#include "runtime.h"
#include "mem.h"
-#define MAX_LEVEL 31
+#define MAX_LEVELS 32
typedef struct node {
map_key_t key;
map_val_t val;
- int top_level;
+ int num_levels;
struct node *next[1];
} node_t;
int high_water; // max level of any item in the list
};
-static int random_level (void) {
+static int random_levels (skiplist_t *sl) {
unsigned r = nbd_rand();
- int n = __builtin_ctz(r) / 2;
- if (n > MAX_LEVEL) { n = MAX_LEVEL; }
- return n;
+ int z = __builtin_ctz(r);
+ int levels = (int)(z / 1.5);
+ if (levels == 0)
+ return 1;
+ if (levels > sl->high_water) {
+ levels = SYNC_ADD(&sl->high_water, 1);
+ TRACE("s2", "random_levels: increased high water mark to %lld", sl->high_water, 0);
+ }
+ if (levels > MAX_LEVELS) { levels = MAX_LEVELS; }
+ return levels;
}
-static node_t *node_alloc (int level, map_key_t key, map_val_t val) {
- assert(level >= 0 && level <= MAX_LEVEL);
- size_t sz = sizeof(node_t) + level * sizeof(node_t *);
+static node_t *node_alloc (int num_levels, map_key_t key, map_val_t val) {
+ assert(num_levels > 0 && num_levels <= MAX_LEVELS);
+ size_t sz = sizeof(node_t) + (num_levels - 1) * sizeof(node_t *);
node_t *item = (node_t *)nbd_malloc(sz);
memset(item, 0, sz);
item->key = key;
item->val = val;
- item->top_level = level;
- TRACE("s2", "node_alloc: new node %p (%llu levels)", item, level);
+ item->num_levels = num_levels;
+ TRACE("s2", "node_alloc: new node %p (%llu levels)", item, num_levels);
return item;
}
skiplist_t *sl_alloc (const datatype_t *key_type) {
skiplist_t *sl = (skiplist_t *)nbd_malloc(sizeof(skiplist_t));
sl->key_type = key_type;
- sl->high_water = 0;
- sl->head = node_alloc(MAX_LEVEL, 0, 0);
- memset(sl->head->next, 0, (MAX_LEVEL+1) * sizeof(skiplist_t *));
+ sl->high_water = 1;
+ sl->head = node_alloc(MAX_LEVELS, 0, 0);
+ memset(sl->head->next, 0, MAX_LEVELS * sizeof(skiplist_t *));
return sl;
}
return count;
}
-static node_t *find_preds (node_t **preds, node_t **succs, int n, skiplist_t *sl, map_key_t key, int help_remove) {
+static node_t *find_preds (node_t **preds, node_t **succs, int n, skiplist_t *sl, map_key_t key, int 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;
- int start_level = sl->high_water;
- if (EXPECT_FALSE(start_level < n)) {
- start_level = n;
- }
// Traverse the levels of <sl> from the top level to the bottom
- for (int level = start_level; level >= 0; --level) {
+ for (int level = sl->high_water - 1; level >= 0; --level) {
node_t *next = pred->next[level];
- if (next == DOES_NOT_EXIST && level > n)
+ if (next == DOES_NOT_EXIST && level >= n)
continue;
TRACE("s3", "find_preds: traversing level %p starting at %p", level, pred);
item = next;
d = sl->key_type->cmp((void *)item->key, (void *)key);
}
- if (d >= 0)
+ if (d >= 0) {
+ if (d == 0 && unlink) {
+ pred->next[level] = next;
+ TRACE("s3", "find_preds: unlinked item from pred %p", pred, 0);
+ item = next;
+ next = (item != NULL) ? item->next[level] : DOES_NOT_EXIST;
+ }
break;
+ }
pred = item;
item = next;
TRACE("s3", "find_preds: found pred %p next %p", pred, item);
- // The cast to unsigned is for the case when n is -1.
- if ((unsigned)level <= (unsigned)n) {
+ if (level < n) {
if (preds != NULL) {
preds[level] = pred;
}
}
}
- // fill in empty levels
- if (n == -1 && item != NULL && preds != NULL) {
- assert(item->top_level <= MAX_LEVEL);
- for (int level = start_level + 1; level <= item->top_level; ++level) {
- preds[level] = sl->head;
- }
- }
-
if (d == 0) {
TRACE("s2", "find_preds: found matching item %p in skiplist, pred is %p", item, pred);
return item;
return NULL;
}
-static void sl_unlink (skiplist_t *sl, map_key_t key) {
- node_t *pred = sl->head;
- node_t *item = NULL;
- TRACE("s2", "sl_unlink: unlinking marked item with key %p", key, 0);
- int d = 0;
-
- // Traverse the levels of <sl>
- for (int level = sl->high_water; level >= 0; --level) {
- node_t *next = pred->next[level];
- if (next == DOES_NOT_EXIST)
- continue;
- TRACE("s3", "sl_unlink: traversing level %p starting at %p", level, pred);
- item = next;
- while (item != NULL) {
- next = item->next[level];
-
- 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) {
- pred->next[level] = next;
- TRACE("s3", "sl_unlink: unlinked item from pred %p", pred, 0);
- item = next;
- next = (item != NULL) ? item->next[level] : DOES_NOT_EXIST;
- break;
- }
- if (d > 0)
- break;
-
- pred = item;
- item = next;
- }
-
- TRACE("s3", "sl_unlink: at pred %p next %p", pred, item);
- }
-}
-
// Fast find that does not return the node's predecessors.
