redis源码笔记-dict.h

这篇介绍redis最后一个基础数据结构——hash表。可以毫不夸张的说,hash表是redis一切存储的基础,也是redis得以快如飞的基础。

注:其实还有个intset,不过intset是在持久化dump到硬盘时为节省空间设计的,和我们这里谈的不一样。

dict的设计呢,简单的说是一个双表,“一主一从”,不定时rehash,建议大家在读代码前能够对这个设计有所了解。Anyway,随便搜一搜,很多文章的。

dict.h

  1 #ifndef __DICT_H
  2 #define __DICT_H
  3 
  4 #define DICT_OK 0
  5 #define DICT_ERR 1
  6 
  7 /* Unused arguments generate annoying warnings... */
  8 #define DICT_NOTUSED(V) ((void) V)          //redis实现里很多这种NOTUSED宏,算是作者偷懒吧
  9 
 10 typedef struct dictEntry {
 11     void *key;
 12     void *val;
 13     struct dictEntry *next;
 14 } dictEntry;                                 //redis的一个dict表项,存的是key , val, 以及因为redis的hash是用的拉链法,所以有一个指向下一个dictEntry的指针;
//一个dictEntry的内存占用为12个字节,记住这个数字。
15 16 typedef struct dictType { 17 unsigned int (*hashFunction)(const void *key); //hash函数 18 void *(*keyDup)(void *privdata, const void *key); //复制key 19 void *(*valDup)(void *privdata, const void *obj); //复制value 20 int (*keyCompare)(void *privdata, const void *key1, const void *key2); //key的compare函数 21 void (*keyDestructor)(void *privdata, void *key); 22 void (*valDestructor)(void *privdata, void *obj); 23 } dictType; //dict的类型 24 25 /* This is our hash table structure. Every dictionary has two of this as we 26 * implement incremental rehashing, for the old to the new table. */ 27 typedef struct dictht { 28 dictEntry **table; 29 unsigned long size; //size 30 unsigned long sizemask; 31 unsigned long used; //used 32 } dictht; //这个是hash table结构,每个dictionary有两个hash 表,实现的是递增的rehash 33 34 typedef struct dict { 35 dictType *type; 36 void *privdata; 37 dictht ht[2]; 38 int rehashidx; /* rehashing not in progress if rehashidx == -1 */ //记录是否在rehash的一个flag,rehash进行过程中,有些操作不能进行 39 int iterators; /* number of iterators currently running */ //记录在dict上正在执行的iter数 40 } dict; //dict的数据结构 41 42 /* If safe is set to 1 this is a safe iteartor, that means, you can call 43 * dictAdd, dictFind, and other functions against the dictionary even while 44 * iterating. Otherwise it is a non safe iterator, and only dictNext() 45 * should be called while iterating. */
//迭代器按照是否可以执行改变hash表的函数区别为safe iterator和non safe iterator, non safe iterator只能执行dictNext函数
46 typedef struct dictIterator { 47 dict *d; 48 int table, index, safe; 49 dictEntry *entry, *nextEntry; 50 } dictIterator; 51 52 /* This is the initial size of every hash table */ 53 #define DICT_HT_INITIAL_SIZE 4 54 55 /* ------------------------------- Macros ------------------------------------*/ 56 #define dictFreeEntryVal(d, entry) \ 57 if ((d)->type->valDestructor) \ 58 (d)->type->valDestructor((d)->privdata, (entry)->val) 59 60 #define dictSetHashVal(d, entry, _val_) do { \ 61 if ((d)->type->valDup) \ 62 entry->val = (d)->type->valDup((d)->privdata, _val_); \ 63 else \ 64 entry->val = (_val_); \ 65 } while(0) 66 67 #define dictFreeEntryKey(d, entry) \ 68 if ((d)->type->keyDestructor) \ 69 (d)->type->keyDestructor((d)->privdata, (entry)->key) 70 71 #define dictSetHashKey(d, entry, _key_) do { \ 72 if ((d)->type->keyDup) \ 73 entry->key = (d)->type->keyDup((d)->privdata, _key_); \ 74 else \ 75 entry->key = (_key_); \ 76 } while(0) 77 78 #define dictCompareHashKeys(d, key1, key2) \ 79 (((d)->type->keyCompare) ? \ 80 (d)->type->keyCompare((d)->privdata, key1, key2) : \ 81 (key1) == (key2)) 82 83 #define dictHashKey(d, key) (d)->type->hashFunction(key) 84 85 #define dictGetEntryKey(he) ((he)->key) 86 #define dictGetEntryVal(he) ((he)->val) 87 #define dictSlots(d) ((d)->ht[0].size+(d)->ht[1].size) 88 #define dictSize(d) ((d)->ht[0].used+(d)->ht[1].used) 89 #define dictIsRehashing(ht) ((ht)->rehashidx != -1) 90 91 /* API */ 92 dict *dictCreate(dictType *type, void *privDataPtr); 93 int dictExpand(dict *d, unsigned long size); 94 int dictAdd(dict *d, void *key, void *val); 95 int dictReplace(dict *d, void *key, void *val); 96 int dictDelete(dict *d, const void *key); 97 int dictDeleteNoFree(dict *d, const void *key); 98 void dictRelease(dict *d); 99 dictEntry * dictFind(dict *d, const void *key); 100 void *dictFetchValue(dict *d, const void *key); 101 int dictResize(dict *d); 102 dictIterator *dictGetIterator(dict *d); 103 dictIterator *dictGetSafeIterator(dict *d); 104 dictEntry *dictNext(dictIterator *iter); 105 void dictReleaseIterator(dictIterator *iter); 106 dictEntry *dictGetRandomKey(dict *d); 107 void dictPrintStats(dict *d); 108 unsigned int dictGenHashFunction(const unsigned char *buf, int len); 109 unsigned int dictGenCaseHashFunction(const unsigned char *buf, int len); 110 void dictEmpty(dict *d); 111 void dictEnableResize(void); 112 void dictDisableResize(void); 113 int dictRehash(dict *d, int n); //进行多少个dictEntry的rehash 114 int dictRehashMilliseconds(dict *d, int ms); //限制rehash执行的时间,这两个函数都在redis的主流程中被调用,避免因为执行rehash,无法响应client请求。 115 116 /* Hash table types */ 117 extern dictType dictTypeHeapStringCopyKey; 118 extern dictType dictTypeHeapStrings; 119 extern dictType dictTypeHeapStringCopyKeyValue; //三种预先定义好的dictType,具体定义参考其他文件。 120 121 #endif /* __DICT_H */

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