struct node *next[];
} node_t;
-typedef struct skiplist {
+typedef struct sl {
node_t *head;
} skiplist_t;
}
skiplist_t *sl_alloc (void) {
- skiplist_t *skiplist = (skiplist_t *)nbd_malloc(sizeof(skiplist_t));
- skiplist->head = node_alloc(MAX_LEVEL, 0, 0);
- memset(skiplist->head->next, 0, (MAX_LEVEL+1) * sizeof(skiplist_t *));
- return skiplist;
+ skiplist_t *sl = (skiplist_t *)nbd_malloc(sizeof(skiplist_t));
+ sl->head = node_alloc(MAX_LEVEL, 0, 0);
+ memset(sl->head->next, 0, (MAX_LEVEL+1) * sizeof(skiplist_t *));
+ return sl;
}
-static node_t *find_preds (node_t *preds[MAX_LEVEL+1], int n, skiplist_t *skiplist, uint64_t key, int help_remove) {
- node_t *pred = skiplist->head;
+static node_t *find_preds (node_t *preds[MAX_LEVEL+1], int n, skiplist_t *sl, uint64_t key, int help_remove) {
+ node_t *pred = sl->head;
node_t *item = NULL;
- TRACE("s3", "find_preds: searching for key %p in skiplist (head is %p)", key, pred);
+ TRACE("s3", "find_preds: searching for key %p in sl (head is %p)", key, pred);
+ int start_level = MAX_LEVEL;
+#if MAX_LEVEL > 2
// Optimization for small lists. No need to traverse empty higher levels.
- assert(MAX_LEVEL > 2);
- int start_level = 2;
+ start_level = 2;
while (pred->next[start_level+1] != NULL) {
start_level += start_level - 1;
if (EXPECT_FALSE(start_level >= MAX_LEVEL)) {
if (EXPECT_FALSE(start_level < n)) {
start_level = n;
}
+#endif
- // Traverse the levels of the skiplist from the top level to the bottom
+ // Traverse the levels of <sl> from the top level to the bottom
for (int level = start_level; level >= 0; --level) {
TRACE("s3", "find_preds: level %llu", level, 0);
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(preds, n, skiplist, key, help_remove); // retry
+ return find_preds(preds, n, sl, key, 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(preds, n, skiplist, key, help_remove); // retry
+ return find_preds(preds, n, sl, key, help_remove); // retry
item = other;
if (EXPECT_FALSE(item == NULL))
break;
if (n == -1 && item != NULL) {
assert(preds != NULL);
for (int level = start_level + 1; level <= item->top_level; ++level) {
- preds[level] = skiplist->head;
+ preds[level] = sl->head;
}
}
return item;
}
// Fast find that does not help unlink partially removed nodes and does not return the node's predecessors.
-uint64_t sl_lookup (skiplist_t *skiplist, uint64_t key) {
- TRACE("s3", "sl_lookup: searching for key %p in skiplist %p", key, skiplist);
- node_t *item = find_preds(NULL, 0, skiplist, key, FALSE);
+uint64_t sl_lookup (skiplist_t *sl, uint64_t key) {
+ TRACE("s3", "sl_lookup: searching for key %p in sl %p", key, sl);
+ node_t *item = find_preds(NULL, 0, sl, key, FALSE);
// If we found an <item> matching the <key> return its value.
return (item && item->key == key) ? item->value : DOES_NOT_EXIST;
}
-// Insert the <key> if it doesn't already exist in the <skiplist>
-uint64_t sl_add (skiplist_t *skiplist, uint64_t key, uint64_t value) {
+// Insert the <key> if it doesn't already exist in <sl>
+uint64_t sl_add (skiplist_t *sl, uint64_t key, uint64_t value) {
TRACE("s3", "sl_add: inserting key %p value %p", key, value);
node_t *preds[MAX_LEVEL+1];
node_t *item = NULL;
do {
int n = random_level();
- node_t *next = find_preds(preds, n, skiplist, key, TRUE);
+ node_t *next = find_preds(preds, n, sl, key, TRUE);
- // If a node matching <key> already exists in the skiplist, return its value.
+ // If a node matching <key> already exists in <sl>, return its value.
if (next != NULL && next->key == key) {
TRACE("s3", "sl_add: there is already an item %p (value %p) with the same key", next, next->value);
if (EXPECT_FALSE(item != NULL)) { nbd_free(item); }
} while (1);
- // Insert <item> into the skiplist from the bottom level up.
+ // Insert <item> into <sl> from the bottom level up.
for (int level = 1; level <= item->top_level; ++level) {
do {
node_t *pred;
break;
if (!IS_TAGGED(next) && next->key > key) // pred's link changed
break;
- find_preds(preds, item->top_level, skiplist, key, TRUE);
+ find_preds(preds, item->top_level, sl, key, TRUE);
} while (1);
do {
return value;
}
-uint64_t sl_remove (skiplist_t *skiplist, uint64_t key) {
- TRACE("s3", "sl_remove: removing item with key %p from skiplist %p", key, skiplist);
+uint64_t sl_remove (skiplist_t *sl, uint64_t key) {
+ TRACE("s3", "sl_remove: removing item with key %p from sl %p", key, sl);
node_t *preds[MAX_LEVEL+1];
- node_t *item = find_preds(preds, -1, skiplist, key, TRUE);
+ node_t *item = find_preds(preds, -1, sl, key, TRUE);
if (item == NULL || item->key != key) {
- TRACE("s3", "sl_remove: remove failed, an item with a matching key does not exist in the skiplist", 0, 0);
+ TRACE("s3", "sl_remove: remove failed, an item with a matching key does not exist in the sl", 0, 0);
return DOES_NOT_EXIST;
}
- // Mark <item> removed at each level of the skiplist from the top down. This must be atomic. If multiple threads
+ // Mark <item> removed at each level of <sl> from the top down. This must be atomic. If multiple threads
// try to remove the same item only one of them should succeed. Marking the bottom level establishes which of
// them succeeds.
for (int level = item->top_level; level >= 0; --level) {
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 the skiplist.
+ // unlinked. Another thread will finish physically removing it from <sl>.
return value;
}
--level;
return value;
}
-void sl_print (skiplist_t *skiplist) {
+void sl_print (skiplist_t *sl) {
for (int level = MAX_LEVEL; level >= 0; --level) {
- node_t *item = skiplist->head;
+ node_t *item = sl->head;
if (item->next[level] == NULL)
continue;
printf("(%d) ", level);
}
printf("\n");
- node_t *item = skiplist->head;
+ node_t *item = sl->head;
while (item) {
int is_marked = IS_TAGGED(item->next[0]);
- printf("%s%p:0x%llx [%d]", is_marked ? "*" : "", item, item->key, item->top_level);
+ printf("%s%p:0x%llx ", is_marked ? "*" : "", item, item->key);
+ if (item != sl->head) {
+ printf("[%d]", item->top_level);
+ } else {
+ printf("[*]");
+ }
for (int level = 1; level <= item->top_level; ++level) {
node_t *next = (node_t *)STRIP_TAG(item->next[level]);
is_marked = IS_TAGGED(item->next[0]);
printf(" %p%s", next, is_marked ? "*" : "");
- if (item == skiplist->head && item->next[level] == NULL)
+ if (item == sl->head && item->next[level] == NULL)
break;
}
printf("\n");
for (int i = 0; i < NUM_ITERATIONS/num_threads_; ++i) {
unsigned r = nbd_rand();
- int key = (r & 0xF) + 1;
+ int key = r & 0xF;
if (r & (1 << 8)) {
sl_add(sl_, key, 1);
} else {
projects / nbds / blobdiff