42源碼10跋山涉水深入字典遍歷天下無(wú)魚

我們知道Redis?字典也會(huì)很?。當(dāng)我們使?keys命令搜尋指定模式的key時(shí)，模式匹配條件的key被找到了，還需要判斷key指向的對(duì)象是否已經(jīng)過(guò)期。如果過(guò)期了就需要從主?字典中將該key刪除。voidkeysCommand(client*c){dictIterator*di;//迭代器dictEntry*de;迭代器當(dāng)前的entrysdspatternc->argv[1]->ptr;keys的匹配模intplen=intallkeys;是否要獲取所有key，?于keys*這樣unsignedlongnumkeys=0;void*replylen=//whydi=dictGetSafeIterator(c->db->dict);allkeys=(pattern[0]=='*'&&pattern[1]==while((de=dictNext(di))!=NULL){sdskey=dictGetKey(de);robjif(allkeys||stringmatchlen(pattern,plen,key,sdslen(key),0)){keyobj=if(expireIfNeeded(c->db,keyobj)0)遍歷需要對(duì)這兩個(gè)hashtable依次進(jìn)?，先遍歷完舊的hashtable，再繼續(xù)遍歷新的hashtable。如果在遍歷的過(guò)程中進(jìn)?了rehashStep，將已經(jīng)遍歷過(guò)的舊的hashtable的元素遷移到了新的hashtable中，那么遍歷會(huì)不會(huì)出現(xiàn)元素的重復(fù)？這也是遍歷需要考慮的疑難之處，下?我們來(lái)看看Redis是如何解決這個(gè)問(wèn)題Redis2種迭代器，?種是安全迭代器，另?}}}}}字典在擴(kuò)容的時(shí)候要進(jìn)?漸進(jìn)式遷移，會(huì)存在新舊兩個(gè)hashtable。hashtable，再繼續(xù)遍歷新的hashtable。如果在遍歷的過(guò)程中進(jìn)?了rehashStep，將已經(jīng)遍歷過(guò)的舊的hashtable的元素遷移到了新的hashtable中，那么遍歷會(huì)不會(huì)出現(xiàn)元素的重復(fù)？這也是遍歷需要考慮的疑難之處，下?我們來(lái)看看Redis是如何解決這個(gè)問(wèn)題Redis為字典的遍歷提供了2種迭代器，?種是安全迭代器，另?i->safei->safe=return}typedefstructdict*dlongindex當(dāng)前遍歷的槽位置，初始化為-1inttable;//ht[0]orht[1]intsafe這個(gè)屬性?常關(guān)鍵，它表示迭代器是否安全dictEntry*entry;//迭代器當(dāng)前指向的對(duì)象dictEntry*nextEntry;//迭代器下?個(gè)指向的對(duì)象longlongfingerprint迭代器指紋，放置迭代過(guò)}獲取?安全迭代器，只讀迭代器，允許rehashStepdictIterator*dictGetIterator(dict*d){dictIterator*iter=iter->d=d;iter->table=0;iter->index=-iter->safe=0;iter->entry=NULL;iter->nextEntry=NULL;returniter;}獲取安全迭代器，允許觸發(fā)過(guò)期處理，禁?rehashStepdictIterator*dictGetSafeIterator(dict*d){dictIterator*i=i->safei->safe=return}typedefstructdictIterator{dict*d;//?標(biāo)字典對(duì)象longindex;當(dāng)前遍歷的槽位置，初始化為-inttable;//ht[0]orintsafe;這個(gè)屬性?常關(guān)鍵，它表示迭代器是否安全dictEntry*entry;//迭代器當(dāng)前指向的對(duì)象dictEntry*nextEntry;//迭代器下?個(gè)指向的對(duì)象longlongfingerprint;//迭代器指紋，放置迭代過(guò)}獲取?安全迭代器，只讀迭代器，允許rehashStepdictIterator*dictGetIterator(dict*d){dictIterator*iter=iter->d=d;iter->table=0;iter->index=-iter->safe=0;iter->entry=NULL;iter->nextEntry=NULL;returniter;}獲取安全迭代器，允許觸發(fā)過(guò)期處理，禁?rehashStepdictIterator*dictGetSafeIterator(dict*d){dictIterator*i=dictGetIterator(d);重復(fù)，就會(huì)禁?rehashStep。dictNext對(duì)字典進(jìn)?持續(xù)遍歷，不得調(diào)?任何可能觸發(fā)過(guò)期判斷的函數(shù)。不過(guò)好處是不影響rehash，代價(jià)就是遍歷的記，rehashStep就不會(huì)執(zhí)?，遍歷時(shí)元素就不會(huì)出現(xiàn)重復(fù)。typedeftypedefstruct{dictType*type;void*privdata;dicththt[2];longrehashidx;量unsignedlong}//如果存在安全的迭代器，就禁?rehashstaticvoid_dictRehashStep(dict*dif(d->iterators==0)}?掛接的鏈表中的元素可能會(huì)被摘?，元素的next指針就會(huì)發(fā)?變重復(fù)，就會(huì)禁?rehashStep。改，你只能調(diào)?dictNext對(duì)字典進(jìn)?持續(xù)遍歷，不得調(diào)?任何可能觸發(fā)過(guò)期判斷的函數(shù)。不過(guò)好處是不影響rehash，代價(jià)就是遍歷的記，rehashStep就不會(huì)執(zhí)?，遍歷時(shí)元素就不會(huì)出現(xiàn)重復(fù)。typedeftypedefstructdict{dictType*type;void*privdata;dicththt[2];longrehashidx;量unsignedlong}//如果存在安全的迭代器，就禁?rehashstaticvoid_dictRehashStep(dict*d)if(d->iterators==0)}?掛接的鏈表中的元素可能會(huì)被摘?，元素的next指針就會(huì)發(fā)?變ifif(dictIsRehashing(iter->d)iter->table==0)dictEntry*dictNext(dictIterator{while(1)if(iter->entry==NULL)遍歷?個(gè)新槽位下?的鏈表，數(shù)組的index==0)表

