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 ] [PX ] */
//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));
}