临摹帖 - redis skiplist
素材
https://github.com/wangzhione/temp/tree/master/code/skiplist
https://github.com/redis/redis/blob/unstable/src/t_zset.c
临摹帖
server.h
#pragma once
#define ZSKIPLIST_MAXLEVEL 32 /* Should be enough for 2^64 elements */
#define ZSKIPLIST_P 0.25 /* Skiplist P = 1/4 */
/* ZSETs use a specialized version of Skiplists */
typedef struct zskiplistNode {
char * ele;
double score;
struct zskiplistNode * backward;
struct zskiplistLevel {
struct zskiplistNode * forward;
unsigned long span;
} level[];
} zskiplistNode;
typedef struct zskiplist {
struct zskiplistNode * header, * tail;
unsigned long length;
int level;
} zskiplist;
t_zset.c
/*
* Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
* Copyright (c) 2009-2012, Pieter Noordhuis <pcnoordhuis at gmail dot com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of Redis nor the names of its contributors may be used
* to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/*-----------------------------------------------------------------------------
* Sorted set API
*----------------------------------------------------------------------------*/
/* 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 a 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").
*
* Note that the SDS string representing the element is the same in both
* the hash table and skiplist in order to save memory. What we do in order
* to manage the shared SDS string more easily is to free the SDS string
* only in zslFreeNode(). The dictionary has no value free method set.
* So we should always remove an element from the dictionary, and later from
* the skiplist.
*
* 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 scores.
* 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. */
#include "server.h"
#include "struct.h"
/*-----------------------------------------------------------------------------
* Skiplist implementation of the low level API
*----------------------------------------------------------------------------*/
/* Create a skiplist node with the specified number of levels.
* The SDS string 'ele' is referenced by the node after the call. */
zskiplistNode * zslCreateNode(int level, double score, char * ele) {
zskiplistNode * zn = malloc(
sizeof(struct zskiplistNode) + level * sizeof(struct zskiplistLevel)
);
if (!zn) {
return NULL;
}
zn->score = score;
zn->ele = ele;
return zn;
}
/* Create a new skiplist. */
zskiplist * zslCreate(void) {
int j;
zskiplist * zsl = malloc(sizeof(struct zskiplist));
if (!zsl) {
return NULL;
}
zsl->level = 1;
zsl->length = 0;
zsl->header = zslCreateNode(ZSKIPLIST_MAXLEVEL, 0, NULL);
if (!zsl->header) {
free(zsl);
return NULL;
}
for (j = 0; j < ZSKIPLIST_MAXLEVEL; j++) {
zsl->header->level[j].forward = NULL;
zsl->header->level[j].span = 0;
}
zsl->header->backward = NULL;
zsl->tail = NULL;
return zsl;
}
/* Free the specified skiplist node. The referenced SDS string representation
* of the element is freed too, unless node->ele is set to NULL before calling
* this function. */
void zslFreeNode(zskiplistNode * node) {
free(node->ele);
free(node);
}
/* Free a whole skiplist. */
void zslFree(zskiplist * zsl) {
zskiplistNode * next;
zskiplistNode * node = zsl->header->level[0].forward;
free(zsl->header);
while (node) {
next = node->level[0].forward;
zslFreeNode(node);
node = next;
}
free(zsl);
}
/* Returns a random level for the new skiplist node we are going to create.
* The return value of this function is between 1 and ZSKIPLIST_MAXLEVEL
* (both inclusive), with a powerlaw-alike distribution where higher
* levels are less likely to be returned. */
int zslRandomLevel(void) {
int level = 1;
while ((random()&0xFFFF) < (ZSKIPLIST_P*0xFFFF) && ++level < ZSKIPLIST_MAXLEVEL)
;
return level;
}
/* Insert a new node in the skiplist. Assumes the element does not already
* exist (up to the caller to enforce that). The skiplist takes ownership
* of the passed SDS string 'ele'. */
zskiplistNode * zslInsert(zskiplist * zsl, double score, char * ele) {
zskiplistNode * update[ZSKIPLIST_MAXLEVEL], * x;
unsigned long rank[ZSKIPLIST_MAXLEVEL];
int i, level;
assert(!isnan(score));
x = zsl->header;
for (i = zsl->level-1; i>=0; i--) {
/* store rank that is crossed to reach the insert position */
rank[i] = i == zsl->level-1 ? 0 : rank[i+1];
while (
x->level[i].forward && (
x->level[i].forward->score < score ||
(x->level[i].forward->score == score &&
strcmp(x->level[i].forward->ele, ele) < 0)
)
) {
rank[i] += x->level[i].span;
x = x->level[i].forward;
}
update[i] = x;
}
/* we assume the element is not already inside, since we allow duplicated
