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1805 lines (1583 loc) · 56.6 KB
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/*
** $Id: lgc.c $
** 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"
/*
** Maximum number of elements to sweep in each single step.
** (Large enough to dissipate fixed overheads but small enough
** to allow small steps for the collector.)
*/
#define GCSWEEPMAX 20
/*
** Cost (in work units) of running one finalizer.
*/
#define CWUFIN 10
/* mask with all color bits */
#define maskcolors (bitmask(BLACKBIT) | WHITEBITS)
/* mask with all GC bits */
#define maskgcbits (maskcolors | AGEBITS)
/* macro to erase all color bits then set only the current white bit */
#define makewhite(g,x) \
(x->marked = cast_byte((x->marked & ~maskcolors) | luaC_white(g)))
/* make an object gray (neither white nor black) */
#define set2gray(x) resetbits(x->marked, maskcolors)
/* make an object black (coming from any color) */
#define set2black(x) \
(x->marked = cast_byte((x->marked & ~WHITEBITS) | bitmask(BLACKBIT)))
#define valiswhite(x) (iscollectable(x) && iswhite(gcvalue(x)))
#define keyiswhite(n) (keyiscollectable(n) && iswhite(gckey(n)))
/*
** Protected access to objects in values
*/
#define gcvalueN(o) (iscollectable(o) ? gcvalue(o) : NULL)
/*
** Access to collectable objects in array part of tables
*/
#define gcvalarr(t,i) \
((*getArrTag(t,i) & BIT_ISCOLLECTABLE) ? getArrVal(t,i)->gc : NULL)
#define markvalue(g,o) { checkliveness(mainthread(g),o); \
if (valiswhite(o)) reallymarkobject(g,gcvalue(o)); }
#define markkey(g, n) { if keyiswhite(n) reallymarkobject(g,gckey(n)); }
#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);
static void atomic (lua_State *L);
static void entersweep (lua_State *L);
/*
** {======================================================
** Generic functions
** =======================================================
*/
/*
** one after last element in a hash array
*/
#define gnodelast(h) gnode(h, cast_sizet(sizenode(h)))
static l_mem objsize (GCObject *o) {
lu_mem res;
switch (o->tt) {
case LUA_VTABLE: {
res = luaH_size(gco2t(o));
break;
}
case LUA_VLCL: {
LClosure *cl = gco2lcl(o);
res = sizeLclosure(cl->nupvalues);
break;
}
case LUA_VCCL: {
CClosure *cl = gco2ccl(o);
res = sizeCclosure(cl->nupvalues);
break;
}
case LUA_VUSERDATA: {
Udata *u = gco2u(o);
res = sizeudata(u->nuvalue, u->len);
break;
}
case LUA_VPROTO: {
res = luaF_protosize(gco2p(o));
break;
}
case LUA_VTHREAD: {
res = luaE_threadsize(gco2th(o));
break;
}
case LUA_VSHRSTR: {
TString *ts = gco2ts(o);
res = sizestrshr(cast_uint(ts->shrlen));
break;
}
case LUA_VLNGSTR: {
TString *ts = gco2ts(o);
res = luaS_sizelngstr(ts->u.lnglen, ts->shrlen);
break;
}
case LUA_VUPVAL: {
res = sizeof(UpVal);
break;
}
default: res = 0; lua_assert(0);
}
return cast(l_mem, res);
}
static GCObject **getgclist (GCObject *o) {
switch (o->tt) {
case LUA_VTABLE: return &gco2t(o)->gclist;
case LUA_VLCL: return &gco2lcl(o)->gclist;
case LUA_VCCL: return &gco2ccl(o)->gclist;
case LUA_VTHREAD: return &gco2th(o)->gclist;
case LUA_VPROTO: return &gco2p(o)->gclist;
case LUA_VUSERDATA: {
Udata *u = gco2u(o);
lua_assert(u->nuvalue > 0);
return &u->gclist;
}
default: lua_assert(0); return 0;
