ITKeyword - 技术文章推荐分享

首页 > Redis源码分析(三)---dict哈希结构

Redis源码分析(三)---dict哈希结构

相关推荐:Redis源码分析(一)--Redis结构解析

从今天起,本人将会展开对Redis源码的学习,Redis的代码规模比较小,非常适合学习,是一份非常不错的学习资料,数了一下大概100个文件左右的样子,用的是C语言写的。希望最终能把他啃完吧,C语言好久不用,快忘光了。分析源码的第一步,先别急着想

昨天分析完adlist的Redis代码,今天马上马不停蹄的继续学习Redis代码中的哈希部分的结构学习,不过在这里他不叫什么hashMap,而是叫dict,而且是一种全新设计的一种哈希结构,他只是通过几个简单的结构体,再搭配上一些比较常见的哈希算法,就实现了类似高级语言中HashMap的作用了。也让我见识了一些哈希算法的实现,比如dbj hash的算法实现,俗称times33,算法,就是不停的*33,。这种算是一种超级简单的哈希算法。

下面说说给我感觉Redis代码中哈希实现的不是那么简单,中间加了一些东西,比如说dictType定义了一些字典集合操作的公共方法,我把dict叫做字典总类,也可以说字典操作类,真正存放键值对的叫dictEntry,我叫做字典集合,字典集合存放在哈希表中,叫dictht,下面给出一张结构图来理理思路。

下面给出2个文件的代码解析:dict.h:<span style="font-size:14px;">/* Hash Tables Implementation. * * This file implements in-memory hash tables with insert/del/replace/find/ * get-random-element operations. Hash tables will auto-resize if needed * tables of power of two in size are used, collisions are handled by * chaining. See the source code for more information... :) * * Copyright (c) 2006-2012, Salvatore Sanfilippo <antirez 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. */#include <stdint.h>#ifndef __DICT_H#define __DICT_H/* 定义了成功与错误的值 */#define DICT_OK 0#define DICT_ERR 1/* Unused arguments generate annoying warnings... *//* dict没有用到时,用来提示警告的 */#define DICT_NOTUSED(V) ((void) V)/* 字典结构体,保存K-V值的结构体 */typedef struct dictEntry { //字典key函数指针

void *key;

union {

void *val;

//无符号整型值

uint64_t u64;

//有符号整型值

int64_t s64;

double d;

} v;

//下一字典结点

struct dictEntry *next;} dictEntry;/* 字典类型 */typedef struct dictType { //哈希计算方法,返回整形变量

unsigned int (*hashFunction)(const void *key);

//复制key方法

void *(*keyDup)(void *privdata, const void *key);

//复制val方法

void *(*valDup)(void *privdata, const void *obj);

//key值比较方法

int (*keyCompare)(void *privdata, const void *key1, const void *key2);

//key的析构函数

void (*keyDestructor)(void *privdata, void *key);

//val的析构函数

void (*valDestructor)(void *privdata, void *obj);} dictType;/* This is our hash table structure. Every dictionary has two of this as we * implement incremental rehashing, for the old to the new table. *//* 哈希表结构体 */typedef struct dictht { //字典实体

dictEntry **table;

//表格可容纳字典数量

unsigned long size;

unsigned long sizemask;

//正在被使用的数量

unsigned long used;} dictht;/* 字典主操作类 */typedef struct dict { //字典类型

dictType *type;

//私有数据指针

void *privdata;

//字典哈希表,共2张,一张旧的,一张新的

dictht ht[2];

//重定位哈希时的下标

long rehashidx; /* rehashing not in progress if rehashidx == -1 */

//当前迭代器数量

int iterators; /* number of iterators currently running */} dict;/* If safe is set to 1 this is a safe iterator, that means, you can call * dictAdd, dictFind, and other functions against the dictionary even while * iterating. Otherwise it is a non safe iterator, and only dictNext() * should be called while iterating. *//* 字典迭代器,如果是安全迭代器,这safe设置为1,可以调用dicAdd,dictFind *//* 如果是不安全的,则只能调用dicNext方法*/typedef struct dictIterator { //当前字典

dict *d;

//下标

long index;

//表格,和安全值的表格代表的是旧的表格,还是新的表格

int table, safe;

//字典实体

dictEntry *entry, *nextEntry;

/* unsafe iterator fingerprint for misuse detection. */

/* 指纹标记,避免不安全的迭代器滥用现象 */

long long fingerprint;} dictIterator;/* 字典扫描方法 */typedef void (dictScanFunction)(void *privdata, const dictEntry *de);/* This is the initial size of every hash table *//* 初始化哈希表的数目 */#define DICT_HT_INITIAL_SIZE

4/* ------------------------------- Macros ------------------------------------*//* 字典释放val函数时候调用,如果dict中的dictType定义了这个函数指针, */#define dictFreeVal(d, entry) \

if ((d)->type->valDestructor) \

(d)->type->valDestructor((d)->privdata, (entry)->v.val)