* scores, reinserting the same element should never happen 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++) {
rank[i] = 0;
update[i] = zsl->header;
update[i]->level[i].span = zsl->length;
}
zsl->level = level;
}
x = zslCreateNode(level, score, ele);
if (!x) {
return NULL;
}
for (i = 0; i < level; i++) {
x->level[i].forward = update[i]->level[i].forward;
update[i]->level[i].forward = x;
/* update span covered by update[i] as x is inserted here */
x->level[i].span = update[i]->level[i].span - (rank[0] - rank[i]);
update[i]->level[i].span = (rank[0] - rank[i]) + 1;
}
/* increment span for untouched levels */
for (i = level; i < zsl->level; i++) {
update[i]->level->span++;
}
x->backward = (update[0] == zsl->header) ? NULL : update[0];
if (x->level[0].forward)
x->level[0].forward->backward = x;
else
zsl->tail = x;
zsl->length++;
return x;
}
/* Internal function used by zslDelete, zslDeleteRangeByScore and
* zslDeleteRangeByRank. */
void zslDeleteNode(zskiplist * zsl, zskiplistNode * x, zskiplistNode ** update) {
int i;
for (i = 0; i < zsl->level; i++) {
if (update[i]->level[i].forward == x) {
update[i]->level[i].span += x->level[i].span - 1;
update[i]->level[i].forward = x->level[i].forward;
} else {
update[i]->level[i].span -= 1;
}
}
if (x->level[0].forward) {
x->level[0].forward->backward = x->backward;
} else {
zsl->tail = x->backward;
}
while (zsl->level > 1 && zsl->header->level[zsl->level-1].forward == NULL)
zsl->length--;
zsl->length--;
}
/* Delete an element with matching score/element from the skiplist.
* The function returns 1 if the node was found and deleted, otherwise
* 0 is returned.
*
* If 'node' is NULL the deleted node is freed by zslFreeNode(), otherwise
* it is not freed (but just unlinked) and *node is set to the node pointer,
* so that it is possible for the caller to reuse the node (including the
* referenced SDS string at node->ele). */
int zslDelete(zskiplist * zsl, double score, char * ele, zskiplistNode ** node) {
zskiplistNode * update[ZSKIPLIST_MAXLEVEL], * x;
int i;
x = zsl->header;
for (i = zsl->level-1; i >= 0; i--) {
while (x->level[i].forward &&
(x->level[i].forward->score < score ||
(x->level[i].forward->score == score &&
strcmp(x->level[i].forward->ele, ele) < 0))) {
x = x->level[i].forward;
}
update[i] = x;
}
/* We may have multiple elements with the same score, what we need
* is to find the element with both the right score and object. */
x = x->level[0].forward;
if (x && score == x->score && strcmp(x->ele, ele) == 0) {
zslDeleteNode(zsl, x, update);
if (!node)
zslFreeNode(x);
else
*node = x;
return 1;
}
return 0; /* not found */
}
/* Update the score of an element inside the sorted set skiplist.
* Note that the element must exist and must match 'score'.
* This function does not update the score in the hash table side, the
* caller should take care of it.
*
* Note that this function attempts to just update the node, in case after
* the score update, the node would be exactly at the same position.
* Otherwise the skiplist is modified by removing and re-adding a new
* element, which is more costly.
*
* The function returns the updated element skiplist node pointer. */
zskiplistNode * zslUpdateScore(zskiplist * zsl, double curscore, char * ele, double newscore) {
zskiplistNode * update[ZSKIPLIST_MAXLEVEL], * x;
int i;
/* We need to seek to element to update to start: this is useful anyway,
* we'll have to update or remove it. */
x = zsl->header;
for (i = zsl->level-1; i >= 0; i--) {
while (x->level[i].forward &&
(x->level[i].forward->score < curscore ||
(x->level[i].forward->score == curscore &&
strcmp(x->level[i].forward->ele, ele) < 0))) {
x = x->level[i].forward;
}
update[i] = x;
}
/* Jump to our element: note that this function assumes that the
* element with the matching score exists. */
x = x->level[0].forward;
assert(x && curscore == x->score && strcmp(x->ele, ele) == 0);
/* If the node, after the score update, would be still exactly
* at the same position, we can just update the score without
* actually removing and re-inserting the element in the skiplist. */
if ((!x->backward || x->backward->score < newscore) &&
(!x->level[0].forward || x->level[0].forward->score > newscore)) {
x->score = newscore;
return x;
}
/* No way to reuse the old node: we need to remove and insert a new
* one at a different place. */
zslDeleteNode(zsl, x, update);
zskiplistNode * newnode = zslInsert(zsl, newscore, x->ele);
/* We reused the old node x->ele SDS string, free the node now
* since zslInsert created a new one. */
x->ele = NULL;
zslFreeNode(x);
return newnode;
}