}
}
/*
** Link a collectable object 'o' with a known type into the list 'p'.
** (Must be a macro to access the 'gclist' field in different types.)
*/
#define linkgclist(o,p) linkgclist_(obj2gco(o), &(o)->gclist, &(p))
static void linkgclist_ (GCObject *o, GCObject **pnext, GCObject **list) {
lua_assert(!isgray(o)); /* cannot be in a gray list */
*pnext = *list;
*list = o;
set2gray(o); /* now it is */
}
/*
** Link a generic collectable object 'o' into the list 'p'.
*/
#define linkobjgclist(o,p) linkgclist_(obj2gco(o), getgclist(o), &(p))
/*
** Clear keys for empty entries in tables. If entry is empty, mark its
** entry as dead. This allows the collection of the key, but keeps its
** entry in the table: its removal could break a chain and could break
** a table traversal. Other places never manipulate dead keys, because
** its associated empty value is enough to signal that the entry is
** logically empty.
*/
static void clearkey (Node *n) {
lua_assert(isempty(gval(n)));
if (keyiscollectable(n))
setdeadkey(n); /* unused 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 GCObject *o) {
if (o == NULL) return 0; /* non-collectable value */
else if (novariant(o->tt) == LUA_TSTRING) {
markobject(g, o); /* strings are 'values', so are never weak */
return 0;
}
else return iswhite(o);
}
/*
** Barrier that moves collector forward, that is, marks the white object
** 'v' being pointed by the black object 'o'. In the generational
** mode, 'v' must also become old, if 'o' is old; however, it cannot
** be changed directly to OLD, because it may still point to non-old
** objects. So, it is marked as OLD0. In the next cycle it will become
** OLD1, and in the next it will finally become OLD (regular old). By
** then, any object it points to will also be old. If called in the
** incremental sweep phase, it clears the black object to white (sweep
** it) to avoid other barrier calls for this same object. (That cannot
** be done is generational mode, as its sweep does not distinguish
** white from dead.)
*/
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 */
if (isold(o)) {
lua_assert(!isold(v)); /* white object could not be old */
setage(v, G_OLD0); /* restore generational invariant */
}
}
else { /* sweep phase */
lua_assert(issweepphase(g));
if (g->gckind != KGC_GENMINOR) /* incremental mode? */
makewhite(g, o); /* mark 'o' 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, GCObject *o) {
global_State *g = G(L);
lua_assert(isblack(o) && !isdead(g, o));
lua_assert((g->gckind != KGC_GENMINOR)
|| (isold(o) && getage(o) != G_TOUCHED1));
if (getage(o) == G_TOUCHED2) /* already in gray list? */
set2gray(o); /* make it gray to become touched1 */
else /* link it in 'grayagain' and paint it gray */
linkobjgclist(o, g->grayagain);
if (isold(o)) /* generational mode? */
setage(o, G_TOUCHED1); /* touched in current cycle */
}
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! */
set2gray(o); /* they will be gray forever */
setage(o, G_OLD); /* and old 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, size, and offset)
** and link it to 'allgc' list.
*/
GCObject *luaC_newobjdt (lua_State *L, lu_byte tt, size_t sz, size_t offset) {
global_State *g = G(L);
char *p = cast_charp(luaM_newobject(L, novariant(tt), sz));
GCObject *o = cast(GCObject *, p + offset);
o->marked = luaC_white(g);
o->tt = tt;
o->next = g->allgc;
g->allgc = o;
return o;
}
/*
** create a new collectable object with no offset.
*/
GCObject *luaC_newobj (lua_State *L, lu_byte tt, size_t sz) {
return luaC_newobjdt(L, tt, sz, 0);
