Redis（五）：hash/hset/hget 命令源碼解析

    {"hset",hsetCommand,4,"wmF",0,NULL,1,1,1,0,0},    {"hsetnx",hsetnxCommand,4,"wmF",0,NULL,1,1,1,0,0},    {"hget",hgetCommand,3,"rF",0,NULL,1,1,1,0,0},    {"hmset",hmsetCommand,-4,"wm",0,NULL,1,1,1,0,0},    {"hmget",hmgetCommand,-3,"r",0,NULL,1,1,1,0,0},    {"hincrby",hincrbyCommand,4,"wmF",0,NULL,1,1,1,0,0},    {"hincrbyfloat",hincrbyfloatCommand,4,"wmF",0,NULL,1,1,1,0,0},    {"hdel",hdelCommand,-3,"wF",0,NULL,1,1,1,0,0},    {"hlen",hlenCommand,2,"rF",0,NULL,1,1,1,0,0},    {"hstrlen",hstrlenCommand,3,"rF",0,NULL,1,1,1,0,0},    {"hkeys",hkeysCommand,2,"rS",0,NULL,1,1,1,0,0},    {"hvals",hvalsCommand,2,"rS",0,NULL,1,1,1,0,0},    {"hgetall",hgetallCommand,2,"r",0,NULL,1,1,1,0,0},    {"hexists",hexistsCommand,3,"rF",0,NULL,1,1,1,0,0},    {"hscan",hscanCommand,-3,"rR",0,NULL,1,1,1,0,0},

typedef struct zlentry {    unsigned int prevrawlensize, prevrawlen;    unsigned int lensize, len;    unsigned int headersize;    unsigned char encoding;    unsigned char *p;} zlentry;#define ZIPLIST_BYTES(zl)       (*((uint32_t*)(zl)))#define ZIPLIST_TAIL_OFFSET(zl) (*((uint32_t*)((zl)+sizeof(uint32_t))))#define ZIPLIST_LENGTH(zl)      (*((uint16_t*)((zl)+sizeof(uint32_t)*2)))#define ZIPLIST_HEADER_SIZE     (sizeof(uint32_t)*2+sizeof(uint16_t))#define ZIPLIST_END_SIZE        (sizeof(uint8_t))#define ZIPLIST_ENTRY_HEAD(zl)  ((zl)+ZIPLIST_HEADER_SIZE)#define ZIPLIST_ENTRY_TAIL(zl)  ((zl)+intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl)))#define ZIPLIST_ENTRY_END(zl)   ((zl)+intrev32ifbe(ZIPLIST_BYTES(zl))-1)

typedef struct dict {    dictType *type;    void *privdata;    dictht ht[2];    long rehashidx; /* rehashing not in progress if rehashidx == -1 */    unsigned long iterators; /* number of iterators currently running */} dict;typedef struct dictht {    dictEntry **table;    unsigned long size;    unsigned long sizemask;    unsigned long used;} dictht;typedef struct dictEntry {    void *key;    void *val;    struct dictEntry *next;} dictEntry;

// t_hash.c, set key field valuevoid hsetCommand(client *c) {    int update;    robj *o;    // 1. 查找hash的key是否存在，不存在則新建一個(gè)，然后在其上進(jìn)行數(shù)據(jù)操作    if ((o = hashTypeLookupWriteOrCreate(c,c->argv[1])) == NULL) return;    // 2. 檢查2-3個(gè)參數(shù)是否需要將簡(jiǎn)單版（ziplist）hash表轉(zhuǎn)換為復(fù)雜的hash表，轉(zhuǎn)換后的表通過(guò) o->ptr 體現(xiàn)    hashTypeTryConversion(o,c->argv,2,3);    // 3. 添加kv到 o 的hash表中    update = hashTypeSet(o,c->argv[2]->ptr,c->argv[3]->ptr,HASH_SET_COPY);    addReply(c, update ? shared.czero : shared.cone);    // 變更命令傳播    signalModifiedKey(c->db,c->argv[1]);    notifyKeyspaceEvent(NOTIFY_HASH,"hset",c->argv[1],c->db->id);    server.dirty++;}
// 1. 獲取db外部的key, 即整體hash數(shù)據(jù)實(shí)例// t_hash.crobj *hashTypeLookupWriteOrCreate(client *c, robj *key) {    robj *o = lookupKeyWrite(c->db,key);    if (o == NULL) {        // 此處創(chuàng)建的hashObject是以 ziplist 形式的        o = createHashObject();        dbAdd(c->db,key,o);    } else {        // 不是hash類型的鍵已存在，不可覆蓋，返回錯(cuò)誤        if (o->type != OBJ_HASH) {            addReply(c,shared.wrongtypeerr);            return NULL;        }    }    return o;}// object.c, 創(chuàng)建hashObject, 以 ziplist 形式創(chuàng)建robj *createHashObject(void) {    unsigned char *zl = ziplistNew();    robj *o = createObject(OBJ_HASH, zl);    o->encoding = OBJ_ENCODING_ZIPLIST;    return o;}// ziplist.cstatic unsigned char *createList() {    unsigned char *zl = ziplistNew();    zl = ziplistPush(zl, (unsigned char*)"foo", 3, ZIPLIST_TAIL);    zl = ziplistPush(zl, (unsigned char*)"quux", 4, ZIPLIST_TAIL);    zl = ziplistPush(zl, (unsigned char*)"hello", 5, ZIPLIST_HEAD);    zl = ziplistPush(zl, (unsigned char*)"1024", 4, ZIPLIST_TAIL);    return zl;}
// 2. 檢查參數(shù)，是否需要將 ziplist 形式的hash表轉(zhuǎn)換為真正的hash表/* Check the length of a number of objects to see if we need to convert a * ziplist to a real hash. Note that we only check string encoded objects * as their string length can be queried in constant time. */void hashTypeTryConversion(robj *o, robj **argv, int start, int end) {    int i;
    if (o->encoding != OBJ_ENCODING_ZIPLIST) return;
    for (i = start; i <= end; i++) {        // 參數(shù)大于設(shè)置的 hash_max_ziplist_value (默認(rèn): 64)時(shí)，會(huì)直接將 ziplist 轉(zhuǎn)換為 ht        // OBJ_ENCODING_RAW, OBJ_ENCODING_EMBSTR        // 循環(huán)檢查參數(shù)，只要發(fā)生了一次轉(zhuǎn)換就結(jié)束檢查（沒(méi)必要繼續(xù)了）        if (sdsEncodedObject(argv[i]) &&            sdslen(argv[i]->ptr) > server.hash_max_ziplist_value)        {            // 這個(gè)轉(zhuǎn)換過(guò)程很有意思，我們深入看看            hashTypeConvert(o, OBJ_ENCODING_HT);            break;        }    }}// t_hash.c, 轉(zhuǎn)換編碼方式 (如上, ziplist -> ht)void hashTypeConvert(robj *o, int enc) {    if (o->encoding == OBJ_ENCODING_ZIPLIST) {        // 此處我們只處理這種情況        hashTypeConvertZiplist(o, enc);    } else if (o->encoding == OBJ_ENCODING_HT) {        serverPanic("Not implemented");    } else {        serverPanic("Unknown hash encoding");    }}// t_hash.c, 轉(zhuǎn)換編碼 ziplist 為目標(biāo) enc (實(shí)際只能是 OBJ_ENCODING_HT) void hashTypeConvertZiplist(robj *o, int enc) {    serverAssert(o->encoding == OBJ_ENCODING_ZIPLIST);
