+/* ==================================== ZSets =============================== */
+
+/* ZSETs are ordered sets using two data structures to hold the same elements
+ * in order to get O(log(N)) INSERT and REMOVE operations into a sorted
+ * data structure.
+ *
+ * The elements are added to an hash table mapping Redis objects to scores.
+ * At the same time the elements are added to a skip list mapping scores
+ * to Redis objects (so objects are sorted by scores in this "view"). */
+
+/* This skiplist implementation is almost a C translation of the original
+ * algorithm described by William Pugh in "Skip Lists: A Probabilistic
+ * Alternative to Balanced Trees", modified in three ways:
+ * a) this implementation allows for repeated values.
+ * b) the comparison is not just by key (our 'score') but by satellite data.
+ * c) there is a back pointer, so it's a doubly linked list with the back
+ * pointers being only at "level 1". This allows to traverse the list
+ * from tail to head, useful for ZREVRANGE. */
+
+static zskiplistNode *zslCreateNode(int level, double score, robj *obj) {
+ zskiplistNode *zn = zmalloc(sizeof(*zn));
+
+ zn->forward = zmalloc(sizeof(zskiplistNode*) * level);
+ zn->score = score;
+ zn->obj = obj;
+ return zn;
+}
+
+static zskiplist *zslCreate(void) {
+ int j;
+ zskiplist *zsl;
+
+ zsl = zmalloc(sizeof(*zsl));
+ zsl->level = 1;
+ zsl->header = zslCreateNode(ZSKIPLIST_MAXLEVEL,0,NULL);
+ for (j = 0; j < ZSKIPLIST_MAXLEVEL; j++)
+ zsl->header->forward[j] = NULL;
+ return zsl;
+}
+
+static void zslFreeNode(zskiplistNode *node) {
+ decrRefCount(node->obj);
+ zfree(node);
+}
+
+static void zslFree(zskiplist *zsl) {
+ zskiplistNode *node = zsl->header->forward[1], *next;
+
+ while(node) {
+ next = node->forward[1];
+ zslFreeNode(node);
+ node = next;
+ }
+}
+
+static int zslRandomLevel(void) {
+ int level = 1;
+ while ((random()&0xFFFF) < (ZSKIPLIST_P * 0xFFFF))
+ level += 1;
+ return level;
+}
+
+static void zslInsert(zskiplist *zsl, double score, robj *obj) {
+ zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
+ int i, level;
+
+ x = zsl->header;
+ for (i = zsl->level-1; i >= 0; i--) {
+ while (x->forward[i]->score < score)
+ x = x->forward[i];
+ update[i] = x;
+ }
+ x = x->forward[1];
+ /* we assume the key is not already inside, since we allow duplicated
+ * scores, and the re-insertion of score and redis object should never
+ * happpen since the caller of zslInsert() should test in the hash table
+ * if the element is already inside or not. */
+ level = zslRandomLevel();
+ if (level > zsl->level) {
+ for (i = zsl->level; i < level; i++)
+ update[i] = zsl->header;
+ zsl->level = level;
+ }
+ x = zslCreateNode(level,score,obj);
+ for (i = 0; i < level; i++) {
+ x->forward[i] = update[i]->forward[i];
+ update[i]->forward[i] = x;
+ }
+}
+
+static int zslDelete(zskiplist *zsl, double score, robj *obj) {
+ return 1;
+}
+
+/* The actual Z-commands implementations */
+
+static void zaddCommand(redisClient *c) {
+ robj *zsetobj;
+ zset *zs;
+ double *score;
+
+ zsetobj = lookupKeyWrite(c->db,c->argv[1]);
+ if (zsetobj == NULL) {
+ zsetobj = createZsetObject();
+ dictAdd(c->db->dict,c->argv[1],zsetobj);
+ incrRefCount(c->argv[1]);
+ } else {
+ if (zsetobj->type != REDIS_ZSET) {
+ addReply(c,shared.wrongtypeerr);
+ return;
+ }
+ }
+ score = zmalloc(sizeof(double));
+ *score = strtod(c->argv[2]->ptr,NULL);
+ zs = zsetobj->ptr;
+ if (dictAdd(zs->dict,c->argv[3],score) == DICT_OK) {
+ /* case 1: New element */
+ incrRefCount(c->argv[3]); /* added to hash */
+ zslInsert(zs->zsl,*score,c->argv[3]);
+ incrRefCount(c->argv[3]); /* added to skiplist */
+ server.dirty++;
+ addReply(c,shared.cone);
+ } else {
+ dictEntry *de;
+ double *oldscore;
+
+ /* case 2: Score update operation */
+ de = dictFind(zs->dict,c->argv[3]);
+ assert(de != NULL);
+ oldscore = dictGetEntryVal(de);
+ if (*score != *oldscore) {
+ int deleted;
+
+ deleted = zslDelete(zs->zsl,*score,c->argv[3]);
+ assert(deleted != 0);
+ zslInsert(zs->zsl,*score,c->argv[3]);
+ incrRefCount(c->argv[3]);
+ server.dirty++;
+ }
+ addReply(c,shared.czero);
+ }
+}
+
+/* ========================= Non type-specific commands ==================== */
+
projects / redis.git / blobdiff