t_string.c

Redis的t_string.c是对于string数据结构的实现。
底层是基于 sds 及 dict 实现的。

首先，了解一下redisDb结构。

/* Redis database representation. There are multiple databases identified
 * by integers from 0 (the default database) up to the max configured
 * database. The database number is the 'id' field in the structure. */
typedef struct redisDb {
    //存储普通key
    dict *dict;                 /* The keyspace for this DB */
    //存储设置了过期时间的key
    dict *expires;              /* Timeout of keys with a timeout set */
    //存储BLPOP下的key
    dict *blocking_keys;        /* Keys with clients waiting for data (BLPOP)*/
    //存储PUSH了的key
    dict *ready_keys;           /* Blocked keys that received a PUSH */
    //存储事务监听的key
    dict *watched_keys;         /* WATCHED keys for MULTI/EXEC CAS */
    //数据库id
    int id;                     /* Database ID */
    //所有key的平均ttl
    long long avg_ttl;          /* Average TTL, just for stats */
    //逐一尝试整理碎片的key名称列表
    list *defrag_later;         /* List of key names to attempt to defrag one by one, gradually. */
} redisDb;

Redis允许的最大字符串长度为512MB。

//string的最大长度512MB
static int checkStringLength(client *c, long long size) {
    if (size > 512*1024*1024) {
        addReplyError(c,"string exceeds maximum allowed size (512MB)");
        return C_ERR;
    }
    return C_OK;
}

1. set类型命令的实现

void setGenericCommand(client *c, int flags, robj *key, robj *val, robj *expire, int unit, robj *ok_reply, robj *abort_reply) {
    long long milliseconds = 0; /* initialized to avoid any harmness warning */

    //如果设置了expire过期时间
    if (expire) {
        //类型转换
        if (getLongLongFromObjectOrReply(c, expire, &milliseconds, NULL) != C_OK)
            return;
        //合法性校验
        if (milliseconds <= 0) {
            addReplyErrorFormat(c,"invalid expire time in %s",c->cmd->name);
            return;
        }
        //单位转换
        if (unit == UNIT_SECONDS) milliseconds *= 1000;
    }

    //检查flags是否包含NX、XX
    if ((flags & OBJ_SET_NX && lookupKeyWrite(c->db,key) != NULL) ||
        (flags & OBJ_SET_XX && lookupKeyWrite(c->db,key) == NULL))
    {
        addReply(c, abort_reply ? abort_reply : shared.nullbulk);
        return;
    }
    //设置key、value
    setKey(c->db,key,val);
    //脏+1，事务中使用
    server.dirty++;
    //设置过期时间
    if (expire) setExpire(c,c->db,key,mstime()+milliseconds);
    //注册定时事件
    notifyKeyspaceEvent(NOTIFY_STRING,"set",key,c->db->id);
    //注册过期事件
    if (expire) notifyKeyspaceEvent(NOTIFY_GENERIC,
        "expire",key,c->db->id);
    //响应客户端
    addReply(c, ok_reply ? ok_reply : shared.ok);
}

/* SET key value [NX] [XX] [EX <seconds>] [PX <milliseconds>] */
//SET命令
void setCommand(client *c) {
    int j;
    robj *expire = NULL;
    int unit = UNIT_SECONDS;
    int flags = OBJ_SET_NO_FLAGS;

    //set key value 后面的参数 NX XX EX PX
    for (j = 3; j < c->argc; j++) {
        char *a = c->argv[j]->ptr;
        robj *next = (j == c->argc-1) ? NULL : c->argv[j+1];

        if ((a[0] == 'n' || a[0] == 'N') &&
            (a[1] == 'x' || a[1] == 'X') && a[2] == '\0' &&
            !(flags & OBJ_SET_XX))
        {
            flags |= OBJ_SET_NX;
        } else if ((a[0] == 'x' || a[0] == 'X') &&
                   (a[1] == 'x' || a[1] == 'X') && a[2] == '\0' &&
                   !(flags & OBJ_SET_NX))
        {
            flags |= OBJ_SET_XX;
        } else if ((a[0] == 'e' || a[0] == 'E') &&
                   (a[1] == 'x' || a[1] == 'X') && a[2] == '\0' &&
                   !(flags & OBJ_SET_PX) && next)
        {
            flags |= OBJ_SET_EX;
            unit = UNIT_SECONDS;
            expire = next;
            j++;
        } else if ((a[0] == 'p' || a[0] == 'P') &&
                   (a[1] == 'x' || a[1] == 'X') && a[2] == '\0' &&
                   !(flags & OBJ_SET_EX) && next)
        {
            flags |= OBJ_SET_PX;
            unit = UNIT_MILLISECONDS;
            expire = next;
            j++;
        } else {
            addReply(c,shared.syntaxerr);
            return;
        }
    }