    if (enc == OBJ_ENCODING_ZIPLIST) {        /* Nothing to do... */
    } else if (enc == OBJ_ENCODING_HT) {        hashTypeIterator *hi;        dict *dict;        int ret;        // 迭代器創(chuàng)建        hi = hashTypeInitIterator(o);        // 一個(gè)hash的數(shù)據(jù)結(jié)構(gòu)就是一個(gè) dict, 從這個(gè)級(jí)別來(lái)說(shuō), hash 與 db 是一個(gè)級(jí)別的        dict = dictCreate(&hashDictType, NULL);        // 依次迭代 o, 賦值到 hi->fptr, hi->vptr        // 依次添加到 dict 中        while (hashTypeNext(hi) != C_ERR) {            sds key, value;            // 從 hi->fptr 中獲取key            // 從 hi->vptr 中獲取value            key = hashTypeCurrentObjectNewSds(hi,OBJ_HASH_KEY);            value = hashTypeCurrentObjectNewSds(hi,OBJ_HASH_VALUE);            // 添加到 dict 中            ret = dictAdd(dict, key, value);            if (ret != DICT_OK) {                serverLogHexDump(LL_WARNING,"ziplist with dup elements dump",                    o->ptr,ziplistBlobLen(o->ptr));                serverPanic("Ziplist corruption detected");            }        }        // 釋放迭代器        hashTypeReleaseIterator(hi);        zfree(o->ptr);        // 將變更反映到o對(duì)象上返回        o->encoding = OBJ_ENCODING_HT;        o->ptr = dict;    } else {        serverPanic("Unknown hash encoding");    }}// 2.1. 迭代ziplist元素// t_hash.c, 迭代器/* Move to the next entry in the hash. Return C_OK when the next entry * could be found and C_ERR when the iterator reaches the end. */int hashTypeNext(hashTypeIterator *hi) {    if (hi->encoding == OBJ_ENCODING_ZIPLIST) {        unsigned char *zl;        unsigned char *fptr, *vptr;        // 每次都是基于原始字符器進(jìn)行計(jì)算偏移        // 迭代的是 fptr,vptr        zl = hi->subject->ptr;        fptr = hi->fptr;        vptr = hi->vptr;        // 第一次查找時(shí)使用index查找，后續(xù)則使用 fptr,vptr 進(jìn)行迭代        if (fptr == NULL) {            /* Initialize cursor */            serverAssert(vptr == NULL);            fptr = ziplistIndex(zl, 0);        } else {            /* Advance cursor */            serverAssert(vptr != NULL);            fptr = ziplistNext(zl, vptr);        }        if (fptr == NULL) return C_ERR;
        /* Grab pointer to the value (fptr points to the field) */        vptr = ziplistNext(zl, fptr);        serverAssert(vptr != NULL);
        /* fptr, vptr now point to the first or next pair */        hi->fptr = fptr;        hi->vptr = vptr;    } else if (hi->encoding == OBJ_ENCODING_HT) {        if ((hi->de = dictNext(hi->di)) == NULL) return C_ERR;    } else {        serverPanic("Unknown hash encoding");    }    return C_OK;}// ziplist.c, 查找 index 的元素/* Returns an offset to use for iterating with ziplistNext. When the given * index is negative, the list is traversed back to front. When the list * doesn't contain an element at the provided index, NULL is returned. */unsigned char *ziplistIndex(unsigned char *zl, int index) {    unsigned char *p;    unsigned int prevlensize, prevlen = 0;    if (index < 0) {        // 小于0時(shí)，反向查找        index = (-index)-1;        p = ZIPLIST_ENTRY_TAIL(zl);        if (p[0] != ZIP_END) {            ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);            while (prevlen > 0 && index--) {                p -= prevlen;                ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);            }        }    } else {        p = ZIPLIST_ENTRY_HEAD(zl);        while (p[0] != ZIP_END && index--) {            p += zipRawEntryLength(p);        }    }    // 迭代完成還沒(méi)找到元素 p[0]=ZIP_END    // index 超出整體ziplist大小則遍歷完成后 index>0    return (p[0] == ZIP_END || index > 0) ? NULL : p;}// ziplist.c, 由 fptr,vptr 進(jìn)行迭代元素/* Return pointer to next entry in ziplist. * * zl is the pointer to the ziplist * p is the pointer to the current element * * The element after 'p' is returned, otherwise NULL if we are at the end. */unsigned char *ziplistNext(unsigned char *zl, unsigned char *p) {    ((void) zl);
    /* "p" could be equal to ZIP_END, caused by ziplistDelete,     * and we should return NULL. Otherwise, we should return NULL     * when the *next* element is ZIP_END (there is no next entry). */    if (p[0] == ZIP_END) {        return NULL;    }    // 當(dāng)前指針偏移當(dāng)前元素長(zhǎng)度（根據(jù)ziplist協(xié)議），即到下一元素指針位置    p += zipRawEntryLength(p);    if (p[0] == ZIP_END) {        return NULL;    }
