return sl;
}
-static node_t *find_preds (int *found, node_t *preds[MAX_LEVEL+1], int n, skiplist_t *sl, const void *key_data, uint32_t key_len, int help_remove) {
+static node_t *find_preds (node_t **preds, node_t **succs, int n, skiplist_t *sl, const void *key_data, uint32_t key_len, int help_remove) {
node_t *pred = sl->head;
node_t *item = NULL;
TRACE("s3", "find_preds: searching for key %p in sl (head is %p)", key_data, pred);
- *found = 0;
-
+ int x;
int start_level = MAX_LEVEL;
#if MAX_LEVEL > 2
// Optimization for small lists. No need to traverse empty higher levels.
item = pred->next[level];
if (EXPECT_FALSE(IS_TAGGED(item))) {
TRACE("s3", "find_preds: pred %p is marked for removal (item %p); retry", pred, item);
- return find_preds(found, preds, n, sl, key_data, key_len, help_remove); // retry
+ return find_preds(preds, succs, n, sl, key_data, key_len, help_remove); // retry
}
while (item != NULL) {
node_t *next = item->next[level];
} else {
TRACE("s3", "find_preds: lost race to unlink from pred %p; its link changed to %p", pred, other);
if (IS_TAGGED(other))
- return find_preds(found, preds, n, sl, key_data, key_len, help_remove); // retry
+ return find_preds(preds, succs, n, sl, key_data, key_len, help_remove); // retry
item = other;
if (EXPECT_FALSE(item == NULL))
break;
break;
// If we reached the key (or passed where it should be), we found a pred. Save it and continue down.
- int x = ns_cmp_raw(item->key, key_data, key_len);
+ x = ns_cmp_raw(item->key, key_data, key_len);
if (x >= 0) {
- if (level == 0 && x == 0) {
- *found = 1;
- }
TRACE("s3", "find_preds: found pred %p item %p", pred, item);
break;
}
pred = item;
item = next;
}
- if (preds != NULL) {
- preds[level] = pred;
+
+ // The comparison is unsigned for the case when n is -1.
+ if ((unsigned)level <= (unsigned)n) {
+ if (preds != NULL) {
+ preds[level] = pred;
+ }
+ if (succs != NULL) {
+ succs[level] = item;
+ }
}
}
if (n == -1 && item != NULL) {
- assert(preds != NULL);
for (int level = start_level + 1; level <= item->top_level; ++level) {
preds[level] = sl->head;
}
}
- return item;
+ return x == 0 ? item : NULL;
}
// Fast find that does not help unlink partially removed nodes and does not return the node's predecessors.
uint64_t sl_lookup (skiplist_t *sl, const void *key_data, uint32_t key_len) {
TRACE("s3", "sl_lookup: searching for key %p in sl %p", key, sl);
- int found;
- node_t *item = find_preds(&found, NULL, 0, sl, key_data, key_len, FALSE);
+ node_t *item = find_preds(NULL, NULL, 0, sl, key_data, key_len, FALSE);
// If we found an <item> matching the <key> return its value.
- return found ? item->value : DOES_NOT_EXIST;
+ return item != NULL ? item->value : DOES_NOT_EXIST;
}
// Insert the <key> if it doesn't already exist in <sl>
uint64_t sl_add (skiplist_t *sl, const void *key_data, uint32_t key_len, uint64_t value) {
TRACE("s3", "sl_add: inserting key %p value %p", key, value);
node_t *preds[MAX_LEVEL+1];
+ node_t *nexts[MAX_LEVEL+1];
node_t *item = NULL;
int n = random_level();
do {
- int found;
- node_t *next = find_preds(&found, preds, n, sl, key_data, key_len, TRUE);
+ node_t *next = find_preds(preds, nexts, n, sl, key_data, key_len, TRUE);
// If a node matching <key> already exists in <sl>, return its value.
- if (found) {
- TRACE("s3", "sl_add: there is already an item %p (value %p) with the same key", next, next->value);
+ if (next != NULL) {
+ TRACE("s3", "sl_add: there is already an item %p (value %p) with the same key", nexts[0], nexts[0]->value);
if (EXPECT_FALSE(item != NULL)) { nbd_free(item); }
- return next->value;
+ return nexts[0]->value;
}
// First insert <item> into the bottom level.
if (EXPECT_TRUE(item == NULL)) { item = node_alloc(n, key_data, key_len, value); }
- TRACE("s3", "sl_add: attempting to insert item between %p and %p", preds[0], next);
- item->next[0] = next;
+ node_t *pred = preds[0];
+ item->next[0] = next = nexts[0];
+ TRACE("s3", "sl_add: attempting to insert item between %p and %p", pred, next);
for (int level = 1; level <= item->top_level; ++level) {
- node_t *pred = preds[level];
- item->next[level] = pred->next[level];
+ item->next[level] = nexts[level];
}
- node_t *pred = preds[0];
node_t *other = SYNC_CAS(&pred->next[0], next, item);
if (other == next) {
TRACE("s3", "sl_add: successfully inserted item %p at level 0", item, 0);
// Insert <item> into <sl> from the bottom level up.
for (int level = 1; level <= item->top_level; ++level) {
+ node_t *pred = preds[level];
+ node_t *next = nexts[level];
do {
- node_t *pred;
- node_t *next;
- do {
- pred = preds[level];
- next = pred->next[level];
- if (next == NULL) // item goes at the end of the list
- break;
- if (!IS_TAGGED(next) && ns_cmp_raw(next->key, key_data, key_len) > 0) // pred's link changed
- break;
- int found;
- find_preds(&found, preds, item->top_level, sl, key_data, key_len, TRUE);
- } while (1);
-
- do {
- // There in no need to continue linking in the item if another thread removed it.
- node_t *old_next = ((volatile node_t *)item)->next[level];
- if (IS_TAGGED(old_next))
- return DOES_NOT_EXIST; // success
-
- // Use a CAS so we to not inadvertantly remove a mark another thread placed on the item.
- if (next == old_next || SYNC_CAS(&item->next[level], old_next, next) == old_next)
- break;
- } while (1);
-
TRACE("s3", "sl_add: attempting to insert item between %p and %p", pred, next);
node_t *other = SYNC_CAS(&pred->next[level], next, item);
if (other == next) {
break; // success
}
TRACE("s3", "sl_add: failed to change pred's link: expected %p found %p", next, other);
+ find_preds(preds, nexts, item->top_level, sl, key_data, key_len, TRUE);
+ pred = preds[level];
+ next = nexts[level];
+ // Update <item>'s next pointer
+ do {
+ // There in no need to continue linking in the item if another thread removed it.
+ node_t *old_next = ((volatile node_t *)item)->next[level];
+ if (IS_TAGGED(old_next))
+ return value;
+
+ // Use a CAS so we to not inadvertantly stomp on a mark another thread placed on the item.
+ if (old_next == next || SYNC_CAS(&item->next[level], old_next, next) == old_next)
+ break;
+ } while (1);
} while (1);
}
return value;
uint64_t sl_remove (skiplist_t *sl, const void *key_data, uint32_t key_len) {
TRACE("s3", "sl_remove: removing item with key %p from sl %p", key_data, sl);
- int found;
node_t *preds[MAX_LEVEL+1];
- node_t *item = find_preds(&found, preds, -1, sl, key_data, key_len, TRUE);
- if (!found) {
+ node_t *item = find_preds(preds, NULL, -1, sl, key_data, key_len, TRUE);
+ if (item == NULL) {
TRACE("s3", "sl_remove: remove failed, an item with a matching key does not exist in the sl", 0, 0);
return DOES_NOT_EXIST;
}