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Clearer handling of gray lists when entering generational mode

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When entering generational mode, all objects are old. So, the only
objects that need to be in a gray list are threads, which can be
assigned without barriers. Changes in anything else (e.g., weak
tables) will trigger barriers that, if needed, will add the object
to a gray list.
This commit is contained in:
Roberto Ierusalimschy
2020-08-03 13:22:57 -03:00
parent 0dc5deca1c
commit b9b554e0f6
3 changed files with 79 additions and 18 deletions
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36
lgc.c
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@@ -368,12 +368,17 @@ static int remarkupvals (global_State *g) {
}
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) {
g->gray = g->grayagain = NULL;
g->weak = g->allweak = g->ephemeron = NULL;
cleargraylists(g);
markobject(g, g->mainthread);
markvalue(g, &g->l_registry);
markmt(g);
@@ -1019,19 +1024,30 @@ static void setpause (global_State *g);
/*
** Sweep a list of objects, deleting dead ones and turning
** the non dead to old (without changing their colors).
** 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.
**
*/
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(L), curr));
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 */
black2gray(th); /* OK if already gray */
}
else /* everything else is black */
gray2black(curr); /* OK if already black */
p = &curr->next; /* go to next element */
}
}
@@ -1221,7 +1237,14 @@ static void youngcollection (lua_State *L, global_State *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);
@@ -1244,7 +1267,8 @@ static void atomic2gen (lua_State *L, global_State *g) {
/*
** Enter generational mode. Must go until the end of an atomic cycle
** to ensure that all threads and weak tables are in the gray lists.
** 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) {