    return p;}/* Return the total number of bytes used by the entry pointed to by 'p'. */static unsigned int zipRawEntryLength(unsigned char *p) {    unsigned int prevlensize, encoding, lensize, len;    ZIP_DECODE_PREVLENSIZE(p, prevlensize);    ZIP_DECODE_LENGTH(p + prevlensize, encoding, lensize, len);    return prevlensize + lensize + len;}
// 2.2. t_hash.c, 獲取 hashTypeIterator 的具體值，寫(xiě)入 vstr, vlen 中/* Return the key or value at the current iterator position as a new * SDS string. */sds hashTypeCurrentObjectNewSds(hashTypeIterator *hi, int what) {    unsigned char *vstr;    unsigned int vlen;    long long vll;
    hashTypeCurrentObject(hi,what,&vstr,&vlen,&vll);    if (vstr) return sdsnewlen(vstr,vlen);    return sdsfromlonglong(vll);}/* Higher level function of hashTypeCurrent*() that returns the hash value * at current iterator position. * * The returned element is returned by reference in either *vstr and *vlen if * it's returned in string form, or stored in *vll if it's returned as * a number. * * If *vll is populated *vstr is set to NULL, so the caller * can always check the function return by checking the return value * type checking if vstr == NULL. */void hashTypeCurrentObject(hashTypeIterator *hi, int what, unsigned char **vstr, unsigned int *vlen, long long *vll) {    if (hi->encoding == OBJ_ENCODING_ZIPLIST) {        *vstr = NULL;        hashTypeCurrentFromZiplist(hi, what, vstr, vlen, vll);    } else if (hi->encoding == OBJ_ENCODING_HT) {        sds ele = hashTypeCurrentFromHashTable(hi, what);        *vstr = (unsigned char*) ele;        *vlen = sdslen(ele);    } else {        serverPanic("Unknown hash encoding");    }}
// t_hash.c, 從ziplist中獲取某個(gè) hashTypeIterator 的具體值，結(jié)果定稿 vstr, vlen/* Get the field or value at iterator cursor, for an iterator on a hash value * encoded as a ziplist. Prototype is similar to `hashTypeGetFromZiplist`. */void hashTypeCurrentFromZiplist(hashTypeIterator *hi, int what,                                unsigned char **vstr,                                unsigned int *vlen,                                long long *vll){    int ret;
    serverAssert(hi->encoding == OBJ_ENCODING_ZIPLIST);    // OBJ_HASH_KEY 從 fptr 中獲取, 否則從 vptr 中獲取    if (what & OBJ_HASH_KEY) {        ret = ziplistGet(hi->fptr, vstr, vlen, vll);        serverAssert(ret);    } else {        ret = ziplistGet(hi->vptr, vstr, vlen, vll);        serverAssert(ret);    }}// ziplist.c, /* Get entry pointed to by 'p' and store in either '*sstr' or 'sval' depending * on the encoding of the entry. '*sstr' is always set to NULL to be able * to find out whether the string pointer or the integer value was set. * Return 0 if 'p' points to the end of the ziplist, 1 otherwise. */unsigned int ziplistGet(unsigned char *p, unsigned char **sstr, unsigned int *slen, long long *sval) {    zlentry entry;    if (p == NULL || p[0] == ZIP_END) return 0;    if (sstr) *sstr = NULL;    // 按照ziplist的編碼協(xié)議, 獲取頭部信息    zipEntry(p, &entry);    if (ZIP_IS_STR(entry.encoding)) {        if (sstr) {            *slen = entry.len;            *sstr = p+entry.headersize;        }    } else {        if (sval) {            *sval = zipLoadInteger(p+entry.headersize,entry.encoding);        }    }    return 1;}// ziplist.c, 解析原始字符串為 zlentry/* Return a struct with all information about an entry. */static void zipEntry(unsigned char *p, zlentry *e) {    // 按照ziplist的編碼協(xié)議,依次讀取 prevrawlensize, prevrawlen    ZIP_DECODE_PREVLEN(p, e->prevrawlensize, e->prevrawlen);    // 指向下一位置偏移，按照ziplist的編碼協(xié)議,依次讀取 encoding, lensize, len    ZIP_DECODE_LENGTH(p + e->prevrawlensize, e->encoding, e->lensize, e->len);    // 除去header得到 body偏移    e->headersize = e->prevrawlensize + e->lensize;    e->p = p;}

// ziplist.c/* Decode the length of the previous element, from the perspective of the entry * pointed to by 'ptr'. */#define ZIP_DECODE_PREVLEN(ptr, prevlensize, prevlen) do {                     \    // 解析第1個(gè)字符為 prevlensize    ZIP_DECODE_PREVLENSIZE(ptr, prevlensize);                                  \    if ((prevlensize) == 1) {                                                  \        (prevlen) = (ptr)[0];                                                  \    } else if ((prevlensize) == 5) {                                           \        assert(sizeof((prevlensize)) == 4);                                    \        // 當(dāng)ptr[0]>254時(shí)，代表內(nèi)容有點(diǎn)大，需要使用 5個(gè)字符保存上一字符長(zhǎng)度        memcpy(&(prevlen), ((char*)(ptr)) + 1, 4);                             \        memrev32ifbe(&prevlen);                                                \    }                                                                          \} while(0);/* Decode the number of bytes required to store the length of the previous * element, from the perspective of the entry pointed to by 'ptr'. */#define ZIP_DECODE_PREVLENSIZE(ptr, prevlensize) do {                          \    if ((ptr)[0] < ZIP_BIGLEN) {                                               \        (prevlensize) = 1;                                                     \    } else {                                                                   \        (prevlensize) = 5;                                                     \    }                                                                          \} while(0);/* Decode the length encoded in 'ptr'. The 'encoding' variable will hold the * entries encoding, the 'lensize' variable will hold the number of bytes * required to encode the entries length, and the 'len' variable will hold the * entries length. */#define ZIP_DECODE_LENGTH(ptr, encoding, lensize, len) do {                    \    // 解析第1個(gè)字符為 編碼格式 &ZIP_STR_MASK=0xc0    ZIP_ENTRY_ENCODING((ptr), (encoding));                                     \    if ((encoding) < ZIP_STR_MASK) {                                           \        // 0 << 6 =0        // 具體解析如下代碼,        if ((encoding) == ZIP_STR_06B) {                                       \            (lensize) = 1;                                                     \            (len) = (ptr)[0] & 0x3f;                                           \        }         // 1 << 6 =64        else if ((encoding) == ZIP_STR_14B) {                                  \            (lensize) = 2;                                                     \            (len) = (((ptr)[0] & 0x3f) << 8) | (ptr)[1];                       \        }        // 2 << 6 =128        else if (encoding == ZIP_STR_32B) {                                    \            (lensize) = 5;                                                     \            (len) = ((ptr)[1] << 24) |                                         \                    ((ptr)[2] << 16) |                                         \                    ((ptr)[3] <<  8) |                                         \                    ((ptr)[4]);                                                \        } else {                                                               \            assert(NULL);                                                      \        }                                                                      \    } else {                                                                   \        // 超過(guò) 0xc0 的長(zhǎng)度了，直接使用 1,2,3,4 表示len        (lensize) = 1;                                                         \        (len) = zipIntSize(encoding);                                          \    }                                                                          \} while(0);/* Extract the encoding from the byte pointed by 'ptr' and set it into * 'encoding'. */#define ZIP_ENTRY_ENCODING(ptr, encoding) do {  \    (encoding) = (ptr[0]); \    if ((encoding) < ZIP_STR_MASK) (encoding) &= ZIP_STR_MASK; \} while(0)
/* Different encoding/length possibilities */#define ZIP_STR_MASK 0xc0#define ZIP_INT_MASK 0x30#define ZIP_STR_06B (0 << 6)        // 0x00#define ZIP_STR_14B (1 << 6)        // 0x40#define ZIP_STR_32B (2 << 6)        // 0x80#define ZIP_INT_16B (0xc0 | 0<<4)    // 0xc0#define ZIP_INT_32B (0xc0 | 1<<4)    // 0xd0#define ZIP_INT_64B (0xc0 | 2<<4)    // 0xe0#define ZIP_INT_24B (0xc0 | 3<<4)    // 0xf0#define ZIP_INT_8B 0xfe                // 0xfe

// 3. 添加kv到 hash表中, 稍微復(fù)雜// t_hash.c, 做變更到hash表中int hashTypeSet(robj *o, sds field, sds value, int flags) {    int update = 0;    // 針對(duì)ziplist 的添加, 與 ht 編碼的添加, 自然是分別處理    if (o->encoding == OBJ_ENCODING_ZIPLIST) {        unsigned char *zl, *fptr, *vptr;
        zl = o->ptr;        // 找到ziplist 的頭節(jié)點(diǎn)指針        fptr = ziplistIndex(zl, ZIPLIST_HEAD);        if (fptr != NULL) {            // 嘗試查找該 field 對(duì)應(yīng)的元素(從1開(kāi)始)，如果找到則先刪除原值，然后統(tǒng)一添加            fptr = ziplistFind(fptr, (unsigned char*)field, sdslen(field), 1);            if (fptr != NULL) {                /* Grab pointer to the value (fptr points to the field) */                // value 不可以為null, 否則 ziplist 將無(wú)法工作                vptr = ziplistNext(zl, fptr);                serverAssert(vptr != NULL);                update = 1;
                /* Delete value */                // 先刪除舊的 value, 再以插入的形式更新, 后續(xù)講刪除時(shí)再詳解                zl = ziplistDelete(zl, &vptr);
