PHP实现的一致性哈希算法完整实例

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：

_hasher = $hasher ? $hasher : new Flexihash_Crc32Hasher();
    if (!empty($replicas)) $this->_replicas = $replicas;
  }
  
  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;
  }
  
  public function addTargets($targets)
  {
    foreach ($targets as $target)
    {
      $this->addTarget($target);
    }
    return $this;
  }
  
  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;
  }
  
  public function getAllTargets()
  {
    return array_keys($this->_targetToPositions);
  }
  
  public function lookup($resource)
  {
    $targets = $this->lookupList($resource, 1);
    if (empty($targets)) throw new Flexihash_Exception('No targets exist');
    return $targets[0];
  }
  
  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
  
  private function _sortPositionTargets()
  {
    // sort by key (position) if not already
    if (!$this->_positionToTargetSorted)
    {
      ksort($this->_positionToTarget, SORT_REGULAR);
      $this->_positionToTargetSorted = true;
    }
  }
}

interface Flexihash_Hasher
{
  
  public function hash($string);
}

class Flexihash_Crc32Hasher
  implements Flexihash_Hasher
{
  
  public function hash($string)
  {
    return crc32($string);
  }
}

class Flexihash_Md5Hasher
  implements Flexihash_Hasher
{
  
  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.
  }
}

class Flexihash_Exception extends Exception
{
}

希望本文所述对大家PHP程序设计有所帮助。