一致性哈希，主要用于redis的整合
代码转载：http://txf2004.iteye.com/blog/612507 作者：txf2004 标题：一致性哈希
主要实现了一致性哈希的算法，php界相当优秀的代码。谢谢txf2004。
<?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[$target] = array();// hash the target into multiple positionsfor ($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 targetsif (empty($this->_positionToTarget))return array();// optimize single targetif ($this->_targetCount == 1)return array_unique(array_values($this->_positionToTarget));// hash resource to a position$resourcePosition = $this->_hasher->hash($resource);$results = array();$collect = false;$this->_sortPositionTargets();// search values above the resourcePositionforeach ($this->_positionToTarget as $key => $value){// start collecting targets after passing resource positionif (!$collect && $key > $resourcePosition){$collect = true;}// only collect the first instance of any targetif ($collect && !in_array($value, $results)){$results []= $value;}// return when enough results, or list exhaustedif (count($results) == $requestedCount || count($results) == $this->_targetCount){return $results;}}// loop to start - search values below the resourcePositionforeach ($this->_positionToTarget as $key => $value){if (!in_array($value, $results)){$results []= $value;}// return when enough results, or list exhaustedif (count($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(',', $this->getAllTargets()));}// ----------------------------------------// private methods/** * Sorts the internal mapping (positions to targets) by position */private function _sortPositionTargets(){// sort by key (position) if not alreadyif (!$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($string);}/** * Uses CRC32 to hash a value into a signed 32bit int address space. * Under 32bit PHP this (safely) overflows into negatives ints. * * @author Paul Annesley * @package Flexihash * @licence http://www.opensource.org/licenses/mit-license.php */class Flexihash_Crc32Hasherimplements Flexihash_Hasher{/* (non-phpdoc) * @see Flexihash_Hasher::hash() */public function hash($string){return crc32($string);}}/** * Uses CRC32 to hash a value into a 32bit binary string data address space. * * @author Paul Annesley * @package Flexihash * @licence http://www.opensource.org/licenses/mit-license.php */class Flexihash_Md5Hasherimplements Flexihash_Hasher{/* (non-phpdoc) * @see Flexihash_Hasher::hash() */public function hash($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{}