                /* Insert new value */                // 重點(diǎn)，將value添加到 ziplist 中                zl = ziplistInsert(zl, vptr, (unsigned char*)value,                        sdslen(value));            }        }        // 沒(méi)有找到對(duì)應(yīng)元素，則直接將元素添加到尾部即可        if (!update) {            /* Push new field/value pair onto the tail of the ziplist */            zl = ziplistPush(zl, (unsigned char*)field, sdslen(field),                    ZIPLIST_TAIL);            zl = ziplistPush(zl, (unsigned char*)value, sdslen(value),                    ZIPLIST_TAIL);        }        o->ptr = zl;
        /* Check if the ziplist needs to be converted to a hash table */        // 大于設(shè)置的閥值后，轉(zhuǎn)換ziplist為ht(默認(rèn): 512)        if (hashTypeLength(o) > server.hash_max_ziplist_entries)            hashTypeConvert(o, OBJ_ENCODING_HT);    } else if (o->encoding == OBJ_ENCODING_HT) {        dictEntry *de = dictFind(o->ptr,field);        if (de) {            sdsfree(dictGetVal(de));            if (flags & HASH_SET_TAKE_VALUE) {                dictGetVal(de) = value;                value = NULL;            } else {                dictGetVal(de) = sdsdup(value);            }            update = 1;        } else {            sds f,v;            if (flags & HASH_SET_TAKE_FIELD) {                f = field;                field = NULL;            } else {                f = sdsdup(field);            }            if (flags & HASH_SET_TAKE_VALUE) {                v = value;                value = NULL;            } else {                v = sdsdup(value);            }            dictAdd(o->ptr,f,v);        }    } else {        serverPanic("Unknown hash encoding");    }
    /* Free SDS strings we did not referenced elsewhere if the flags     * want this function to be responsible. */    if (flags & HASH_SET_TAKE_FIELD && field) sdsfree(field);    if (flags & HASH_SET_TAKE_VALUE && value) sdsfree(value);    return update;}// 3.1. 使用ziplist進(jìn)行保存 field -> value// ziplist.c, 查找某個(gè) field 是否存在于ziplist中/* Find pointer to the entry equal to the specified entry. Skip 'skip' entries * between every comparison. Returns NULL when the field could not be found. */unsigned char *ziplistFind(unsigned char *p, unsigned char *vstr, unsigned int vlen, unsigned int skip) {    int skipcnt = 0;    unsigned char vencoding = 0;    long long vll = 0;
    while (p[0] != ZIP_END) {        unsigned int prevlensize, encoding, lensize, len;        unsigned char *q;        // 解析整個(gè)字符串p的 prevlensize,encoding,lensize,len        ZIP_DECODE_PREVLENSIZE(p, prevlensize);        ZIP_DECODE_LENGTH(p + prevlensize, encoding, lensize, len);        q = p + prevlensize + lensize;        // 傳入1, 代表要跳過(guò)一個(gè)元素, 比如: 查找key時(shí),跳過(guò)1個(gè)v,然后繼續(xù)迭代        // 跳過(guò)了n個(gè)元素后，再?gòu)拇碎_(kāi)始key的比對(duì)過(guò)程        if (skipcnt == 0) {            /* Compare current entry with specified entry */            // 針對(duì)不同的編碼使用不同的比較方式            if (ZIP_IS_STR(encoding)) {                // 找到相應(yīng)的元素，直接返回 p 指針                if (len == vlen && memcmp(q, vstr, vlen) == 0) {                    return p;                }            } else {                /* Find out if the searched field can be encoded. Note that                 * we do it only the first time, once done vencoding is set                 * to non-zero and vll is set to the integer value. */                if (vencoding == 0) {                    if (!zipTryEncoding(vstr, vlen, &vll, &vencoding)) {                        /* If the entry can't be encoded we set it to                         * UCHAR_MAX so that we don't retry again the next                         * time. */                        vencoding = UCHAR_MAX;                    }                    /* Must be non-zero by now */                    assert(vencoding);                }
                /* Compare current entry with specified entry, do it only                 * if vencoding != UCHAR_MAX because if there is no encoding                 * possible for the field it can't be a valid integer. */                if (vencoding != UCHAR_MAX) {                    long long ll = zipLoadInteger(q, encoding);                    if (ll == vll) {                        return p;                    }                }            }
            /* Reset skip count */            // 查找一次，跳過(guò)skip次            skipcnt = skip;        } else {            /* Skip entry */            skipcnt--;        }
        /* Move to next entry */        p = q + len;    }
