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：
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<?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{} |
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