}
/* }====================================================== */
/*
** {======================================================
** Mark functions
** =======================================================
*/
/*
** Mark an object. Userdata with no user values, strings, and closed
** upvalues are visited and turned black here. Open upvalues are
** already indirectly linked through their respective threads in the
** 'twups' list, so they don't go to the gray list; nevertheless, they
** are kept gray to avoid barriers, as their values will be revisited
** by the thread or by 'remarkupvals'. Other objects are added to the
** gray list to be visited (and turned black) later. Both userdata and
** upvalues can call this function recursively, but this recursion goes
** for at most two levels: An upvalue cannot refer to another upvalue
** (only closures can), and a userdata's metatable must be a table.
*/
static void reallymarkobject (global_State *g, GCObject *o) {
g->GCmarked += objsize(o);
switch (o->tt) {
case LUA_VSHRSTR:
case LUA_VLNGSTR: {
set2black(o); /* nothing to visit */
break;
}
case LUA_VUPVAL: {
UpVal *uv = gco2upv(o);
if (upisopen(uv))
set2gray(uv); /* open upvalues are kept gray */
else
set2black(uv); /* closed upvalues are visited here */
markvalue(g, uv->v.p); /* mark its content */
break;
}
case LUA_VUSERDATA: {
Udata *u = gco2u(o);
if (u->nuvalue == 0) { /* no user values? */
markobjectN(g, u->metatable); /* mark its metatable */
set2black(u); /* nothing else to mark */
break;
}
/* else... */
} /* FALLTHROUGH */
case LUA_VLCL: case LUA_VCCL: case LUA_VTABLE:
case LUA_VTHREAD: case LUA_VPROTO: {
linkobjgclist(o, g->gray); /* to be visited later */
break;
}
default: lua_assert(0); break;
}
}
/*
** mark metamethods for basic types
*/
static void markmt (global_State *g) {
int i;
for (i=0; i < LUA_NUMTYPES; 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);
}
/*
** For each non-marked thread, simulates a barrier between each open
** upvalue and its value. (If the thread is collected, the value will be
** assigned to the upvalue, but then it can be too late for the barrier
** to act. The "barrier" does not need to check colors: A non-marked
** thread must be young; upvalues cannot be older than their threads; so
** any visited upvalue must be young too.) Also removes the thread from
** the list, as it was already visited. Removes also threads with no
** upvalues, as they have nothing to be checked. (If the thread gets an
** upvalue later, it will be linked in the list again.)
*/
static void remarkupvals (global_State *g) {
lua_State *thread;
lua_State **p = &g->twups;
while ((thread = *p) != NULL) {
if (!iswhite(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;
lua_assert(!isold(thread) || thread->openupval == NULL);
*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) {
lua_assert(getage(uv) <= getage(thread));
if (!iswhite(uv)) { /* upvalue already visited? */
lua_assert(upisopen(uv) && isgray(uv));
markvalue(g, uv->v.p); /* mark its value */
}
}
}
}
}
static void cleargraylists (global_State *g) {
g->gray = g->grayagain = NULL;
g->weak = g->allweak = g->ephemeron = NULL;
}
/*
** mark root set and reset all gray lists, to start a new collection.
** 'GCmarked' is initialized to count the total number of live bytes
** during a cycle.
*/
static void restartcollection (global_State *g) {
cleargraylists(g);
g->GCmarked = 0;
markobject(g, mainthread(g));
markvalue(g, &g->l_registry);
markmt(g);
markbeingfnz(g); /* mark any finalizing object left from previous cycle */
}
/* }====================================================== */
/*
** {======================================================
** Traverse functions
** =======================================================
*/
/*
** Check whether object 'o' should be kept in the 'grayagain' list for
** post-processing by 'correctgraylist'. (It could put all old objects
** in the list and leave all the work to 'correctgraylist', but it is
** more efficient to avoid adding elements that will be removed.) Only
** TOUCHED1 objects need to be in the list. TOUCHED2 doesn't need to go
** back to a gray list, but then it must become OLD. (That is what
** 'correctgraylist' does when it finds a TOUCHED2 object.)
** This function is a no-op in incremental mode, as objects cannot be
** marked as touched in that mode.
*/
static void genlink (global_State *g, GCObject *o) {
lua_assert(isblack(o));
if (getage(o) == G_TOUCHED1) { /* touched in this cycle? */
linkobjgclist(o, g->grayagain); /* link it back in 'grayagain' */
} /* everything else do not need to be linked back */
else if (getage(o) == G_TOUCHED2)
setage(o, G_OLD); /* advance age */
}
/*
** 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; otherwise, call 'genlink'
** to check table age in generational mode.
*/
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->asize > 0);
for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
if (isempty(gval(n))) /* entry is empty? */
clearkey(n); /* clear its key */
else {
lua_assert(!keyisnil(n));
markkey(g, n);
if (!hasclears && iscleared(g, gcvalueN(gval(n)))) /* 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 */
else
genlink(g, obj2gco(h));
