lgc.c
(5.4.6)
/*
** $Id: lgc.c $
** Garbage Collector
** See Copyright Notice in lua.h
*/
#define lgc_c
#define LUA_CORE
#include "lprefix.h"
#include <stdio.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 100
/*
** Maximum number of finalizers to call in each single step.
*/
#define GCFINMAX 10
/*
** Cost of calling one finalizer.
*/
#define GCFINALIZECOST 50
/*
** The equivalent, in bytes, of one unit of "work" (visiting a slot,
** sweeping an object, etc.)
*/
#define WORK2MEM sizeof(TValue)
/*
** macro to adjust 'pause': 'pause' is actually used like
** 'pause / PAUSEADJ' (value chosen by tests)
*/
#define PAUSEADJ 100
/* 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)
#define markvalue(g,o) { checkliveness(g->mainthread,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 lu_mem 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 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
** whites from deads.)
*/
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_INC) /* 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_GEN) == (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, int 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;
}
GCObject *luaC_newobj (lua_State *L, int 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) {
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_NUMTAGS; i++)
markobjectN(g, g->mt[i]);
}
/*
** mark all objects in list of being-finalized
*/
static lu_mem markbeingfnz (global_State *g) {
GCObject *o;
lu_mem count = 0;
for (o = g->tobefnz; o != NULL; o = o->next) {
count++;
markobject(g, o);
}
return count;
}
/*
** 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 int remarkupvals (global_State *g) {
lua_State *thread;
lua_State **p = &g->twups;
int work = 0; /* estimate of how much work was done here */
while ((thread = *p) != NULL) {
work++;
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));
work++;
if (!iswhite(uv)) { /* upvalue already visited? */
lua_assert(upisopen(uv) && isgray(uv));
markvalue(g, uv->v.p); /* mark its value */
}
}
}
}
return work;
}
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
*/
static void restartcollection (global_State *g) {
cleargraylists(g);
markobject(g, g->mainthread);
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.)
*/
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)
changeage(o, G_TOUCHED2, 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.
*/
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->alimit > 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 == GCSatomic && hasclears)
linkgclist(h, g->weak); /* has to be cleared later */
else
linkgclist(h, g->grayagain); /* must retraverse it in atomic phase */
}
/*
** 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 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" */
unsigned int i;
unsigned int asize = luaH_realasize(h);
unsigned int nsize = sizenode(h);
/* traverse array part */
for (i = 0; i < asize; i++) {
if (valiswhite(&h->array[i])) {
marked = 1;
reallymarkobject(g, gcvalue(&h->array[i]));
}
}
/* 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);
unsigned int i;
unsigned int asize = luaH_realasize(h);
for (i = 0; i < asize; i++) /* traverse array part */
markvalue(g, &h->array[i]);
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));
}
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? */
(cast_void(weakkey = strchr(svalue(mode), 'k')),
cast_void(weakvalue = strchr(svalue(mode), 'v')),
(weakkey || weakvalue))) { /* is really weak? */
if (!weakkey) /* strong keys? */
traverseweakvalue(g, h);
else if (!weakvalue) /* strong values? */
traverseephemeron(g, h, 0);
else /* all weak */
linkgclist(h, g->allweak); /* nothing to traverse now */
}
else /* not weak */
traversestrongtable(g, h);
return 1 + h->alimit + 2 * allocsizenode(h);
}
static int 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 int 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 int 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 int 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 int 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 1; /* 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? */
for (; o < th->stack_last.p + EXTRA_STACK; o++)
setnilvalue(s2v(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;
}
}
else if (!g->gcemergency)
luaD_shrinkstack(th); /* do not change stack in emergency cycle */
return 1 + stacksize(th);
}
/*
** traverse one gray object, turning it to black.
*/
static lu_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 lu_mem propagateall (global_State *g) {
lu_mem tot = 0;
while (g->gray)
tot += propagatemark(g);
return tot;
}
/*
** 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 = luaH_realasize(h);
for (i = 0; i < asize; i++) {
TValue *o = &h->array[i];
if (iscleared(g, gcvalueN(o))) /* value was collected? */
setempty(o); /* 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) {
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, sizelstring(ts->shrlen));
break;
}
case LUA_VLNGSTR: {
TString *ts = gco2ts(o);
luaM_freemem(L, ts, sizelstring(ts->u.lnglen));
break;
}
default: lua_assert(0);
