--- /dev/null
+/*
+ * Written by Josh Dybnis and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ *
+ * non thread safe skiplist
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+#include "common.h"
+#include "skiplist.h"
+#include "runtime.h"
+#include "mem.h"
+
+#define MAX_LEVEL 31
+
+typedef struct node {
+ map_key_t key;
+ map_val_t val;
+ int top_level;
+ struct node *next[1];
+} node_t;
+
+struct sl_iter {
+ node_t *next;
+};
+
+struct sl {
+ node_t *head;
+ const datatype_t *key_type;
+ int high_water; // max level of any item in the list
+};
+
+static int random_level (void) {
+ unsigned r = nbd_rand();
+ int n = __builtin_ctz(r) / 2;
+ if (n > MAX_LEVEL) { n = MAX_LEVEL; }
+ return n;
+}
+
+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 *);
+ 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);
+ 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 *));
+ return sl;
+}
+
+void sl_free (skiplist_t *sl) {
+ node_t *item = sl->head->next[0];
+ while (item) {
+ node_t *next = item->next[0];
+ if (sl->key_type != NULL) {
+ nbd_free((void *)item->key);
+ }
+ nbd_free(item);
+ item = next;
+ }
+}
+
+size_t sl_count (skiplist_t *sl) {
+ size_t count = 0;
+ node_t *item = sl->head->next[0];
+ while (item) {
+ count++;
+ item = item->next[0];
+ }
+ 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) {
+ 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) {
+ node_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);
+ 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)
+ 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 (preds != NULL) {
+ preds[level] = pred;
+ }
+ if (succs != NULL) {
+ succs[level] = item;
+ }
+ }
+ }
+
+ // 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;
+ }
+ TRACE("s2", "find_preds: found proper place for key %p in skiplist, pred is %p. returning null", key, pred);
+ 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);
+ node_t *item = find_preds(NULL, NULL, 0, sl, key, FALSE);
+
+ // If we found an <item> matching the <key> return its value.
+ if (item != NULL) {
+ map_val_t val = item->val;
+ return val;
+ }
+
+ TRACE("l1", "sl_lookup: no item in the skiplist matched the key", 0, 0);
+ return DOES_NOT_EXIST;
+}
+
+map_key_t sl_min_key (skiplist_t *sl) {
+ node_t *item = sl->head->next[0];
+ while (item != NULL)
+ return item->key;
+ return DOES_NOT_EXIST;
+}
+
+map_val_t sl_cas (skiplist_t *sl, map_key_t key, map_val_t expectation, map_val_t new_val) {
+ TRACE("s1", "sl_cas: key %p skiplist %p", key, sl);
+ 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 *new_item = NULL;
+ int n = random_level();
+ node_t *old_item = find_preds(preds, nexts, n, sl, key, TRUE);
+
+ // 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);
+ return old_val;
+ }
+ old_item->val = new_val;
+ return old_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);
+ return DOES_NOT_EXIST; // failure, the caller expected an item for the <key> to already exist
+ }
+
+ TRACE("s3", "sl_cas: inserting a new item between %p and %p", preds[0], nexts[0]);
+
+ // 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) {
+ new_item->next[level] = nexts[level];
+ }
+
+ // Link <new_item> into <sl>
+ for (int level = 0; level <= new_item->top_level; ++level) {
+ preds[level]->next[level] = new_item;
+ }
+
+ return DOES_NOT_EXIST; // success, inserted a 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);
+ 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);
+
+ // free the node
+ if (sl->key_type != NULL) {
+ nbd_free((void *)item->key);
+ }
+ nbd_free(item);
+
+ return val;
+}
+
+void sl_print (skiplist_t *sl) {
+
+ printf("high water: %d levels\n", sl->high_water);
+ for (int level = MAX_LEVEL; level >= 0; --level) {
+ node_t *item = sl->head;
+ if (item->next[level] == DOES_NOT_EXIST)
+ continue;
+ printf("(%d) ", level);
+ int i = 0;
+ while (item) {
+ node_t *next = item->next[level];
+ printf("%p ", item);
+ item = next;
+ if (i++ > 30) {
+ printf("...");
+ break;
+ }
+ }
+ printf("\n");
+ fflush(stdout);
+ }
+ node_t *item = sl->head;
+ int i = 0;
+ while (item) {
+ printf("%p:0x%llx ", item, (uint64_t)item->key);
+ if (item != sl->head) {
+ printf("[%d]", item->top_level);
+ } else {
+ printf("[HEAD]");
+ }
+ for (int level = 1; level <= item->top_level; ++level) {
+ node_t *next = item->next[level];
+ printf(" %p", next);
+ if (item == sl->head && item->next[level] == DOES_NOT_EXIST)
+ break;
+ }
+ printf("\n");
+ fflush(stdout);
+ item = item->next[0];
+ if (i++ > 30) {
+ printf("...\n");
+ break;
+ }
+ }
+}
+
+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);
+ } else {
+ iter->next = sl->head->next[0];
+ }
+ return iter;
+}
+
+map_val_t sl_iter_next (sl_iter_t *iter, map_key_t *key_ptr) {
+ assert(iter);
+ node_t *item = iter->next;
+ if (item == NULL) {
+ iter->next = NULL;
+ return DOES_NOT_EXIST;
+ }
+ iter->next = item->next[0];
+ if (key_ptr != NULL) {
+ *key_ptr = item->key;
+ }
+ return item->val;
+}
+
+void sl_iter_free (sl_iter_t *iter) {
+ nbd_free(iter);
+}
projects / nbds / blobdiff