}
/*
** Traverse the array part of a table.
*/
static int traversearray (global_State *g, Table *h) {
unsigned asize = h->asize;
int marked = 0; /* true if some object is marked in this traversal */
unsigned i;
for (i = 0; i < asize; i++) {
GCObject *o = gcvalarr(h, i);
if (o != NULL && iswhite(o)) {
marked = 1;
reallymarkobject(g, o);
}
}
return marked;
}
/*
** 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). In generational mode, some tables
** must be kept in some gray list for post-processing; this is done
** by 'genlink'.
*/
static int traverseephemeron (global_State *g, Table *h, int inv) {
int hasclears = 0; /* true if table has white keys */
int hasww = 0; /* true if table has entry "white-key -> white-value" */
unsigned int i;
unsigned int nsize = sizenode(h);
int marked = traversearray(g, h); /* traverse array part */
/* traverse hash part; if 'inv', traverse descending
(see 'convergeephemerons') */
for (i = 0; i < nsize; i++) {
Node *n = inv ? gnode(h, nsize - 1 - i) : gnode(h, i);
if (isempty(gval(n))) /* entry is empty? */
clearkey(n); /* clear its key */
else if (iscleared(g, gckeyN(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 */
else
genlink(g, obj2gco(h)); /* check whether collector still needs to see it */
return marked;
}
static void traversestrongtable (global_State *g, Table *h) {
Node *n, *limit = gnodelast(h);
traversearray(g, h);
for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
if (isempty(gval(n))) /* entry is empty? */
clearkey(n); /* clear its key */
else {
lua_assert(!keyisnil(n));
markkey(g, n);
markvalue(g, gval(n));
}
}
genlink(g, obj2gco(h));
}
/*
** (result & 1) iff weak values; (result & 2) iff weak keys.
*/
static int getmode (global_State *g, Table *h) {
const TValue *mode = gfasttm(g, h->metatable, TM_MODE);
if (mode == NULL || !ttisstring(mode))
return 0; /* ignore non-string modes */
else {
const char *smode = getstr(tsvalue(mode));
const char *weakkey = strchr(smode, 'k');
const char *weakvalue = strchr(smode, 'v');
return ((weakkey != NULL) << 1) | (weakvalue != NULL);
}
}
static l_mem traversetable (global_State *g, Table *h) {
markobjectN(g, h->metatable);
switch (getmode(g, h)) {
case 0: /* not weak */
traversestrongtable(g, h);
break;
case 1: /* weak values */
traverseweakvalue(g, h);
break;
case 2: /* weak keys */
traverseephemeron(g, h, 0);
break;
case 3: /* all weak; nothing to traverse */
if (g->gcstate == GCSpropagate)
linkgclist(h, g->grayagain); /* must visit again its metatable */
else
linkgclist(h, g->allweak); /* must clear collected entries */
break;
}
return cast(l_mem, 1 + 2*sizenode(h) + h->asize);
}
static l_mem traverseudata (global_State *g, Udata *u) {
int i;
markobjectN(g, u->metatable); /* mark its metatable */
for (i = 0; i < u->nuvalue; i++)
markvalue(g, &u->uv[i].uv);
genlink(g, obj2gco(u));
return 1 + u->nuvalue;
}
/*
** 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 l_mem traverseproto (global_State *g, Proto *f) {
int i;
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 1 + f->sizek + f->sizeupvalues + f->sizep + f->sizelocvars;
}
static l_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 1 + cl->nupvalues;
}
/*
** Traverse a Lua closure, marking its prototype and its upvalues.
** (Both can be NULL while closure is being created.)
*/
static l_mem traverseLclosure (global_State *g, LClosure *cl) {
int i;
markobjectN(g, cl->p); /* mark its prototype */
for (i = 0; i < cl->nupvalues; i++) { /* visit its upvalues */
UpVal *uv = cl->upvals[i];
markobjectN(g, uv); /* mark upvalue */
}
return 1 + cl->nupvalues;
