Redis内部数据结构的实现

typedef char *sds;

/*下面是sds数据结构的具体实现*/
 
/* Note: sdshdr5 is never used, we just access the flags byte directly.
 * However is here to document the layout of type 5 SDS strings. */
struct __attribute__ ((__packed__)) sdshdr5 {
    unsigned char flags; /* 3 lsb of type, and 5 msb of string length */
    char buf[];
};
struct __attribute__ ((__packed__)) sdshdr8 {
    uint8_t len; /* used */
    uint8_t alloc; /* excluding the header and null terminator */
    unsigned char flags; /* 3 lsb of type, 5 unused bits */
    char buf[];
};
struct __attribute__ ((__packed__)) sdshdr16 {
    uint16_t len; /* used */
    uint16_t alloc; /* excluding the header and null terminator */
    unsigned char flags; /* 3 lsb of type, 5 unused bits */
    char buf[];
};
struct __attribute__ ((__packed__)) sdshdr32 {
    uint32_t len; /* used */
    uint32_t alloc; /* excluding the header and null terminator */
    unsigned char flags; /* 3 lsb of type, 5 unused bits */
    char buf[];
};
struct __attribute__ ((__packed__)) sdshdr64 {
    uint64_t len; /* used */
    uint64_t alloc; /* excluding the header and null terminator */
    unsigned char flags; /* 3 lsb of type, 5 unused bits */
    char buf[];
};

#define SDS_HDR(T,s) ((struct sdshdr##T *)((s)-(sizeof(struct sdshdr##T))))

static inline size_t sdslen(const sds s) {
    unsigned char flags = s[-1];
    switch(flags&SDS_TYPE_MASK) {
        case SDS_TYPE_5:
            return SDS_TYPE_5_LEN(flags);
        case SDS_TYPE_8:
            return SDS_HDR(8,s)->len;
        case SDS_TYPE_16:
            return SDS_HDR(16,s)->len;
        case SDS_TYPE_32:
            return SDS_HDR(32,s)->len;
        case SDS_TYPE_64:
            return SDS_HDR(64,s)->len;
    }
    return 0;
}

typedef struct listNode {   /*节点*/
    struct listNode *prev;
    struct listNode *next;
    void *value;     /*value用函数指针类型，决定了value可以是sds，list，set，dict等类型*/
} listNode;

typedef struct listIter {
    listNode *next;
    int direction;   //标注迭代器的运行方向
} listIter;

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

typedef struct dictht {
    dictEntry **table;
    unsigned long size;
    unsigned long sizemask;  /*hash表的掩码，总是size-1，用于计算hash表的索引值*/
    unsigned long used;
} dictht;

typedef struct dict {
    dictType *type;
    void *privdata;
    dictht ht[2];
    long rehashidx; /* rehashing not in progress if rehashidx == -1 */
    int iterators; /* number of iterators currently running */
} dict;

typedef struct intset {    /*整数集合的数据结构*/
    uint32_t encoding; //编码方式
    uint32_t length;
    int8_t contents[];
} intset;

typedef struct zskiplistNode {
    robj *obj;   //存储对象的指针
    double score;   //分数
    struct zskiplistNode *backward;   //后退指针，每次只能退一步
    struct zskiplistLevel {
        struct zskiplistNode *forward;   //前进指针，每次可以跳跃好几步
        unsigned int span;   //这个就是决定前进指针能跳跃几步的跨度标志
    } level[];   
} zskiplistNode;

typedef struct zskiplist {
    struct zskiplistNode *header, *tail;
    unsigned long length;
    int level;
} zskiplist;

typedef struct zlentry {
    //prevrawlen为上一个数据结点的长度，prevrawlensize为记录该长度数值所需要的字节数  
    unsigned int prevrawlensize, prevrawlen;  
    //len为当前数据结点的长度，lensize表示表示当前长度表示所需的字节数  
    unsigned int lensize, len;  
    //数据结点的头部信息长度的字节数  
    unsigned int headersize;  
    //编码的方式  
    unsigned char encoding;  
    //数据结点的数据(已包含头部等信息)，以字符串形式保存  
    unsigned char *p;  
} zlentry;