[php]对服务器进行一致性hash分布算法

<?php
/**
 * 对服务器进行一致性hash分布算法
 */
class HashRing
{
    private $servers = array();
    private $nodeList = array();
    private $nodeHashList = array();
    private $nodeTotalNum = 0;
    private $virtualNodeNum = 32;
    private $keyHash = '';

    public function __construct($servers)
    {
        $this->servers = $servers;
        foreach ($servers as $server) {
            for ($i = 0; $i < $this->virtualNodeNum; $i++) {
                $this->nodeList[sprintf("%u", crc32($server.'-'.$i))] = array($server, $i);
            }
        }
        ksort($this->nodeList);
        $this->nodeHashList = array_keys($this->nodeList);
    }

    private function getNodeIndex($key)
    {
        $this->keyHash = sprintf("%u", crc32($key));
        if ($this->keyHash > end($this->nodeHashList)) {
            $this->keyHash = $this->keyHash % end($this->nodeHashList);
        }
        if ($this->keyHash <= reset($this->nodeHashList)) {
            return 0;
        }
        $this->nodeTotalNum = count($this->nodeHashList);
        return $this->binaryChopIndex(0, $this->nodeTotalNum);
    }

    private function binaryChopIndex($l=0, $r=0)
    {
        if ($l < $r) {
            $avg = intval(($l+$r) / 2);
            if ($this->nodeHashList[$avg] == $this->keyHash) {
                return $avg;
            } elseif ($this->keyHash < $this->nodeHashList[$avg] && ($avg > 0)) {
                return $this->binaryChopIndex($l, $avg-1);
            } else {
                return $this->binaryChopIndex($avg+1, $r);
            }
        } else {
            return $l;
        }
    }

    public function getServersByKey($key, $num=1)
    {
        $index = $this->getNodeIndex($key);
        $server = $this->nodeList[$this->nodeHashList[$index]];
        if ($num == 1) {
            return $server[0];
        }
        if ($num >= count($this->servers)) {
            $num = count($this->servers);
        }
        $result = array($server[0]);
        for ($i=$index+1; true; $i++) {
            if ($i >= $this->nodeTotalNum) {
                $i = 0;
            }
            $nextServer = $this->nodeList[$this->nodeHashList[$i]];
            if (!in_array($nextServer[0], $result)) {
                $result[] = $nextServer[0];
            }
            if (count($result) == $num) {
                break;
            }
        }
        return $result;
    }
}



//示例
$servers = array(
    '127.0.0.1:11211',
    '127.0.0.1:11212',
    '127.0.0.1:11213',
    '127.0.0.1:11214',
    '127.0.0.1:11215'
);
$obj = new HashRing($servers);
$servers = $obj->getServersByKey('testkey', 2);
print_r($servers);
echo "\n";