15天玩转redis —— 第五篇 集合对象类型

　　这篇我们来看看Redis五大类型中的第四大类型：“集合类型”，集合类型还是蛮有意思的，第一个是因为它算是只使用key的Dictionary简易版，

这样说来的话，它就比Dictionary节省很多内存消耗，第二个是因为它和C#中的HashSet是一个等同类型，废话不多说，先看redis手册，如下：

上面就是redis中的set类型使用到的所有方法，还是老话，常用的方法也就那么四个（CURD）。。。

一： 常用方法

1. SAdd

　　这个方法毫无疑问，就是向集合里面添加数据，比如下面这样，我往fruits集合里面添加喜爱的水果。

127.0.0.1:> sadd fruits apple
(integer)
127.0.0.1:> sadd fruits banana
(integer)
127.0.0.1:> smembers fruits
) "banana"
) "apple"
127.0.0.1:> 

上面这个sadd你也看到了，我往集合里面成功添加了两个元素，现在你可能不满足这么简单的添加，你或许想知道set这个集合在redis底层是使用

什么来实现的，你可以用object encoding查看一下便知:

127.0.0.1:> object encoding fruits
"hashtable"
127.0.0.1:> 

看到了吧，是hashtable这个吊毛，现在闭上眼睛都能想到，肯定就是只用key的dictionary啦，对不对，如果你还有疑问的话，我还可以找到底层

代码给你看，好不啦？？？

有没有看到dictAdd方法，而其中的第三个参数正好是Null。。。对应着*val形参，你看牛叉不牛叉。。。然后我再带你看看dictAdd方法的定义。

好了，关于hashtable的实现理论，我在上一篇文章中也已经说过了，这里就不再赘叙了。

2. SPOP,SMEMBERS

既然元素进来了，总不能不出来吧，这里的第一个SPOP：移除并返回集合中的一个随机元素，有一点奇怪的是，这种奇怪的方法其实在我们

C#中的HashSet并没有好办法解决，就比如”这个随机“就有点烦人了，下面这是我能想到的方法。

刚才随便插了一句话，下面我们继续SAdd，再SPop出来。

127.0.0.1:> sadd fruits pear
(integer)
127.0.0.1:> sadd fruits grape
(integer)
127.0.0.1:> sadd fruits chestnut
(integer)
127.0.0.1:> smembers fruits
) "grape"
) "pear"
) "banana"
) "apple"
) "chestnut"
127.0.0.1:> spop fruits
"apple"
127.0.0.1:> spop fruits
"chestnut"
127.0.0.1:> smembers fruits
) "grape"
) "pear"
) "banana"
127.0.0.1:> 

这个方法确实还是蛮好的，起码它是原子性操作，如果要我自己实现的话，起码还是要10行左右代码的。

3. SREM

既然说到了CURD，那怎么能少了D呢，它的功能定义就是：移除集合 key 中的一个或多个 member 元素，不存在的 member 元素会被忽略，

下面我随便举个例子，删除fruits中的pear。

127.0.0.1:> smembers fruits
) "grape"
) "pear"
) "banana"
127.0.0.1:> srem fruits pear
(integer)
127.0.0.1:> smembers fruits
) "grape"
) "banana"
127.0.0.1:> 

好了，常用的操作就那么几个，是不是觉得好傻瓜哦。。。傻瓜就对了，方法是简单的，关键你需要了解这个方法底层是如何实现的，这样才能做到

心里有数，就比如Set函数，它的源代码全部都在 “t.set.c” 中。

 /*
  * Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *   * Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *   * Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
  *     documentation and/or other materials provided with the distribution.
  *   * Neither the name of Redis nor the names of its contributors may be used
  *     to endorse or promote products derived from this software without
  *     specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  */

 #include "redis.h"

 /*-----------------------------------------------------------------------------
  * Set Commands
  *----------------------------------------------------------------------------*/

 void sunionDiffGenericCommand(redisClient *c, robj **setkeys, int setnum, robj *dstkey, int op);

