leveldb -- 2 [LRUCache C++ 实现]

来源：互联网发布：淘宝微信优惠小助手编辑：程序博客网时间：2024/05/14 20:06

在看leveldb实现过程中发现小和尚的藏经阁里提到 LRUCache，翻书，发现是内存的普遍实现。

Cache有种实现：hit一次就让计数器+1，这样需要覆盖，就找count最少的。每次都需要轮询，效率低。所以LRUCache就出来了

C++实现这里已经有很好的实现了如何用C++实现一个LRU Cache

我下面就是抄了一遍。是的，抄了一遍，关键要记住

//A simple LRUCache demo//double linked list + hashmap#include <iostream>#include <cassert>#include <vector>#include <ext/hash_map>using namespace std;using namespace __gnu_cxx;template< class K, class T>struct Node{    K key;    T value;    Node *prev,*next;};template< class K, class T>class LRUCache {public:    LRUCache(size_t size){        entries_ = new Node<K,T>[size];        for(int i=0;i<size;i++)            free_entries_.push_back(entries_+i);        head_ = new Node<K,T>;        tail_ = new Node<K,T>;        head_->prev = NULL;        head_->next = tail_;        tail_->prev = head_;        tail_->next = NULL;    }    ~LRUCache(){       delete head_;       delete tail_;       delete[] entries_;    }     T Get(K key){        Node<K,T>* node = hashmap_[key];        if(node){            detach(node);            attach(node);            return node->value;        }        else{            return T();        }    }    void Put(K key, T value){        Node<K,T> *node = hashmap_[key];        if(node){//node exist            detach(node);            node->value = value;            attach(node);        }else{            if(free_entries_.empty()){//cache full                node = tail_->prev;                detach(tail_->prev);                hashmap_.erase(node->key);            }else{                //cache available                node = free_entries_.back();                free_entries_.pop_back();            }            node->key =  key;            node->value = value;            hashmap_[key] = node;            attach(node);        }    }private:        Node<K,T> *head_,*tail_;        Node<K,T> *entries_;        hash_map<K, Node<K,T>* > hashmap_;        vector<Node<K,T>* > free_entries_;        void detach(Node<K,T>* node){            node->next->prev = node->prev;            node->prev->next = node->next;        }        void attach(Node<K,T>* node){            node->prev = head_;            node->next = head_->next;            head_->next = node;            head_->next->prev = node;        }};int main(int argc, char* argv[]){    hash_map<int,int> map;    map[9]= 999;    cout<<map[9]<<endl;    cout<<map[10]<<endl;    LRUCache<int,string> lruCache(100);    lruCache.Put(1,"hello");    cout<<lruCache.Get(1)<<endl;    if(lruCache.Get(2) == ""){        cout<<"Put 2!"<<endl;        lruCache.Put(2,"world");    }    cout<<lruCache.Get(2)<<endl;    return 0;}

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