PHP实现的一致性哈希算法完整实例


Posted in PHP onNovember 14, 2015

本文实例讲述了PHP实现的一致性哈希算法。分享给大家供大家参考,具体如下:

<?php
/**
 * Flexihash - A simple consistent hashing implementation for PHP.
 * 
 * The MIT License
 * 
 * Copyright (c) 2008 Paul Annesley
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 * 
 * @author Paul Annesley
 * @link http://paul.annesley.cc/
 * @copyright Paul Annesley, 2008
 * @comment by MyZ (http://blog.csdn.net/mayongzhan)
 */
/**
 * A simple consistent hashing implementation with pluggable hash algorithms.
 *
 * @author Paul Annesley
 * @package Flexihash
 * @licence http://www.opensource.org/licenses/mit-license.php
 */
class Flexihash
{
  /**
   * The number of positions to hash each target to.
   *
   * @var int
   * @comment 虚拟节点数,解决节点分布不均的问题
   */
  private $_replicas = 64;
  /**
   * The hash algorithm, encapsulated in a Flexihash_Hasher implementation.
   * @var object Flexihash_Hasher
   * @comment 使用的hash方法 : md5,crc32
   */
  private $_hasher;
  /**
   * Internal counter for current number of targets.
   * @var int
   * @comment 节点记数器
   */
  private $_targetCount = 0;
  /**
   * Internal map of positions (hash outputs) to targets
   * @var array { position => target, ... }
   * @comment 位置对应节点,用于lookup中根据位置确定要访问的节点
   */
  private $_positionToTarget = array();
  /**
   * Internal map of targets to lists of positions that target is hashed to.
   * @var array { target => [ position, position, ... ], ... }
   * @comment 节点对应位置,用于删除节点
   */
  private $_targetToPositions = array();
  /**
   * Whether the internal map of positions to targets is already sorted.
   * @var boolean
   * @comment 是否已排序
   */
  private $_positionToTargetSorted = false;
  /**
   * Constructor
   * @param object $hasher Flexihash_Hasher
   * @param int $replicas Amount of positions to hash each target to.
   * @comment 构造函数,确定要使用的hash方法和需拟节点数,虚拟节点数越多,分布越均匀,但程序的分布式运算越慢
   */
  public function __construct(Flexihash_Hasher $hasher = null, $replicas = null)
  {
    $this->_hasher = $hasher ? $hasher : new Flexihash_Crc32Hasher();
    if (!empty($replicas)) $this->_replicas = $replicas;
  }
  /**
   * Add a target.
   * @param string $target
   * @chainable
   * @comment 添加节点,根据虚拟节点数,将节点分布到多个虚拟位置上
   */
  public function addTarget($target)
  {
    if (isset($this->_targetToPositions[$target]))
    {
      throw new Flexihash_Exception("Target '$target' already exists.");
    }
    $this->_targetToPositions[$target] = array();
    // hash the target into multiple positions
    for ($i = 0; $i < $this->_replicas; $i++)
    {
      $position = $this->_hasher->hash($target . $i);
      $this->_positionToTarget[$position] = $target; // lookup
      $this->_targetToPositions[$target] []= $position; // target removal
    }
    $this->_positionToTargetSorted = false;
    $this->_targetCount++;
    return $this;
  }
  /**
   * Add a list of targets.
   * @param array $targets
   * @chainable
   */
  public function addTargets($targets)
  {
    foreach ($targets as $target)
    {
      $this->addTarget($target);
    }
    return $this;
  }
  /**
   * Remove a target.
   * @param string $target
   * @chainable
   */
  public function removeTarget($target)
  {
    if (!isset($this->_targetToPositions[$target]))
    {
      throw new Flexihash_Exception("Target '$target' does not exist.");
    }
    foreach ($this->_targetToPositions[$target] as $position)
    {
      unset($this->_positionToTarget[$position]);
    }
    unset($this->_targetToPositions[$target]);
    $this->_targetCount--;
    return $this;
  }
  /**
   * A list of all potential targets
   * @return array
   */
  public function getAllTargets()
  {
    return array_keys($this->_targetToPositions);
  }
  /**
   * Looks up the target for the given resource.
   * @param string $resource
   * @return string
   */
  public function lookup($resource)
  {
    $targets = $this->lookupList($resource, 1);
    if (empty($targets)) throw new Flexihash_Exception('No targets exist');
    return $targets[0];
  }
  /**
   * Get a list of targets for the resource, in order of precedence.
   * Up to $requestedCount targets are returned, less if there are fewer in total.
   *
   * @param string $resource
   * @param int $requestedCount The length of the list to return
