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;
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.size+(d)->ht.size)
88 #define dictSize(d) ((d)->ht.used+(d)->ht.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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