 /* Factory method to return a set that *can* hold "value". When the object has
  * an integer-encodable value, an intset will be returned. Otherwise a regular
  * hash table. */
 robj *setTypeCreate(robj *value) {
     if (isObjectRepresentableAsLongLong(value,NULL) == REDIS_OK)
         return createIntsetObject();
     return createSetObject();
 }

 int setTypeAdd(robj *subject, robj *value) {
     long long llval;
     if (subject->encoding == REDIS_ENCODING_HT) {
         if (dictAdd(subject->ptr,value,NULL) == DICT_OK) {
             incrRefCount(value);
             return ;
         }
     } else if (subject->encoding == REDIS_ENCODING_INTSET) {
         if (isObjectRepresentableAsLongLong(value,&llval) == REDIS_OK) {
             uint8_t success = ;
             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,REDIS_ENCODING_HT);
                 return ;
             }
         } else {
             /* Failed to get integer from object, convert to regular set. */
             setTypeConvert(subject,REDIS_ENCODING_HT);

             /* The set *was* an intset and this value is not integer
              * encodable, so dictAdd should always work. */
             redisAssertWithInfo(NULL,value,dictAdd(subject->ptr,value,NULL) == DICT_OK);
             incrRefCount(value);
             return ;
         }
     } else {
         redisPanic("Unknown set encoding");
     }
     return ;
 }

 int setTypeRemove(robj *setobj, robj *value) {
     long long llval;
     if (setobj->encoding == REDIS_ENCODING_HT) {
         if (dictDelete(setobj->ptr,value) == DICT_OK) {
             if (htNeedsResize(setobj->ptr)) dictResize(setobj->ptr);
             return ;
         }
     } else if (setobj->encoding == REDIS_ENCODING_INTSET) {
         if (isObjectRepresentableAsLongLong(value,&llval) == REDIS_OK) {
             int success;
             setobj->ptr = intsetRemove(setobj->ptr,llval,&success);
             if (success) return ;
         }
     } else {
         redisPanic("Unknown set encoding");
     }
     return ;
 }

 int setTypeIsMember(robj *subject, robj *value) {
     long long llval;
     if (subject->encoding == REDIS_ENCODING_HT) {
         return dictFind((dict*)subject->ptr,value) != NULL;
     } else if (subject->encoding == REDIS_ENCODING_INTSET) {
         if (isObjectRepresentableAsLongLong(value,&llval) == REDIS_OK) {
             return intsetFind((intset*)subject->ptr,llval);
         }
     } else {
         redisPanic("Unknown set encoding");
     }
     return ;
 }

 setTypeIterator *setTypeInitIterator(robj *subject) {
     setTypeIterator *si = zmalloc(sizeof(setTypeIterator));
     si->subject = subject;
     si->encoding = subject->encoding;
     if (si->encoding == REDIS_ENCODING_HT) {
         si->di = dictGetIterator(subject->ptr);
     } else if (si->encoding == REDIS_ENCODING_INTSET) {
         si->ii = ;
     } else {
         redisPanic("Unknown set encoding");
     }
     return si;
 }

 void setTypeReleaseIterator(setTypeIterator *si) {
     if (si->encoding == REDIS_ENCODING_HT)
         dictReleaseIterator(si->di);
     zfree(si);
 }

 /* Move to the next entry in the set. Returns the object at the current
  * position.
  *
  * Since set elements can be internally be stored as redis objects or
  * simple arrays of integers, setTypeNext returns the encoding of the
  * set object you are iterating, and will populate the appropriate pointer
  * (eobj) or (llobj) accordingly.
  *
  * When there are no longer elements -1 is returned.
  * Returned objects ref count is not incremented, so this function is
  * copy on write friendly. */
 int setTypeNext(setTypeIterator *si, robj **objele, int64_t *llele) {
     if (si->encoding == REDIS_ENCODING_HT) {
         dictEntry *de = dictNext(si->di);
         if (de == NULL) return -;
         *objele = dictGetKey(de);
     } else if (si->encoding == REDIS_ENCODING_INTSET) {
         if (!intsetGet(si->subject->ptr,si->ii++,llele))
             return -;
     }
     return si->encoding;
 }