    //尝试进行编码
    c->argv[2] = tryObjectEncoding(c->argv[2]);
    setGenericCommand(c,flags,c->argv[1],c->argv[2],expire,unit,NULL,NULL);
}

//setnx命令
void setnxCommand(client *c) {
    c->argv[2] = tryObjectEncoding(c->argv[2]);
    setGenericCommand(c,OBJ_SET_NX,c->argv[1],c->argv[2],NULL,0,shared.cone,shared.czero);
}

//set ex命令
void setexCommand(client *c) {
    c->argv[3] = tryObjectEncoding(c->argv[3]);
    setGenericCommand(c,OBJ_SET_NO_FLAGS,c->argv[1],c->argv[3],c->argv[2],UNIT_SECONDS,NULL,NULL);
}

//set px命令  psetex命令
void psetexCommand(client *c) {
    c->argv[3] = tryObjectEncoding(c->argv[3]);
    setGenericCommand(c,OBJ_SET_NO_FLAGS,c->argv[1],c->argv[3],c->argv[2],UNIT_MILLISECONDS,NULL,NULL);
}

setKey的实现如下：

/* High level Set operation. This function can be used in order to set
 * a key, whatever it was existing or not, to a new object.
 *
 * 1) The ref count of the value object is incremented.
 * 2) clients WATCHing for the destination key notified.
 * 3) The expire time of the key is reset (the key is made persistent).
 *
 * All the new keys in the database should be created via this interface. */
void setKey(redisDb *db, robj *key, robj *val) {
    //查找key
    if (lookupKeyWrite(db,key) == NULL) {
        //没有，就直接添加
        dbAdd(db,key,val);
    } else {
        //存在的话，就覆盖
        dbOverwrite(db,key,val);
    }
    //引用数+1
    incrRefCount(val);
    //移除expire dict
    removeExpire(db,key);
    signalModifiedKey(db,key);
}

dbAdd的实现如下：

/* Add the key to the DB. It's up to the caller to increment the reference
 * counter of the value if needed.
 *
 * The program is aborted if the key already exists. */
void dbAdd(redisDb *db, robj *key, robj *val) {
    //创建对象
    sds copy = sdsdup(key->ptr);
    //add 到 db的dict里
    int retval = dictAdd(db->dict, copy, val);

    serverAssertWithInfo(NULL,key,retval == DICT_OK);

    //list\zset类型存储
    if (val->type == OBJ_LIST ||
        val->type == OBJ_ZSET)
        signalKeyAsReady(db, key);
    //集群找slot及存储
    if (server.cluster_enabled) slotToKeyAdd(key);
}

dbOverwrite的实现如下：

/* Overwrite an existing key with a new value. Incrementing the reference
 * count of the new value is up to the caller.
 * This function does not modify the expire time of the existing key.
 *
 * The program is aborted if the key was not already present. */
void dbOverwrite(redisDb *db, robj *key, robj *val) {
    //在db的dict中查找key
    dictEntry *de = dictFind(db->dict,key->ptr);

    serverAssertWithInfo(NULL,key,de != NULL);
    dictEntry auxentry = *de;
    //获取value
    robj *old = dictGetVal(de);
    //lru
    if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
        val->lru = old->lru;
    }
    //设置新值
    dictSetVal(db->dict, de, val);
    
    //异步回收老对象,逻辑删除
    if (server.lazyfree_lazy_server_del) {
        freeObjAsync(old);
        dictSetVal(db->dict, &auxentry, NULL);
    }
    //调用析构函数
    dictFreeVal(db->dict, &auxentry);
}

2. get类型命令的实现

int getGenericCommand(client *c) {
    robj *o;
    //在dict中查找key
    if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.nullbulk)) == NULL)
        return C_OK;

    if (o->type != OBJ_STRING) {
        addReply(c,shared.wrongtypeerr);
        return C_ERR;
    } else {
        addReplyBulk(c,o);
        return C_OK;
    }
}

//get命令
void getCommand(client *c) {
    getGenericCommand(c);
}

//getset命令
void getsetCommand(client *c) {
    //get
    if (getGenericCommand(c) == C_ERR) return;
    //set
    c->argv[2] = tryObjectEncoding(c->argv[2]);
    setKey(c->db,c->argv[1],c->argv[2]);
    notifyKeyspaceEvent(NOTIFY_STRING,"set",c->argv[1],c->db->id);
    server.dirty++;
}

3. 字符串覆盖

//setrange命令
void setrangeCommand(client *c) {
    robj *o;
    long offset;
    sds value = c->argv[3]->ptr;

    if (getLongFromObjectOrReply(c,c->argv[2],&offset,NULL) != C_OK)
        return;

    if (offset < 0) {
        addReplyError(c,"offset is out of range");
        return;
    }

