g->GCmemtrav = g->strt.size * sizeof(GCObject*);
restartcollection(g);
g->gcstate = GCSpropagate;
return g->GCmemtrav;
}
case GCSpropagate: {
g->GCmemtrav = 0;
lua_assert(g->gray);
propagatemark(g);
if (g->gray == NULL) /* no more gray objects? */
g->gcstate = GCSatomic; /* finish propagate phase */
return g->GCmemtrav; /* memory traversed in this step */
}
case GCSatomic: {
lu_mem work;
propagateall(g); /* make sure gray list is empty */
work = atomic(L); /* work is what was traversed by 'atomic' */
entersweep(L);
g->GCestimate = gettotalbytes(g); /* first estimate */;
return work;
}
case GCSswpallgc: { /* sweep "regular" objects */
return sweepstep(L, g, GCSswpfinobj, &g->finobj);
}
case GCSswpfinobj: { /* sweep objects with finalizers */
return sweepstep(L, g, GCSswptobefnz, &g->tobefnz);
}
case GCSswptobefnz: { /* sweep objects to be finalized */
return sweepstep(L, g, GCSswpend, NULL);
}
case GCSswpend: { /* finish sweeps */
makewhite(g, g->mainthread); /* sweep main thread */
checkSizes(L, g);
g->gcstate = GCScallfin;
return 0;
}
case GCScallfin: { /* call remaining finalizers */
if (g->tobefnz && g->gckind != KGC_EMERGENCY) {
int n = runafewfinalizers(L);
return (n * GCFINALIZECOST);
}
else { /* emergency mode or no more finalizers */
g->gcstate = GCSpause; /* finish collection */
return 0;
}
}
default: lua_assert(0); return 0;
}
}
/*
** advances the garbage collector until it reaches a state allowed
** by 'statemask'
*/
void luaC_runtilstate (lua_State *L, int statesmask) {
global_State *g = G(L);
while (!testbit(statesmask, g->gcstate))
singlestep(L);
}
/*
** get GC debt and convert it from Kb to 'work units' (avoid zero debt
** and overflows)
*/
static l_mem getdebt (global_State *g) {
l_mem debt = g->GCdebt;
int stepmul = g->gcstepmul;
if (debt <= 0) return 0; /* minimal debt */
else {
debt = (debt / STEPMULADJ) + 1;
debt = (debt < MAX_LMEM / stepmul) ? debt * stepmul : MAX_LMEM;
return debt;
}
}
/*
** performs a basic GC step when collector is running
*/
void luaC_step (lua_State *L) {
global_State *g = G(L);
l_mem debt = getdebt(g); /* GC deficit (be paid now) */
if (!g->gcrunning) { /* not running? */
luaE_setdebt(g, -GCSTEPSIZE * 10); /* avoid being called too often */
return;
}
do { /* repeat until pause or enough "credit" (negative debt) */
lu_mem work = singlestep(L); /* perform one single step */
debt -= work;
} while (debt > -GCSTEPSIZE && g->gcstate != GCSpause);
if (g->gcstate == GCSpause)
setpause(g); /* pause until next cycle */
else {
debt = (debt / g->gcstepmul) * STEPMULADJ; /* convert 'work units' to Kb */
luaE_setdebt(g, debt);
runafewfinalizers(L);
}
}
/*
** Performs a full GC cycle; if 'isemergency', set a flag to avoid
** some operations which could change the interpreter state in some
** unexpected ways (running finalizers and shrinking some structures).
** Before running the collection, check 'keepinvariant'; if it is true,
** there may be some objects marked as black, so the collector has
** to sweep all objects to turn them back to white (as white has not
** changed, nothing will be collected).
*/
void luaC_fullgc (lua_State *L, int isemergency) {
global_State *g = G(L);
lua_assert(g->gckind == KGC_NORMAL);
if (isemergency) g->gckind = KGC_EMERGENCY; /* set flag */
if (keepinvariant(g)) { /* black objects? */
entersweep(L); /* sweep everything to turn them back to white */
}
/* finish any pending sweep phase to start a new cycle */
luaC_runtilstate(L, bitmask(GCSpause));
luaC_runtilstate(L, ~bitmask(GCSpause)); /* start new collection */
luaC_runtilstate(L, bitmask(GCScallfin)); /* run up to finalizers */
/* estimate must be correct after a full GC cycle */
lua_assert(g->GCestimate == gettotalbytes(g));
luaC_runtilstate(L, bitmask(GCSpause)); /* finish collection */
g->gckind = KGC_NORMAL;
setpause(g);
}
/* }====================================================== */