}
/*
** Traverse a thread, marking the elements in the stack up to its top
** and cleaning the rest of the stack in the final traversal. That
** ensures that the entire stack have valid (non-dead) objects.
** Threads have no barriers. In gen. mode, old threads must be visited
** at every cycle, because they might point to young objects. In inc.
** mode, the thread can still be modified before the end of the cycle,
** and therefore it must be visited again in the atomic phase. To ensure
** these visits, threads must return to a gray list if they are not new
** (which can only happen in generational mode) or if the traverse is in
** the propagate phase (which can only happen in incremental mode).
*/
static l_mem traversethread (global_State *g, lua_State *th) {
UpVal *uv;
StkId o = th->stack.p;
if (isold(th) || g->gcstate == GCSpropagate)
linkgclist(th, g->grayagain); /* insert into 'grayagain' list */
if (o == NULL)
return 0; /* stack not completely built yet */
lua_assert(g->gcstate == GCSatomic ||
th->openupval == NULL || isintwups(th));
for (; o < th->top.p; o++) /* mark live elements in the stack */
markvalue(g, s2v(o));
for (uv = th->openupval; uv != NULL; uv = uv->u.open.next)
markobject(g, uv); /* open upvalues cannot be collected */
if (g->gcstate == GCSatomic) { /* final traversal? */
if (!g->gcemergency)
luaD_shrinkstack(th); /* do not change stack in emergency cycle */
for (o = th->top.p; o < th->stack_last.p + EXTRA_STACK; o++)
setnilvalue2s(o); /* clear dead stack slice */
/* '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;
}
}
return 1 + (th->top.p - th->stack.p);
}
/*
** traverse one gray object, turning it to black. Return an estimate
** of the number of slots traversed.
*/
static l_mem propagatemark (global_State *g) {
GCObject *o = g->gray;
nw2black(o);
g->gray = *getgclist(o); /* remove from 'gray' list */
switch (o->tt) {
case LUA_VTABLE: return traversetable(g, gco2t(o));
case LUA_VUSERDATA: return traverseudata(g, gco2u(o));
case LUA_VLCL: return traverseLclosure(g, gco2lcl(o));
case LUA_VCCL: return traverseCclosure(g, gco2ccl(o));
case LUA_VPROTO: return traverseproto(g, gco2p(o));
case LUA_VTHREAD: return traversethread(g, gco2th(o));
default: lua_assert(0); return 0;
}
}
static void propagateall (global_State *g) {
while (g->gray)
propagatemark(g);
}
/*
** Traverse all ephemeron tables propagating marks from keys to values.
** Repeat until it converges, that is, nothing new is marked. 'dir'
** inverts the direction of the traversals, trying to speed up
** convergence on chains in the same table.
*/
static void convergeephemerons (global_State *g) {
int changed;
int dir = 0;
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) { /* for each ephemeron table */
Table *h = gco2t(w);
next = h->gclist; /* list is rebuilt during loop */
nw2black(h); /* out of the list (for now) */
if (traverseephemeron(g, h, dir)) { /* marked some value? */
propagateall(g); /* propagate changes */
changed = 1; /* will have to revisit all ephemeron tables */
}
}
dir = !dir; /* invert direction next time */
} while (changed); /* repeat until no more changes */
}
/* }====================================================== */
/*
** {======================================================
** Sweep Functions
** =======================================================
*/
/*
** clear entries with unmarked keys from all weaktables in list 'l'
*/
static void clearbykeys (global_State *g, GCObject *l) {
for (; l; l = gco2t(l)->gclist) {
Table *h = gco2t(l);
Node *limit = gnodelast(h);
Node *n;
for (n = gnode(h, 0); n < limit; n++) {
if (iscleared(g, gckeyN(n))) /* unmarked key? */
setempty(gval(n)); /* remove entry */
if (isempty(gval(n))) /* is entry empty? */
clearkey(n); /* clear its key */
}
}
}
/*
** clear entries with unmarked values from all weaktables in list 'l' up
** to element 'f'
*/