 /* The not copy on write friendly version but easy to use version
  * of setTypeNext() is setTypeNextObject(), returning new objects
  * or incrementing the ref count of returned objects. So if you don't
  * retain a pointer to this object you should call decrRefCount() against it.
  *
  * This function is the way to go for write operations where COW is not
  * an issue as the result will be anyway of incrementing the ref count. */
 robj *setTypeNextObject(setTypeIterator *si) {
     int64_t intele;
     robj *objele;
     int encoding;

     encoding = setTypeNext(si,&objele,&intele);
     switch(encoding) {
         case -:    return NULL;
         case REDIS_ENCODING_INTSET:
             return createStringObjectFromLongLong(intele);
         case REDIS_ENCODING_HT:
             incrRefCount(objele);
             return objele;
         default:
             redisPanic("Unsupported encoding");
     }
     return NULL; /* just to suppress warnings */
 }

 /* Return random element from a non empty set.
  * The returned element can be a int64_t value if the set is encoded
  * as an "intset" blob of integers, or a redis object if the set
  * is a regular set.
  *
  * The caller provides both pointers to be populated with the right
  * object. The return value of the function is the object->encoding
  * field of the object and is used by the caller to check if the
  * int64_t pointer or the redis object pointer was populated.
  *
  * When an object is returned (the set was a real set) the ref count
  * of the object is not incremented so this function can be considered
  * copy on write friendly. */
 int setTypeRandomElement(robj *setobj, robj **objele, int64_t *llele) {
     if (setobj->encoding == REDIS_ENCODING_HT) {
         dictEntry *de = dictGetRandomKey(setobj->ptr);
         *objele = dictGetKey(de);
     } else if (setobj->encoding == REDIS_ENCODING_INTSET) {
         *llele = intsetRandom(setobj->ptr);
     } else {
         redisPanic("Unknown set encoding");
     }
     return setobj->encoding;
 }

 unsigned long setTypeSize(robj *subject) {
     if (subject->encoding == REDIS_ENCODING_HT) {
         return dictSize((dict*)subject->ptr);
     } else if (subject->encoding == REDIS_ENCODING_INTSET) {
         return intsetLen((intset*)subject->ptr);
     } else {
         redisPanic("Unknown set encoding");
     }
 }

 /* 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. */
 void setTypeConvert(robj *setobj, int enc) {
     setTypeIterator *si;
     redisAssertWithInfo(NULL,setobj,setobj->type == REDIS_SET &&
                              setobj->encoding == REDIS_ENCODING_INTSET);

     if (enc == REDIS_ENCODING_HT) {
         int64_t intele;
         dict *d = dictCreate(&setDictType,NULL);
         robj *element;

         /* Presize the dict to avoid rehashing */
         dictExpand(d,intsetLen(setobj->ptr));

         /* To add the elements we extract integers and create redis objects */
         si = setTypeInitIterator(setobj);
         while (setTypeNext(si,NULL,&intele) != -) {
             element = createStringObjectFromLongLong(intele);
             redisAssertWithInfo(NULL,element,dictAdd(d,element,NULL) == DICT_OK);
         }
         setTypeReleaseIterator(si);

         setobj->encoding = REDIS_ENCODING_HT;
         zfree(setobj->ptr);
         setobj->ptr = d;
     } else {
         redisPanic("Unsupported set conversion");
     }
 }

 void saddCommand(redisClient *c) {
     robj *set;
     int j, added = ;

     set = lookupKeyWrite(c->db,c->argv[]);
     if (set == NULL) {
         set = setTypeCreate(c->argv[]);
         dbAdd(c->db,c->argv[],set);
     } else {
         if (set->type != REDIS_SET) {
             addReply(c,shared.wrongtypeerr);
             return;
         }
     }

     for (j = ; j < c->argc; j++) {
         c->argv[j] = tryObjectEncoding(c->argv[j]);
         if (setTypeAdd(set,c->argv[j])) added++;
     }
     if (added) {
         signalModifiedKey(c->db,c->argv[]);
         notifyKeyspaceEvent(REDIS_NOTIFY_SET,"sadd",c->argv[],c->db->id);
     }
     server.dirty += added;
     addReplyLongLong(c,added);
 }

 void sremCommand(redisClient *c) {
     robj *set;
     int j, deleted = , keyremoved = ;

