一致性hash的c++简单实现

很晚了，一致性hash的理论不再多说，直接上我写的c++代码

代码功能：
1，初始化一些实际的server节点，每个server节点生成一堆虚拟节点
2，将所有的虚拟节点根据它的名字生成的hash key散布到一个环内
3，对新插入环内的元素（随机生成），计算它的hash key，然后在环中寻找大于等于它的虚拟节点，根据虚拟节点即可找到物理节点。随机生成很多歌元素，查看散布到各个节点的元素数量是否均衡。

代码一些特点：
对于server节点，只需要存储它的虚拟节点hash值以及与实际server名字的对应。对于新插入的元素，为了快速找到它所存放的位置（即大于等于它的hash值的虚拟节点），应该采用二分查找。 故而，虚拟节点使用map结构存储，底层是红黑树的实现，类似于二分，同时支持高效的插入删除。 当新的虚拟节点插入到环内，只需要移动很少量的元素到它上面。

还有chord算法要好好看看，还没有看。

#include<iostream>
#include <sstream>
#include <string>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <algorithm>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <iomanip>
#include <random>

#include <cstring>
#include <cmath>
#include <cstdlib>
#include <cstdio>

using namespace std;
typedef unsigned long Key;

template <class T>
struct NodeHasher
{
    template <class T>
    Key operator() (const T& t){
        return 0;
    }

    template <>
    Key operator()<string> (const string& t){
        return hash2((unsigned char*)t.c_str());
    }
public:
    //not a good hash function
    static unsigned long hash(unsigned char *str)
    {
        unsigned long hash = 5381;
        int c;

        while (c = *str++)
            hash = ((hash << 5) + hash) + c; /* hash * 33 + c */

        return hash;
    }
    static unsigned long hash2(unsigned char *str)
    {
        int p = 16777619;
        int hash = (int)2166136261L;
        int c;
        while (c = *str++)
            hash = (hash ^ c) * p;

        hash += hash << 13;
        hash ^= hash >> 7;
        hash += hash << 3;
        hash ^= hash >> 17;
        hash += hash << 5;

        // 如果算出来的值为负数则取其绝对值 
        if (hash < 0)
            hash = abs(hash);
        return hash;
    }
};

template <class T>
class ConsistentHash
{
public:
    ConsistentHash(int numberOfReplica = 150, bool isTest = false, int server=5): numOfReplicas(numberOfReplica){
        if (isTest)
        {
            for (int c = 0; c < server; ++c)
            {
                addServer(to_string(c));
            }
        }
    }
public:
    void addServer(T node){
        cout << "add real server:" << node << endl;
        for (int i = 0; i < numOfReplicas; ++i)
        {
            Key k = NodeHasher<T>()(node + std::to_string(i));
            if (i < 2)
                cout << "   virtual server: " << k << endl;
            else if (i == 2)
                cout << "   ... " <<numOfReplicas<< endl;
            circles.insert({ k, node });
        }
    }
    void removeServer(T node){
        cout << "remove real server:" << node << endl;
        for (int i = 0; i < numOfReplicas; ++i)
        {
            Key k = NodeHasher<T>()(node+std::to_string(i));
            auto it = circles.find(k);
            if (it != circles.end()) circles.erase(it);
        }
    }
public:
    T get(Key k){
        auto it = circles.find(k);
        if (it != circles.end()) return it->second;
        it = circles.lower_bound(k);
        return (it == circles.end()) ? circles.begin()->second : it->second;
    }
public:
    static void testIt(){
        int number = 100000;
        int server = 10;
        int virutal_server = 150;
        ConsistentHash chash(virutal_server, true, server);

        struct {
            void operator()(int number, ConsistentHash& chash) {
                map<T, int> countNumMap;

                std::random_device seed;
                std::mt19937 gen(seed());
                std::uniform_int_distribution<int> dist(0, LONG_MAX);
                for (int i = 0; i < number; ++i)
                {
                    Key k = dist(gen);
                    T node = chash.get(k);
                    countNumMap[node]++;
                }
                cout << "server numOfElems:" << endl;
                for (auto it : countNumMap){
                    cout << it.first << " " << it.second << " " << std::setprecision(2) << it.second*1.0 / number << endl;
                }
            }
        }show;

        for (int i = 0; i < server; ++i)
        {
            show(number, chash);
            chash.removeServer(std::to_string(i));
        }
    }
private:
    int numOfReplicas;
    map<Key, T> circles;
};
int main()
{
    ConsistentHash<string>::testIt();
    return 0;
}