t_set.c
Redis的t_set.c是个set数据结构的实现。
当元素都是Integer类型的时候，采用intset来实现。
当元素有非Integer类型的时候，采用dict来实现。
当 intset 插入非整型元素的时候，需要将类型转换为 dict。
操作集合的时候，一旦集合为空，需要清除。
类型转换代码如下：
/* Convert the set to specified encoding. The resulting dict (when converting
* to a hash table) is presized to hold the number of elements in the original
* set. */
//类型转换，将intset中的元素都添加到dict中
void setTypeConvert(robj *setobj, int enc) {
setTypeIterator *si;
serverAssertWithInfo(NULL,setobj,setobj->type == OBJ_SET &&
setobj->encoding == OBJ_ENCODING_INTSET);
if (enc == OBJ_ENCODING_HT) {
int64_t intele;
dict *d = dictCreate(&setDictType,NULL);
sds element;
/* Presize the dict to avoid rehashing */
//提前分配intsetLen大小的空间，避免rehash
dictExpand(d,intsetLen(setobj->ptr));
/* To add the elements we extract integers and create redis objects */
si = setTypeInitIterator(setobj);
//遍历
while (setTypeNext(si,&element,&intele) != -1) {
element = sdsfromlonglong(intele);
serverAssert(dictAdd(d,element,NULL) == DICT_OK);
}
setTypeReleaseIterator(si);
setobj->encoding = OBJ_ENCODING_HT;
zfree(setobj->ptr);
setobj->ptr = d;
} else {
serverPanic("Unsupported set conversion");
}
}
1. 新增元素
//sadd命令 sadd key member [member...]
void saddCommand(client *c) {
robj *set;
int j, added = 0;
//在dict查找key
set = lookupKeyWrite(c->db,c->argv[1]);
if (set == NULL) {
//查找不到，则创建set
set = setTypeCreate(c->argv[2]->ptr);
//将set加入到dict
dbAdd(c->db,c->argv[1],set);
} else {
//类型不正确，报错
if (set->type != OBJ_SET) {
addReply(c,shared.wrongtypeerr);
return;
}
}
//添加元素
for (j = 2; j < c->argc; j++) {
if (setTypeAdd(set,c->argv[j]->ptr)) added++;
}
if (added) {
signalModifiedKey(c->db,c->argv[1]);
notifyKeyspaceEvent(NOTIFY_SET,"sadd",c->argv[1],c->db->id);
}
server.dirty += added;
addReplyLongLong(c,added);
}
/* Add the specified value into a set.
*
* If the value was already member of the set, nothing is done and 0 is
* returned, otherwise the new element is added and 1 is returned. */
//添加元素
int setTypeAdd(robj *subject, sds value) {
long long llval;
//如果编码是dict
if (subject->encoding == OBJ_ENCODING_HT) {
dict *ht = subject->ptr;
dictEntry *de = dictAddRaw(ht,value,NULL);
if (de) {
dictSetKey(ht,de,sdsdup(value));
dictSetVal(ht,de,NULL);
return 1;
}
}
//如果编码是intset
else if (subject->encoding == OBJ_ENCODING_INTSET) {
//如果插入的值是整型，则直接插入
if (isSdsRepresentableAsLongLong(value,&llval) == C_OK) {
uint8_t success = 0;
//会进行二分查找，实现去重
subject->ptr = intsetAdd(subject->ptr,llval,&success);
if (success) {
/* Convert to regular set when the intset contains
* too many entries. */
if (intsetLen(subject->ptr) > server.set_max_intset_entries)
setTypeConvert(subject,OBJ_ENCODING_HT);
return 1;
}
}
//如果插入的值不是整型，则需要进行类型转换，将intset转为dict
else {
/* Failed to get integer from object, convert to regular set. */
setTypeConvert(subject,OBJ_ENCODING_HT);
/* The set *was* an intset and this value is not integer
* encodable, so dictAdd should always work. */
serverAssert(dictAdd(subject->ptr,sdsdup(value),NULL) == DICT_OK);
return 1;
}
} else {
serverPanic("Unknown set encoding");
}
return 0;
}
2. 删除元素
//srem命令 srem key member [member...]