     if ((set = lookupKeyWriteOrReply(c,c->argv[],shared.czero)) == NULL ||
         checkType(c,set,REDIS_SET)) return;

     for (j = ; j < c->argc; j++) {
         if (setTypeRemove(set,c->argv[j])) {
             deleted++;
             if (setTypeSize(set) == ) {
                 dbDelete(c->db,c->argv[]);
                 keyremoved = ;
                 break;
             }
         }
     }
     if (deleted) {
         signalModifiedKey(c->db,c->argv[]);
         notifyKeyspaceEvent(REDIS_NOTIFY_SET,"srem",c->argv[],c->db->id);
         if (keyremoved)
             notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",c->argv[],
                                 c->db->id);
         server.dirty += deleted;
     }
     addReplyLongLong(c,deleted);
 }

 void smoveCommand(redisClient *c) {
     robj *srcset, *dstset, *ele;
     srcset = lookupKeyWrite(c->db,c->argv[]);
     dstset = lookupKeyWrite(c->db,c->argv[]);
     ele = c->argv[] = tryObjectEncoding(c->argv[]);

     /* If the source key does not exist return 0 */
     if (srcset == NULL) {
         addReply(c,shared.czero);
         return;
     }

     /* If the source key has the wrong type, or the destination key
      * is set and has the wrong type, return with an error. */
     if (checkType(c,srcset,REDIS_SET) ||
         (dstset && checkType(c,dstset,REDIS_SET))) return;

     /* If srcset and dstset are equal, SMOVE is a no-op */
     if (srcset == dstset) {
         addReply(c,setTypeIsMember(srcset,ele) ? shared.cone : shared.czero);
         return;
     }

     /* If the element cannot be removed from the src set, return 0. */
     if (!setTypeRemove(srcset,ele)) {
         addReply(c,shared.czero);
         return;
     }
     notifyKeyspaceEvent(REDIS_NOTIFY_SET,"srem",c->argv[],c->db->id);

     /* Remove the src set from the database when empty */
     if (setTypeSize(srcset) == ) {
         dbDelete(c->db,c->argv[]);
         notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",c->argv[],c->db->id);
     }
     signalModifiedKey(c->db,c->argv[]);
     signalModifiedKey(c->db,c->argv[]);
     server.dirty++;

     /* Create the destination set when it doesn't exist */
     if (!dstset) {
         dstset = setTypeCreate(ele);
         dbAdd(c->db,c->argv[],dstset);
     }

     /* An extra key has changed when ele was successfully added to dstset */
     if (setTypeAdd(dstset,ele)) {
         server.dirty++;
         notifyKeyspaceEvent(REDIS_NOTIFY_SET,"sadd",c->argv[],c->db->id);
     }
     addReply(c,shared.cone);
 }

 void sismemberCommand(redisClient *c) {
     robj *set;

     if ((set = lookupKeyReadOrReply(c,c->argv[],shared.czero)) == NULL ||
         checkType(c,set,REDIS_SET)) return;

     c->argv[] = tryObjectEncoding(c->argv[]);
     if (setTypeIsMember(set,c->argv[]))
         addReply(c,shared.cone);
     else
         addReply(c,shared.czero);
 }

 void scardCommand(redisClient *c) {
     robj *o;

     if ((o = lookupKeyReadOrReply(c,c->argv[],shared.czero)) == NULL ||
         checkType(c,o,REDIS_SET)) return;

     addReplyLongLong(c,setTypeSize(o));
 }

 void spopCommand(redisClient *c) {
     robj *set, *ele, *aux;
     int64_t llele;
     int encoding;

     if ((set = lookupKeyWriteOrReply(c,c->argv[],shared.nullbulk)) == NULL ||
         checkType(c,set,REDIS_SET)) return;

     encoding = setTypeRandomElement(set,&ele,&llele);
     if (encoding == REDIS_ENCODING_INTSET) {
         ele = createStringObjectFromLongLong(llele);
         set->ptr = intsetRemove(set->ptr,llele,NULL);
     } else {
         incrRefCount(ele);
         setTypeRemove(set,ele);
     }
     notifyKeyspaceEvent(REDIS_NOTIFY_SET,"spop",c->argv[],c->db->id);