/* 字典val函数复制时候调用,如果dict中的dictType定义了这个函数指针, */#define dictSetVal(d, entry, _val_) do { \

if ((d)->type->valDup) \

entry->v.val = (d)->type->valDup((d)->privdata, _val_); \

else \

entry->v.val = (_val_); \} while(0)/* 设置dictEntry中共用体v中有符号类型的值 */#define dictSetSignedIntegerVal(entry, _val_) \

do { entry->v.s64 = _val_; } while(0)/* 设置dictEntry中共用体v中无符号类型的值 */#define dictSetUnsignedIntegerVal(entry, _val_) \

do { entry->v.u64 = _val_; } while(0)/* 设置dictEntry中共用体v中double类型的值 */#define dictSetDoubleVal(entry, _val_) \

do { entry->v.d = _val_; } while(0)/* 调用dictType定义的key析构函数 */#define dictFreeKey(d, entry) \

if ((d)->type->keyDestructor) \

(d)->type->keyDestructor((d)->privdata, (entry)->key)/* 调用dictType定义的key复制函数,没有定义直接赋值 */#define dictSetKey(d, entry, _key_) do { \

if ((d)->type->keyDup) \

entry->key = (d)->type->keyDup((d)->privdata, _key_); \

else \

entry->key = (_key_); \} while(0)/* 调用dictType定义的key比较函数,没有定义直接key值直接比较 */#define dictCompareKeys(d, key1, key2) \

(((d)->type->keyCompare) ? \

(d)->type->keyCompare((d)->privdata, key1, key2) : \

(key1) == (key2))#define dictHashKey(d, key) (d)->type->hashFunction(key)

//哈希定位方法#define dictGetKey(he) ((he)->key)

//获取dictEntry的key值#define dictGetVal(he) ((he)->v.val)

//获取dicEntry中共用体v中定义的val值#define dictGetSignedIntegerVal(he) ((he)->v.s64) //获取dicEntry中共用体v中定义的有符号值#define dictGetUnsignedIntegerVal(he) ((he)->v.u64)

//获取dicEntry中共用体v中定义的无符号值#define dictGetDoubleVal(he) ((he)->v.d)

//获取dicEntry中共用体v中定义的double类型值#define dictSlots(d) ((d)->ht[0].size+(d)->ht[1].size)

//获取dict字典中总的表大小#define dictSize(d) ((d)->ht[0].used+(d)->ht[1].used)

//获取dict字典中总的表的总正在被使用的数量#define dictIsRehashing(d) ((d)->rehashidx != -1)

//字典有无被重定位过/* API */dict *dictCreate(dictType *type, void *privDataPtr);

//创建dict字典总类int dictExpand(dict *d, unsigned long size);

//字典扩增方法int dictAdd(dict *d, void *key, void *val);

//字典根据key, val添加一个字典集dictEntry *dictAddRaw(dict *d, void *key);

//字典添加一个只有key值的dicEntryint dictReplace(dict *d, void *key, void *val); //替代dict中一个字典集dictEntry *dictReplaceRaw(dict *d, void *key);

//替代dict中的一个字典,只提供一个key值int dictDelete(dict *d, const void *key);

//根据key删除一个字典集int dictDeleteNoFree(dict *d, const void *key);

//字典集删除无、不调用free方法void dictRelease(dict *d);

//释放整个dictdictEntry * dictFind(dict *d, const void *key);

//根据key寻找字典集void *dictFetchValue(dict *d, const void *key);

//根据key值寻找相应的val值int dictResize(dict *d);

//重新计算大小dictIterator *dictGetIterator(dict *d); //获取字典迭代器dictIterator *dictGetSafeIterator(dict *d);

//获取字典安全迭代器

dictEntry *dictNext(dictIterator *iter);

//根据字典迭代器获取字典集的下一字典集void dictReleaseIterator(dictIterator *iter); //释放迭代器dictEntry *dictGetRandomKey(dict *d);

//随机获取一个字典集void dictPrintStats(dict *d);

//打印当前字典状态unsigned int dictGenHashFunction(const void *key, int len); //输入的key值,目标长度,此方法帮你计算出索引值unsigned int dictGenCaseHashFunction(const unsigned char *buf, int len); //这里提供了一种比较简单的哈希算法void dictEmpty(dict *d, void(callback)(void*)); //清空字典void dictEnableResize(void);

//启用调整方法void dictDisableResize(void); //禁用调整方法int dictRehash(dict *d, int n); //hash重定位,主要从旧的表映射到新表中,分n轮定位int dictRehashMilliseconds(dict *d, int ms);

//在给定时间内,循环执行哈希重定位void dictSetHashFunctionSeed(unsigned int initval); //设置哈希方法种子unsigned int dictGetHashFunctionSeed(void);

//获取哈希种子unsigned long dictScan(dict *d, unsigned long v, dictScanFunction *fn, void *privdata); //字典扫描方法/* Hash table types *//* 哈希表类型

*/extern dictType dictTypeHeapStringCopyKey;extern dictType dictTypeHeapStrings;extern dictType dictTypeHeapStringCopyKeyValue;#endif /* __DICT_H */</span>dict.c;<span style="font-size:14px;">/* Hash Tables Implementation. * * This file implements in memory hash tables with insert/del/replace/find/ * get-random-element operations. Hash tables will auto resize if needed * tables of power of two in size are used, collisions are handled by * chaining. See the source code for more information... :) * * Copyright (c) 2006-2012, Salvatore Sanfilippo <antirez 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. */#include "fmacros.h"#include <stdio.h>#include <stdlib.h>#include <string.h>#include <stdarg.h>#include <limits.h>#include <sys/time.h>#include <ctype.h>#include "dict.h"#include "zmalloc.h"#include "redisassert.h"/* Using dictEnableResize() / dictDisableResize() we make possible to * enable/disable resizing of the hash table as needed. This is very important * for Redis, as we use copy-on-write and don't want to move too much memory * around when there is a child performing saving operations. * * Note that even when dict_can_resize is set to 0, not all resizes are * prevented: a hash table is still allowed to grow if the ratio between * the number of elements and the buckets > dict_force_resize_ratio. *//* redis用了dictEnableResize() / dictDisableResize()方法可以重新调整哈希表的长度, *因为redis采用的是写时复制的算法,不会挪动太多的内存,只有当调整数量大于一定比例才可能有效 */static int dict_can_resize = 1;static unsigned int dict_force_resize_ratio = 5;/* -------------------------- private prototypes ---------------------------- *//* 私有方法 */static int _dictExpandIfNeeded(dict *ht);

