PHP实现的一致性哈希算法完整实例

php  /  管理员 发布于 7年前   154

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：

 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。

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