     /* Replicate/AOF this command as an SREM operation */
     aux = createStringObject("SREM",);
     rewriteClientCommandVector(c,,aux,c->argv[],ele);
     decrRefCount(ele);
     decrRefCount(aux);

     addReplyBulk(c,ele);
     if (setTypeSize(set) == ) {
         dbDelete(c->db,c->argv[]);
         notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",c->argv[],c->db->id);
     }
     signalModifiedKey(c->db,c->argv[]);
     server.dirty++;
 }

 /* handle the "SRANDMEMBER key <count>" variant. The normal version of the
  * command is handled by the srandmemberCommand() function itself. */

 /* How many times bigger should be the set compared to the requested size
  * for us to don't use the "remove elements" strategy? Read later in the
  * implementation for more info. */
 #define SRANDMEMBER_SUB_STRATEGY_MUL 3

 void srandmemberWithCountCommand(redisClient *c) {
     long l;
     unsigned long count, size;
     int uniq = ;
     robj *set, *ele;
     int64_t llele;
     int encoding;

     dict *d;

     if (getLongFromObjectOrReply(c,c->argv[],&l,NULL) != REDIS_OK) return;
     if (l >= ) {
         count = (unsigned) 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 = ;
     }

     if ((set = lookupKeyReadOrReply(c,c->argv[],shared.emptymultibulk))
         == NULL || checkType(c,set,REDIS_SET)) return;
     size = setTypeSize(set);

     /* If count is zero, serve it ASAP to avoid special cases later. */
     if (count == ) {
         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. */
     if (!uniq) {
         addReplyMultiBulkLen(c,count);
         while(count--) {
             encoding = setTypeRandomElement(set,&ele,&llele);
             if (encoding == REDIS_ENCODING_INTSET) {
                 addReplyBulkLongLong(c,llele);
             } else {
                 addReplyBulk(c,ele);
             }
         }
         return;
     }

     /* CASE 2:
      * The number of requested elements is greater than the number of
      * elements inside the set: simply return the whole set. */
     if (count >= size) {
         sunionDiffGenericCommand(c,c->argv+,,NULL,REDIS_OP_UNION);
         return;
     }

     /* For CASE 3 and CASE 4 we need an auxiliary dictionary. */
     d = dictCreate(&setDictType,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. */
     if (count*SRANDMEMBER_SUB_STRATEGY_MUL > size) {
         setTypeIterator *si;

         /* Add all the elements into the temporary dictionary. */
         si = setTypeInitIterator(set);
         while((encoding = setTypeNext(si,&ele,&llele)) != -) {
             int retval = DICT_ERR;

             if (encoding == REDIS_ENCODING_INTSET) {
                 retval = dictAdd(d,createStringObjectFromLongLong(llele),NULL);
             } else {
                 retval = dictAdd(d,dupStringObject(ele),NULL);
             }
             redisAssert(retval == DICT_OK);
         }
         setTypeReleaseIterator(si);
         redisAssert(dictSize(d) == size);

         /* Remove random elements to reach the right count. */
         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. */
     else {
         unsigned long added = ;

         while(added < count) {
             encoding = setTypeRandomElement(set,&ele,&llele);
             if (encoding == REDIS_ENCODING_INTSET) {
                 ele = createStringObjectFromLongLong(llele);
             } else {
                 ele = dupStringObject(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,ele,NULL) == DICT_OK)
                 added++;
             else
                 decrRefCount(ele);
         }
     }

     /* 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);
     }
 }

 void srandmemberCommand(redisClient *c) {
     robj *set, *ele;
     int64_t llele;
     int encoding;

     if (c->argc == ) {
         srandmemberWithCountCommand(c);
         return;
     } else if (c->argc > ) {
         addReply(c,shared.syntaxerr);
         return;
     }

     if ((set = lookupKeyReadOrReply(c,c->argv[],shared.nullbulk)) == NULL ||
         checkType(c,set,REDIS_SET)) return;

     encoding = setTypeRandomElement(set,&ele,&llele);
     if (encoding == REDIS_ENCODING_INTSET) {
         addReplyBulkLongLong(c,llele);
     } else {
         addReplyBulk(c,ele);
     }
 }

 int qsortCompareSetsByCardinality(const void *s1, const void *s2) {
     return setTypeSize(*(robj**)s1)-setTypeSize(*(robj**)s2);
 }