static void clearbyvalues (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;
unsigned int asize = h->asize;
for (i = 0; i < asize; i++) {
GCObject *o = gcvalarr(h, i);
if (iscleared(g, o)) /* value was collected? */
*getArrTag(h, i) = LUA_VEMPTY; /* remove entry */
}
for (n = gnode(h, 0); n < limit; n++) {
if (iscleared(g, gcvalueN(gval(n)))) /* unmarked value? */
setempty(gval(n)); /* remove entry */
if (isempty(gval(n))) /* is entry empty? */
clearkey(n); /* clear its key */
}
}
}
static void freeupval (lua_State *L, UpVal *uv) {
if (upisopen(uv))
luaF_unlinkupval(uv);
luaM_free(L, uv);
}
static void freeobj (lua_State *L, GCObject *o) {
assert_code(l_mem newmem = gettotalbytes(G(L)) - objsize(o));
switch (o->tt) {
case LUA_VPROTO:
luaF_freeproto(L, gco2p(o));
break;
case LUA_VUPVAL:
freeupval(L, gco2upv(o));
break;
case LUA_VLCL: {
LClosure *cl = gco2lcl(o);
luaM_freemem(L, cl, sizeLclosure(cl->nupvalues));
break;
}
case LUA_VCCL: {
CClosure *cl = gco2ccl(o);
luaM_freemem(L, cl, sizeCclosure(cl->nupvalues));
break;
}
case LUA_VTABLE:
luaH_free(L, gco2t(o));
break;
case LUA_VTHREAD:
luaE_freethread(L, gco2th(o));
break;
case LUA_VUSERDATA: {
Udata *u = gco2u(o);
luaM_freemem(L, o, sizeudata(u->nuvalue, u->len));
break;
}
case LUA_VSHRSTR: {
TString *ts = gco2ts(o);
luaS_remove(L, ts); /* remove it from hash table */
luaM_freemem(L, ts, sizestrshr(cast_uint(ts->shrlen)));
break;
}
case LUA_VLNGSTR: {
TString *ts = gco2ts(o);
if (ts->shrlen == LSTRMEM) /* must free external string? */
(*ts->falloc)(ts->ud, ts->contents, ts->u.lnglen + 1, 0);
luaM_freemem(L, ts, luaS_sizelngstr(ts->u.lnglen, ts->shrlen));
break;
}
default: lua_assert(0);
}
lua_assert(gettotalbytes(G(L)) == newmem);
}
/*
** sweep at most 'countin' 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 (and new), 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, l_mem countin) {
global_State *g = G(L);
int ow = otherwhite(g);
int white = luaC_white(g); /* current white */
while (*p != NULL && countin-- > 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' and age to 'new' */
curr->marked = cast_byte((marked & ~maskgcbits) | white | G_NEW);
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->gcemergency) {
if (g->strt.nuse < g->strt.size / 4) /* string table too big? */
luaS_resize(L, g->strt.size / 2);
}
}
/*
** Get the next udata to be finalized from the 'tobefnz' list, and
** link it back into the 'allgc' list.
*/
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 */
else if (getage(o) == G_OLD1)
g->firstold1 = o; /* it is the first OLD1 object in the list */
return o;
}
static void dothecall (lua_State *L, void *ud) {
UNUSED(ud);
luaD_callnoyield(L, L->top.p - 2, 0);
}
static void GCTM (lua_State *L) {
global_State *g = G(L);
const TValue *tm;
TValue v;
lua_assert(!g->gcemergency);
setgcovalue(L, &v, udata2finalize(g));
tm = luaT_gettmbyobj(L, &v, TM_GC);
if (!notm(tm)) { /* is there a finalizer? */
TStatus status;
lu_byte oldah = L->allowhook;
lu_byte oldgcstp = g->gcstp;
g->gcstp |= GCSTPGC; /* avoid GC steps */
L->allowhook = 0; /* stop debug hooks during GC metamethod */
setobj2s(L, L->top.p++, tm); /* push finalizer... */
setobj2s(L, L->top.p++, &v); /* ... and its argument */
L->ci->callstatus |= CIST_FIN; /* will run a finalizer */
status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top.p - 2), 0);
L->ci->callstatus &= ~CIST_FIN; /* not running a finalizer anymore */
L->allowhook = oldah; /* restore hooks */
g->gcstp = oldgcstp; /* restore state */
if (l_unlikely(status != LUA_OK)) { /* error while running __gc? */
luaE_warnerror(L, "__gc");
L->top.p--; /* pops error object */
}
}
}
/*
** call all pending finalizers
*/
static void callallpendingfinalizers (lua_State *L) {
global_State *g = G(L);
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