//字典是否需要扩展static unsigned long _dictNextPower(unsigned long size);static int _dictKeyIndex(dict *ht, const void *key);static int _dictInit(dict *ht, dictType *type, void *privDataPtr);

//字典初始化方法/* -------------------------- hash functions -------------------------------- *//* 哈希索引计算的方法 *//* Thomas Wang's 32 bit Mix Function *//* Thomas Wang's 32 bit Mix 的哈希算法直接输入key值,获取索引值,据说这种冲突的概率很低 */unsigned int dictIntHashFunction(unsigned int key){

key += ~(key << 15);

key ^=

(key >> 10);

key +=

(key << 3);

key ^=

(key >> 6);

key += ~(key << 11);

key ^=

(key >> 16);

return key;}//哈希方法种子,跟产生随机数的种子作用应该是一样的static uint32_t dict_hash_function_seed = 5381;/* 重设哈希种子 */void dictSetHashFunctionSeed(uint32_t seed) {

dict_hash_function_seed = seed;}/* 获取哈希种子 */uint32_t dictGetHashFunctionSeed(void) {

return dict_hash_function_seed;}/* MurmurHash2, by Austin Appleby * Note - This code makes a few assumptions about how your machine behaves - * 1. We can read a 4-byte value from any address without crashing * 2. sizeof(int) == 4 * * And it has a few limitations - * * 1. It will not work incrementally. * 2. It will not produce the same results on little-endian and big-endian *

machines. *//* 输入的key值,目标长度,此方法帮你计算出索引值,此方法特别表明, * 不会因为机器之间高低位存储的不同而产生相同的结果 */unsigned int dictGenHashFunction(const void *key, int len) {

/* 'm' and 'r' are mixing constants generated offline.

They're not really 'magic', they just happen to work well.

*/

//seed种子,m,r的值都将会参与到计算中

uint32_t seed = dict_hash_function_seed;

const uint32_t m = 0x5bd1e995;

const int r = 24;

/* Initialize the hash to a 'random' value */

uint32_t h = seed ^ len;

/* Mix 4 bytes at a time into the hash */

const unsigned char *data = (const unsigned char *)key;

while(len >= 4) {

uint32_t k = *(uint32_t*)data;

k *= m;

k ^= k >> r;

k *= m;

h *= m;

h ^= k;

data += 4;

len -= 4;

}

/* Handle the last few bytes of the input array

*/

switch(len) {

case 3: h ^= data[2] << 16;

case 2: h ^= data[1] << 8;

case 1: h ^= data[0]; h *= m;

};

/* Do a few final mixes of the hash to ensure the last few

* bytes are well-incorporated. */

h ^= h >> 13;

h *= m;

h ^= h >> 15;

return (unsigned int)h;}/* And a case insensitive hash function (based on djb hash) *//* 这里提供了一种比较简单的哈希算法 */unsigned int dictGenCaseHashFunction(const unsigned char *buf, int len) { //以djb hash为基础,俗称“times33”就是不断的乘33 //几乎所有的流行的hash map都采用了DJB hash function

unsigned int hash = (unsigned int)dict_hash_function_seed;

while (len--)

hash = ((hash << 5) + hash) + (tolower(*buf++)); /* hash * 33 + c */

return hash;}/* ----------------------------- API implementation ------------------------- *//* Reset a hash table already initialized with ht_init(). * NOTE: This function should only be called by ht_destroy(). *//* 重置哈希表方法,只在ht_destroy时使用 */static void _dictReset(dictht *ht){ //清空相应的变量,ht->table的类型其实是dictEntry,叫table名字太有歧义了

ht->table = NULL;

ht->size = 0;

ht->sizemask = 0;

ht->used = 0;}/* Create a new hash table *//* 创建dict操作类 */dict *dictCreate(dictType *type,

void *privDataPtr){

dict *d = zmalloc(sizeof(*d));

//创建好空间之后调用初始化方法

_dictInit(d,type,privDataPtr);

return d;}/* Initialize the hash table *//* 初始化dict类中的type,ht等变量 */int _dictInit(dict *d, dictType *type,

void *privDataPtr){ //重置2个ht哈希表

_dictReset(&d->ht[0]);

_dictReset(&d->ht[1]);

//赋值dictType

d->type = type;

d->privdata = privDataPtr;

//-1代表还没有rehash过,

d->rehashidx = -1;

//当前使用中的迭代器为0

d->iterators = 0;

//返回DICT_OK,代表初始化成功

return DICT_OK;}/* Resize the table to the minimal size that contains all the elements, * but with the invariant of a USED/BUCKETS ratio near to <= 1 *//* 调整哈希表,用最少的值容纳所有的字典集合 */int dictResize(dict *d){

int minimal; //如果系统默认调整值不大于0或已经调rehash过的就提示出错,拒绝操作

if (!dict_can_resize || dictIsRehashing(d)) return DICT_ERR;

//最少数等于哈希标准鸿正在使用的数

minimal = d->ht[0].used;

if (minimal < DICT_HT_INITIAL_SIZE)

minimal = DICT_HT_INITIAL_SIZE;

//调用expand扩容

return dictExpand(d, minimal);}/* Expand or create the hash table *//* 哈希表扩增方法 */int dictExpand(dict *d, unsigned long size){

dictht n; /* the new hash table */

//获取调整值,以2的幂次向上取

unsigned long realsize = _dictNextPower(size);

