int l_remove(node_t *head, key_t key) {
node_t *pred, *item, *sitem;
while (TRUE) {
if (!l_find(&pred, &item, head, key)) {
trace("remove item failed %d\n", key);
return FALSE;
}
sitem = STRIP_MARK(item);
node_t *inext = sitem->next;
/* 先标记再删除 */
if (!CAS(&sitem->next, inext, MARK(inext))) {
trace("cas item %p mark failed\n", sitem->next);
continue;
}
sitem->val = NULL_VALUE;
int tag = GET_TAG(pred->next) + 1;
if (CAS(&pred->next, item, TAG(STRIP_MARK(sitem->next), tag))) {
trace("remove item %p success\n", item);
haz_defer_free(sitem);
return TRUE;
}
trace("cas item remove item %p failed\n", item);
}
return FALSE;
}
int l_find(node_t **pred_ptr, node_t **item_ptr, node_t *head, key_t key) {
node_t *pred = head;
node_t *item = head->next;
/* pred和next会被使用，所以进行标记 */
hazard_t *hp1 = haz_get(0);
hazard_t *hp2 = haz_get(1);
while (item) {
node_t *sitem = STRIP_MARK(item);
haz_set_ptr(hp1, STRIP_MARK(pred));
haz_set_ptr(hp2, STRIP_MARK(item));
/*
如果已被标记，那么紧接着item可能被移除链表甚至释放，所以需要重头查找
*/
if (HAS_MARK(sitem->next)) {
trace("item->next %p %p marked, retry\n", item, sitem->next);
return l_find(pred_ptr, item_ptr, head, key);
}
int d = KEY_CMP(sitem->key, key);
if (d >= 0) {
trace("item %p match key %d, pred %p\n", item, key, pred);
*pred_ptr = pred;
*item_ptr = item;
return d == 0 ? TRUE : FALSE;
}
pred = item;
item = sitem->next;
}
trace("not found key %d\n", key);
*pred_ptr = pred;
*item_ptr = NULL;
return FALSE;
}
void l_free(node_t *head) {
node_t *item = head->next;
while (item) {
node_t *next = STRIP_MARK(item->next);
free((STRIP_MARK(item)));
item = next;
}
free(head);
}
int l_count(node_t *head) {
int cnt = 0;
node_t *item = STRIP_MARK(head->next);
while (item) {
if (!HAS_MARK(item->next)) {
cnt ++;
}
item = STRIP_MARK(item->next);
}
return cnt;
}
void sl_print (skiplist_t *sl, int verbose) {
if (verbose) {
for (int level = MAX_LEVELS - 1; level >= 0; --level) {
node_t *item = sl->head;
if (item->next[level] == DOES_NOT_EXIST)
continue;
printf("(%d) ", level);
int i = 0;
while (item) {
markable_t next = item->next[level];
printf("%s%p ", HAS_MARK(next) ? "*" : "", item);
item = STRIP_MARK(next);
if (i++ > 30) {
printf("...");
break;
}
}
printf("\n");
fflush(stdout);
}
node_t *item = sl->head;
int i = 0;
while (item) {
int is_marked = HAS_MARK(item->next[0]);
printf("%s%p:0x%llx ", is_marked ? "*" : "", item, (uint64_t)item->key);
if (item != sl->head) {
printf("[%d]", item->num_levels);
} else {
printf("[HEAD]");
}
for (int level = 1; level < item->num_levels; ++level) {
node_t *next = STRIP_MARK(item->next[level]);
is_marked = HAS_MARK(item->next[0]);
printf(" %p%s", next, is_marked ? "*" : "");
if (item == sl->head && item->next[level] == DOES_NOT_EXIST)
break;
}
printf("\n");
fflush(stdout);
item = STRIP_MARK(item->next[0]);
if (i++ > 30) {
printf("...\n");
break;
}
}
}
printf("levels:%-2d count:%-6lld \n", sl->high_water, (uint64_t)sl_count(sl));
}
map_val_t sl_iter_next (sl_iter_t *iter, map_key_t *key_ptr) {
assert(iter);
node_t *item = iter->next;
while (item != NULL && HAS_MARK(item->next[0])) {
item = STRIP_MARK(item->next[0]);
}
if (item == NULL) {
iter->next = NULL;
return DOES_NOT_EXIST;
}
iter->next = STRIP_MARK(item->next[0]);
if (key_ptr != NULL) {
*key_ptr = item->key;
}
return item->val;
}
value_t l_lookup(node_t *head, key_t key) {
node_t *pred, *item;
if (l_find(&pred, &item, head, key)) {
return STRIP_MARK(item)->val;
}
return NULL_VALUE;
}
map_key_t sl_min_key (skiplist_t *sl) {
node_t *item = GET_NODE(sl->head->next[0]);
while (item != NULL) {
markable_t next = item->next[0];
if (!HAS_MARK(next))
return item->key;
item = STRIP_MARK(next);
}
return DOES_NOT_EXIST;
}
size_t sl_count (skiplist_t *sl) {
size_t count = 0;
node_t *item = GET_NODE(sl->head->next[0]);
while (item) {
if (!HAS_MARK(item->next[0])) {
count++;
}
item = STRIP_MARK(item->next[0]);
}
return count;
}
void sl_free (skiplist_t *sl) {