    //查找key
    o = lookupKeyWrite(c->db,c->argv[1]);
    if (o == NULL) {
        /* Return 0 when setting nothing on a non-existing string */
        if (sdslen(value) == 0) {
            addReply(c,shared.czero);
            return;
        }

        //检查是否超过512MB
        if (checkStringLength(c,offset+sdslen(value)) != C_OK)
            return;

        o = createObject(OBJ_STRING,sdsnewlen(NULL, offset+sdslen(value)));
        //新增key
        dbAdd(c->db,c->argv[1],o);
    } else {
        size_t olen;

        /* Key exists, check type */
        if (checkType(c,o,OBJ_STRING))
            return;

        /* Return existing string length when setting nothing */
        olen = stringObjectLen(o);
        if (sdslen(value) == 0) {
            addReplyLongLong(c,olen);
            return;
        }

        /* Return when the resulting string exceeds allowed size */
        if (checkStringLength(c,offset+sdslen(value)) != C_OK)
            return;

        /* Create a copy when the object is shared or encoded. */
        o = dbUnshareStringValue(c->db,c->argv[1],o);
    }

    if (sdslen(value) > 0) {
        //填充\x00
        o->ptr = sdsgrowzero(o->ptr,offset+sdslen(value));
        //赋值
        memcpy((char*)o->ptr+offset,value,sdslen(value));
        signalModifiedKey(c->db,c->argv[1]);
        notifyKeyspaceEvent(NOTIFY_STRING,
            "setrange",c->argv[1],c->db->id);
        server.dirty++;
    }
    addReplyLongLong(c,sdslen(o->ptr));
}

//getrange命令
void getrangeCommand(client *c) {
    robj *o;
    long long start, end;
    char *str, llbuf[32];
    size_t strlen;

    //start
    if (getLongLongFromObjectOrReply(c,c->argv[2],&start,NULL) != C_OK)
        return;
    //end
    if (getLongLongFromObjectOrReply(c,c->argv[3],&end,NULL) != C_OK)
        return;
    //key
    if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.emptybulk)) == NULL ||
        checkType(c,o,OBJ_STRING)) return;

    //类型转换
    if (o->encoding == OBJ_ENCODING_INT) {
        str = llbuf;
        strlen = ll2string(llbuf,sizeof(llbuf),(long)o->ptr);
    } else {
        str = o->ptr;
        strlen = sdslen(str);
    }

    //起止索引校验
    if (start < 0 && end < 0 && start > end) {
        addReply(c,shared.emptybulk);
        return;
    }
    if (start < 0) start = strlen+start;
    if (end < 0) end = strlen+end;
    if (start < 0) start = 0;
    if (end < 0) end = 0;
    if ((unsigned long long)end >= strlen) end = strlen-1;

    /* Precondition: end >= 0 && end < strlen, so the only condition where
     * nothing can be returned is: start > end. */
    if (start > end || strlen == 0) {
        addReply(c,shared.emptybulk);
    } else {
        addReplyBulkCBuffer(c,(char*)str+start,end-start+1);
    }
}

4. 多个key的操作

//mget命令
void mgetCommand(client *c) {
    int j;

    addReplyMultiBulkLen(c,c->argc-1);
    //for循环获取所有输入的key
    for (j = 1; j < c->argc; j++) {
        //查找dict上的key
        robj *o = lookupKeyRead(c->db,c->argv[j]);
        if (o == NULL) {
            addReply(c,shared.nullbulk);
        } else {
            if (o->type != OBJ_STRING) {
                addReply(c,shared.nullbulk);
            } else {
                addReplyBulk(c,o);
            }
        }
    }
}

//mset命令、msetnx命令
void msetGenericCommand(client *c, int nx) {
    int j;

    if ((c->argc % 2) == 0) {
        addReplyError(c,"wrong number of arguments for MSET");
        return;
    }

    /* Handle the NX flag. The MSETNX semantic is to return zero and don't
     * set anything if at least one key alerady exists. */
    if (nx) {
        for (j = 1; j < c->argc; j += 2) {
            if (lookupKeyWrite(c->db,c->argv[j]) != NULL) {
                addReply(c, shared.czero);
                return;
            }
        }
    }

    for (j = 1; j < c->argc; j += 2) {
        c->argv[j+1] = tryObjectEncoding(c->argv[j+1]);
        setKey(c->db,c->argv[j],c->argv[j+1]);
        notifyKeyspaceEvent(NOTIFY_STRING,"set",c->argv[j],c->db->id);
    }
    server.dirty += (c->argc-1)/2;
    addReply(c, nx ? shared.cone : shared.ok);
}

void msetCommand(client *c) {
    msetGenericCommand(c,0);
}

void msetnxCommand(client *c) {
    msetGenericCommand(c,1);
}

5. 增加减少key的值

//incr命令、decr命令、incrby命令、decrby命令
void incrDecrCommand(client *c, long long incr) {
    long long value, oldvalue;
    robj *o, *new;