}
}
/*
** 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, preparing for next
** collection cycle. Return where to continue the traversal or NULL if
** list is finished. ('*countout' gets the number of elements traversed.)
*/
static GCObject **sweeplist (lua_State *L, GCObject **p, int countin,
int *countout) {
global_State *g = G(L);
int ow = otherwhite(g);
int i;
int white = luaC_white(g); /* current white */
for (i = 0; *p != NULL && i < countin; i++) {
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 & ~maskgcbits) | white);
p = &curr->next; /* go to next element */
}
}
if (countout)
*countout = i; /* number of elements traversed */
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, NULL);
} 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? */
l_mem olddebt = g->GCdebt;
luaS_resize(L, g->strt.size / 2);
g->GCestimate += g->GCdebt - olddebt; /* correct estimate */
}
}
}
/*
** 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? */
int status;
lu_byte oldah = L->allowhook;
int 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 a few finalizers
*/
static int runafewfinalizers (lua_State *L, int n) {
global_State *g = G(L);
int i;
for (i = 0; i < n && g->tobefnz; i++)
GCTM(L); /* call one finalizer */
return i;
}
/*
** call all pending finalizers
*/
static void callallpendingfinalizers (lua_State *L) {
global_State *g = G(L);
while (g->tobefnz)
GCTM(L);
}
/*
** 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).
** (Note that objects after 'finobjold1' cannot be white, so they
** don't need to be traversed. In incremental mode, 'finobjold1' is NULL,
** so the whole list is traversed.)
*/
static void separatetobefnz (global_State *g, int all) {
GCObject *curr;
GCObject **p = &g->finobj;
GCObject **lastnext = findlast(&g->tobefnz);
while ((curr = *p) != g->finobjold1) { /* traverse all finalizable objects */
lua_assert(tofinalize(curr));
if (!(iswhite(curr) || all)) /* not being collected? */
p = &curr->next; /* don't bother with it */
else {
if (curr == g->finobjsur) /* removing 'finobjsur'? */
g->finobjsur = curr->next; /* correct it */
*p = curr->next; /* remove 'curr' from 'finobj' list */
curr->next = *lastnext; /* link at the end of 'tobefnz' list */
*lastnext = curr;
lastnext = &curr->next;
}
}
}
/*
** If pointer 'p' points to 'o', move it to the next element.
*/
static void checkpointer (GCObject **p, GCObject *o) {
if (o == *p)
*p = o->next;
}
/*
** Correct pointers to objects inside 'allgc' list when
** object 'o' is being removed from the list.
*/
static void correctpointers (global_State *g, GCObject *o) {
checkpointer(&g->survival, o);
checkpointer(&g->old1, o);
checkpointer(&g->reallyold, o);
checkpointer(&g->firstold1, o);
}
/*
** 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... */
(g->gcstp & GCSTPCLS)) /* or closing state? */
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' */
}
else
correctpointers(g, o);
/* 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 */
}
}
/* }====================================================== */
/*
** {======================================================
** Generational Collector
** =======================================================
*/
/*
** Set the "time" to wait before starting a new GC cycle; cycle will
** start when memory use hits the threshold of ('estimate' * pause /
** PAUSEADJ). (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;
int pause = getgcparam(g->gcpause);
l_mem estimate = g->GCestimate / PAUSEADJ; /* adjust 'estimate' */
lua_assert(estimate > 0);
threshold = (pause < MAX_LMEM / estimate) /* overflow? */
? estimate * pause /* no overflow */
: MAX_LMEM; /* overflow; truncate to maximum */
debt = gettotalbytes(g) - threshold;
if (debt > 0) debt = 0;
luaE_setdebt(g, debt);
