typedef struct node {
nstring_t *key;
- uint64_t value;
+ uint64_t val;
int top_level;
struct node *next[];
} node_t;
return n;
}
-node_t *node_alloc (int level, const void *key_data, uint32_t key_len, uint64_t value) {
+node_t *node_alloc (int level, const void *key_data, uint32_t key_len, uint64_t val) {
assert(level >= 0 && level <= MAX_LEVEL);
size_t sz = sizeof(node_t) + (level + 1) * sizeof(node_t *);
node_t *item = (node_t *)nbd_malloc(sz);
item->key = (key_len == (unsigned)-1)
? (void *)TAG_VALUE(key_data)
: ns_alloc(key_data, key_len);
- item->value = value;
+ item->val = val;
item->top_level = level;
return item;
}
+static void node_free (node_t *item) {
+ if (!IS_TAGGED(item->key)) {
+ nbd_free(item->key);
+ }
+ nbd_free(item);
+}
+
+static void node_defer_free (node_t *item) {
+ if (!IS_TAGGED(item->key)) {
+ nbd_defer_free(item->key);
+ }
+ nbd_defer_free(item);
+}
+
skiplist_t *sl_alloc (void) {
skiplist_t *sl = (skiplist_t *)nbd_malloc(sizeof(skiplist_t));
sl->head = node_alloc(MAX_LEVEL, " ", 0, 0);
while (item != NULL) {
node_t *next = item->next[level];
TRACE("s3", "find_preds: visiting item %p (next %p)", item, next);
- TRACE("s3", "find_preds: key %p", STRIP_TAG(item->key), item->value);
+ TRACE("s3", "find_preds: key %p", STRIP_TAG(item->key), item->val);
// A tag means an item is logically removed but not physically unlinked yet.
while (EXPECT_FALSE(IS_TAGGED(next))) {
TRACE("s3", "find_preds: now item is %p next is %p", item, next);
// The thread that completes the unlink should free the memory.
- if (level == 0) { nbd_defer_free(other); }
+ if (level == 0) { node_defer_free(other); }
} else {
TRACE("s3", "find_preds: lost race to unlink from pred %p; its link changed to %p", pred, other);
if (IS_TAGGED(other))
// 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);
+ TRACE("s3", "sl_lookup: searching for key %p in skiplist %p", key, sl);
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 item != NULL ? item->value : DOES_NOT_EXIST;
+ return item != NULL ? item->val : 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_data, value);
+uint64_t sl_add (skiplist_t *sl, const void *key_data, uint32_t key_len, uint64_t val) {
+ TRACE("s3", "sl_add: inserting key %p val %p", key_data, val);
node_t *preds[MAX_LEVEL+1];
node_t *nexts[MAX_LEVEL+1];
- node_t *item = NULL;
+ node_t *new_item = NULL;
int n = random_level();
do {
- node_t *next = find_preds(preds, nexts, n, sl, key_data, key_len, TRUE);
+ node_t *old_item = find_preds(preds, nexts, n, sl, key_data, key_len, TRUE);
// If a node matching <key> already exists in <sl>, return its 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 nexts[0]->value;
+ if (old_item != NULL) {
+ TRACE("s3", "sl_add: there is already an item %p (value %p) with the same key", nexts[0], nexts[0]->val);
+ return nexts[0]->val;
}
- // First insert <item> into the bottom level.
- if (EXPECT_TRUE(item == NULL)) { item = node_alloc(n, key_data, key_len, value); }
+ // First insert <new_item> into the bottom level.
+ TRACE("s3", "sl_add: attempting to insert item between %p and %p", preds[0], nexts[0]);
+ new_item = node_alloc(n, key_data, key_len, val);
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) {
- item->next[level] = nexts[level];
+ node_t *next = new_item->next[0] = nexts[0];
+ for (int level = 1; level <= new_item->top_level; ++level) {
+ new_item->next[level] = nexts[level];
}
- node_t *other = SYNC_CAS(&pred->next[0], next, item);
+ node_t *other = SYNC_CAS(&pred->next[0], next, new_item);
if (other == next) {
- TRACE("s3", "sl_add: successfully inserted item %p at level 0", item, 0);
+ TRACE("s3", "sl_add: successfully inserted item %p at level 0", new_item, 0);
break; // success
}
TRACE("s3", "sl_add: failed to change pred's link: expected %p found %p", next, other);
+ node_free(new_item);
} while (1);
- // Insert <item> into <sl> from the bottom level up.
- for (int level = 1; level <= item->top_level; ++level) {
+ // Insert <new_item> into <sl> from the bottom level up.
+ for (int level = 1; level <= new_item->top_level; ++level) {
node_t *pred = preds[level];
node_t *next = nexts[level];
do {
TRACE("s3", "sl_add: attempting to insert item between %p and %p", pred, next);
- node_t *other = SYNC_CAS(&pred->next[level], next, item);
+ node_t *other = SYNC_CAS(&pred->next[level], next, new_item);
if (other == next) {
- TRACE("s3", "sl_add: successfully inserted item %p at level %llu", item, level);
+ TRACE("s3", "sl_add: successfully inserted item %p at level %llu", new_item, level);
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);
+ find_preds(preds, nexts, new_item->top_level, sl, key_data, key_len, TRUE);
pred = preds[level];
next = nexts[level];
- // Update <item>'s next pointer
+ // Update <new_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];
+ node_t *old_next = ((volatile node_t *)new_item)->next[level];
if (IS_TAGGED(old_next))
- return value;
+ return val;
- // 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)
+ // Use a CAS so we do not inadvertantly stomp on a mark another thread placed on the item.
+ if (old_next == next || SYNC_CAS(&new_item->next[level], old_next, next) == old_next)
break;
} while (1);
} while (1);
}
- return value;
+ return val;
}
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);
+ TRACE("s3", "sl_remove: removing item with key %p from skiplist %p", key_data, sl);
node_t *preds[MAX_LEVEL+1];
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);
+ TRACE("s3", "sl_remove: remove failed, an item with a matching key does not exist in the skiplist", 0, 0);
return DOES_NOT_EXIST;
}
}
}
- uint64_t value = item->value;
+ uint64_t val = item->val;
- // Unlink <item> from the top down.
+ // Unlink <item> from <ll>. If we lose a race to another thread just back off. It is safe to leave the
+ // item partially unlinked for a later call (or some other thread) to physically unlink. By marking the
+ // item earlier, we logically removed it.
int level = item->top_level;
while (level >= 0) {
node_t *pred = preds[level];
node_t *other = NULL;
if ((other = SYNC_CAS(&pred->next[level], item, STRIP_TAG(next))) != item) {
TRACE("s3", "sl_remove: unlink failed; pred's link changed from %p to %p", item, other);
- // By marking the item earlier, we logically removed it. It is safe to leave the item partially
- // unlinked. Another thread will finish physically removing it from <sl>.
- return value;
+ return val;
}
--level;
}
// The thread that completes the unlink should free the memory.
- nbd_defer_free(item);
- return value;
+ node_defer_free(item);
+ return val;
}
void sl_print (skiplist_t *sl) {
projects / nbds / blobdiff