<?php
/**
 * 一致性hash分布式算法
 * @param $key
 * @return int
 * 實現(xiàn)步驟
 * 1.先將0~ 是32位最大帶符號整數(shù)（0x7FFFFFFF） 想象成一個閉環(huán)
 * 2.將服務器列表通過hash算法分布在 圓環(huán)之中
 * 3.將key值也分布在圓環(huán)之中
 * 4.通過_isSorted判斷服務器是否需要進行倒序排序 排序后遍歷服務器 找到最近的服務器 返回
 * hash算法是不保證平衡的 為了盡量保證平衡性 我們應該加入虛擬節(jié)點數(shù) 將一個服務器節(jié)點虛擬化成為多個 較大程度上保證了平衡性
 */
class FlexiHash{
  private $_serverList = array();
  private $_isSorted = false;
  private $_virtual_node_num = 20;//虛擬節(jié)點數(shù) 服務器越少 增加的虛擬節(jié)點數(shù)應該越多
  //通過hash算法返回一個整數(shù)值
  protected function myHash($key){
    $md5 = substr(md5($key),0,8);
    $seed = 31; //種子值
    $hash=0;
    for($i=0;$i<8;$i++){
      $hash = $hash*$seed+ord($md5{$i}); //ord 返回ascii值
      $i++;
    }
    return $hash&0x7FFFFFFF; //0x7FFFFFFF表示最大值
  }
  //添加服務器
  function addServer($server){
    $hash =$this->myHash($server. '#1');
    if(!isset($this->_serverList[$hash])) {
      for ($i = 1; $i <= $this->_virtual_node_num; $i++) {
        $hash = $this->myHash($server . '#' . $i);
        $this->_serverList[$hash] = $server;
      }
    }
    $this->_isSorted = false;
    return true;
  }
  //刪除服務器
  function removeServer($server){
    for ($i = 1; $i <= $this->_virtual_node_num; $i++) {
      $hash = $this->myHash($server . '#' . $i);
      unset($this->_serverList[$hash]);
    }
    $this->_isSorted = false;
    return true;
  }
  //獲取服務器
  function lookup($key){
    $hash =$this->myHash($key);
    if(!$this->_isSorted){
      krsort($this->_serverList,SORT_NUMERIC);
      $this->_isSorted = true;
    }
    foreach($this->_serverList as $pos=>$server){
      if($hash >= $pos) return $server;
    }
    return end($this->_serverList);
  }
  public function getServerList(){
    krsort($this->_serverList,SORT_NUMERIC);
    return $this->_serverList;
  }
}
//demo test
$hserver = new FlexiHash();
//添加服務器
$hserver->addServer('192.168.1.1');
$hserver->addServer('192.168.1.2');
$hserver->addServer('192.168.1.3');
$hserver->addServer('192.168.1.4');
$hserver->addServer('192.168.1.5');
$key1='Key1111';
$key2='Key2222';
$key2='Key3333';
$key2='Key4444';
$key2='Key5555';
$key2='Key6666';
echo "save key1 in server: ".$hserver->lookup($key1).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key2).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key3).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key4).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key5).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key6).PHP_EOL;
echo "================================================".PHP_EOL;
//移除服務器 key值將自動轉義到下一臺服務器
$hserver->removeServer('192.168.1.4');
echo "save key1 in server: ".$hserver->lookup($key1).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key2).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key3).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key4).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key5).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key6).PHP_EOL;
echo "================================================".PHP_EOL;
//恢復故障服務器 key值將恢復原來服務器
$hserver->addServer('192.168.1.4');
echo "save key1 in server: ".$hserver->lookup($key1).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key2).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key3).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key4).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key5).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key6).PHP_EOL;