Redis源码分析（二十八）--- object创建和释放redisObject对象
今天的学习效率比较高，把Rio分析完了，又顺便学习了其中的RedisObject的文件，只要讲的就是RedisObject的一些转换和创建。里面的大多数方法都是非常类似的。列出里面长长的API列表:
/* ------------ API --------------------- */
robj *createObject(int type, void *ptr) /* 最初的创建robj对象方法，后面的创建方法与此类似 */
robj *createStringObject(char *ptr, size_t len)
robj *createStringObjectFromLongLong(long long value)
robj *createStringObjectFromLongDouble(long double value)
robj *dupStringObject(robj *o)
robj *createListObject(void)
robj *createZiplistObject(void)
robj *createSetObject(void)
robj *createIntsetObject(void)
robj *createHashObject(void)
robj *createZsetObject(void)
robj *createZsetZiplistObject(void)
void freeStringObject(robj *o) /* free Obj中的特定对象，这里free的是r->ptr */
void freeListObject(robj *o)
void freeSetObject(robj *o)
void freeZsetObject(robj *o)
void freeHashObject(robj *o) /* 释放hashObject有2种形式，1个是o-ptr的字典对象，还有1个回事压缩表o->ptr */
void incrRefCount(robj *o) /* robj对象增减引用计数,递增robj中的refcount的值 */
void decrRefCount(robj *o) /* 递减robj中的引用计数，引用到0后，释放对象 */
void decrRefCountVoid(void *o)
robj *resetRefCount(robj *obj)
int checkType(redisClient *c, robj *o, int type) /* 检查robj的类型是否为给定的Type类型 */
int isObjectRepresentableAsLongLong(robj *o, long long *llval)
robj *tryObjectEncoding(robj *o) /* 编码一个robj中的额字符对象，主要是为了省空间 */
robj *getDecodedObject(robj *o) /* 获取解码后的robj */
int compareStringObjectsWithFlags(robj *a, robj *b, int flags)
int compareStringObjects(robj *a, robj *b)
int collateStringObjects(robj *a, robj *b)
int equalStringObjects(robj *a, robj *b)
size_t stringObjectLen(robj *o)
int getDoubleFromObject(robj *o, double *target) /* 从robj中获取double数值 */
int getDoubleFromObjectOrReply(redisClient *c, robj *o, double *target, const char *msg)
int getLongDoubleFromObject(robj *o, long double *target)
int getLongDoubleFromObjectOrReply(redisClient *c, robj *o, long double *target, const char *msg)
int getLongLongFromObject(robj *o, long long *target)
int getLongLongFromObjectOrReply(redisClient *c, robj *o, long long *target, const char *msg)
int getLongFromObjectOrReply(redisClient *c, robj *o, long *target, const char *msg)
char *strEncoding(int encoding)
unsigned long estimateObjectIdleTime(robj *o)
robj *objectCommandLookup(redisClient *c, robj *key) /* obj的查找命令， */
robj *objectCommandLookupOrReply(redisClient *c, robj *key, robj *reply)
void objectCommand(redisClient *c)/* 最初的创建robj对象方法 */
robj *createObject(int type, void *ptr) {
robj *o = zmalloc(sizeof(*o));
o->type = type;
o->encoding = REDIS_ENCODING_RAW;
o->ptr = ptr;
o->refcount = 1;
/* Set the LRU to the current lruclock (minutes resolution). */
o->lru = server.lruclock;
return o;
}/* free Obj中的特定对象 */
void freeStringObject(robj *o) {
if (o->encoding == REDIS_ENCODING_RAW) {
sdsfree(o->ptr);
}
} switch(o->type) {
case REDIS_STRING: freeStringObject(o); break;
case REDIS_LIST: freeListObject(o); break;
case REDIS_SET: freeSetObject(o); break;
case REDIS_ZSET: freeZsetObject(o); break;
case REDIS_HASH: freeHashObject(o); break;
default: redisPanic("Unknown object type"); break;
}/* robj对象增减引用计数,递增robj中的refcount的值 */
void incrRefCount(robj *o) {
//递增robj中的refcount的值
o->refcount++;
}/* 递减robj中的引用计数，引用到0后，释放对象 */
void decrRefCount(robj *o) {
//如果之前的引用计数已经<=0了，说明出现异常情况了
if (o->refcount <= 0) redisPanic("decrRefCount against refcount <= 0");
if (o->refcount == 1) {
//如果之前的引用计数为1，再递减一次，恰好内有被任何对象引用了，所以就可以释放对象了
switch(o->type) {
case REDIS_STRING: freeStringObject(o); break;
case REDIS_LIST: freeListObject(o); break;
case REDIS_SET: freeSetObject(o); break;
case REDIS_ZSET: freeZsetObject(o); break;
case REDIS_HASH: freeHashObject(o); break;
default: redisPanic("Unknown object type"); break;
}
zfree(o);
} else {
//其他对于>1的引用计数的情况，只需要按常规的递减引用计数即可
o->refcount--;
}
}/* Try to encode a string object in order to save space */
/* 编码一个robj中的额字符对象，主要是为了省空间 */
robj *tryObjectEncoding(robj *o) {
long value;
sds s = o->ptr;
size_t len;
if (o->encoding != REDIS_ENCODING_RAW)
//如果robj已经被编码了，则直接返回
return o; /* Already encoded */
/* It's not safe to encode shared objects: shared objects can be shared
* everywhere in the "object space" of Redis. Encoded objects can only
* appear as "values" (and not, for instance, as keys) */
/* 如果robj的引用计数超过1个人引用的时候，是不安全的去编码obj,因为对象是共享的 */
if (o->refcount > 1) return o;
/* Currently we try to encode only strings */
redisAssertWithInfo(NULL,o,o->type == REDIS_STRING);
/* Check if we can represent this string as a long integer */
len = sdslen(s);
if (len > 21 || !string2l(s,len,&value)) {
/* We can't encode the object...
*
* Do the last try, and at least optimize the SDS string inside
* the string object to require little space, in case there
* is more than 10% of free space at the end of the SDS string.
*
* We do that for larger strings, using the arbitrary value
* of 32 bytes. This code was backported from the unstable branch
* where this is performed when the object is too large to be
* encoded as EMBSTR. */
if (len > 32 &&
o->encoding == REDIS_ENCODING_RAW &&
sdsavail(s) > len/10)
{
//调用sdsRemoveFreeSpace把0->ptr中的字符串中的空格给移除掉
o->ptr = sdsRemoveFreeSpace(o->ptr);
}
/* Return the original object. */
return o;
}
...../* Get a decoded version of an encoded object (returned as a new object).
* If the object is already raw-encoded just increment the ref count. */
/* 获取解码后的robj */
robj *getDecodedObject(robj *o) {
robj *dec;
if (o->encoding == REDIS_ENCODING_RAW) {
//如果没有编码方式，则直接增加引用计数，并返回
incrRefCount(o);
return o;
}
if (o->type == REDIS_STRING && o->encoding == REDIS_ENCODING_INT) {
char buf[32];
//如果是string，Type而且是encoding_int方式的，先做一步转换
ll2string(buf,32,(long)o->ptr);
dec = createStringObject(buf,strlen(buf));
return dec;
} else {
redisPanic("Unknown encoding type");
}
}