 /* This is used by SDIFF and in this case we can receive NULL that should
  * be handled as empty sets. */
 int qsortCompareSetsByRevCardinality(const void *s1, const void *s2) {
     robj *o1 = *(robj**)s1, *o2 = *(robj**)s2;

     return  (o2 ? setTypeSize(o2) : ) - (o1 ? setTypeSize(o1) : );
 }

 void sinterGenericCommand(redisClient *c, robj **setkeys, unsigned long setnum, robj *dstkey) {
     robj **sets = zmalloc(sizeof(robj*)*setnum);
     setTypeIterator *si;
     robj *eleobj, *dstset = NULL;
     int64_t intobj;
     void *replylen = NULL;
     unsigned long j, cardinality = ;
     int encoding;

     for (j = ; j < setnum; j++) {
         robj *setobj = dstkey ?
             lookupKeyWrite(c->db,setkeys[j]) :
             lookupKeyRead(c->db,setkeys[j]);
         if (!setobj) {
             zfree(sets);
             if (dstkey) {
                 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,REDIS_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[]);
     while((encoding = setTypeNext(si,&eleobj,&intobj)) != -) {
         for (j = ; j < setnum; j++) {
             if (sets[j] == sets[]) continue;
             if (encoding == REDIS_ENCODING_INTSET) {
                 /* intset with intset is simple... and fast */
                 if (sets[j]->encoding == REDIS_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 */
                 } else if (sets[j]->encoding == REDIS_ENCODING_HT) {
                     eleobj = createStringObjectFromLongLong(intobj);
                     if (!setTypeIsMember(sets[j],eleobj)) {
                         decrRefCount(eleobj);
                         break;
                     }
                     decrRefCount(eleobj);
                 }
             } else if (encoding == REDIS_ENCODING_HT) {
                 /* Optimization... if the source object is integer
                  * encoded AND the target set is an intset, we can get
                  * a much faster path. */
                 if (eleobj->encoding == REDIS_ENCODING_INT &&
                     sets[j]->encoding == REDIS_ENCODING_INTSET &&
                     !intsetFind((intset*)sets[j]->ptr,(long)eleobj->ptr))
                 {
                     break;
                 /* else... object to object check is easy as we use the
                  * type agnostic API here. */
                 } else if (!setTypeIsMember(sets[j],eleobj)) {
                     break;
                 }
             }
         }

         /* Only take action when all sets contain the member */
         if (j == setnum) {
             if (!dstkey) {
                 if (encoding == REDIS_ENCODING_HT)
                     addReplyBulk(c,eleobj);
                 else
                     addReplyBulkLongLong(c,intobj);
                 cardinality++;
             } else {
                 if (encoding == REDIS_ENCODING_INTSET) {
                     eleobj = createStringObjectFromLongLong(intobj);
                     setTypeAdd(dstset,eleobj);
                     decrRefCount(eleobj);
                 } else {
                     setTypeAdd(dstset,eleobj);
                 }
             }
         }
     }
     setTypeReleaseIterator(si);

     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) > ) {
             dbAdd(c->db,dstkey,dstset);
             addReplyLongLong(c,setTypeSize(dstset));
             notifyKeyspaceEvent(REDIS_NOTIFY_SET,"sinterstore",
                 dstkey,c->db->id);
         } else {
             decrRefCount(dstset);
             addReply(c,shared.czero);
             if (deleted)
                 notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",
                     dstkey,c->db->id);
         }
         signalModifiedKey(c->db,dstkey);
         server.dirty++;
     } else {
         setDeferredMultiBulkLength(c,replylen,cardinality);
     }
     zfree(sets);
 }

 void sinterCommand(redisClient *c) {
     sinterGenericCommand(c,c->argv+,c->argc-,NULL);
 }

 void sinterstoreCommand(redisClient *c) {
     sinterGenericCommand(c,c->argv+,c->argc-,c->argv[]);
 }

