Redis源码阅读三:哈希表

栏目: 数据库 · 发布时间: 6年前

内容简介:直接上代码:

直接上代码:

typedef struct dictEntry {
    void *key;
    union {
        void *val;
        uint64_t u64;
        int64_t s64;
        double d;
    } v;
    struct dictEntry *next;
} dictEntry;

typedef struct dictType {
    uint64_t (*hashFunction)(const void *key);
    void *(*keyDup)(void *privdata, const void *key);
    void *(*valDup)(void *privdata, const void *obj);
    int (*keyCompare)(void *privdata, const void *key1, const void *key2);
    void (*keyDestructor)(void *privdata, void *key);
    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. */
typedef struct dictht {
    dictEntry **table;
    unsigned long size;
    unsigned long sizemask;
    unsigned long used;
} dictht;

typedef struct dict {
    dictType *type;
    void *privdata;
    dictht ht[2];
    long rehashidx; /* rehashing not in progress if rehashidx == -1 */
    unsigned long iterators; /* number of iterators currently running */
} dict;
  • 采用面向接口编程,把函数定义放到 struct dictType 里,这里是对字典中所有 元素进行操作的函数

  • struct dictEntry 是字典中K-V真正存放的地方, void *key 是K,而 union ... v 是V

  • 每个字典有两张哈希表,在 dictht ht[2] 这里定义。 rehashidx 是一个标记位,代表是否处于 重新哈希。其中rehash采用的是渐进式rehash,可以看到代码中有好几个地方有这样的代码:

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

/* 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. */
static void _dictRehashStep(dict *d) {
    if (d->iterators == 0) dictRehash(d,1);
}

以上就是本文的全部内容,希望本文的内容对大家的学习或者工作能带来一定的帮助,也希望大家多多支持 码农网

查看所有标签

猜你喜欢:

本站部分资源来源于网络,本站转载出于传递更多信息之目的,版权归原作者或者来源机构所有,如转载稿涉及版权问题,请联系我们

Beginning Apache Struts

Beginning Apache Struts

Arnold Doray / Apress / 2006-02-20 / USD 44.99

Beginning Apache Struts will provide you a working knowledge of Apache Struts 1.2. This book is ideal for you Java programmers who have some JSP familiarity, but little or no prior experience with Ser......一起来看看 《Beginning Apache Struts》 这本书的介绍吧!

URL 编码/解码
URL 编码/解码

URL 编码/解码

HEX HSV 转换工具
HEX HSV 转换工具

HEX HSV 互换工具

HSV CMYK 转换工具
HSV CMYK 转换工具

HSV CMYK互换工具