Redis源代码分析(二十八)--- object创建和释放redisObject物
今天的学习更有效率。该Rio分析过,学习之间的另一种方式RedisObject文件,只想说RedisObject有些生成和转换。都是很类似的。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相似 */ 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)从前往后看。第一个创建obj:
/* 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; }有创建就必定会有释放的free方法:
/* free Obj中的特定对象 */ void freeStringObject(robj *o) { if (o->encoding == REDIS_ENCODING_RAW) { sdsfree(o->ptr); } }free方法有非常多衍生的方法。看你要释放哪种类型的空间了,能够,set,dict,ziplist等等。有以下的一些类型:
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; }重点介绍里面的关于引用计数的相关方法,通过robj->refcount的数值进行控制的:
/* 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++; }添加引用计数就一行代码,可是递减的话。我们猜也能够猜到,引用计数变为0的时候,说明无人使用了,就能够释放空间了;
/* 递减robj中的引用计数,引用到0后。释放对象 */ void decrRefCount(robj *o) { //假设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) { //假设之前的引用计数为1,再递减一次。恰好内有被不论什么对象引用了,所以就能够释放对象了 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 { //其它对于>1的引用计数的情况,仅仅须要按常规的递减引用计数就可以 o->refcount--; } }标准的引用计数法控制内存的管理。(提醒一下,在JVM中的对象的生命周期管理用的是根搜索法。不是引用计数)。另一个在robj中的编码方法的实现也是定义在这个文件里:
/* 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) //假设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) */ /* 假设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,由于对象是共享的 */ 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; } .....就是移除字符串中的空格所占的空间。
想相应也存在一个getDecodeObject(),:
/* 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) { //假设没有编码方式。则直接添加引用计数。并返回 incrRefCount(o); return o; } if (o->type == REDIS_STRING && o->encoding == REDIS_ENCODING_INT) { char buf[32]; //假设是string。Type并且是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"); } }以上是对RedisObject简单分析。
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