当前位置:Gxlcms > mysql > Redis源码分析(二十八)---object创建和释放redisObject对象

Redis源码分析(二十八)---object创建和释放redisObject对象

时间:2021-07-01 10:21:17 帮助过:52人阅读

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 ty

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)
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;
}
有创建就必然会有释放的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方法有很多衍生的方法,看你要释放哪种类型的空间了,可以,set,dict,ziplist等等。有下面的一些类型:
 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++;
}
增加引用计数就一行代码,但是递减的话,我们猜也可以猜到,引用计数变为0的时候,说明无人使用了,就可以释放空间了;
/* 递减robj中的引用计数,引用到0后,释放对象 */
void decrRefCount(robj *o) {
	//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--;
    }
}
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),还有一个在robj中的编码方法的实现也是定义在这个文件中:
/* 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;
    }
    	.....
就是移除字符串中的空格所占的空间。想对应也存在一个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) {
    	//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");
    }
}
以上就是对于对于RedisObject的简单分析。

人气教程排行