}
/*
** Sweep a list of objects to enter generational mode. Deletes dead
** objects and turns the non dead to old. All non-dead threads---which
** are now old---must be in a gray list. Everything else is not in a
** gray list. Open upvalues are also kept gray.
*/
static void sweep2old (lua_State *L, GCObject **p) {
GCObject *curr;
global_State *g = G(L);
while ((curr = *p) != NULL) {
if (iswhite(curr)) { /* is 'curr' dead? */
lua_assert(isdead(g, curr));
*p = curr->next; /* remove 'curr' from list */
freeobj(L, curr); /* erase 'curr' */
}
else { /* all surviving objects become old */
setage(curr, G_OLD);
if (curr->tt == LUA_VTHREAD) { /* threads must be watched */
lua_State *th = gco2th(curr);
linkgclist(th, g->grayagain); /* insert into 'grayagain' list */
}
else if (curr->tt == LUA_VUPVAL && upisopen(gco2upv(curr)))
set2gray(curr); /* open upvalues are always gray */
else /* everything else is black */
nw2black(curr);
p = &curr->next; /* go to next element */
}
}
}
/*
** Sweep for generational mode. Delete dead objects. (Because the
** collection is not incremental, there are no "new white" objects
** during the sweep. So, any white object must be dead.) For
** non-dead objects, advance their ages and clear the color of
** new objects. (Old objects keep their colors.)
** The ages of G_TOUCHED1 and G_TOUCHED2 objects cannot be advanced
** here, because these old-generation objects are usually not swept
** here. They will all be advanced in 'correctgraylist'. That function
** will also remove objects turned white here from any gray list.
*/
static GCObject **sweepgen (lua_State *L, global_State *g, GCObject **p,
GCObject *limit, GCObject **pfirstold1) {
static const lu_byte nextage[] = {
G_SURVIVAL, /* from G_NEW */
G_OLD1, /* from G_SURVIVAL */
G_OLD1, /* from G_OLD0 */
G_OLD, /* from G_OLD1 */
G_OLD, /* from G_OLD (do not change) */
G_TOUCHED1, /* from G_TOUCHED1 (do not change) */
G_TOUCHED2 /* from G_TOUCHED2 (do not change) */
};
int white = luaC_white(g);
GCObject *curr;
while ((curr = *p) != limit) {
if (iswhite(curr)) { /* is 'curr' dead? */
lua_assert(!isold(curr) && isdead(g, curr));
*p = curr->next; /* remove 'curr' from list */
freeobj(L, curr); /* erase 'curr' */
}
else { /* correct mark and age */
if (getage(curr) == G_NEW) { /* new objects go back to white */
int marked = curr->marked & ~maskgcbits; /* erase GC bits */
curr->marked = cast_byte(marked | G_SURVIVAL | white);
}
else { /* all other objects will be old, and so keep their color */
setage(curr, nextage[getage(curr)]);
if (getage(curr) == G_OLD1 && *pfirstold1 == NULL)
*pfirstold1 = curr; /* first OLD1 object in the list */
}
p = &curr->next; /* go to next element */
}
}
return p;
}
/*
** Traverse a list making all its elements white and clearing their
** age. In incremental mode, all objects are 'new' all the time,
** except for fixed strings (which are always old).
*/
static void whitelist (global_State *g, GCObject *p) {
int white = luaC_white(g);
for (; p != NULL; p = p->next)
p->marked = cast_byte((p->marked & ~maskgcbits) | white);
}
/*
** Correct a list of gray objects. Return pointer to where rest of the
** list should be linked.
** Because this correction is done after sweeping, young objects might
** be turned white and still be in the list. They are only removed.
** 'TOUCHED1' objects are advanced to 'TOUCHED2' and remain on the list;
** Non-white threads also remain on the list; 'TOUCHED2' objects become
** regular old; they and anything else are removed from the list.
*/
static GCObject **correctgraylist (GCObject **p) {
GCObject *curr;
while ((curr = *p) != NULL) {
GCObject **next = getgclist(curr);
if (iswhite(curr))
goto remove; /* remove all white objects */
else if (getage(curr) == G_TOUCHED1) { /* touched in this cycle? */
lua_assert(isgray(curr));
nw2black(curr); /* make it black, for next barrier */
changeage(curr, G_TOUCHED1, G_TOUCHED2);
goto remain; /* keep it in the list and go to next element */
}
else if (curr->tt == LUA_VTHREAD) {
lua_assert(isgray(curr));
goto remain; /* keep non-white threads on the list */
}
else { /* everything else is removed */
lua_assert(isold(curr)); /* young objects should be white here */
if (getage(curr) == G_TOUCHED2) /* advance from TOUCHED2... */
changeage(curr, G_TOUCHED2, G_OLD); /* ... to OLD */
nw2black(curr); /* make object black (to be removed) */
goto remove;
}
remove: *p = *next; continue;
remain: p = next; continue;
}
return p;
