typedef struct dict {
dictType *type; //函数指针
void *privdata;
/*ht属性是一个包含两个项的数组，数组中的每个项都是一个dictht哈希表，一般情况下， 字典只使用ht[0]哈希表，ht[1]哈希表只会在对ht[0]哈希表进行rehash时使用*/
dictht ht[2]; //hash表
/*它记录了rehash目前的进度，如果目前没有在进行rehash，那么它的值为-1*/
long rehashidx; /* rehashing not in progress if rehashidx == -1 重新排列*/ //数据量特别大时一个数组槽位一个数组槽位的移动
unsigned long iterators; /* number of iterators currently running */
} dict;
typedef struct dictht {
dictEntry **table; //哈希表，哈希冲突通过链表进行连接
unsigned long size; //哈希表大小
unsigned long sizemask; //哈希表大小掩码，用于计算索引值。总是等于size-1
unsigned long used; //该哈希表已有节点的数量
} dictht;
typedef struct dictEntry {
void *key; //key值
union {
void *val;
uint64_t u64;
int64_t s64;
double d;
} v;
struct dictEntry *next;
} dictEntry;
typedef struct redisObject {//value结构体
unsigned type:4; // 数据类型
unsigned encoding:4; // 数据编码
unsigned lru:LRU_BITS; /* LRU time (relative to global lru_clock) or
* LFU data (least significant 8 bits frequency
* and most significant 16 bits access time). */ // LRU时钟
int refcount; //引用计数
void *ptr; // 指向数据的指针。当robj存储的数据可以使用long类型表示的时候，数据直接存储在ptr字段
//当使用OBJ_ENCODING_EMBSTR编码时，ptr指向sdshdr8的flags字段之后
} robj;
typedef char *sds;
/* 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 */ //用户已用的内存
uint8_t alloc; /* excluding the header and null terminator */ //申请的内存
unsigned char flags; /* 3 lsb of type, 5 unused bits */ //标记SDS_TYPE_8
char buf[]; //字符串数据区域
};
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[];
};
void readQueryFromClient(connection *conn) {
...
nread = connRead(c->conn, c->querybuf+qblen, readlen);
printf("c->querybuf_peak=%ld,qblen=%ld,nread=%d,c->querybuf+qblen=%s",c->querybuf_peak,qblen,nread,c->querybuf+qblen);
...
}
调用命令
127.0.0.1:6379> set abcd aa
OK
打印结果如下：
c->querybuf_peak=0,qblen=0,nread=31,c->querybuf+qblen=*3
set
abcd
aa
对c->querybuf中的数据解析出参数argc和argv
void processInputBuffer(client *c) {
...
if (c->reqtype == PROTO_REQ_MULTIBULK) { //redis-cli命令请求的协议类型
if (processMultibulkBuffer(c) != C_OK) break; //解析read出来的参数
}
...
}
int processMultibulkBuffer(client *c) {
...
serverAssertWithInfo(c,NULL,c->querybuf[c->qb_pos] == '*'); //*2表示后面有2个参数，*3表示后面有3个参数
ok = string2ll(c->querybuf+1+c->qb_pos,newline-(c->querybuf+1+c->qb_pos),&ll);
...
c->multibulklen = ll;//参数数量
/* Setup argv array on client structure */
if (c->argv) zfree(c->argv);
c->argv = zmalloc(sizeof(robj*)*c->multibulklen);
...
while(c->multibulklen) { //参数数量
...
if (c->querybuf[c->qb_pos] != '$') {
addReplyErrorFormat(c,
"Protocol error: expected '$', got '%c'",
c->querybuf[c->qb_pos]);
setProtocolError("expected $ but got something else",c);
return C_ERR;
}
ok = string2ll(c->querybuf+c->qb_pos+1,newline-(c->querybuf+c->qb_pos+1),&ll);
....
c->bulklen = ll; //参数长度 表示5个字节，表示7个字节
...
c->argv[c->argc++] =createStringObject(c->querybuf+c->qb_pos,c->bulklen); //加入到参数argv里面
...
}
}
robj *createStringObject(const char *ptr, size_t len) {
if (len <= OBJ_ENCODING_EMBSTR_SIZE_LIMIT)
return createEmbeddedStringObject(ptr,len);
else
return createRawStringObject(ptr,len);
}
其中createEmbeddedStringObject为创建一整片内存，即robj结构体和ptr指针都在一片内存当中。createRawStringObject为创建两片内存，robj和ptr指向的内存为不同内存片。
robj *createEmbeddedStringObject(const char *ptr, size_t len) {
robj *o = zmalloc(sizeof(robj)+sizeof(struct sdshdr8)+len+1);
struct sdshdr8 *sh = (void*)(o+1);
o->type = OBJ_STRING;
o->encoding = OBJ_ENCODING_EMBSTR;
o->ptr = sh+1;
o->refcount = 1;
if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
o->lru = (LFUGetTimeInMinutes()<<8) | LFU_INIT_VAL;
} else {
o->lru = LRU_CLOCK();
}
sh->len = len;
sh->alloc = len;
sh->flags = SDS_TYPE_8;
if (ptr == SDS_NOINIT)
sh->buf[len] = ';'else
if ( )ptrmemcpy {
(,sh->buf,ptr)len;[
sh->buf]len= ';' }else
memset ( {
,0sh->buf,+1len);}return
;
} o*
createRawStringObject
robj (constchar* , size_tptr) return lencreateObject {
( ,sdsnewlenOBJ_STRING( ,)ptr)len;}#
define
sds类型内存模型如下：