dictht*ht=&iter->d-if(iter->index==-1&&iter-也就是ht[0]if(iter->safe)}else記錄迭代器指紋，就好?字典的md5}

iter->index++index=0if(iter->index>=(long)ht->size)ifif(dictIsRehashing(iter->d)iter->table==0)dictEntry*dictNext(dictIterator{while(1)if(iter->entry==NULL)遍歷?個(gè)新槽位下?的鏈表，數(shù)組的index==0)表

dictht*ht=&iter->d-if(iter->index==-1&&iter-也就是ht[0]if(iter->safe)}else記錄迭代器指紋，就好?字典的md5iter->fingerprint}

iter->index++;index=0if(iter->index>=(long)ht->size)iteriter->nextEntry=iter->entry-returniter-第?個(gè)

iter->index=0;ht=&iter->d-}else}}iter->entry=ht->table[iter-}elseiter->entry=iter-}if(iter->entry)鍵試想如果后?發(fā)?了rehash，當(dāng)前遍歷的鏈表舊的鏈表將?分為?，打散后重新掛接到新數(shù)如果rehash的鏈表是index前?的鏈表，那么iteriter->nextEntry=iter->entry-returniter-第?個(gè)

如果處于rehashiter->index=0;ht=&iter->d-}else}}iter->entry=ht->table[iter-}elseiter->entry=iter-}if(iter->entry)鍵試想如果后?發(fā)?了rehash，當(dāng)前遍歷的鏈表

如果rehash的鏈表是index前?的鏈表，那么}}return}}return}====(long)d-{if(!(iter->index==-1&&iter->table=={if(iter-iter->d->iterators去掉禁?

}}longlongdictFingerprint(dict{longlongintegers[6],hash=0;intj;voiddictReleaseIterator(dictIterator{if(!(iter->index==-1&&iter->table=={if(iter-iter->d->iterators去掉禁?

assert(iter->fingerprint}}如果只是某個(gè)元素的valuelonglongdictFingerprint(dict*d){longlongintegers[6],hash=0;intj;====(long)d-for(j=0;j<6;{+=hash(~hash)+(hash<<hashhash^(hash>>hash(hash+(hash<<3))+(hashhashhash^(hash>>hash(hash+(hash<<2))+(hashhashhash^(hash>>hashhash+(hash<<}return}值得注意的是在字典擴(kuò)容時(shí)進(jìn)?rehash，將舊數(shù)組中的鏈表遷移到hashhashmod2^n=hashmod2^(n+1)=korkeys指令使?了安全迭代器，因?yàn)榻Y(jié)果不允許重復(fù)。那還有其===(long)d-forfor(j=0;j<6;j++){hash+=integers[j];hash=(~hash)+(hash<<21);hash=hash^(hash>>24);hash=(hash+(hash<<3))+(hashhash=hash^(hash>>hash=(hash+(hash<<