/* the size is invalid if it is smaller than the number of

* elements already inside the hash table */

//再次判断数量符合不符合

if (dictIsRehashing(d) || d->ht[0].used > size)

return DICT_ERR;

/* Allocate the new hash table and initialize all pointers to NULL */

//初始化大小

n.size = realsize;

n.sizemask = realsize-1;

//为表格申请realsize个字典集的大小

n.table = zcalloc(realsize*sizeof(dictEntry*));

n.used = 0;

/* Is this the first initialization? If so it's not really a rehashing

* we just set the first hash table so that it can accept keys. */

if (d->ht[0].table == NULL) {

d->ht[0] = n;

return DICT_OK;

}

/* Prepare a second hash table for incremental rehashing */

//赋值给第二张表格

d->ht[1] = n;

d->rehashidx = 0;

return DICT_OK;}/* Performs N steps of incremental rehashing. Returns 1 if there are still * keys to move from the old to the new hash table, otherwise 0 is returned. * Note that a rehashing step consists in moving a bucket (that may have more * than one key as we use chaining) from the old to the new hash table. *//* hash重定位,主要从旧的表映射到新表中 * 如果返回1说明旧的表中还存在key迁移到新表中,0代表没有 */int dictRehash(dict *d, int n) {

if (!dictIsRehashing(d)) return 0;

/* 根据参数分n步多次循环操作 */

while(n--) {

dictEntry *de, *nextde;

/* Check if we already rehashed the whole table... */

if (d->ht[0].used == 0) {

zfree(d->ht[0].table);

d->ht[0] = d->ht[1];

_dictReset(&d->ht[1]);

d->rehashidx = -1;

return 0;

}

/* Note that rehashidx can't overflow as we are sure there are more

* elements because ht[0].used != 0 */

assert(d->ht[0].size > (unsigned long)d->rehashidx);

while(d->ht[0].table[d->rehashidx] == NULL) d->rehashidx++;

de = d->ht[0].table[d->rehashidx];

/* Move all the keys in this bucket from the old to the new hash HT */

/* 移动的关键操作 */

while(de) {

unsigned int h;

nextde = de->next;

/* Get the index in the new hash table */

h = dictHashKey(d, de->key) & d->ht[1].sizemask;

de->next = d->ht[1].table[h];

d->ht[1].table[h] = de;

d->ht[0].used--;

d->ht[1].used++;

de = nextde;

}

d->ht[0].table[d->rehashidx] = NULL;

d->rehashidx++;

}

return 1;}/* 获取当前毫秒的时间 */long long timeInMilliseconds(void) {

struct timeval tv;

gettimeofday(&tv,NULL);

return (((long long)tv.tv_sec)*1000)+(tv.tv_usec/1000);}/* Rehash for an amount of time between ms milliseconds and ms+1 milliseconds *//* 在给定时间内,循环执行哈希重定位 */int dictRehashMilliseconds(dict *d, int ms) {

long long start = timeInMilliseconds();

int rehashes = 0;

while(dictRehash(d,100)) {

//重定位的次数累加

rehashes += 100;

//时间超出给定时间范围,则终止

if (timeInMilliseconds()-start > ms) break;

}

return rehashes;}/* This function performs just a step of rehashing, and only if there are * no safe iterators bound to our hash table. When we have iterators in the * middle of a rehashing we can't mess with the two hash tables otherwise * some element can be missed or duplicated. * * This function is called by common lookup or update operations in the * dictionary so that the hash table automatically migrates from H1 to H2 * while it is actively used. *//* 当没有迭代器时候,进行重定位算法 */static void _dictRehashStep(dict *d) {

if (d->iterators == 0) dictRehash(d,1);}/* Add an element to the target hash table *//* 添加一个dicEntry */int dictAdd(dict *d, void *key, void *val){

dictEntry *entry = dictAddRaw(d,key);

if (!entry) return DICT_ERR;

dictSetVal(d, entry, val);

return DICT_OK;}/* Low level add. This function adds the entry but instead of setting * a value returns the dictEntry structure to the user, that will make * sure to fill the value field as he wishes. * * This function is also directly exposed to user API to be called * mainly in order to store non-pointers inside the hash value, example: * * entry = dictAddRaw(dict,mykey); * if (entry != NULL) dictSetSignedIntegerVal(entry,1000); * * Return values: * * If key already exists NULL is returned. * If key was added, the hash entry is returned to be manipulated by the caller. *//* 添加一个指定key值的Entry */dictEntry *dictAddRaw(dict *d, void *key){

int index;

dictEntry *entry;

dictht *ht;

if (dictIsRehashing(d)) _dictRehashStep(d);

/* Get the index of the new element, or -1 if

* the element already exists. */

/* 如果指定的key已经存在,则直接返回NULL说明添加失败 */

if ((index = _dictKeyIndex(d, key)) == -1)

return NULL;

/* Allocate the memory and store the new entry */

ht = dictIsRehashing(d) ? &d->ht[1] : &d->ht[0];

entry = zmalloc(sizeof(*entry));

entry->next = ht->table[index];

ht->table[index] = entry;

ht->used++;

/* Set the hash entry fields. */

dictSetKey(d, entry, key);

return entry;}/* Add an element, discarding the old if the key already exists. * Return 1 if the key was added from scratch, 0 if there was already an * element with such key and dictReplace() just performed a value update * operation. *//* 替换一个子字典集,如果不存在直接添加,存在,覆盖val的值 */int dictReplace(dict *d, void *key, void *val){

dictEntry *entry, auxentry;