 #define REDIS_OP_UNION 0
 #define REDIS_OP_DIFF 1
 #define REDIS_OP_INTER 2

 void sunionDiffGenericCommand(redisClient *c, robj **setkeys, int setnum, robj *dstkey, int op) {
     robj **sets = zmalloc(sizeof(robj*)*setnum);
     setTypeIterator *si;
     robj *ele, *dstset = NULL;
     int j, cardinality = ;
     int diff_algo = ;

     for (j = ; 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,REDIS_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 == REDIS_OP_DIFF && sets[]) {
         long long algo_one_work = , algo_two_work = ;

         for (j = ; j < setnum; j++) {
             if (sets[j] == NULL) continue;

             algo_one_work += setTypeSize(sets[]);
             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 /= ;
         diff_algo = (algo_one_work <= algo_two_work) ?  : ;

         if (diff_algo ==  && setnum > ) {
             /* 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+,setnum-,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*/
     dstset = createIntsetObject();

     if (op == REDIS_OP_UNION) {
         /* Union is trivial, just add every element of every set to the
          * temporary set. */
         for (j = ; j < setnum; j++) {
             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++;
                 decrRefCount(ele);
             }
             setTypeReleaseIterator(si);
         }
     } else if (op == REDIS_OP_DIFF && sets[] && diff_algo == ) {
         /* 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. */
         si = setTypeInitIterator(sets[]);
         while((ele = setTypeNextObject(si)) != NULL) {
             for (j = ; j < setnum; j++) {
                 if (!sets[j]) continue; /* no key is an empty set. */
                 if (sets[j] == sets[]) break; /* same set! */
                 if (setTypeIsMember(sets[j],ele)) break;
             }
             if (j == setnum) {
                 /* There is no other set with this element. Add it. */
                 setTypeAdd(dstset,ele);
                 cardinality++;
             }
             decrRefCount(ele);
         }
         setTypeReleaseIterator(si);
     } else if (op == REDIS_OP_DIFF && sets[] && diff_algo == ) {
         /* 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. */
         for (j = ; 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 == ) {
                     if (setTypeAdd(dstset,ele)) cardinality++;
                 } else {
                     if (setTypeRemove(dstset,ele)) cardinality--;
                 }
                 decrRefCount(ele);
             }
             setTypeReleaseIterator(si);

             /* Exit if result set is empty as any additional removal
              * of elements will have no effect. */
             if (cardinality == ) 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) {
             addReplyBulk(c,ele);
             decrRefCount(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) > ) {
             dbAdd(c->db,dstkey,dstset);
             addReplyLongLong(c,setTypeSize(dstset));
             notifyKeyspaceEvent(REDIS_NOTIFY_SET,
                 op == REDIS_OP_UNION ? "sunionstore" : "sdiffstore",
                 dstkey,c->db->id);
         } else {
             decrRefCount(dstset);
             addReply(c,shared.czero);
             if (deleted)
                 notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",
                     dstkey,c->db->id);
         }
         signalModifiedKey(c->db,dstkey);
         server.dirty++;
     }
     zfree(sets);
 }

 void sunionCommand(redisClient *c) {
     sunionDiffGenericCommand(c,c->argv+,c->argc-,NULL,REDIS_OP_UNION);
 }

 void sunionstoreCommand(redisClient *c) {
     sunionDiffGenericCommand(c,c->argv+,c->argc-,c->argv[],REDIS_OP_UNION);
 }

 void sdiffCommand(redisClient *c) {
     sunionDiffGenericCommand(c,c->argv+,c->argc-,NULL,REDIS_OP_DIFF);
 }

 void sdiffstoreCommand(redisClient *c) {
     sunionDiffGenericCommand(c,c->argv+,c->argc-,c->argv[],REDIS_OP_DIFF);
 }

 void sscanCommand(redisClient *c) {
     robj *set;
     unsigned long cursor;

     if (parseScanCursorOrReply(c,c->argv[],&cursor) == REDIS_ERR) return;
     if ((set = lookupKeyReadOrReply(c,c->argv[],shared.emptyscan)) == NULL ||
         checkType(c,set,REDIS_SET)) return;
     scanGenericCommand(c,set,cursor);
 }