void sremCommand(client *c) {
robj *set;
int j, deleted = 0, keyremoved = 0;
//根据key查找set
if ((set = lookupKeyWriteOrReply(c,c->argv[1],shared.czero)) == NULL ||
checkType(c,set,OBJ_SET)) return;
//删除member
for (j = 2; j < c->argc; j++) {
if (setTypeRemove(set,c->argv[j]->ptr)) {
deleted++;
if (setTypeSize(set) == 0) {
dbDelete(c->db,c->argv[1]);
keyremoved = 1;
break;
}
}
}
if (deleted) {
signalModifiedKey(c->db,c->argv[1]);
notifyKeyspaceEvent(NOTIFY_SET,"srem",c->argv[1],c->db->id);
//集合为空，需要移除key
if (keyremoved)
notifyKeyspaceEvent(NOTIFY_GENERIC,"del",c->argv[1],
c->db->id);
server.dirty += deleted;
}
addReplyLongLong(c,deleted);
}
//移除元素
int setTypeRemove(robj *setobj, sds value) {
long long llval;
//dict类型
if (setobj->encoding == OBJ_ENCODING_HT) {
if (dictDelete(setobj->ptr,value) == DICT_OK) {
if (htNeedsResize(setobj->ptr)) dictResize(setobj->ptr);
return 1;
}
}
//intset类型
else if (setobj->encoding == OBJ_ENCODING_INTSET) {
if (isSdsRepresentableAsLongLong(value,&llval) == C_OK) {
int success;
setobj->ptr = intsetRemove(setobj->ptr,llval,&success);
if (success) return 1;
}
} else {
serverPanic("Unknown set encoding");
}
return 0;
}
//spop命令
void spopCommand(client *c) {
robj *set, *ele, *aux;
sds sdsele;
int64_t llele;
int encoding;
//带有count的
if (c->argc == 3) {
spopWithCountCommand(c);
return;
} else if (c->argc > 3) {
addReply(c,shared.syntaxerr);
return;
}
/* Make sure a key with the name inputted exists, and that it's type is
* indeed a set */
if ((set = lookupKeyWriteOrReply(c,c->argv[1],shared.nullbulk)) == NULL ||
checkType(c,set,OBJ_SET)) return;
/* Get a random element from the set */
encoding = setTypeRandomElement(set,&sdsele,&llele);
/* Remove the element from the set */
//intset
if (encoding == OBJ_ENCODING_INTSET) {
ele = createStringObjectFromLongLong(llele);
set->ptr = intsetRemove(set->ptr,llele,NULL);
}
//dict
else {
ele = createStringObject(sdsele,sdslen(sdsele));
setTypeRemove(set,ele->ptr);
}
notifyKeyspaceEvent(NOTIFY_SET,"spop",c->argv[1],c->db->id);
/* Replicate/AOF this command as an SREM operation */
aux = createStringObject("SREM",4);
rewriteClientCommandVector(c,3,aux,c->argv[1],ele);
decrRefCount(aux);
/* Add the element to the reply */
addReplyBulk(c,ele);
decrRefCount(ele);
/* Delete the set if it's empty */
if (setTypeSize(set) == 0) {
dbDelete(c->db,c->argv[1]);
notifyKeyspaceEvent(NOTIFY_GENERIC,"del",c->argv[1],c->db->id);
}
/* Set has been modified */
signalModifiedKey(c->db,c->argv[1]);
server.dirty++;
}
//spop命令 spop key [count] 移除count个元素
void spopWithCountCommand(client *c) {
long l;
unsigned long count, size;
robj *set;
/* Get the count argument */
if (getLongFromObjectOrReply(c,c->argv[2],&l,NULL) != C_OK) return;
if (l >= 0) {
count = (unsigned long) l;
} else {
addReply(c,shared.outofrangeerr);
return;
}
/* Make sure a key with the name inputted exists, and that it's type is
* indeed a set. Otherwise, return nil */
if ((set = lookupKeyReadOrReply(c,c->argv[1],shared.emptymultibulk))
== NULL || checkType(c,set,OBJ_SET)) return;
/* If count is zero, serve an empty multibulk ASAP to avoid special
* cases later. */
if (count == 0) {
addReply(c,shared.emptymultibulk);
return;
}
size = setTypeSize(set);
/* Generate an SPOP keyspace notification */
notifyKeyspaceEvent(NOTIFY_SET,"spop",c->argv[1],c->db->id);
server.dirty += count;
/* CASE 1:
* The number of requested elements is greater than or equal to
* the number of elements inside the set: simply return the whole set. */
//将要移除的个数和集合大小对比
//如果移除个数大于等于集合大小，则直接移除key
if (count >= size) {
/* We just return the entire set */
sunionDiffGenericCommand(c,c->argv+1,1,NULL,SET_OP_UNION);
/* Delete the set as it is now empty */
dbDelete(c->db,c->argv[1]);
notifyKeyspaceEvent(NOTIFY_GENERIC,"del",c->argv[1],c->db->id);
/* Propagate this command as an DEL operation */
rewriteClientCommandVector(c,2,shared.del,c->argv[1]);
signalModifiedKey(c->db,c->argv[1]);
server.dirty++;
return;
}
/* Case 2 and 3 require to replicate SPOP as a set of SREM commands.