/* Try to add the element. If the key

* does not exists dictAdd will suceed. */

//不存在,这个key直接添加

if (dictAdd(d, key, val) == DICT_OK)

return 1;

/* It already exists, get th

相关推荐:Redis源码分析(二)--结构体分析(1)

继上次的redis源码分析(一)之后,本人开始订制着一份非常伟大的计划-啃完redis源代码,也对他进行了切块划分,鉴于本人目前对他的整个运行流畅还不特别清楚的情况下,所以决定第一个要解决的就是与逻辑无关的代码,也就是一些基本模块,因为是相互

e entry */

entry = dictFind(d, key);

/* Set the new value and free the old one. Note that it is important

* to do that in this order, as the value may just be exactly the same

* as the previous one. In this context, think to reference counting,

* you want to increment (set), and then decrement (free), and not the

* reverse. */

//赋值方法

auxentry = *entry;

dictSetVal(d, entry, val);

dictFreeVal(d, &auxentry);

return 0;}/* dictReplaceRaw() is simply a version of dictAddRaw() that always * returns the hash entry of the specified key, even if the key already * exists and can't be added (in that case the entry of the already * existing key is returned.) * * See dictAddRaw() for more information. *//* 添加字典,没有函数方法,如果存在,就不添加 */dictEntry *dictReplaceRaw(dict *d, void *key) {

dictEntry *entry = dictFind(d,key);

return entry ? entry : dictAddRaw(d,key);}/* Search and remove an element *//* 删除给定key的结点,可控制是否调用释放方法 */static int dictGenericDelete(dict *d, const void *key, int nofree){

unsigned int h, idx;

dictEntry *he, *prevHe;

int table;

if (d->ht[0].size == 0) return DICT_ERR; /* d->ht[0].table is NULL */

if (dictIsRehashing(d)) _dictRehashStep(d);

//计算key对应的哈希索引

h = dictHashKey(d, key);

for (table = 0; table <= 1; table++) {

idx = h & d->ht[table].sizemask;

//找到具体的索引对应的结点

he = d->ht[table].table[idx];

prevHe = NULL;

while(he) {

if (dictCompareKeys(d, key, he->key)) {

/* Unlink the element from the list */

if (prevHe)

prevHe->next = he->next;

else

d->ht[table].table[idx] = he->next;

if (!nofree) {

//判断是否需要调用dict定义的free方法

dictFreeKey(d, he);

dictFreeVal(d, he);

}

zfree(he);

d->ht[table].used--;

return DICT_OK;

}

prevHe = he;

he = he->next;

}

if (!dictIsRehashing(d)) break;

}

return DICT_ERR; /* not found */}/* 会调用free方法的删除方法 */int dictDelete(dict *ht, const void *key) {

return dictGenericDelete(ht,key,0);}/* 不会调用free方法的删除方法 */int dictDeleteNoFree(dict *ht, const void *key) {

return dictGenericDelete(ht,key,1);}/* Destroy an entire dictionary *//* 清空整个哈希表 */int _dictClear(dict *d, dictht *ht, void(callback)(void *)) {

unsigned long i;

/* Free all the elements */

for (i = 0; i < ht->size && ht->used > 0; i++) {

dictEntry *he, *nextHe;

//每次情况会调用回调方法

if (callback && (i & 65535) == 0) callback(d->privdata);

if ((he = ht->table[i]) == NULL) continue;

while(he) {

//依次释放结点

nextHe = he->next;

dictFreeKey(d, he);

dictFreeVal(d, he);

zfree(he);

ht->used--;

he = nextHe;

}

}

/* Free the table and the allocated cache structure */

zfree(ht->table);

/* Re-initialize the table */

_dictReset(ht);

return DICT_OK; /* never fails */}/* Clear & Release the hash table *//* 重置字典总类,清空2张表 */void dictRelease(dict *d){

_dictClear(d,&d->ht[0],NULL);

_dictClear(d,&d->ht[1],NULL);

zfree(d);}/* 根据key返回具体的字典集 */dictEntry *dictFind(dict *d, const void *key){

dictEntry *he;

unsigned int h, idx, table;

if (d->ht[0].size == 0) return NULL; /* We don't have a table at all */

if (dictIsRehashing(d)) _dictRehashStep(d);

h = dictHashKey(d, key);

for (table = 0; table <= 1; table++) {

idx = h & d->ht[table].sizemask;

he = d->ht[table].table[idx];

while(he) {

if (dictCompareKeys(d, key, he->key))

return he;

he = he->next;

}

if (!dictIsRehashing(d)) return NULL;

}

return NULL;}/* 获取目标字典集的方法 */void *dictFetchValue(dict *d, const void *key) {

dictEntry *he;

he = dictFind(d,key);

/* 获取字典集的方法 */

return he ? dictGetVal(he) : NULL;}/* A fingerprint is a 64 bit number that represents the state of the dictionary * at a given time, it's just a few dict properties xored together. * When an unsafe iterator is initialized, we get the dict fingerprint, and check * the fingerprint again when the iterator is released. * If the two fingerprints are different it means that the user of the iterator * performed forbidden operations against the dictionary while iterating. *//* 通过指纹来禁止每个不安全的哈希迭代器的非法操作,每个不安全迭代器只能有一个指纹 */long long dictFingerprint(dict *d) {

long long integers[6], hash = 0;

int j;

integers[0] = (long) d->ht[0].table;

integers[1] = d->ht[0].size;

integers[2] = d->ht[0].used;

integers[3] = (long) d->ht[1].table;

integers[4] = d->ht[1].size;

integers[5] = d->ht[1].used;

/* We hash N integers by summing every successive integer with the integer

* hashing of the previous sum. Basically:

*

* Result = hash(hash(hash(int1)+int2)+int3) ...

