漫话Redis源码之九

在redis源码中，hash的思想无处不在，这不，又见到了：

/* This is a helper function for the COPY command.
 * Duplicate a hash object, with the guarantee that the returned object
 * has the same encoding as the original one.
 *
 * The resulting object always has refcount set to 1 */
robj *hashTypeDup(robj *o) {
    robj *hobj;
    hashTypeIterator *hi;

    serverAssert(o->type == OBJ_HASH);

    if(o->encoding == OBJ_ENCODING_ZIPLIST){
        unsigned char *zl = o->ptr;
        size_t sz = ziplistBlobLen(zl);
        unsigned char *new_zl = zmalloc(sz);
        memcpy(new_zl, zl, sz);
        hobj = createObject(OBJ_HASH, new_zl);
        hobj->encoding = OBJ_ENCODING_ZIPLIST;
    } else if(o->encoding == OBJ_ENCODING_HT){
        dict *d = dictCreate(&hashDictType, NULL);
        dictExpand(d, dictSize((const dict*)o->ptr));

        hi = hashTypeInitIterator(o);
        while (hashTypeNext(hi) != C_ERR) {
            sds field, value;
            sds newfield, newvalue;
            /* Extract a field-value pair from an original hash object.*/
            field = hashTypeCurrentFromHashTable(hi, OBJ_HASH_KEY);
            value = hashTypeCurrentFromHashTable(hi, OBJ_HASH_VALUE);
            newfield = sdsdup(field);
            newvalue = sdsdup(value);

            /* Add a field-value pair to a new hash object. */
            dictAdd(d,newfield,newvalue);
        }
        hashTypeReleaseIterator(hi);

        hobj = createObject(OBJ_HASH, d);
        hobj->encoding = OBJ_ENCODING_HT;
    } else {
        serverPanic("Unknown hash encoding");
    }
    return hobj;
}

/* callback for to check the ziplist doesn't have duplicate recoreds */
static int _hashZiplistEntryValidation(unsigned char *p, void *userdata) {
    struct {
        long count;
        dict *fields;
    } *data = userdata;

    /* Odd records are field names, add to dict and check that's not a dup */
    if (((data->count) & 1) == 0) {
        unsigned char *str;
        unsigned int slen;
        long long vll;
        if (!ziplistGet(p, &str, &slen, &vll))
            return 0;
        sds field = str? sdsnewlen(str, slen): sdsfromlonglong(vll);;
        if (dictAdd(data->fields, field, NULL) != DICT_OK) {
            /* Duplicate, return an error */
            sdsfree(field);
            return 0;
        }
    }

    (data->count)++;
    return 1;
}