}
/*
** Correct all gray lists, coalescing them into 'grayagain'.
*/
static void correctgraylists (global_State *g) {
GCObject **list = correctgraylist(&g->grayagain);
*list = g->weak; g->weak = NULL;
list = correctgraylist(list);
*list = g->allweak; g->allweak = NULL;
list = correctgraylist(list);
*list = g->ephemeron; g->ephemeron = NULL;
correctgraylist(list);
}
/*
** Mark black 'OLD1' objects when starting a new young collection.
** Gray objects are already in some gray list, and so will be visited
** in the atomic step.
*/
static void markold (global_State *g, GCObject *from, GCObject *to) {
GCObject *p;
for (p = from; p != to; p = p->next) {
if (getage(p) == G_OLD1) {
lua_assert(!iswhite(p));
changeage(p, G_OLD1, G_OLD); /* now they are old */
if (isblack(p))
reallymarkobject(g, p);
}
}
}
/*
** Finish a young-generation collection.
*/
static void finishgencycle (lua_State *L, global_State *g) {
correctgraylists(g);
checkSizes(L, g);
g->gcstate = GCSpropagate; /* skip restart */
if (!g->gcemergency)
callallpendingfinalizers(L);
}
/*
** Does a young collection. First, mark 'OLD1' objects. Then does the
** atomic step. Then, sweep all lists and advance pointers. Finally,
** finish the collection.
*/
static void youngcollection (lua_State *L, global_State *g) {
GCObject **psurvival; /* to point to first non-dead survival object */
GCObject *dummy; /* dummy out parameter to 'sweepgen' */
lua_assert(g->gcstate == GCSpropagate);
if (g->firstold1) { /* are there regular OLD1 objects? */
markold(g, g->firstold1, g->reallyold); /* mark them */
g->firstold1 = NULL; /* no more OLD1 objects (for now) */
}
markold(g, g->finobj, g->finobjrold);
markold(g, g->tobefnz, NULL);
atomic(L);
/* sweep nursery and get a pointer to its last live element */
g->gcstate = GCSswpallgc;
psurvival = sweepgen(L, g, &g->allgc, g->survival, &g->firstold1);
/* sweep 'survival' */
sweepgen(L, g, psurvival, g->old1, &g->firstold1);
g->reallyold = g->old1;
g->old1 = *psurvival; /* 'survival' survivals are old now */
g->survival = g->allgc; /* all news are survivals */
/* repeat for 'finobj' lists */
dummy = NULL; /* no 'firstold1' optimization for 'finobj' lists */
psurvival = sweepgen(L, g, &g->finobj, g->finobjsur, &dummy);
/* sweep 'survival' */
sweepgen(L, g, psurvival, g->finobjold1, &dummy);
g->finobjrold = g->finobjold1;
g->finobjold1 = *psurvival; /* 'survival' survivals are old now */
g->finobjsur = g->finobj; /* all news are survivals */
sweepgen(L, g, &g->tobefnz, NULL, &dummy);
finishgencycle(L, g);
}
/*
** Clears all gray lists, sweeps objects, and prepare sublists to enter
** generational mode. The sweeps remove dead objects and turn all
** surviving objects to old. Threads go back to 'grayagain'; everything
** else is turned black (not in any gray list).
*/
static void atomic2gen (lua_State *L, global_State *g) {
cleargraylists(g);
/* sweep all elements making them old */
g->gcstate = GCSswpallgc;
sweep2old(L, &g->allgc);
/* everything alive now is old */
g->reallyold = g->old1 = g->survival = g->allgc;
g->firstold1 = NULL; /* there are no OLD1 objects anywhere */
/* repeat for 'finobj' lists */
sweep2old(L, &g->finobj);
g->finobjrold = g->finobjold1 = g->finobjsur = g->finobj;
sweep2old(L, &g->tobefnz);
g->gckind = KGC_GEN;
g->lastatomic = 0;
g->GCestimate = gettotalbytes(g); /* base for memory control */
finishgencycle(L, g);