* Prepare our replication argument vector. Also send the array length
* which is common to both the code paths. */
robj *propargv[3];
propargv[0] = createStringObject("SREM",4);
propargv[1] = c->argv[1];
addReplyMultiBulkLen(c,count);
/* Common iteration vars. */
sds sdsele;
robj *objele;
int encoding;
int64_t llele;
unsigned long remaining = size-count; /* Elements left after SPOP. */
/* If we are here, the number of requested elements is less than the
* number of elements inside the set. Also we are sure that count < size.
* Use two different strategies.
*
* CASE 2: The number of elements to return is small compared to the
* set size. We can just extract random elements and return them to
* the set. */
//如果要移除的元素较少，则直接操作原集合
if (remaining*SPOP_MOVE_STRATEGY_MUL > count) {
while(count--) {
/* Emit and remove. */
encoding = setTypeRandomElement(set,&sdsele,&llele);
if (encoding == OBJ_ENCODING_INTSET) {
addReplyBulkLongLong(c,llele);
objele = createStringObjectFromLongLong(llele);
set->ptr = intsetRemove(set->ptr,llele,NULL);
} else {
addReplyBulkCBuffer(c,sdsele,sdslen(sdsele));
objele = createStringObject(sdsele,sdslen(sdsele));
setTypeRemove(set,sdsele);
}
/* Replicate/AOF this command as an SREM operation */
propargv[2] = objele;
alsoPropagate(server.sremCommand,c->db->id,propargv,3,
PROPAGATE_AOF|PROPAGATE_REPL);
decrRefCount(objele);
}
}
//若要移除的元素较多，接近于原集合，则取出不被移除的部分，建立一个新集合，再释放原来的集合
else {
/* CASE 3: The number of elements to return is very big, approaching
* the size of the set itself. After some time extracting random elements
* from such a set becomes computationally expensive, so we use
* a different strategy, we extract random elements that we don't
* want to return (the elements that will remain part of the set),
* creating a new set as we do this (that will be stored as the original
* set). Then we return the elements left in the original set and
* release it. */
robj *newset = NULL;
/* Create a new set with just the remaining elements. */
while(remaining--) {
encoding = setTypeRandomElement(set,&sdsele,&llele);
if (encoding == OBJ_ENCODING_INTSET) {
sdsele = sdsfromlonglong(llele);
} else {
sdsele = sdsdup(sdsele);
}
if (!newset) newset = setTypeCreate(sdsele);
setTypeAdd(newset,sdsele);
setTypeRemove(set,sdsele);
sdsfree(sdsele);
}
/* Transfer the old set to the client. */
setTypeIterator *si;
si = setTypeInitIterator(set);
while((encoding = setTypeNext(si,&sdsele,&llele)) != -1) {
if (encoding == OBJ_ENCODING_INTSET) {
addReplyBulkLongLong(c,llele);
objele = createStringObjectFromLongLong(llele);
} else {
addReplyBulkCBuffer(c,sdsele,sdslen(sdsele));
objele = createStringObject(sdsele,sdslen(sdsele));
}
/* Replicate/AOF this command as an SREM operation */
propargv[2] = objele;
alsoPropagate(server.sremCommand,c->db->id,propargv,3,
PROPAGATE_AOF|PROPAGATE_REPL);
decrRefCount(objele);
}
setTypeReleaseIterator(si);
/* Assign the new set as the key value. */
dbOverwrite(c->db,c->argv[1],newset);
}
/* Don't propagate the command itself even if we incremented the
* dirty counter. We don't want to propagate an SPOP command since
* we propagated the command as a set of SREMs operations using
* the alsoPropagate() API. */
decrRefCount(propargv[0]);
preventCommandPropagation(c);
signalModifiedKey(c->db,c->argv[1]);
server.dirty++;
}
根据要移除的元素个数和集合的大小考量。
要移除的元素个数较多，则取出不移除的部分，再直接移除原集合。
要移除的元素个数较少，则直接操作原集合。
3. 集合操作（交、并、差）
//sinter命令 sinter key [key...]
void sinterCommand(client *c) {
sinterGenericCommand(c,c->argv+1,c->argc-1,NULL);
}
//sinterstore命令 sinterstore destination key [key...]