map_val_t sl_lookup (skiplist_t *sl, map_key_t key) {
TRACE("s1", "sl_lookup: searching for key %p in skiplist %p", key, sl);
return val;
}
- TRACE("l1", "sl_lookup: no item in the skiplist matched the key", 0, 0);
+ TRACE("s1", "sl_lookup: no item in the skiplist matched the key", 0, 0);
return DOES_NOT_EXIST;
}
TRACE("s1", "sl_cas: expectation %p new value %p", expectation, new_val);
ASSERT((int64_t)new_val > 0);
- node_t *preds[MAX_LEVEL+1];
- node_t *nexts[MAX_LEVEL+1];
+ node_t *preds[MAX_LEVELS];
+ node_t *nexts[MAX_LEVELS];
node_t *new_item = NULL;
- int n = random_level();
- node_t *old_item = find_preds(preds, nexts, n, sl, key, TRUE);
+ int n = random_levels(sl);
+ node_t *old_item = find_preds(preds, nexts, n, sl, key, FALSE);
// If there is already an item in the skiplist that matches the key just update its value.
if (old_item != NULL) {
map_val_t old_val = old_item->val;
if (expectation == CAS_EXPECT_DOES_NOT_EXIST ||
(expectation != CAS_EXPECT_WHATEVER && expectation != CAS_EXPECT_EXISTS && expectation != old_val)) {
- TRACE("s1", "update_item: found an item %p in the skiplist that matched the key. the expectation was "
- "not met, the skiplist was not changed", item, old_val);
+ TRACE("s1", "sl_cas: the expectation was not met; the skiplist was not changed", 0, 0);
return old_val;
}
old_item->val = new_val;
}
if (EXPECT_FALSE(expectation != CAS_EXPECT_DOES_NOT_EXIST && expectation != CAS_EXPECT_WHATEVER)) {
- TRACE("l1", "sl_cas: the expectation was not met, the skiplist was not changed", 0, 0);
+ TRACE("s1", "sl_cas: the expectation was not met, the skiplist was not changed", 0, 0);
return DOES_NOT_EXIST; // failure, the caller expected an item for the <key> to already exist
}
// Create a new node and insert it into the skiplist.
map_key_t new_key = sl->key_type == NULL ? key : (map_key_t)sl->key_type->clone((void *)key);
- if (n > sl->high_water) {
- n = ++sl->high_water;
- TRACE("s2", "sl_cas: incremented high water mark to %p", sl->high_water, 0);
- }
new_item = node_alloc(n, new_key, new_val);
// Set <new_item>'s next pointers to their proper values
- for (int level = 0; level <= new_item->top_level; ++level) {
+ for (int level = 0; level < new_item->num_levels; ++level) {
new_item->next[level] = nexts[level];
}
// Link <new_item> into <sl>
- for (int level = 0; level <= new_item->top_level; ++level) {
+ for (int level = 0; level < new_item->num_levels; ++level) {
preds[level]->next[level] = new_item;
}
map_val_t sl_remove (skiplist_t *sl, map_key_t key) {
TRACE("s1", "sl_remove: removing item with key %p from skiplist %p", key, sl);
- node_t *preds[MAX_LEVEL+1];
- node_t *item = find_preds(preds, NULL, -1, sl, key, TRUE);
+ node_t *preds[MAX_LEVELS];
+ node_t *item = find_preds(preds, NULL, sl->high_water, sl, key, FALSE);
if (item == NULL) {
TRACE("s3", "sl_remove: remove failed, an item with a matching key does not exist in the skiplist", 0, 0);
return DOES_NOT_EXIST;
map_val_t val = item->val;
// unlink the item
- sl_unlink(sl, key);
+ find_preds(NULL, NULL, 0, sl, key, TRUE);
// free the node
if (sl->key_type != NULL) {
void sl_print (skiplist_t *sl) {
printf("high water: %d levels\n", sl->high_water);
- for (int level = MAX_LEVEL; level >= 0; --level) {
+ for (int level = MAX_LEVELS - 1; level >= 0; --level) {
node_t *item = sl->head;
if (item->next[level] == DOES_NOT_EXIST)
continue;
while (item) {
printf("%p:0x%llx ", item, (uint64_t)item->key);
if (item != sl->head) {
- printf("[%d]", item->top_level);
+ printf("[%d]", item->num_levels);
} else {
printf("[HEAD]");
}
- for (int level = 1; level <= item->top_level; ++level) {
+ for (int level = 1; level < item->num_levels; ++level) {
node_t *next = item->next[level];
printf(" %p", next);
if (item == sl->head && item->next[level] == DOES_NOT_EXIST)
sl_iter_t *sl_iter_begin (skiplist_t *sl, map_key_t key) {
sl_iter_t *iter = (sl_iter_t *)nbd_malloc(sizeof(sl_iter_t));
if (key != DOES_NOT_EXIST) {
- find_preds(NULL, &iter->next, 0, sl, key, FALSE);
+ find_preds(NULL, &iter->next, 1, sl, key, FALSE);
} else {
iter->next = sl->head->next[0];
}
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