Redis源码分析（三）---dict哈希结构

          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 the 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。