//取完交集并存入一个新集合c->argv[1]中
void sinterstoreCommand(client *c) {
sinterGenericCommand(c,c->argv+2,c->argc-2,c->argv[1]);
}
//取交集通用实现
void sinterGenericCommand(client *c, robj **setkeys,
unsigned long setnum, robj *dstkey) {
robj **sets = zmalloc(sizeof(robj*)*setnum);
setTypeIterator *si;
robj *dstset = NULL;
sds elesds;
int64_t intobj;
void *replylen = NULL;
unsigned long j, cardinality = 0;
int encoding;
//setnum 集合的个数
//dstkey 交集存入的新集合
for (j = 0; j < setnum; j++) {
robj *setobj = dstkey ?
lookupKeyWrite(c->db,setkeys[j]) :
lookupKeyRead(c->db,setkeys[j]);
//如果参与做交集操作的集合不存在
if (!setobj) {
zfree(sets);
//如果交集存入的新集合存在
if (dstkey) {
//删除掉
if (dbDelete(c->db,dstkey)) {
signalModifiedKey(c->db,dstkey);
server.dirty++;
}
addReply(c,shared.czero);
} else {
addReply(c,shared.emptymultibulk);
}
return;
}
if (checkType(c,setobj,OBJ_SET)) {
zfree(sets);
return;
}
sets[j] = setobj;
}
/* Sort sets from the smallest to largest, this will improve our
* algorithm's performance */
qsort(sets,setnum,sizeof(robj*),qsortCompareSetsByCardinality);
/* The first thing we should output is the total number of elements...
* since this is a multi-bulk write, but at this stage we don't know
* the intersection set size, so we use a trick, append an empty object
* to the output list and save the pointer to later modify it with the
* right length */
if (!dstkey) {
replylen = addDeferredMultiBulkLength(c);
} else {
/* If we have a target key where to store the resulting set
* create this key with an empty set inside */
dstset = createIntsetObject();
}
/* Iterate all the elements of the first (smallest) set, and test
* the element against all the other sets, if at least one set does
* not include the element it is discarded */
si = setTypeInitIterator(sets[0]);
//遍历第一个集合set
while((encoding = setTypeNext(si,&elesds,&intobj)) != -1) {
//和其它集合取交集，通过查找其它集合中是否都存在当前元素
for (j = 1; j < setnum; j++) {
if (sets[j] == sets[0]) continue;
//intset
if (encoding == OBJ_ENCODING_INTSET) {
/* intset with intset is simple... and fast */
//都是intset
if (sets[j]->encoding == OBJ_ENCODING_INTSET &&
!intsetFind((intset*)sets[j]->ptr,intobj))
{
break;
/* in order to compare an integer with an object we
* have to use the generic function, creating an object
* for this */
}
//有的是dict
else if (sets[j]->encoding == OBJ_ENCODING_HT) {
elesds = sdsfromlonglong(intobj);
if (!setTypeIsMember(sets[j],elesds)) {
sdsfree(elesds);
break;
}
sdsfree(elesds);
}
}
//dict
else if (encoding == OBJ_ENCODING_HT) {
if (!setTypeIsMember(sets[j],elesds)) {
break;
}
}
}
/* Only take action when all sets contain the member */
if (j == setnum) {
if (!dstkey) {
if (encoding == OBJ_ENCODING_HT)
addReplyBulkCBuffer(c,elesds,sdslen(elesds));
else
addReplyBulkLongLong(c,intobj);
cardinality++;
} else {
if (encoding == OBJ_ENCODING_INTSET) {
elesds = sdsfromlonglong(intobj);
setTypeAdd(dstset,elesds);
sdsfree(elesds);
} else {
setTypeAdd(dstset,elesds);
}
}
}
}
setTypeReleaseIterator(si);
//如果需要将交集结果存入一个新集合，且非空
if (dstkey) {
/* Store the resulting set into the target, if the intersection
* is not an empty set. */
int deleted = dbDelete(c->db,dstkey);
if (setTypeSize(dstset) > 0) {
dbAdd(c->db,dstkey,dstset);
addReplyLongLong(c,setTypeSize(dstset));
notifyKeyspaceEvent(NOTIFY_SET,"sinterstore",
dstkey,c->db->id);
} else {
decrRefCount(dstset);
addReply(c,shared.czero);
if (deleted)
notifyKeyspaceEvent(NOTIFY_GENERIC,"del",
dstkey,c->db->id);
}
signalModifiedKey(c->db,dstkey);
server.dirty++;
} else {
setDeferredMultiBulkLength(c,replylen,cardinality);
}
zfree(sets);
}
交集，主要通过辅助集合及取出一个集合遍历来和其它集合比较。
//sunion命令 sunion key [key...]