其中关键的宏定义和函数定义如下：
SDS_TYPE_50 # define
SDS_TYPE_81 # define
SDS_TYPE_162 # define
SDS_TYPE_323 # define
SDS_TYPE_644 # define
SDS_TYPE_MASK7 # define
SDS_TYPE_BITS3 # define
SDS_HDR_VAR( ,)Tstructssdshdr ## *=T (sh void *)(()-s(sizeof(structsdshdr## ))T);#define
SDS_HDR( ,)T(s( structsdshdr## *)T (()-s(sizeof(structsdshdr## ))T))#define
SDS_TYPE_5_LEN( )(f( ))fstatic>>SDS_TYPE_BITSinline
size_t sdslen ( const)//已使用的内存 sds sunsigned { char
= [ flags - s1];switch(
&)flagscaseSDS_TYPE_MASK: {
return SDS_TYPE_5SDS_TYPE_5_LEN
( );flagscase:
return SDS_TYPE_8SDS_HDR
( 8,);scase->len:
return SDS_TYPE_16SDS_HDR
( 16,);scase->len:
return SDS_TYPE_32SDS_HDR
( 32,);scase->len:
return SDS_TYPE_64SDS_HDR
( 64,);s}->lenreturn
0
; }static
inline
size_t sdsavail ( const)//剩余内存 sds sunsigned { char
= [ flags - s1];switch(
&)flagscaseSDS_TYPE_MASK: {
return SDS_TYPE_50 {
; }case
:
SDS_HDR_VAR SDS_TYPE_8( {
8,);sreturn-
; sh->alloc } sh->lencase
:
SDS_HDR_VAR SDS_TYPE_16( {
16,);sreturn-
; sh->alloc } sh->lencase
:
SDS_HDR_VAR SDS_TYPE_32( {
32,);sreturn-
; sh->alloc } sh->lencase
:
SDS_HDR_VAR SDS_TYPE_64( {
64,);sreturn-
; sh->alloc } sh->len}
return
0
; }int
dictResize
( *)dict //哈希表缩容dunsigned long
{
; if minimal(
! ||dictIsRehashingdict_can_resize ( ))dreturn; = DICT_ERR[
minimal 0 d->ht].;ifused(
< )minimal = DICT_HT_INITIAL_SIZE;
minimal return DICT_HT_INITIAL_SIZEdictExpand
( ,)d; minimal}int
dictExpand
( *,dict unsigneddlong ) //哈希表进行扩容 size/* the size is invalid if it is smaller than the number of
* elements already inside the hash table */ if
{
(
dictIsRehashing ()||d[ 0 d->ht].)returnused > size;
; DICT_ERR/* the new hash table */
dictht n/*
1.如果执行的是扩展 *** 作，那么ht[1]的大小为第一个大于等于ht[0].used*2的2^n。 例如ht[0].used为5，ht[0].used*2=10，第一个大于的2^n次方为2^4即16。
2.如果执行的是收缩 *** 作，那么ht[1]的大小为第一个大于等于ht[0].used的2^n。 例如ht[0].used为5，ht[0].used=5，第一个大于的2^n次方为2^3即8。
*/ unsigned
long
= _dictNextPower realsize ( );size/* Rehashing to the same table size is not useful. */if
(
== [realsize 0 d->ht].)returnsize; /* Allocate the new hash table and initialize all pointers to NULL */ DICT_ERR.
=
n;size . realsize=
n-sizemask 1 realsize;.=
nzcalloctable ( *sizeofrealsize(*)dictEntry);.=
n0used ; /* 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
(
[ 0d->ht].==NULLtable ) [0 {
d->ht]=; return n;
} DICT_OK/* Prepare a second hash table for incremental rehashing */
[
1
d->ht]=; = n0
d->rehashidx ; return;
} DICT_OKint
dictRehash
其中哈希表dict包含两个哈希表项在通过key进行查找时ht[0]和ht[1]都会进行查找匹配表项中的key值。在int dictRehash(dict *d, int n)函数中每次移动哈希表中的一个n个槽位，从从ht[0]哈希表上重新哈希到ht[1].table[h]位置。
当ht[0]中已使用节点数为0时，将ht[1]赋值给ht[0]即d->ht[0] = d->ht[1];随后ht[1]进行复位，为下次扩容缩容做好准备。
( *,dict intd) //挪动数据，n表示几个槽位 扩容缩容时同时通过key进行find时哈希表1和哈希表2同时进行查找 nint { =
* empty_visits 10 n;/* Max number of empty buckets to visit. 最大访问空桶数*/if (
! dictIsRehashing())dreturn0 ; while(
--&&n[ 0 d->ht].!=0used ) *, {
dictEntry *de; /* Note that rehashidx can't overflow as we are sure there are more
* elements because ht[0].used != 0 */nextdeassert
(
[0d->ht].(unsignedsize > long) );d->rehashidxwhile(
[0d->ht].[]table==d->rehashidxNULL ) ++; {
d->rehashidxif(
-- ==0empty_visits ) return1 ; }=
[
de 0 d->ht].[]table;d->rehashidx/* Move all the keys in this bucket from the old to the new hash HT */while
(
)uint64_tde; {
= h;
nextde /* Get the index in the new hash table */ de->next=
dictHashKey
h ( ,)d& de->key[ 1 d->ht].;=sizemask[
de->next 1 d->ht].[]table;h[1
d->ht].[]table=h; //de节点从ht[0]哈希表上重新哈希到ht[1].table[h]位置 de[ 0
d->ht].--;used[1
d->ht].++;used=;
de } nextde[
0
d->ht].[]table=d->rehashidxNULL ; ++;
d->rehashidx}/* Check if we already rehashed the whole table... */
if
(
[ 0d->ht].==0used ) zfree( {
[0d->ht].);table[0
d->ht]=[ 1 d->ht];_dictReset(
&[1d->ht]);//哈希表1复位= -
d->rehashidx 1 ;return0
; }/* More to rehash... */
return
1
; }
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