}
/*
** Set debt for the next minor collection, which will happen when
** memory grows 'genminormul'%.
*/
static void setminordebt (global_State *g) {
luaE_setdebt(g, -(cast(l_mem, (gettotalbytes(g) / 100)) * g->genminormul));
}
/*
** Enter generational mode. Must go until the end of an atomic cycle
** to ensure that all objects are correctly marked and weak tables
** are cleared. Then, turn all objects into old and finishes the
** collection.
*/
static lu_mem entergen (lua_State *L, global_State *g) {
lu_mem numobjs;
luaC_runtilstate(L, bitmask(GCSpause)); /* prepare to start a new cycle */
luaC_runtilstate(L, bitmask(GCSpropagate)); /* start new cycle */
numobjs = atomic(L); /* propagates all and then do the atomic stuff */
atomic2gen(L, g);
setminordebt(g); /* set debt assuming next cycle will be minor */
return numobjs;
}
/*
** Enter incremental mode. Turn all objects white, make all
** intermediate lists point to NULL (to avoid invalid pointers),
** and go to the pause state.
*/
static void enterinc (global_State *g) {
whitelist(g, g->allgc);
g->reallyold = g->old1 = g->survival = NULL;
whitelist(g, g->finobj);
whitelist(g, g->tobefnz);
g->finobjrold = g->finobjold1 = g->finobjsur = NULL;
g->gcstate = GCSpause;
g->gckind = KGC_INC;
g->lastatomic = 0;
}
/*
** Change collector mode to 'newmode'.
*/
void luaC_changemode (lua_State *L, int newmode) {
global_State *g = G(L);
if (newmode != g->gckind) {
if (newmode == KGC_GEN) /* entering generational mode? */
entergen(L, g);
else
enterinc(g); /* entering incremental mode */
}
g->lastatomic = 0;
}
/*
** Does a full collection in generational mode.
*/
static lu_mem fullgen (lua_State *L, global_State *g) {
enterinc(g);
return entergen(L, g);
}
/*
** Does a major collection after last collection was a "bad collection".
**
** When the program is building a big structure, it allocates lots of
** memory but generates very little garbage. In those scenarios,
** the generational mode just wastes time doing small collections, and
** major collections are frequently what we call a "bad collection", a
** collection that frees too few objects. To avoid the cost of switching
** between generational mode and the incremental mode needed for full
** (major) collections, the collector tries to stay in incremental mode
** after a bad collection, and to switch back to generational mode only
** after a "good" collection (one that traverses less than 9/8 objects
** of the previous one).
** The collector must choose whether to stay in incremental mode or to
** switch back to generational mode before sweeping. At this point, it
** does not know the real memory in use, so it cannot use memory to
** decide whether to return to generational mode. Instead, it uses the
** number of objects traversed (returned by 'atomic') as a proxy. The
** field 'g->lastatomic' keeps this count from the last collection.
** ('g->lastatomic != 0' also means that the last collection was bad.)
*/
static void stepgenfull (lua_State *L, global_State *g) {
lu_mem newatomic; /* count of traversed objects */
lu_mem lastatomic = g->lastatomic; /* count from last collection */
if (g->gckind == KGC_GEN) /* still in generational mode? */
enterinc(g); /* enter incremental mode */
luaC_runtilstate(L, bitmask(GCSpropagate)); /* start new cycle */
newatomic = atomic(L); /* mark everybody */
if (newatomic < lastatomic + (lastatomic >> 3)) { /* good collection? */
atomic2gen(L, g); /* return to generational mode */
setminordebt(g);
}
else { /* another bad collection; stay in incremental mode */
g->GCestimate = gettotalbytes(g); /* first estimate */;
entersweep(L);
luaC_runtilstate(L, bitmask(GCSpause)); /* finish collection */
setpause(g);
g->lastatomic = newatomic;