void sunionCommand(client *c) {
sunionDiffGenericCommand(c,c->argv+1,c->argc-1,NULL,SET_OP_UNION);
}
//sunionstore命令 sunionstore destination key [key...]
void sunionstoreCommand(client *c) {
sunionDiffGenericCommand(c,c->argv+2,c->argc-2,c->argv[1],SET_OP_UNION);
}
//sdiff命令 sdiff key [key...]
void sdiffCommand(client *c) {
sunionDiffGenericCommand(c,c->argv+1,c->argc-1,NULL,SET_OP_DIFF);
}
//sdiffstore命令 sdiffstore destination key [key...]
void sdiffstoreCommand(client *c) {
sunionDiffGenericCommand(c,c->argv+2,c->argc-2,c->argv[1],SET_OP_DIFF);
}
//并集和差集的通用实现
void sunionDiffGenericCommand(client *c, robj **setkeys, int setnum,
robj *dstkey, int op) {
robj **sets = zmalloc(sizeof(robj*)*setnum);
setTypeIterator *si;
robj *dstset = NULL;
sds ele;
int j, cardinality = 0;
int diff_algo = 1;
//dstkey 并集或者差集要存入的目标集合
for (j = 0; j < setnum; j++) {
robj *setobj = dstkey ?
lookupKeyWrite(c->db,setkeys[j]) :
lookupKeyRead(c->db,setkeys[j]);
if (!setobj) {
sets[j] = NULL;
continue;
}
if (checkType(c,setobj,OBJ_SET)) {
zfree(sets);
return;
}
sets[j] = setobj;
}
/* Select what DIFF algorithm to use.
*
* Algorithm 1 is O(N*M) where N is the size of the element first set
* and M the total number of sets.
*
* Algorithm 2 is O(N) where N is the total number of elements in all
* the sets.
*
* We compute what is the best bet with the current input here. */
if (op == SET_OP_DIFF && sets[0]) {
long long algo_one_work = 0, algo_two_work = 0;
for (j = 0; j < setnum; j++) {
if (sets[j] == NULL) continue;
algo_one_work += setTypeSize(sets[0]);
algo_two_work += setTypeSize(sets[j]);
}
/* Algorithm 1 has better constant times and performs less operations
* if there are elements in common. Give it some advantage. */
algo_one_work /= 2;
diff_algo = (algo_one_work <= algo_two_work) ? 1 : 2;
if (diff_algo == 1 && setnum > 1) {
/* With algorithm 1 it is better to order the sets to subtract
* by decreasing size, so that we are more likely to find
* duplicated elements ASAP. */
qsort(sets+1,setnum-1,sizeof(robj*),
qsortCompareSetsByRevCardinality);
}
}
/* We need a temp set object to store our union. If the dstkey
* is not NULL (that is, we are inside an SUNIONSTORE operation) then
* this set object will be the resulting object to set into the target key*/
//辅助集合
dstset = createIntsetObject();
//取并集
if (op == SET_OP_UNION) {
/* Union is trivial, just add every element of every set to the
* temporary set. */
//遍历每一个set的所有元素，加入到dstset即可。
for (j = 0; j < setnum; j++) {
//空集合略过
if (!sets[j]) continue; /* non existing keys are like empty sets */
si = setTypeInitIterator(sets[j]);
while((ele = setTypeNextObject(si)) != NULL) {
if (setTypeAdd(dstset,ele)) cardinality++;
sdsfree(ele);
}
setTypeReleaseIterator(si);
}
}
//取差集，算法1
else if (op == SET_OP_DIFF && sets[0] && diff_algo == 1) {
/* DIFF Algorithm 1:
*
* We perform the diff by iterating all the elements of the first set,
* and only adding it to the target set if the element does not exist
* into all the other sets.