*

* This way the same set of integers in a different order will (likely) hash

* to a different number. */

for (j = 0; j < 6; j++) {

hash += integers[j];

/* For the hashing step we use Tomas Wang's 64 bit integer hash. */

hash = (~hash) + (hash << 21); // hash = (hash << 21) - hash - 1;

hash = hash ^ (hash >> 24);

hash = (hash + (hash << 3)) + (hash << 8); // hash * 265

hash = hash ^ (hash >> 14);

hash = (hash + (hash << 2)) + (hash << 4); // hash * 21

hash = hash ^ (hash >> 28);

hash = hash + (hash << 31);

}

return hash;}/* 获取哈希迭代器,默认不安全的 */dictIterator *dictGetIterator(dict *d){

dictIterator *iter = zmalloc(sizeof(*iter));

iter->d = d;

iter->table = 0;

iter->index = -1;

iter->safe = 0;

iter->entry = NULL;

iter->nextEntry = NULL;

return iter;}/* 获取安全哈希迭代器 */dictIterator *dictGetSafeIterator(dict *d) {

dictIterator *i = dictGetIterator(d);

i->safe = 1;

return i;}/* 迭代器获取下一个集合点 */dictEntry *dictNext(dictIterator *iter){

while (1) {

if (iter->entry == NULL) {

dictht *ht = &iter->d->ht[iter->table];

if (iter->index == -1 && iter->table == 0) {

//如果迭代器index下标为-1说明还没开始使用,设置迭代器的指纹或增加引用计数量

if (iter->safe)

iter->d->iterators++;

else

iter->fingerprint = dictFingerprint(iter->d);

}

//迭代器下标递增

iter->index++;

if (iter->index >= (long) ht->size) {

if (dictIsRehashing(iter->d) && iter->table == 0) {

iter->table++;

iter->index = 0;

ht = &iter->d->ht[1];

} else {

break;

}

}

//根据下标选择集合点

iter->entry = ht->table[iter->index];

} else {

iter->entry = iter->nextEntry;

}

if (iter->entry) {

/* We need to save the 'next' here, the iterator user

* may delete the entry we are returning. */

iter->nextEntry = iter->entry->next;

return iter->entry;

}

}

return NULL;}/* 释放迭代器 */void dictReleaseIterator(dictIterator *iter){

if (!(iter->index == -1 && iter->table == 0)) {

if (iter->safe)

iter->d->iterators--;

else

//这时判断指纹是否还是之前定义的那个

assert(iter->fingerprint == dictFingerprint(iter->d));

}

zfree(iter);}/* Return a random entry from the hash table. Useful to * implement randomized algorithms *//* 随机获取一个集合点 */dictEntry *dictGetRandomKey(dict *d){

dictEntry *he, *orighe;

unsigned int h;

int listlen, listele;

if (dictSize(d) == 0) return NULL;

if (dictIsRehashing(d)) _dictRehashStep(d);

if (dictIsRehashing(d)) {

do {

//随机数向2个表格的总数求余运算

h = random() % (d->ht[0].size+d->ht[1].size);

he = (h >= d->ht[0].size) ? d->ht[1].table[h - d->ht[0].size] :

d->ht[0].table[h];

} while(he == NULL);

} else {

do {

h = random() & d->ht[0].sizemask;

he = d->ht[0].table[h];

} while(he == NULL);

}

/* Now we found a non empty bucket, but it is a linked

* list and we need to get a random element from the list.

* The only sane way to do so is counting the elements and

* select a random index. */

listlen = 0;

orighe = he;

while(he) {

he = he->next;

listlen++;

}

listele = random() % listlen;

he = orighe;

while(listele--) he = he->next;

return he;}/* Function to reverse bits. Algorithm from: * http://graphics.stanford.edu/~seander/bithacks.html#ReverseParallel *//* 很神奇的翻转位 */static unsigned long rev(unsigned long v) {

unsigned long s = 8 * sizeof(v); // bit size; must be power of 2

unsigned long mask = ~0;

while ((s >>= 1) > 0) {

mask ^= (mask << s);

v = ((v >> s) & mask) | ((v << s) & ~mask);

}

return v;}/* dictScan() is used to iterate over the elements of a dictionary. * * Iterating works in the following way: * * 1) Initially you call the function using a cursor (v) value of 0. * 2) The function performs one step of the iteration, and returns the *

new cursor value that you must use in the next call. * 3) When the returned cursor is 0, the iteration is complete. * * The function guarantees that all the elements that are present in the * dictionary from the start to the end of the iteration are returned. * However it is possible that some element is returned multiple time. * * For every element returned, the callback 'fn' passed as argument is * called, with 'privdata' as first argument and the dictionar entry * 'de' as second argument. * * HOW IT WORKS. * * The algorithm used in the iteration was designed by Pieter Noordhuis. * The main idea is to increment a cursor starting from the higher order * bits, that is, instead of incrementing the cursor normally, the bits * of the cursor are reversed, then the cursor is incremented, and finally * the bits are reversed again. * * This strategy is needed because the hash table may be resized from one * call to the other call of the same iteration. * * dict.c hash tables are always power of two in size, and they * use chaining, so the position of an element in a given table is given * always by computing the bitwise AND between Hash(key) and SIZE-1 * (where SIZE-1 is always the mask that is equivalent to taking the rest *