}
}
/*
** Does a generational "step".
** Usually, this means doing a minor collection and setting the debt to
** make another collection when memory grows 'genminormul'% larger.
**
** However, there are exceptions. If memory grows 'genmajormul'%
** larger than it was at the end of the last major collection (kept
** in 'g->GCestimate'), the function does a major collection. At the
** end, it checks whether the major collection was able to free a
** decent amount of memory (at least half the growth in memory since
** previous major collection). If so, the collector keeps its state,
** and the next collection will probably be minor again. Otherwise,
** we have what we call a "bad collection". In that case, set the field
** 'g->lastatomic' to signal that fact, so that the next collection will
** go to 'stepgenfull'.
**
** 'GCdebt <= 0' means an explicit call to GC step with "size" zero;
** in that case, do a minor collection.
*/
static void genstep (lua_State *L, global_State *g) {
if (g->lastatomic != 0) /* last collection was a bad one? */
stepgenfull(L, g); /* do a full step */
else {
lu_mem majorbase = g->GCestimate; /* memory after last major collection */
lu_mem majorinc = (majorbase / 100) * getgcparam(g->genmajormul);
if (g->GCdebt > 0 && gettotalbytes(g) > majorbase + majorinc) {
lu_mem numobjs = fullgen(L, g); /* do a major collection */
if (gettotalbytes(g) < majorbase + (majorinc / 2)) {
/* collected at least half of memory growth since last major
collection; keep doing minor collections. */
lua_assert(g->lastatomic == 0);
}
else { /* bad collection */
g->lastatomic = numobjs; /* signal that last collection was bad */
setpause(g); /* do a long wait for next (major) collection */
}
}
else { /* regular case; do a minor collection */
youngcollection(L, g);
setminordebt(g);
g->GCestimate = majorbase; /* preserve base value */
}
}
lua_assert(isdecGCmodegen(g));
}
/* }====================================================== */
/*
** {======================================================
** GC control
** =======================================================
*/
/*
** Enter first sweep phase.
** The call to 'sweeptolive' makes the 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 = sweeptolive(L, &g->allgc);
}
/*
** Delete all objects in list 'p' until (but not including) object
** 'limit'.
*/
static void deletelist (lua_State *L, GCObject *p, GCObject *limit) {
while (p != limit) {
GCObject *next = p->next;
freeobj(L, p);
p = next;
}
}
/*
** Call all finalizers of the objects in the given Lua state, and
** then free all objects, except for the main thread.
*/
void luaC_freeallobjects (lua_State *L) {
global_State *g = G(L);
g->gcstp = GCSTPCLS; /* no extra finalizers after here */
luaC_changemode(L, KGC_INC);
separatetobefnz(g, 1); /* separate all objects with finalizers */
lua_assert(g->finobj == NULL);
callallpendingfinalizers(L);
deletelist(L, g->allgc, obj2gco(g->mainthread));
lua_assert(g->finobj == NULL); /* no new finalizers */
deletelist(L, g->fixedgc, NULL); /* collect fixed objects */
lua_assert(g->strt.nuse == 0);
}
static lu_mem atomic (lua_State *L) {
global_State *g = G(L);
lu_mem work = 0;
GCObject *origweak, *origall;
GCObject *grayagain = g->grayagain; /* save original list */
g->grayagain = NULL;
lua_assert(g->ephemeron == NULL && g->weak == NULL);
lua_assert(!iswhite(g->mainthread));
g->gcstate = GCSatomic;
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 */
work += propagateall(g); /* empties 'gray' list */
/* remark occasional upvalues of (maybe) dead threads */
work += remarkupvals(g);
work += propagateall(g); /* propagate changes */
g->gray = grayagain;
work += propagateall(g); /* traverse 'grayagain' list */
convergeephemerons(g);
/* at this point, all strongly accessible objects are marked. */
/* Clear values from weak tables, before checking finalizers */
clearbyvalues(g, g->weak, NULL);
clearbyvalues(g, g->allweak, NULL);
origweak = g->weak; origall = g->allweak;
separatetobefnz(g, 0); /* separate objects to be finalized */
work += markbeingfnz(g); /* mark objects that will be finalized */
work += propagateall(g); /* remark, to propagate 'resurrection' */
convergeephemerons(g);
/* at this point, all resurrected objects are marked. */
/* remove dead objects from weak tables */
clearbykeys(g, g->ephemeron); /* clear keys from all ephemeron tables */
