Redis数据结构之——redisObject
定义在server.h文件中
redisObject结构体
#define LRU_BITS 24
#define LRU_CLOCK_MAX ((1<lru */
#define LRU_CLOCK_RESOLUTION 1000 /* LRU clock resolution in ms */
#define OBJ_SHARED_REFCOUNT INT_MAX
typedef struct redisObject {
unsigned type:4;
unsigned encoding:4;
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). */
int refcount;
void *ptr;
} robj; - type：标记对象的类型
- encoding：标记对象的底层数据结构
- lru：用于lru和lfu，占24位，前16位保存上次访问时间，后8位保存访问频率计数
- refcount：引用计数，用于垃圾回收
- *ptr：指向底层数据结构的指针
type类型：
/* A redis object, that is a type able to hold a string / list / set */
/* The actual Redis Object */
#define OBJ_STRING 0 /* String object. */
#define OBJ_LIST 1 /* List object. */
#define OBJ_SET 2 /* Set object. */
#define OBJ_ZSET 3 /* Sorted set object. */
#define OBJ_HASH 4 /* Hash object. */
/* The "module" object type is a special one that signals that the object
* is one directly managed by a Redis module. In this case the value points
* to a moduleValue struct, which contains the object value (which is only
* handled by the module itself) and the RedisModuleType struct which lists
* function pointers in order to serialize, deserialize, AOF-rewrite and
* free the object.
*
* Inside the RDB file, module types are encoded as OBJ_MODULE followed
* by a 64 bit module type ID, which has a 54 bits module-specific signature
* in order to dispatch the loading to the right module, plus a 10 bits
* encoding version. */
#define OBJ_MODULE 5 /* Module object. */
#define OBJ_STREAM 6 /* Stream object. */encoding类型：
/* Objects encoding. Some kind of objects like Strings and Hashes can be
* internally represented in multiple ways. The 'encoding' field of the object
* is set to one of this fields for this object. */
#define OBJ_ENCODING_RAW 0 /* Raw representation */
#define OBJ_ENCODING_INT 1 /* Encoded as integer */
#define OBJ_ENCODING_HT 2 /* Encoded as hash table */
#define OBJ_ENCODING_ZIPMAP 3 /* Encoded as zipmap */
#define OBJ_ENCODING_LINKEDLIST 4 /* No longer used: old list encoding. */
#define OBJ_ENCODING_ZIPLIST 5 /* Encoded as ziplist */
#define OBJ_ENCODING_INTSET 6 /* Encoded as intset */
#define OBJ_ENCODING_SKIPLIST 7 /* Encoded as skiplist */
#define OBJ_ENCODING_EMBSTR 8 /* Embedded sds string encoding */
#define OBJ_ENCODING_QUICKLIST 9 /* Encoded as linked list of ziplists */
#define OBJ_ENCODING_STREAM 10 /* Encoded as a radix tree of listpacks */
类型检查：
在执行每一条命令之前，会先检查对应键的type是否为指定type，如果是的话则继续执行，否则向客户端返回类型错误，接下来看个 llen 命令的例子：
首先找到命令入口，命令都定义在server.c文件中的redisCommandTable数组中。
list对应操作都定义在t_list.c文件中：
void llenCommand(client *c) {
robj *o = lookupKeyReadOrReply(c,c->argv[1],shared.czero); //检查key对应的obj是否存在
if (o == NULL || checkType(c,o,OBJ_LIST)) return;
addReplyLongLong(c,listTypeLength(o));
}我们可以看到里面会执行checkType方法去检测当前key对应redisObject的type属性是否是上面提到的OBJ_LIST，这个方法定义在object.c文件中：
int checkType(client *c, robj *o, int type) {
if (o->type != type) {
addReply(c,shared.wrongtypeerr);
return 1;
}
return 0;
}如果type不符，则会调用addReply方法，向客户端返回响应，方法定义在networking.c文件中：
/* -----------------------------------------------------------------------------
* Higher level functions to queue data on the client output buffer.
* The following functions are the ones that commands implementations will call.
* -------------------------------------------------------------------------- */
/* Add the object 'obj' string representation to the client output buffer. */
void addReply(client *c, robj *obj) {
if (prepareClientToWrite(c) != C_OK) return;
if (sdsEncodedObject(obj)) {
if (_addReplyToBuffer(c,obj->ptr,sdslen(obj->ptr)) != C_OK)
_addReplyProtoToList(c,obj->ptr,sdslen(obj->ptr));
} else if (obj->encoding == OBJ_ENCODING_INT) {
/* For integer encoded strings we just convert it into a string
* using our optimized function, and attach the resulting string
* to the output buffer. */
char buf[32];
size_t len = ll2string(buf,sizeof(buf),(long)obj->ptr);
if (_addReplyToBuffer(c,buf,len) != C_OK)
_addReplyProtoToList(c,buf,len);
} else {
serverPanic("Wrong obj->encoding in addReply()");
}
}多态命令
比如我们要用strlen命令获取string的长度，需要判断string的数据结构是raw还是embstr，根据不同的底层数据结构调用不同的API
首先看命令入口t_string.c中的strlenCommand方法：
void strlenCommand(client *c) {
robj *o;
if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.czero)) == NULL ||
checkType(c,o,OBJ_STRING)) return;
addReplyLongLong(c,stringObjectLen(o));
}判断字符串存在和非空后，调用object.c文件中的stringObjectLen方法计算字符串长度：
size_t stringObjectLen(robj *o) {
serverAssertWithInfo(NULL,o,o->type == OBJ_STRING);
if (sdsEncodedObject(o)) {
return sdslen(o->ptr);
} else {
return sdigits10((long)o->ptr);
}
}通过sdsEncodedObject宏定义判断encoding否是sds（raw和embstr都属于sds）：
#define sdsEncodedObject(objptr) (objptr->encoding == OBJ_ENCODING_RAW || objptr->encoding == OBJ_ENCODING_EMBSTR)如果是sds类型，则调用sds.h中的sdslen方法：
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;
}否则该字符串为整型，调用util.c文件中的sdigits10方法计算长度：
/* Like digits10() but for signed values. */
uint32_t sdigits10(int64_t v) {
if (v < 0) {
/* Abs value of LLONG_MIN requires special handling. */
uint64_t uv = (v != LLONG_MIN) ?
(uint64_t)-v : ((uint64_t) LLONG_MAX)+1;
return digits10(uv)+1; /* +1 for the minus. */
} else {
return digits10(v);
}
}