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dicEntry int 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dict dictEntry * 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 part of the library. */ /* redis中还存着调试的代码 */ /* ----------------------- Debugging ------------------------*/ #define DICT_STATS_VECTLEN 50 static 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。