*
* This way we perform at max N*M operations, where N is the size of
* the first set, and M the number of sets. */
//取出第一个集合
si = setTypeInitIterator(sets[0]);
//遍历第一个集合
while((ele = setTypeNextObject(si)) != NULL) {
//将第一个集合的元素和其它所有集合的比较
for (j = 1; j < setnum; j++) {
if (!sets[j]) continue; /* no key is an empty set. */
if (sets[j] == sets[0]) break; /* same set! */
if (setTypeIsMember(sets[j],ele)) break;
}
//只有这个元素是没有交集的才可以加入dstset中
if (j == setnum) {
/* There is no other set with this element. Add it. */
setTypeAdd(dstset,ele);
cardinality++;
}
sdsfree(ele);
}
setTypeReleaseIterator(si);
}
//取差集，算法2
else if (op == SET_OP_DIFF && sets[0] && diff_algo == 2) {
/* DIFF Algorithm 2:
*
* Add all the elements of the first set to the auxiliary set.
* Then remove all the elements of all the next sets from it.
*
* This is O(N) where N is the sum of all the elements in every
* set. */
//将第一个集合的所有元素加入到辅助集合中，然后跟第二个集合对比，移除相同的元素，以此类推。
//此法应该是参考的单个集合异或去重大法
for (j = 0; j < setnum; j++) {
if (!sets[j]) continue; /* non existing keys are like empty sets */
si = setTypeInitIterator(sets[j]);
while((ele = setTypeNextObject(si)) != NULL) {
if (j == 0) {
if (setTypeAdd(dstset,ele)) cardinality++;
} else {
if (setTypeRemove(dstset,ele)) cardinality--;
}
sdsfree(ele);
}
setTypeReleaseIterator(si);
/* Exit if result set is empty as any additional removal
* of elements will have no effect. */
if (cardinality == 0) break;
}
}
/* Output the content of the resulting set, if not in STORE mode */
if (!dstkey) {
addReplyMultiBulkLen(c,cardinality);
si = setTypeInitIterator(dstset);
while((ele = setTypeNextObject(si)) != NULL) {
addReplyBulkCBuffer(c,ele,sdslen(ele));
sdsfree(ele);
}
setTypeReleaseIterator(si);
decrRefCount(dstset);
} else {
/* If we have a target key where to store the resulting set
* create this key with the result set inside */
int deleted = dbDelete(c->db,dstkey);
if (setTypeSize(dstset) > 0) {
dbAdd(c->db,dstkey,dstset);
addReplyLongLong(c,setTypeSize(dstset));
notifyKeyspaceEvent(NOTIFY_SET,
op == SET_OP_UNION ? "sunionstore" : "sdiffstore",
dstkey,c->db->id);
} else {
decrRefCount(dstset);
addReply(c,shared.czero);
if (deleted)
notifyKeyspaceEvent(NOTIFY_GENERIC,"del",
dstkey,c->db->id);
}
signalModifiedKey(c->db,dstkey);
server.dirty++;
}
zfree(sets);
}
并集，直接将所有集合的所有元素加入到辅助集合即可。
差集，用了2种算法，1种通过拿出一个集合并和其它集合比较取差集，另外1种是通过集合之间两两合并去除重复元素。
4. 随机返回元素
//srandmember命令
void srandmemberCommand(client *c) {
robj *set;
sds ele;
int64_t llele;
int encoding;
//带有count的
if (c->argc == 3) {
srandmemberWithCountCommand(c);
return;
} else if (c->argc > 3) {
addReply(c,shared.syntaxerr);
return;
}
if ((set = lookupKeyReadOrReply(c,c->argv[1],shared.nullbulk)) == NULL ||
checkType(c,set,OBJ_SET)) return;
encoding = setTypeRandomElement(set,&ele,&llele);
if (encoding == OBJ_ENCODING_INTSET) {
addReplyBulkLongLong(c,llele);
} else {
addReplyBulkCBuffer(c,ele,sdslen(ele));
}
}
#define SRANDMEMBER_SUB_STRATEGY_MUL 3
//srandmember命令 srandmember key [count]
void srandmemberWithCountCommand(client *c) {
long l;
unsigned long count, size;
int uniq = 1;
robj *set;
sds ele;
int64_t llele;
int encoding;
dict *d;
if (getLongFromObjectOrReply(c,c->argv[2],&l,NULL) != C_OK) return;
if (l >= 0) {
count = (unsigned long) l;
} else {
/* A negative count means: return the same elements multiple times
* (i.e. don't remove the extracted element after every extraction). */
count = -l;
uniq = 0;
}
if ((set = lookupKeyReadOrReply(c,c->argv[1],shared.emptymultibulk))
== NULL || checkType(c,set,OBJ_SET)) return;
size = setTypeSize(set);
/* If count is zero, serve it ASAP to avoid special cases later. */
if (count == 0) {
addReply(c,shared.emptymultibulk);
return;
}
/* CASE 1: The count was negative, so the extraction method is just:
* "return N random elements" sampling the whole set every time.