   * @return array List of targets
   * @comment 查找当前的资源对应的节点,
   *     节点为空则返回空,节点只有一个则返回该节点,
   *     对当前资源进行hash,对所有的位置进行排序,在有序的位置列上寻找当前资源的位置
   *     当全部没有找到的时候,将资源的位置确定为有序位置的第一个(形成一个环)
   *     返回所找到的节点
   */
  public function lookupList($resource, $requestedCount)
  {
    if (!$requestedCount)
      throw new Flexihash_Exception('Invalid count requested');
    // handle no targets
    if (empty($this->_positionToTarget))
      return array();
    // optimize single target
    if ($this->_targetCount == 1)
      return array_unique(array_values($this->_positionToTarget));
    // hash resource to a position
    $resourcePosition = $this->_hasher->hash($resource);
    $results = array();
    $collect = false;
    $this->_sortPositionTargets();
    // search values above the resourcePosition
    foreach ($this->_positionToTarget as $key => $value)
    {
      // start collecting targets after passing resource position
      if (!$collect && $key > $resourcePosition)
      {
        $collect = true;
      }
      // only collect the first instance of any target
      if ($collect && !in_array($value, $results))
      {
        $results []= $value;
      }
      // return when enough results, or list exhausted
      if (count($results) == $requestedCount || count($results) == $this->_targetCount)
      {
        return $results;
      }
    }
    // loop to start - search values below the resourcePosition
    foreach ($this->_positionToTarget as $key => $value)
    {
      if (!in_array($value, $results))
      {
        $results []= $value;
      }
      // return when enough results, or list exhausted
      if (count($results) == $requestedCount || count($results) == $this->_targetCount)
      {
        return $results;
      }
    }
    // return results after iterating through both "parts"
    return $results;
  }
  public function __toString()
  {
    return sprintf(
      '%s{targets:[%s]}',
      get_class($this),
      implode(',', $this->getAllTargets())
    );
  }
  // ----------------------------------------
  // private methods
  /**
   * Sorts the internal mapping (positions to targets) by position
   */
  private function _sortPositionTargets()
  {
    // sort by key (position) if not already
    if (!$this->_positionToTargetSorted)
    {
      ksort($this->_positionToTarget, SORT_REGULAR);
      $this->_positionToTargetSorted = true;
    }
  }
}
/**
 * Hashes given values into a sortable fixed size address space.
 *
 * @author Paul Annesley
 * @package Flexihash
 * @licence http://www.opensource.org/licenses/mit-license.php
 */
interface Flexihash_Hasher
{
  /**
   * Hashes the given string into a 32bit address space.
   *
   * Note that the output may be more than 32bits of raw data, for example
   * hexidecimal characters representing a 32bit value.
   *
   * The data must have 0xFFFFFFFF possible values, and be sortable by
   * PHP sort functions using SORT_REGULAR.
   *
   * @param string
   * @return mixed A sortable format with 0xFFFFFFFF possible values
   */
  public function hash($string);
}
/**
 * Uses CRC32 to hash a value into a signed 32bit int address space.
 * Under 32bit PHP this (safely) overflows into negatives ints.
 *
 * @author Paul Annesley
 * @package Flexihash
 * @licence http://www.opensource.org/licenses/mit-license.php
 */
class Flexihash_Crc32Hasher
  implements Flexihash_Hasher
{
  /* (non-phpdoc)
   * @see Flexihash_Hasher::hash()
   */
  public function hash($string)
  {
    return crc32($string);
  }
}
/**
 * Uses CRC32 to hash a value into a 32bit binary string data address space.
 *
 * @author Paul Annesley
 * @package Flexihash
 * @licence http://www.opensource.org/licenses/mit-license.php
 */
class Flexihash_Md5Hasher
  implements Flexihash_Hasher
{
  /* (non-phpdoc)
   * @see Flexihash_Hasher::hash()
   */
  public function hash($string)
  {
    return substr(md5($string), 0, 8); // 8 hexits = 32bit
    // 4 bytes of binary md5 data could also be used, but
    // performance seems to be the same.
  }
}
/**
 * An exception thrown by Flexihash.
 *
 * @author Paul Annesley
 * @package Flexihash
 * @licence http://www.opensource.org/licenses/mit-license.php
 */
class Flexihash_Exception extends Exception
{
}