clearbykeys(g, g->allweak); /* clear keys from all 'allweak' tables */
/* clear values from resurrected weak tables */
clearbyvalues(g, g->weak, origweak);
clearbyvalues(g, g->allweak, origall);
luaS_clearcache(g);
g->currentwhite = cast_byte(otherwhite(g)); /* flip current white */
lua_assert(g->gray == NULL);
return work; /* estimate of slots marked by 'atomic' */
}
static int sweepstep (lua_State *L, global_State *g,
int nextstate, GCObject **nextlist) {
if (g->sweepgc) {
l_mem olddebt = g->GCdebt;
int count;
g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX, &count);
g->GCestimate += g->GCdebt - olddebt; /* update estimate */
return count;
}
else { /* enter next state */
g->gcstate = nextstate;
g->sweepgc = nextlist;
return 0; /* no work done */
}
}
static lu_mem singlestep (lua_State *L) {
global_State *g = G(L);
lu_mem work;
lua_assert(!g->gcstopem); /* collector is not reentrant */
g->gcstopem = 1; /* no emergency collections while collecting */
switch (g->gcstate) {
case GCSpause: {
restartcollection(g);
g->gcstate = GCSpropagate;
work = 1;
break;
}
case GCSpropagate: {
if (g->gray == NULL) { /* no more gray objects? */
g->gcstate = GCSenteratomic; /* finish propagate phase */
work = 0;
}
else
work = propagatemark(g); /* traverse one gray object */
break;
}
case GCSenteratomic: {
work = atomic(L); /* work is what was traversed by 'atomic' */
entersweep(L);
g->GCestimate = gettotalbytes(g); /* first estimate */;
break;
}
case GCSswpallgc: { /* sweep "regular" objects */
work = sweepstep(L, g, GCSswpfinobj, &g->finobj);
break;
}
case GCSswpfinobj: { /* sweep objects with finalizers */
work = sweepstep(L, g, GCSswptobefnz, &g->tobefnz);
break;
}
case GCSswptobefnz: { /* sweep objects to be finalized */
work = sweepstep(L, g, GCSswpend, NULL);
break;
}
case GCSswpend: { /* finish sweeps */
checkSizes(L, g);
g->gcstate = GCScallfin;
work = 0;
break;
}
case GCScallfin: { /* call remaining finalizers */
if (g->tobefnz && !g->gcemergency) {
g->gcstopem = 0; /* ok collections during finalizers */
work = runafewfinalizers(L, GCFINMAX) * GCFINALIZECOST;
}
else { /* emergency mode or no more finalizers */
g->gcstate = GCSpause; /* finish collection */
work = 0;
}
break;
}
default: lua_assert(0); return 0;
}
g->gcstopem = 0;
return work;
}
/*
** 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);
}
/*
** Performs a basic incremental step. The debt and step size are
** converted from bytes to "units of work"; then the function loops
** running single steps until adding that many units of work or
** finishing a cycle (pause state). Finally, it sets the debt that
** controls when next step will be performed.
*/
static void incstep (lua_State *L, global_State *g) {
int stepmul = (getgcparam(g->gcstepmul) | 1); /* avoid division by 0 */
l_mem debt = (g->GCdebt / WORK2MEM) * stepmul;
l_mem stepsize = (g->gcstepsize <= log2maxs(l_mem))
? ((cast(l_mem, 1) << g->gcstepsize) / WORK2MEM) * stepmul
: MAX_LMEM; /* overflow; keep maximum value */
do { /* repeat until pause or enough "credit" (negative debt) */
lu_mem work = singlestep(L); /* perform one single step */
debt -= work;
} while (debt > -stepsize && g->gcstate != GCSpause);
if (g->gcstate == GCSpause)
setpause(g); /* pause until next cycle */
else {
debt = (debt / stepmul) * WORK2MEM; /* convert 'work units' to bytes */
luaE_setdebt(g, debt);
}
}
/*
** Performs a basic GC step if collector is running. (If collector is
** not running, set a reasonable debt to avoid it being called at
** every single check.)
*/
void luaC_step (lua_State *L) {
global_State *g = G(L);
if (!gcrunning(g)) /* not running? */
luaE_setdebt(g, -2000);
else {
if(isdecGCmodegen(g))
genstep(L, g);
else
incstep(L, g);
}
}
/*
** Perform a full collection in incremental mode.
** 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).
*/
static void fullinc (lua_State *L, global_State *g) {
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(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 */
setpause(g);
}
/*
** 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).
*/
void luaC_fullgc (lua_State *L, int isemergency) {
global_State *g = G(L);
lua_assert(!g->gcemergency);
g->gcemergency = isemergency; /* set flag */
if (g->gckind == KGC_INC)
fullinc(L, g);
else
fullgen(L, g);
g->gcemergency = 0;
}
/* }====================================================== */