Better control of gray objects
Avoid turning an object to gray except at the moment it is inserted in a
gray list or in the explicit exceptional cases such as open upvalues and
fixed strings.
diff --git a/lgc.c b/lgc.c
index be125dd..4a7bcae 100644
--- a/lgc.c
+++ b/lgc.c
@@ -75,6 +75,11 @@
#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)))
@@ -135,15 +140,23 @@
/*
-** Link a collectable object 'o' with a known type into list pointed by 'p'.
+** 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) ((o)->gclist = (p), (p) = obj2gco(o))
+#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 list pointed by 'p'.
+** Link a generic collectable object 'o' into the list 'p'.
*/
-#define linkobjgclist(o,p) (*getgclist(o) = (p), (p) = obj2gco(o))
+#define linkobjgclist(o,p) linkgclist_(obj2gco(o), getgclist(o), &(p))
@@ -219,9 +232,10 @@
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) /* not already in gray list? */
- linkobjgclist(o, g->grayagain); /* link it in 'grayagain' */
- set2gray(o); /* make object gray (again) */
+ 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 */
}
@@ -264,25 +278,30 @@
/*
-** 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 indirectly linked through the 'twups' list. They
-** are kept gray to avoid barriers, as their values will be revisited by
-** the thread or by 'remarkupvals'.)
+** 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) {
- set2gray(o);
switch (o->tt) {
case LUA_VSHRSTR:
case LUA_VLNGSTR: {
- nw2black(o); /* nothing to visit */
+ set2black(o); /* nothing to visit */
break;
}
case LUA_VUPVAL: {
UpVal *uv = gco2upv(o);
- if (!upisopen(uv)) /* open upvalues are kept gray */
- nw2black(o); /* closed upvalues are visited here */
+ if (upisopen(uv))
+ set2gray(uv); /* open upvalues are kept gray */
+ else
+ set2black(o); /* closed upvalues are visited here */
markvalue(g, uv->v); /* mark its content */
break;
}
@@ -290,7 +309,7 @@
Udata *u = gco2u(o);
if (u->nuvalue == 0) { /* no user values? */
markobjectN(g, u->metatable); /* mark its metatable */
- nw2black(o); /* nothing else to mark */
+ set2black(o); /* nothing else to mark */
break;
}
/* else... */
@@ -402,17 +421,11 @@
** 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.)
-** It is defined as a macro because 'gclist' is not a unique field in
-** different collectable objects.
*/
-#define genlink(g,o) genlink_(g, obj2gco(o), &(o)->gclist)
-
-static void genlink_ (global_State *g, GCObject *o, GCObject **pnext) {
+static void genlink (global_State *g, GCObject *o) {
lua_assert(isblack(o));
if (getage(o) == G_TOUCHED1) { /* touched in this cycle? */
- *pnext = g->grayagain; /* link it back in 'grayagain' */
- g->grayagain = o;
- set2gray(o);
+ 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 */
@@ -496,10 +509,8 @@
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 {
- nw2black(h); /* 'genlink' expects black objects */
- genlink(g, h); /* check whether collector still needs to see it */
- }
+ else
+ genlink(g, obj2gco(h)); /* check whether collector still needs to see it */
return marked;
}
@@ -519,7 +530,7 @@
markvalue(g, gval(n));
}
}
- genlink(g, h);
+ genlink(g, obj2gco(h));
}
@@ -531,7 +542,6 @@
(cast_void(weakkey = strchr(svalue(mode), 'k')),
cast_void(weakvalue = strchr(svalue(mode), 'v')),
(weakkey || weakvalue))) { /* is really weak? */
- set2gray(h); /* turn it back to gray, as it probably goes to a list */
if (!weakkey) /* strong keys? */
traverseweakvalue(g, h);
else if (!weakvalue) /* strong values? */
@@ -550,7 +560,7 @@
markobjectN(g, u->metatable); /* mark its metatable */
for (i = 0; i < u->nuvalue; i++)
markvalue(g, &u->uv[i].uv);
- genlink(g, u);
+ genlink(g, obj2gco(u));
return 1 + u->nuvalue;
}
@@ -612,10 +622,8 @@
static int traversethread (global_State *g, lua_State *th) {
UpVal *uv;
StkId o = th->stack;
- if (isold(th) || g->gcstate == GCSpropagate) {
+ if (isold(th) || g->gcstate == GCSpropagate)
linkgclist(th, g->grayagain); /* insert into 'grayagain' list */
- set2gray(th);
- }
if (o == NULL)
return 1; /* stack not completely built yet */
lua_assert(g->gcstate == GCSatomic ||
@@ -641,8 +649,7 @@
/*
-** traverse one gray object, turning it to black (except for threads,
-** which are always gray).
+** traverse one gray object, turning it to black.
*/
static lu_mem propagatemark (global_State *g) {
GCObject *o = g->gray;
@@ -684,8 +691,10 @@
g->ephemeron = NULL; /* tables may return to this list when traversed */
changed = 0;
while ((w = next) != NULL) { /* for each ephemeron table */
- next = gco2t(w)->gclist; /* list is rebuilt during loop */
- if (traverseephemeron(g, gco2t(w), dir)) { /* marked some value? */
+ 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 */
}
@@ -1048,7 +1057,6 @@
if (curr->tt == LUA_VTHREAD) { /* threads must be watched */
lua_State *th = gco2th(curr);
linkgclist(th, g->grayagain); /* insert into 'grayagain' list */
- set2gray(th);
}
else if (curr->tt == LUA_VUPVAL && upisopen(gco2upv(curr)))
set2gray(curr); /* open upvalues are always gray */
@@ -1183,10 +1191,8 @@
if (getage(p) == G_OLD1) {
lua_assert(!iswhite(p));
changeage(p, G_OLD1, G_OLD); /* now they are old */
- if (isblack(p)) {
- set2gray(p); /* should be '2white', but gray works too */
+ if (isblack(p))
reallymarkobject(g, p);
- }
}
}
}