    //查找key
    o = lookupKeyWrite(c->db,c->argv[1]);
    if (o != NULL && checkType(c,o,OBJ_STRING)) return;
    if (getLongLongFromObjectOrReply(c,o,&value,NULL) != C_OK) return;

    oldvalue = value;

    //校验域
    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;
    }
    value += incr;

    if (o && o->refcount == 1 && o->encoding == OBJ_ENCODING_INT &&
        (value < 0 || value >= OBJ_SHARED_INTEGERS) &&
        value >= LONG_MIN && value <= LONG_MAX)
    {
        new = o;
        o->ptr = (void*)((long)value);
    } else {
        new = createStringObjectFromLongLongForValue(value);
        if (o) {
            //覆盖原值
            dbOverwrite(c->db,c->argv[1],new);
        } else {
            //新建
            dbAdd(c->db,c->argv[1],new);
        }
    }
    signalModifiedKey(c->db,c->argv[1]);
    notifyKeyspaceEvent(NOTIFY_STRING,"incrby",c->argv[1],c->db->id);
    server.dirty++;
    addReply(c,shared.colon);
    addReply(c,new);
    addReply(c,shared.crlf);
}

void incrCommand(client *c) {
    incrDecrCommand(c,1);
}

void decrCommand(client *c) {
    incrDecrCommand(c,-1);
}

void incrbyCommand(client *c) {
    long long incr;

    if (getLongLongFromObjectOrReply(c, c->argv[2], &incr, NULL) != C_OK) return;
    incrDecrCommand(c,incr);
}

void decrbyCommand(client *c) {
    long long incr;

    if (getLongLongFromObjectOrReply(c, c->argv[2], &incr, NULL) != C_OK) return;
    incrDecrCommand(c,-incr);
}

void incrbyfloatCommand(client *c) {
    long double incr, value;
    robj *o, *new, *aux;

    o = lookupKeyWrite(c->db,c->argv[1]);
    if (o != NULL && checkType(c,o,OBJ_STRING)) return;
    if (getLongDoubleFromObjectOrReply(c,o,&value,NULL) != C_OK ||
        getLongDoubleFromObjectOrReply(c,c->argv[2],&incr,NULL) != C_OK)
        return;

    value += incr;
    if (isnan(value) || isinf(value)) {
        addReplyError(c,"increment would produce NaN or Infinity");
        return;
    }
    new = createStringObjectFromLongDouble(value,1);
    if (o)
        dbOverwrite(c->db,c->argv[1],new);
    else
        dbAdd(c->db,c->argv[1],new);
    signalModifiedKey(c->db,c->argv[1]);
    notifyKeyspaceEvent(NOTIFY_STRING,"incrbyfloat",c->argv[1],c->db->id);
    server.dirty++;
    addReplyBulk(c,new);

    /* Always replicate INCRBYFLOAT as a SET command with the final value
     * in order to make sure that differences in float precision or formatting
     * will not create differences in replicas or after an AOF restart. */
    aux = createStringObject("SET",3);
    rewriteClientCommandArgument(c,0,aux);
    decrRefCount(aux);
    rewriteClientCommandArgument(c,2,new);
}

6. 追加

//append命令
void appendCommand(client *c) {
    size_t totlen;
    robj *o, *append;

    //查找key
    o = lookupKeyWrite(c->db,c->argv[1]);
    //不存在
    if (o == NULL) {
        //创建新key
        c->argv[2] = tryObjectEncoding(c->argv[2]);
        //dict存储
        dbAdd(c->db,c->argv[1],c->argv[2]);
        //引用次数+1
        incrRefCount(c->argv[2]);
        totlen = stringObjectLen(c->argv[2]);
    } else {
        /* Key exists, check type */
        if (checkType(c,o,OBJ_STRING))
            return;

        /* "append" is an argument, so always an sds */
        append = c->argv[2];
        //append后的长度
        totlen = stringObjectLen(o)+sdslen(append->ptr);
        if (checkStringLength(c,totlen) != C_OK)
            return;

        /* Append the value */
        o = dbUnshareStringValue(c->db,c->argv[1],o);
        //合并及赋值
        o->ptr = sdscatlen(o->ptr,append->ptr,sdslen(append->ptr));
        totlen = sdslen(o->ptr);
    }
    signalModifiedKey(c->db,c->argv[1]);
    notifyKeyspaceEvent(NOTIFY_STRING,"append",c->argv[1],c->db->id);
    server.dirty++;
    addReplyLongLong(c,totlen);
}

7. 字符串长度

//strlen命令
void strlenCommand(client *c) {
    robj *o;
    if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.czero)) == NULL ||
        checkType(c,o,OBJ_STRING)) return;
    //计算长度并返回
    addReplyLongLong(c,stringObjectLen(o));
}