    return NULL;}// ziplist.c, 添加value到ziplist中// zl:ziplist實(shí)例, p:要插入的key字串, s:要插入的value字串, len:要插入的value的長(zhǎng)度/* Insert an entry at "p". */unsigned char *ziplistInsert(unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen) {    return __ziplistInsert(zl,p,s,slen);}/* Insert item at "p". */static unsigned char *__ziplistInsert(unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen) {    size_t curlen = intrev32ifbe(ZIPLIST_BYTES(zl)), reqlen;    unsigned int prevlensize, prevlen = 0;    size_t offset;    int nextdiff = 0;    unsigned char encoding = 0;    long long value = 123456789; /* initialized to avoid warning. Using a value                                    that is easy to see if for some reason                                    we use it uninitialized. */    zlentry tail;
    /* Find out prevlen for the entry that is inserted. */    if (p[0] != ZIP_END) {        ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);    } else {        unsigned char *ptail = ZIPLIST_ENTRY_TAIL(zl);        if (ptail[0] != ZIP_END) {            prevlen = zipRawEntryLength(ptail);        }    }
    /* See if the entry can be encoded */    if (zipTryEncoding(s,slen,&value,&encoding)) {        /* 'encoding' is set to the appropriate integer encoding */        reqlen = zipIntSize(encoding);    } else {        /* 'encoding' is untouched, however zipEncodeLength will use the         * string length to figure out how to encode it. */        reqlen = slen;    }    /* We need space for both the length of the previous entry and     * the length of the payload. */    // 加上prevlen,encoding,slen 的長(zhǎng)度，以計(jì)算value的存放位置    reqlen += zipPrevEncodeLength(NULL,prevlen);    reqlen += zipEncodeLength(NULL,encoding,slen);
    /* When the insert position is not equal to the tail, we need to     * make sure that the next entry can hold this entry's length in     * its prevlen field. */    nextdiff = (p[0] != ZIP_END) ? zipPrevLenByteDiff(p,reqlen) : 0;
    /* Store offset because a realloc may change the address of zl. */    // 存儲(chǔ)當(dāng)前偏移位置，以便在擴(kuò)容之后，還能找到相應(yīng)位置    // p = p -zl + zl    offset = p-zl;    zl = ziplistResize(zl,curlen+reqlen+nextdiff);    p = zl+offset;
    /* Apply memory move when necessary and update tail offset. */    if (p[0] != ZIP_END) {        /* Subtract one because of the ZIP_END bytes */        // 字符拷貝        memmove(p+reqlen,p-nextdiff,curlen-offset-1+nextdiff);
        /* Encode this entry's raw length in the next entry. */        zipPrevEncodeLength(p+reqlen,reqlen);
        /* Update offset for tail */        ZIPLIST_TAIL_OFFSET(zl) =            intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+reqlen);
        /* When the tail contains more than one entry, we need to take         * "nextdiff" in account as well. Otherwise, a change in the         * size of prevlen doesn't have an effect on the *tail* offset. */        zipEntry(p+reqlen, &tail);        if (p[reqlen+tail.headersize+tail.len] != ZIP_END) {            ZIPLIST_TAIL_OFFSET(zl) =                intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+nextdiff);        }    } else {        /* This element will be the new tail. */        ZIPLIST_TAIL_OFFSET(zl) = intrev32ifbe(p-zl);    }
    /* When nextdiff != 0, the raw length of the next entry has changed, so     * we need to cascade the update throughout the ziplist */    if (nextdiff != 0) {        // 如果本次更新后數(shù)據(jù)位置變化，則需要更新后續(xù)的元素位置        offset = p-zl;        zl = __ziplistCascadeUpdate(zl,p+reqlen);        p = zl+offset;    }
    /* Write the entry */    // 將 value 寫(xiě)入 p 中, 即寫(xiě)入了 ziplist 中    p += zipPrevEncodeLength(p,prevlen);    p += zipEncodeLength(p,encoding,slen);    if (ZIP_IS_STR(encoding)) {        memcpy(p,s,slen);    } else {        zipSaveInteger(p,value,encoding);    }    ZIPLIST_INCR_LENGTH(zl,1);    return zl;}// 另外，如果沒(méi)有舊的元素值時(shí)，直接在hash表的末尾添加對(duì)應(yīng)的field->value 即可// ziplist.c, 在尾部進(jìn)行添加元素，沒(méi)有許多的情況要考慮，但是代碼完全復(fù)用 __ziplistInsert()unsigned char *ziplistPush(unsigned char *zl, unsigned char *s, unsigned int slen, int where) {    unsigned char *p;    p = (where == ZIPLIST_HEAD) ? ZIPLIST_ENTRY_HEAD(zl) : ZIPLIST_ENTRY_END(zl);    return __ziplistInsert(zl,p,s,slen);}

// 3.2. OBJ_ENCODING_HT 的 field -> value 的添加    if (o->encoding == OBJ_ENCODING_HT) {        // hash 表中查找對(duì)應(yīng)的 field        dictEntry *de = dictFind(o->ptr,field);        if (de) {            sdsfree(dictGetVal(de));            // hset 時(shí)使用 HASH_SET_COPY, 所以直接使用 sdsdup() 即可            if (flags & HASH_SET_TAKE_VALUE) {                dictGetVal(de) = value;                value = NULL;            } else {                dictGetVal(de) = sdsdup(value);            }            update = 1;        } else {            // 新增 field -> value            sds f,v;            if (flags & HASH_SET_TAKE_FIELD) {                f = field;                field = NULL;            } else {                f = sdsdup(field);            }            if (flags & HASH_SET_TAKE_VALUE) {                v = value;                value = NULL;            } else {                v = sdsdup(value);            }            // 添加到 hash 表中，前些篇章講解過(guò)，大概就是計(jì)算hash，放入v的過(guò)程            dictAdd(o->ptr,f,v);        }    }