希望本文所述对大家PHP程序设计有所帮助。

PHP 相关文章推荐
用PHP的ob_start();控制您的浏览器cache!
Nov 25 PHP
PHP HTML代码串 截取实现代码
Jun 29 PHP
超级实用的7个PHP代码片段分享
Jan 05 PHP
浅析PHP原理之变量(Variables inside PHP)
Aug 09 PHP
php自定义函数截取汉字长度
May 15 PHP
简单谈谈favicon
Jun 10 PHP
Yii框架表单模型和验证用法
May 20 PHP
php注册和登录界面的实现案例(推荐)
Oct 24 PHP
深入解析PHP中SESSION反序列化机制
Mar 01 PHP
PHP更安全的密码加密机制Bcrypt详解
Jun 18 PHP
Laravel5.5 手动分页和自定义分页样式的简单实现
Oct 15 PHP
PHP设计模式(八)装饰器模式Decorator实例详解【结构型】
May 02 PHP
PHP使用redis实现统计缓存mysql压力的方法
Nov 14 #PHP
PHP+redis实现添加处理投票的方法
Nov 14 #PHP
PHP实现操作redis的封装类完整实例
Nov 14 #PHP
php实现的递归提成方案实例
Nov 14 #PHP
PHP使用Pthread实现的多线程操作实例
Nov 14 #PHP
开启PHP Static 关键字之旅模式
Nov 13 #PHP
php正则表达式学习笔记
Nov 13 #PHP
You might like
在PHP中检查PHP文件是否有语法错误的方法
2009/12/23 PHP
PHP依赖倒置(Dependency Injection)代码实例
2014/10/11 PHP
PHP获取文件夹内文件数的方法
2015/03/12 PHP
CodeIgniter配置之SESSION用法实例分析
2016/01/19 PHP
总结PHP内存释放以及垃圾回收
2018/03/29 PHP
经典的解除许多网站无法复制文字的绝招
2006/12/31 Javascript
JavaScript对象之间的转换 jQuery对象和原声DOM
2011/03/07 Javascript
分享XmlHttpRequest调用Webservice的一点心得
2012/07/20 Javascript
jquery和javascript的区别(常用方法比较)
2013/07/04 Javascript
通过onmouseover选项卡实现img图片的变化
2014/02/12 Javascript
javascript实现table表格隔行变色的方法
2015/05/13 Javascript
学习JavaScript设计模式之代理模式
2016/01/12 Javascript
JS实现回到页面顶部动画效果的简单实例
2016/05/24 Javascript
AngulaJS路由 ui-router 传参实例
2017/04/28 Javascript
利用vue开发一个所谓的数独方法实例
2017/12/21 Javascript
Vue写一个简单的倒计时按钮功能
2018/04/20 Javascript
实例详解BootStrap的动态模态框及静态模态框
2018/08/13 Javascript
JS利用prototype给类添加方法操作详解
2019/06/21 Javascript
微信小程序npm引入vant-weapp的踩坑记录
2019/08/01 Javascript
使用vue制作滑动标签
2019/09/21 Javascript
Python中的__SLOTS__属性使用示例
2015/02/18 Python
Swift 3.0在集合类数据结构上的一些新变化总结
2016/07/11 Python
解决Ubuntu pip 安装 mysql-python包出错的问题
2018/06/11 Python
详解python单元测试框架unittest
2018/07/02 Python
python tkinter canvas 显示图片的示例
2019/06/13 Python
python GUI库图形界面开发之PyQt5布局控件QVBoxLayout详细使用方法与实例
2020/03/06 Python
Html5页面在微信端的分享的实现方法
2018/08/30 HTML / CSS
HTML5 Canvas实现图片缩放、翻转、颜色渐变的代码示例
2016/02/28 HTML / CSS
法国一家芭蕾舞鞋公司:Repetto
2018/11/12 全球购物
违纪检讨书2000字
2014/02/08 职场文书
诚信考试倡议书
2014/04/15 职场文书
党支部班子“四风”问题自我剖析材料
2014/09/28 职场文书
买卖合同协议书范本
2014/10/18 职场文书
保险公司增员口号
2015/12/25 职场文书
MySQL 时间类型的选择
2021/06/05 MySQL
SpringBoot整合JWT的入门指南
2021/06/29 Java/Android