node_t *item = GET_NODE(sl->head->next[0]);
while (item) {
node_t *next = STRIP_MARK(item->next[0]);
if (sl->key_type != NULL) {
nbd_free((void *)item->key);
}
nbd_free(item);
item = next;
}
}
value_t l_insert(node_t *head, key_t key, value_t val) {
node_t *pred, *item, *new_item;
while (TRUE) {
if (l_find(&pred, &item, head, key)) { /* update its value */
/* 更新值时，使用item->val互斥，NULL_VALUE表示被删除 */
node_t *sitem = STRIP_MARK(item);
value_t old_val = sitem->val;
while (old_val != NULL_VALUE) {
value_t ret = CAS_V(&sitem->val, old_val, val);
if (ret == old_val) {
trace("update item %p value success\n", item);
return ret;
}
trace("update item lost race %p\n", item);
old_val = ret;
}
trace("item %p removed, retry\n", item);
continue; /* the item has been removed, we retry */
}
new_item = (node_t*) malloc(sizeof(node_t));
new_item->key = key;
new_item->val = val;
new_item->next = item;
/* a). pred是否有效问题：无效只会发生在使用pred->next时，而l_remove正移除该pred
就会在CAS(&item->next)中竞争，如果remove中成功，那么insert CAS就失败，
然后重试；反之，remove失败重试，所以保证了pred有效
b). item本身增加tag一定程度上降低ABA问题几率
*/
if (CAS(&pred->next, item, new_item)) {
trace("insert item %p(next) %p success\n", item, new_item);
return val;
}
trace("cas item %p failed, retry\n", item);
free(new_item);
}
return NULL_VALUE;
}
static node_t *find_preds (node_t **preds, node_t **succs, int n, skiplist_t *sl, map_key_t key, enum unlink unlink) {
node_t *pred = sl->head;
node_t *item = NULL;
TRACE("s2", "find_preds: searching for key %p in skiplist (head is %p)", key, pred);
int d = 0;
// Traverse the levels of <sl> from the top level to the bottom
for (int level = sl->high_water - 1; level >= 0; --level) {
markable_t next = pred->next[level];
if (next == DOES_NOT_EXIST && level >= n)
continue;
TRACE("s3", "find_preds: traversing level %p starting at %p", level, pred);
if (EXPECT_FALSE(HAS_MARK(next))) {
TRACE("s2", "find_preds: pred %p is marked for removal (next %p); retry", pred, next);
ASSERT(level == pred->num_levels - 1 || HAS_MARK(pred->next[level+1]));
return find_preds(preds, succs, n, sl, key, unlink); // retry
}
item = GET_NODE(next);
while (item != NULL) {
next = item->next[level];
// A tag means an item is logically removed but not physically unlinked yet.
while (EXPECT_FALSE(HAS_MARK(next))) {
TRACE("s3", "find_preds: found marked item %p (next is %p)", item, next);
if (unlink == DONT_UNLINK) {
// Skip over logically removed items.
item = STRIP_MARK(next);
if (EXPECT_FALSE(item == NULL))
break;
next = item->next[level];
} else {
// Unlink logically removed items.
markable_t other = SYNC_CAS(&pred->next[level], (markable_t)item, (markable_t)STRIP_MARK(next));
if (other == (markable_t)item) {
TRACE("s3", "find_preds: unlinked item from pred %p", pred, 0);
item = STRIP_MARK(next);
} else {
TRACE("s3", "find_preds: lost race to unlink item pred %p's link changed to %p", pred, other);
if (HAS_MARK(other))
return find_preds(preds, succs, n, sl, key, unlink); // retry
item = GET_NODE(other);
}
next = (item != NULL) ? item->next[level] : DOES_NOT_EXIST;
}
}
if (EXPECT_FALSE(item == NULL)) {
TRACE("s3", "find_preds: past the last item in the skiplist", 0, 0);
break;
}
TRACE("s4", "find_preds: visiting item %p (next is %p)", item, next);
TRACE("s4", "find_preds: key %p val %p", STRIP_MARK(item->key), item->val);
if (EXPECT_TRUE(sl->key_type == NULL)) {
d = item->key - key;
} else {
d = sl->key_type->cmp((void *)item->key, (void *)key);
}
if (d > 0)
break;
if (d == 0 && unlink != FORCE_UNLINK)
break;
pred = item;
item = GET_NODE(next);
}
TRACE("s3", "find_preds: found pred %p next %p", pred, item);
if (level < n) {
if (preds != NULL) {
preds[level] = pred;
}
if (succs != NULL) {
succs[level] = item;
}
}
}
if (d == 0) {
TRACE("s2", "find_preds: found matching item %p in skiplist, pred is %p", item, pred);
return item;
}
TRACE("s2", "find_preds: found proper place for key %p in skiplist, pred is %p. returning null", key, pred);
return NULL;
}
