在redis.c的代码里 redisCommandTable ,找到set对应的setComnmand 对应的function
底下为函数的预览
所有函数里的新增的变量都是使用redisObject类
/* SET key value [NX] [XX] [EX <seconds>] [PX <milliseconds>] */
void setCommand(redisClient *c) {
int j;
robj *expire = NULL;
int unit = UNIT_SECONDS;
int flags = REDIS_SET_NO_FLAGS;
// 设置选项参数 是否val后面携带了参数啥的
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 |= REDIS_SET_NX;
} else if ((a[0] == 'x' || a[0] == 'X') &&
(a[1] == 'x' || a[1] == 'X') && a[2] == '\0') {
flags |= REDIS_SET_XX;
} else if ((a[0] == 'e' || a[0] == 'E') &&
(a[1] == 'x' || a[1] == 'X') && a[2] == '\0' && next) {
unit = UNIT_SECONDS;
expire = next;
j++;
} else if ((a[0] == 'p' || a[0] == 'P') &&
(a[1] == 'x' || a[1] == 'X') && a[2] == '\0' && next) {
unit = UNIT_MILLISECONDS;
expire = next;
j++;
} else {
addReply(c,shared.syntaxerr);
return;
}
}
// 尝试对值对象进行编码 => 使用更节省内存的数据格式 将raw改为embstr
c->argv[2] = tryObjectEncoding(c->argv[2]);// 函数说明在下
setGenericCommand(c,flags,c->argv[1],c->argv[2],expire,unit,NULL,NULL);
}
shared 为结构体吗，在redis.h里的
需要复习下c语言的共享对象
// 通过复用来减少内存碎片，以及减少操作耗时的共享对象
struct sharedObjectsStruct {
robj *crlf, *ok, *err, *emptybulk, *czero, *cone, *cnegone, *pong, *space,
*colon, *nullbulk, *nullmultibulk, *queued,
*emptymultibulk, *wrongtypeerr, *nokeyerr, *syntaxerr, *sameobjecterr,
*outofrangeerr, *noscripterr, *loadingerr, *slowscripterr, *bgsaveerr,
*masterdownerr, *roslaveerr, *execaborterr, *noautherr, *noreplicaserr,
*busykeyerr, *oomerr, *plus, *messagebulk, *pmessagebulk, *subscribebulk,
*unsubscribebulk, *psubscribebulk, *punsubscribebulk, *del, *rpop, *lpop,
*lpush, *emptyscan, *minstring, *maxstring,
*select[REDIS_SHARED_SELECT_CMDS],
*integers[REDIS_SHARED_INTEGERS],
*mbulkhdr[REDIS_SHARED_BULKHDR_LEN], /* "*<value>\r\n" */
*bulkhdr[REDIS_SHARED_BULKHDR_LEN]; /* "$<value>\r\n" */
};
/* Try to encode a string object in order to save space */
// 尝试对字符串对象进行编码，以节约内存。
robj *tryObjectEncoding(robj *o) {
long value;
sds s = o->ptr;
size_t len;
/* Make sure this is a string object, the only type we encode
* in this function. Other types use encoded memory efficient
* representations but are handled by the commands implementing
* the type. */
redisAssertWithInfo(NULL,o,o->type == REDIS_STRING);
/* We try some specialized encoding only for objects that are
* RAW or EMBSTR encoded, in other words objects that are still
* in represented by an actually array of chars. */
// 只在字符串的编码为 RAW 或者 EMBSTR 时尝试进行编码
if (!sdsEncodedObject(o)) return o;
/* It's not safe to encode shared objects: shared objects can be shared
* everywhere in the "object space" of Redis and may end in places where
* they are not handled. We handle them only as values in the keyspace. */
// 不对共享对象进行编码
if (o->refcount > 1) return o;
/* Check if we can represent this string as a long integer.
* Note that we are sure that a string larger than 21 chars is not
* representable as a 32 nor 64 bit integer. */
// 对字符串进行检查
// 只对长度小于或等于 21 字节，并且可以被解释为整数的字符串进行编码
len = sdslen(s);
if (len <= 21 && string2l(s,len,&value)) {
/* This object is encodable as a long. Try to use a shared object.
* Note that we avoid using shared integers when maxmemory is used
* because every object needs to have a private LRU field for the LRU
* algorithm to work well. */
if (server.maxmemory == 0 &&
value >= 0 &&
value < REDIS_SHARED_INTEGERS)
{
decrRefCount(o);
incrRefCount(shared.integers[value]);
return shared.integers[value];
} else {
if (o->encoding == REDIS_ENCODING_RAW) sdsfree(o->ptr);
o->encoding = REDIS_ENCODING_INT;
o->ptr = (void*) value;
return o;
}
}
/* If the string is small and is still RAW encoded,
* try the EMBSTR encoding which is more efficient.
* In this representation the object and the SDS string are allocated
* in the same chunk of memory to save space and cache misses. */
// 尝试将 RAW 编码的字符串编码为 EMBSTR 编码
if (len <= REDIS_ENCODING_EMBSTR_SIZE_LIMIT) {
robj *emb;
if (o->encoding == REDIS_ENCODING_EMBSTR) return o;
emb = createEmbeddedStringObject(s,sdslen(s));
decrRefCount(o);
return emb;
}
/* 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 only for relatively large strings as this branch
* is only entered if the length of the string is greater than
* REDIS_ENCODING_EMBSTR_SIZE_LIMIT. */
// 这个对象没办法进行编码，尝试从 SDS 中移除所有空余空间
if (o->encoding == REDIS_ENCODING_RAW &&
sdsavail(s) > len/10)
{
o->ptr = sdsRemoveFreeSpace(o->ptr);
}
/* Return the original object. */
return o;
}上方代码，在尝试将raw编码的字符串修改为embstr的时候。会先判断是不是embstr，然后再重新生成一个新的emb。将旧的o 调用decrRefCount 进行销毁。之后返回emb
最后如果无法编码。freee的空间会被释放
关于上方的 raw转为embstr，尽量使用使用embstr的原因
之后走的 是 setGenericCommand 这个方法
个人理解的 flag刚好比是标该命令有没有携带过期时间 等 函数实现了 SET 、 SETEX 、 PSETEX 和 SETNX 命令
void setGenericCommand(redisClient *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 */
if (expire) {
if (getLongLongFromObjectOrReply(c, expire, &milliseconds, NULL) != REDIS_OK)
return;
if (milliseconds <= 0) {
addReplyErrorFormat(c,"invalid expire time in %s",c->cmd->name);
return;
}
if (unit == UNIT_SECONDS) milliseconds *= 1000;
}
if ((flags & REDIS_SET_NX && lookupKeyWrite(c->db,key) != NULL) ||
(flags & REDIS_SET_XX && lookupKeyWrite(c->db,key) == NULL))
{
addReply(c, abort_reply ? abort_reply : shared.nullbulk);
return;
}
setKey(c->db,key,val);
server.dirty++; // 记录更新到次数，在redisServer结构体，用于rdb更新
if (expire) setExpire(c->db,key,mstime()+milliseconds);
notifyKeyspaceEvent(REDIS_NOTIFY_STRING,"set",key,c->db->id);
if (expire) notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,
"expire",key,c->db->id);
addReply(c, ok_reply ? ok_reply : shared.ok);
}
关于setKey函数的用法
/* 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). */
void setKey(redisDb *db, robj *key, robj *val) {
if (lookupKeyWrite(db,key) == NULL) {
dbAdd(db,key,val);
} else {
dbOverwrite(db,key,val);
}
incrRefCount(val);
removeExpire(db,key);
signalModifiedKey(db,key);
}