* This case is trivial and can be served without auxiliary data
* structures. */
//获取个数为负数的情况
if (!uniq) {
addReplyMultiBulkLen(c,count);
//随机count次
while(count--) {
encoding = setTypeRandomElement(set,&ele,&llele);
if (encoding == OBJ_ENCODING_INTSET) {
addReplyBulkLongLong(c,llele);
} else {
addReplyBulkCBuffer(c,ele,sdslen(ele));
}
}
return;
}
/* CASE 2:
* The number of requested elements is greater than the number of
* elements inside the set: simply return the whole set. */
//如果count大于集合大小，那么直接返回整个集合
if (count >= size) {
sunionDiffGenericCommand(c,c->argv+1,1,NULL,SET_OP_UNION);
return;
}
/* For CASE 3 and CASE 4 we need an auxiliary dictionary. */
//创建一个辅助的dict
d = dictCreate(&objectKeyPointerValueDictType,NULL);
/* CASE 3:
* The number of elements inside the set is not greater than
* SRANDMEMBER_SUB_STRATEGY_MUL times the number of requested elements.
* In this case we create a set from scratch with all the elements, and
* subtract random elements to reach the requested number of elements.
*
* This is done because if the number of requsted elements is just
* a bit less than the number of elements in the set, the natural approach
* used into CASE 3 is highly inefficient. */
//要获取的元素较多的情况下
if (count*SRANDMEMBER_SUB_STRATEGY_MUL > size) {
setTypeIterator *si;
/* Add all the elements into the temporary dictionary. */
si = setTypeInitIterator(set);
//把所有set中的元素放到dict中
while((encoding = setTypeNext(si,&ele,&llele)) != -1) {
int retval = DICT_ERR;
if (encoding == OBJ_ENCODING_INTSET) {
retval = dictAdd(d,createStringObjectFromLongLong(llele),NULL);
} else {
retval = dictAdd(d,createStringObject(ele,sdslen(ele)),NULL);
}
serverAssert(retval == DICT_OK);
}
setTypeReleaseIterator(si);
serverAssert(dictSize(d) == size);
/* Remove random elements to reach the right count. */
//随机移除size-count个元素
while(size > count) {
dictEntry *de;
de = dictGetRandomKey(d);
dictDelete(d,dictGetKey(de));
size--;
}
}
/* CASE 4: We have a big set compared to the requested number of elements.
* In this case we can simply get random elements from the set and add
* to the temporary set, trying to eventually get enough unique elements
* to reach the specified count. */
//要获取的元素个数较少的情况
else {
unsigned long added = 0;
robj *objele;
//随机获取count个元素存放到dict中
while(added < count) {
encoding = setTypeRandomElement(set,&ele,&llele);
if (encoding == OBJ_ENCODING_INTSET) {
objele = createStringObjectFromLongLong(llele);
} else {
objele = createStringObject(ele,sdslen(ele));
}
/* Try to add the object to the dictionary. If it already exists
* free it, otherwise increment the number of objects we have
* in the result dictionary. */
if (dictAdd(d,objele,NULL) == DICT_OK)
added++;
else
decrRefCount(objele);
}
}
//返回dict
/* CASE 3 & 4: send the result to the user. */
{
dictIterator *di;
dictEntry *de;
addReplyMultiBulkLen(c,count);
di = dictGetIterator(d);
while((de = dictNext(di)) != NULL)
addReplyBulk(c,dictGetKey(de));
dictReleaseIterator(di);
dictRelease(d);
}
}
根据要随机取的个数和集合的个数考量。
要取的元素较多，则移除较少部分元素。
要取的元素较少，则直接取。
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