of the division between the Hash of the key and SIZE). * * For example if the current hash table size is 16, the mask is * (in binary) 1111. The position of a key in the hash table will be always * the last four bits of the hash output, and so forth. * * WHAT HAPPENS IF THE TABLE CHANGES IN SIZE? * * If the hash table grows, elements can go anyway in one multiple of * the old bucket: for example let's say that we already iterated with * a 4 bit cursor 1100, since the mask is 1111 (hash table size = 16). * * If the hash table will be resized to 64 elements, and the new mask will * be 111111, the new buckets that you obtain substituting in ??1100 * either 0 or 1, can be targeted only by keys that we already visited * when scanning the bucket 1100 in the smaller hash table. * * By iterating the higher bits first, because of the inverted counter, the * cursor does not need to restart if the table size gets bigger, and will * just continue iterating with cursors that don't have '1100' at the end, * nor any other combination of final 4 bits already explored. * * Similarly when the table size shrinks over time, for example going from * 16 to 8, If a combination of the lower three bits (the mask for size 8 * is 111) was already completely explored, it will not be visited again * as we are sure that, we tried for example, both 0111 and 1111 (all the * variations of the higher bit) so we don't need to test it again. * * WAIT... YOU HAVE *TWO* TABLES DURING REHASHING! * * Yes, this is true, but we always iterate the smaller one of the tables, * testing also all the expansions of the current cursor into the larger * table. So for example if the current cursor is 101 and we also have a * larger table of size 16, we also test (0)101 and (1)101 inside the larger * table. This reduces the problem back to having only one table, where * the larger one, if exists, is just an expansion of the smaller one. * * LIMITATIONS * * This iterator is completely stateless, and this is a huge advantage, * including no additional memory used. * * The disadvantages resulting from this design are: * * 1) It is possible that we return duplicated elements. However this is usually *

easy to deal with in the application level. * 2) The iterator must return multiple elements per call, as it needs to always *

return all the keys chained in a given bucket, and all the expansions, so *

we are sure we don't miss keys moving. * 3) The reverse cursor is somewhat hard to understand at first, but this *

comment is supposed to help. *//* 扫描方法 */unsigned long dictScan(dict *d,

unsigned long v,

dictScanFunction *fn,

void *privdata){

dictht *t0, *t1;

const dictEntry *de;

unsigned long m0, m1;

if (dictSize(d) == 0) return 0;

if (!dictIsRehashing(d)) {

t0 = &(d->ht[0]);

m0 = t0->sizemask;

/* Emit entries at cursor */

de = t0->table[v & m0];

while (de) {

fn(privdata, de);

de = de->next;

}

} else {

t0 = &d->ht[0];

t1 = &d->ht[1];

/* Make sure t0 is the smaller and t1 is the bigger table */

if (t0->size > t1->size) {

t0 = &d->ht[1];

t1 = &d->ht[0];

}

m0 = t0->sizemask;

m1 = t1->sizemask;

/* Emit entries at cursor */

de = t0->table[v & m0];

while (de) {

fn(privdata, de);

de = de->next;

}

/* Iterate over indices in larger table that are the expansion

* of the index pointed to by the cursor in the smaller table */

do {

/* Emit entries at cursor */

de = t1->table[v & m1];

while (de) {

fn(privdata, de);

de = de->next;

}

/* Increment bits not covered by the smaller mask */

v = (((v | m0) + 1) & ~m0) | (v & m0);

/* Continue while bits covered by mask difference is non-zero */

} while (v & (m0 ^ m1));

}

/* Set unmasked bits so incrementing the reversed cursor

* operates on the masked bits of the smaller table */

v |= ~m0;

/* Increment the reverse cursor */

v = rev(v);

v++;

v = rev(v);

return v;}/* ------------------------- private functions ------------------------------ *//* Expand the hash table if needed *//* 判断是否需要扩容 */static int _dictExpandIfNeeded(dict *d){

/* Incremental rehashing already in progress. Return. */

if (dictIsRehashing(d)) return DICT_OK;

/* If the hash table is empty expand it to the initial size. */

if (d->ht[0].size == 0) return dictExpand(d, DICT_HT_INITIAL_SIZE);

/* If we reached the 1:1 ratio, and we are allowed to resize the hash

* table (global setting) or we should avoid it but the ratio between

* elements/buckets is over the "safe" threshold, we resize doubling

* the number of buckets. */

/* 判断是否需要扩容 */

if (d->ht[0].used >= d->ht[0].size &&

(dict_can_resize ||

d->ht[0].used/d->ht[0].size > dict_force_resize_ratio))

{

return dictExpand(d, d->ht[0].used*2);

}

return DICT_OK;}/* Our hash table capability is a power of two *//* 哈希表的容量以2的幂次方,所以数量以2的幂次向上取 */static unsigned long _dictNextPower(unsigned long size){

unsigned long i = DICT_HT_INITIAL_SIZE;

if (size >= LONG_MAX) return LONG_MAX;

while(1) {

if (i >= size)

return i;

i *= 2;

}}/* Returns the index of a free slot that can be populated with * a hash entry for the given 'key'. * If the key already exists, -1 is returned. * * Note that if we are in the process of rehashing the hash table, the * index is always returned in the context of the second (new) hash table. *//* 获取key值对应的哈希索引值,如果已经存在此key则返回-1 */static int _dictKeyIndex(dict *d, const void *key){

unsigned int h, idx, table;

dictEntry *he;

/* Expand the hash table if needed */

if (_dictExpandIfNeeded(d) == DICT_ERR)

return -1;

/* Compute the key hash value */

h = dictHashKey(d, key);

for (table = 0; table <= 1; table++) {

idx = h & d->ht[table].sizemask;