// t_hash.c, hmset key f1 v1 f2 v2void hmsetCommand(client *c) {    int i;    robj *o;    // 參數(shù)個(gè)數(shù)檢查，必定是2n    if ((c->argc % 2) == 1) {        addReplyError(c,"wrong number of arguments for HMSET");        return;    }    // 插入方式與 hset 一毛一樣，差別在于批量插入時(shí)，會(huì)循環(huán)向 key-hash表中添加field->value    if ((o = hashTypeLookupWriteOrCreate(c,c->argv[1])) == NULL) return;    hashTypeTryConversion(o,c->argv,2,c->argc-1);    // 循環(huán)insert    for (i = 2; i < c->argc; i += 2) {        hashTypeSet(o,c->argv[i]->ptr,c->argv[i+1]->ptr,HASH_SET_COPY);    }    addReply(c, shared.ok);    signalModifiedKey(c->db,c->argv[1]);    notifyKeyspaceEvent(NOTIFY_HASH,"hset",c->argv[1],c->db->id);    server.dirty++;}

// t_hash.c    void hgetCommand(client *c) {    robj *o;    // 查找key, 不存在或者類型不一致則直接返回    if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.nullbulk)) == NULL ||        checkType(c,o,OBJ_HASH)) return;    // 基于o, 返回 field 對(duì)應(yīng)的元素值即可    addHashFieldToReply(c, o, c->argv[2]->ptr);}// t_hash.cstatic void addHashFieldToReply(client *c, robj *o, sds field) {    int ret;
    if (o == NULL) {        addReply(c, shared.nullbulk);        return;    }
    if (o->encoding == OBJ_ENCODING_ZIPLIST) {        unsigned char *vstr = NULL;        unsigned int vlen = UINT_MAX;        long long vll = LLONG_MAX;        // 基于 ziplist,         ret = hashTypeGetFromZiplist(o, field, &vstr, &vlen, &vll);        if (ret < 0) {            // 響應(yīng)為空            addReply(c, shared.nullbulk);        } else {            // 添加到輸出緩沖            if (vstr) {                addReplyBulkCBuffer(c, vstr, vlen);            } else {                addReplyBulkLongLong(c, vll);            }        }
    } else if (o->encoding == OBJ_ENCODING_HT) {        // hash 表類型則查找 hash 表即可        sds value = hashTypeGetFromHashTable(o, field);        // 添加到輸出緩沖        if (value == NULL)            // 響應(yīng)為空            addReply(c, shared.nullbulk);        else            addReplyBulkCBuffer(c, value, sdslen(value));    } else {        serverPanic("Unknown hash encoding");    }}// t_hash.c, 從 ziplist 中查找 field 值/* Get the value from a ziplist encoded hash, identified by field. * Returns -1 when the field cannot be found. */int hashTypeGetFromZiplist(robj *o, sds field,                           unsigned char **vstr,                           unsigned int *vlen,                           long long *vll){    unsigned char *zl, *fptr = NULL, *vptr = NULL;    int ret;
    serverAssert(o->encoding == OBJ_ENCODING_ZIPLIST);
    zl = o->ptr;    fptr = ziplistIndex(zl, ZIPLIST_HEAD);    if (fptr != NULL) {        fptr = ziplistFind(fptr, (unsigned char*)field, sdslen(field), 1);        if (fptr != NULL) {            /* Grab pointer to the value (fptr points to the field) */            vptr = ziplistNext(zl, fptr);            serverAssert(vptr != NULL);        }    }
    if (vptr != NULL) {        ret = ziplistGet(vptr, vstr, vlen, vll);        serverAssert(ret);        return 0;    }
    return -1;}
// t_hash.c, 從hash表中查找 field 字段的值/* Get the value from a hash table encoded hash, identified by field. * Returns NULL when the field cannot be found, otherwise the SDS value * is returned. */sds hashTypeGetFromHashTable(robj *o, sds field) {    dictEntry *de;
    serverAssert(o->encoding == OBJ_ENCODING_HT);
    de = dictFind(o->ptr, field);    if (de == NULL) return NULL;    return dictGetVal(de);}

// t_hash.cvoid hmgetCommand(client *c) {    robj *o;    int i;
    /* Don't abort when the key cannot be found. Non-existing keys are empty     * hashes, where HMGET should respond with a series of null bulks. */    o = lookupKeyRead(c->db, c->argv[1]);    if (o != NULL && o->type != OBJ_HASH) {        addReply(c, shared.wrongtypeerr);        return;    }    // 循環(huán)輸出值    addReplyMultiBulkLen(c, c->argc-2);    for (i = 2; i < c->argc; i++) {        addHashFieldToReply(c, o, c->argv[i]->ptr);    }}

// t_hash.cvoid hgetallCommand(client *c) {    genericHgetallCommand(c,OBJ_HASH_KEY|OBJ_HASH_VALUE);}void genericHgetallCommand(client *c, int flags) {    robj *o;    hashTypeIterator *hi;    int multiplier = 0;    int length, count = 0;
    if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.emptymultibulk)) == NULL        || checkType(c,o,OBJ_HASH)) return;
    if (flags & OBJ_HASH_KEY) multiplier++;    if (flags & OBJ_HASH_VALUE) multiplier++;