/* Search if this slot does not already contain the given key */

he = d->ht[table].table[idx];

while(he) {

if (dictCompareKeys(d, key, he->key))

return -1;

he = he->next;

}

if (!dictIsRehashing(d)) break;

}

return idx;}/* 清空整个字典,即清空里面的2张哈希表 */void dictEmpty(dict *d, void(callback)(void*)) {

_dictClear(d,&d->ht[0],callback);

_dictClear(d,&d->ht[1],callback);

d->rehashidx = -1;

d->iterators = 0;}/*启用哈希表调整*/void dictEnableResize(void) {

dict_can_resize = 1;}/* 启用哈希表调整 */void dictDisableResize(void) {

dict_can_resize = 0;}#if 0/* The following is code that we don't use for Redis currently, but that is partof the library. *//* redis中还存着调试的代码 *//* ----------------------- Debugging ------------------------*/#define DICT_STATS_VECTLEN 50static void _dictPrintStatsHt(dictht *ht) {

unsigned long i, slots = 0, chainlen, maxchainlen = 0;

unsigned long totchainlen = 0;

unsigned long clvector[DICT_STATS_VECTLEN];

if (ht->used == 0) {

printf("No stats available for empty dictionaries\n");

return;

}

for (i = 0; i < DICT_STATS_VECTLEN; i++) clvector[i] = 0;

for (i = 0; i < ht->size; i++) {

dictEntry *he;

if (ht->table[i] == NULL) {

clvector[0]++;

continue;

}

slots++;

/* For each hash entry on this slot... */

chainlen = 0;

he = ht->table[i];

while(he) {

chainlen++;

he = he->next;

}

clvector[(chainlen < DICT_STATS_VECTLEN) ? chainlen : (DICT_STATS_VECTLEN-1)]++;

if (chainlen > maxchainlen) maxchainlen = chainlen;

totchainlen += chainlen;

}

printf("Hash table stats:\n");

printf(" table size: %ld\n", ht->size);

printf(" number of elements: %ld\n", ht->used);

printf(" different slots: %ld\n", slots);

printf(" max chain length: %ld\n", maxchainlen);

printf(" avg chain length (counted): %.02f\n", (float)totchainlen/slots);

printf(" avg chain length (computed): %.02f\n", (float)ht->used/slots);

printf(" Chain length distribution:\n");

for (i = 0; i < DICT_STATS_VECTLEN-1; i++) {

if (clvector[i] == 0) continue;

printf("

%s%ld: %ld (%.02f%%)\n",(i == DICT_STATS_VECTLEN-1)?">= ":"", i, clvector[i], ((float)clvector[i]/ht->size)*100);

}}void dictPrintStats(dict *d) {

_dictPrintStatsHt(&d->ht[0]);

if (dictIsRehashing(d)) {

printf("-- Rehashing into ht[1]:\n");

_dictPrintStatsHt(&d->ht[1]);

}}/* ----------------------- StringCopy Hash Table Type ------------------------*/static unsigned int _dictStringCopyHTHashFunction(const void *key){

return dictGenHashFunction(key, strlen(key));}static void *_dictStringDup(void *privdata, const void *key){

int len = strlen(key);

char *copy = zmalloc(len+1);

DICT_NOTUSED(privdata);

memcpy(copy, key, len);

copy[len] = '\0';

return copy;}static int _dictStringCopyHTKeyCompare(void *privdata, const void *key1,

const void *key2){

DICT_NOTUSED(privdata);

return strcmp(key1, key2) == 0;}static void _dictStringDestructor(void *privdata, void *key){

DICT_NOTUSED(privdata);

zfree(key);}/* 定义了3种类型的dictType,有些类型无val dup方法的定义 */dictType dictTypeHeapStringCopyKey = {

_dictStringCopyHTHashFunction, /* hash function */

_dictStringDup,

/* key dup */

NULL,

/* val dup */

_dictStringCopyHTKeyCompare,

/* key compare */

_dictStringDestructor,

/* key destructor */

NULL

/* val destructor */};/* This is like StringCopy but does not auto-duplicate the key. * It's used for intepreter's shared strings. */dictType dictTypeHeapStrings = {

_dictStringCopyHTHashFunction, /* hash function */

NULL,

/* key dup */

NULL,

/* val dup */

_dictStringCopyHTKeyCompare,

/* key compare */

_dictStringDestructor,

/* key destructor */

NULL

/* val destructor */};/* This is like StringCopy but also automatically handle dynamic * allocated C strings as values. */dictType dictTypeHeapStringCopyKeyValue = {

_dictStringCopyHTHashFunction, /* hash function */

_dictStringDup,

/* key dup */

_dictStringDup,

/* val dup */

_dictStringCopyHTKeyCompare,

/* key compare */

_dictStringDestructor,

/* key destructor */

_dictStringDestructor,

/* val destructor */};#endif</span>哈希算法的索引计算其实我还是有点不理解的地方的,比如他的索引计算,会从一张旧表映射到一个新表,作者出于什么目的,也许以后再看的时候才会明白吧。

相关推荐:Redis源码分析(三十六)--- Redis中的11大优秀设计

坚持了一个月左右的时间,从最开始的对Redis的代码做分类,从struct结构体分析开始,到最后分析main主程序结束,中间,各大模块的代码逐个击破,学习,总之,收获了非常多,好久没有这么久的耐心把一个框架学透,学习一个框架,会用那只是小小的

? ? ? ? ? 昨天分析完adlist的Redis代码,今天马上马不停蹄的继续学习Redis代码中的哈希部分的结构学习,不过在这里他不叫什么hashMap,而是叫dict,而且是一种全新设计的一种哈希结构,他只是...

------分隔线----------------------------