    length = hashTypeLength(o) * multiplier;    addReplyMultiBulkLen(c, length);
    hi = hashTypeInitIterator(o);    while (hashTypeNext(hi) != C_ERR) {        if (flags & OBJ_HASH_KEY) {            addHashIteratorCursorToReply(c, hi, OBJ_HASH_KEY);            count++;        }        if (flags & OBJ_HASH_VALUE) {            addHashIteratorCursorToReply(c, hi, OBJ_HASH_VALUE);            count++;        }    }
    hashTypeReleaseIterator(hi);    serverAssert(count == length);}static void addHashIteratorCursorToReply(client *c, hashTypeIterator *hi, int what) {    if (hi->encoding == OBJ_ENCODING_ZIPLIST) {        unsigned char *vstr = NULL;        unsigned int vlen = UINT_MAX;        long long vll = LLONG_MAX;
        hashTypeCurrentFromZiplist(hi, what, &vstr, &vlen, &vll);        if (vstr)            addReplyBulkCBuffer(c, vstr, vlen);        else            addReplyBulkLongLong(c, vll);    } else if (hi->encoding == OBJ_ENCODING_HT) {        sds value = hashTypeCurrentFromHashTable(hi, what);        addReplyBulkCBuffer(c, value, sdslen(value));    } else {        serverPanic("Unknown hash encoding");    }}

// t_hash.c, void hincrbyCommand(client *c) {    long long value, incr, oldvalue;    robj *o;    sds new;    unsigned char *vstr;    unsigned int vlen;    // 解析增加字段值到 incr 中    if (getLongLongFromObjectOrReply(c,c->argv[3],&incr,NULL) != C_OK) return;    // 獲取原值或者設(shè)置為0    if ((o = hashTypeLookupWriteOrCreate(c,c->argv[1])) == NULL) return;    if (hashTypeGetValue(o,c->argv[2]->ptr,&vstr,&vlen,&value) == C_OK) {        if (vstr) {            if (string2ll((char*)vstr,vlen,&value) == 0) {                addReplyError(c,"hash value is not an integer");                return;            }        } /* Else hashTypeGetValue() already stored it into &value */    } else {        value = 0;    }
    oldvalue = value;    if ((incr < 0 && oldvalue < 0 && incr < (LLONG_MIN-oldvalue)) ||        (incr > 0 && oldvalue > 0 && incr > (LLONG_MAX-oldvalue))) {        addReplyError(c,"increment or decrement would overflow");        return;    }    // 將相加后的值重置設(shè)置回hash表中    value += incr;    new = sdsfromlonglong(value);    hashTypeSet(o,c->argv[2]->ptr,new,HASH_SET_TAKE_VALUE);    addReplyLongLong(c,value);    signalModifiedKey(c->db,c->argv[1]);    notifyKeyspaceEvent(NOTIFY_HASH,"hincrby",c->argv[1],c->db->id);    server.dirty++;}

// t_hash.c, void hdelCommand(client *c) {    robj *o;    int j, deleted = 0, keyremoved = 0;
    if ((o = lookupKeyWriteOrReply(c,c->argv[1],shared.czero)) == NULL ||        checkType(c,o,OBJ_HASH)) return;    // 循環(huán)刪除給定字段列表    for (j = 2; j < c->argc; j++) {        if (hashTypeDelete(o,c->argv[j]->ptr)) {            deleted++;            // 當(dāng)沒(méi)有任何元素后，直接將key刪除            if (hashTypeLength(o) == 0) {                dbDelete(c->db,c->argv[1]);                keyremoved = 1;                break;            }        }    }    if (deleted) {        signalModifiedKey(c->db,c->argv[1]);        notifyKeyspaceEvent(NOTIFY_HASH,"hdel",c->argv[1],c->db->id);        if (keyremoved)            notifyKeyspaceEvent(NOTIFY_GENERIC,"del",c->argv[1],                                c->db->id);        server.dirty += deleted;    }    addReplyLongLong(c,deleted);}// 具體刪除 field, 同樣區(qū)分編碼類型，不同處理邏輯/* Delete an element from a hash. * Return 1 on deleted and 0 on not found. */int hashTypeDelete(robj *o, sds field) {    int deleted = 0;
    if (o->encoding == OBJ_ENCODING_ZIPLIST) {        unsigned char *zl, *fptr;
        zl = o->ptr;        fptr = ziplistIndex(zl, ZIPLIST_HEAD);        if (fptr != NULL) {            // ziplist 刪除，依次刪除 field, value            fptr = ziplistFind(fptr, (unsigned char*)field, sdslen(field), 1);            if (fptr != NULL) {                // ziplistDelete 為原地刪除，所以只要調(diào)用2次，即把kv刪除                zl = ziplistDelete(zl,&fptr);                zl = ziplistDelete(zl,&fptr);                o->ptr = zl;                deleted = 1;            }        }    } else if (o->encoding == OBJ_ENCODING_HT) {        if (dictDelete((dict*)o->ptr, field) == C_OK) {            deleted = 1;
            /* Always check if the dictionary needs a resize after a delete. */            // hash 刪除的，可能需要進(jìn)行縮容操作，這種處理方法相對(duì)特殊些            if (htNeedsResize(o->ptr)) dictResize(o->ptr);        }
    } else {        serverPanic("Unknown hash encoding");    }    return deleted;}// server.c, 是否需要進(jìn)行 resizeint htNeedsResize(dict *dict) {    long long size, used;
    size = dictSlots(dict);    used = dictSize(dict);    // HASHTABLE_MIN_FILL=10, 即使用率小于 1/10 時(shí)，可以進(jìn)行縮容操作了    return (size && used && size > DICT_HT_INITIAL_SIZE &&            (used*100/size < HASHTABLE_MIN_FILL));}