架构师训练营 - 第五周 - 作业

class Flexihash
{
    /**
     * @var int
     * @comment 虚拟节点数,解决节点分布不均的问题
     */
    private $_replicas = 64;

    /**
     * @var object Flexihash_Hasher
     * @comment 使用的hash方法 : md5,crc32
     */
    private $_hasher;

    /**
     * @var int
     * @comment 节点记数器
     */
    private $_targetCount = 0;

    /**
     * @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();

    /**
     * @var array { target => [ position, position, ... ], ... }
     * @comment 节点对应位置,用于删除节点
     */
    private $_targetToPositions = array();

    /**
     * @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;
    }

    /**
     * 添加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;
    }

    /**
     * 添加
     */
    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 getAll()
    {
        return array(
            "targers"=>$this->_positionToTarget,
            "positions"=>$this->_targetToPositions);
    }

    public function lookup($resource)
    {
        $targets = $this->lookupList($resource, 1);
        if (empty($targets)) throw new Flexihash_Exception('No targets exist');
        return $targets[0]; //0表示返回离资源位置最近的机器节点
    }

    /**
     * @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');

        if (empty($this->_positionToTarget))
            return array();

        if ($this->_targetCount == 1)
            return array_unique(array_values($this->_positionToTarget));

        $resourcePosition = $this->_hasher->hash($resource);

        $results = array();
        $collect = false;

        $this->_sortPositionTargets();

        foreach ($this->_positionToTarget as $key => $value)
        {
            if (!$collect && $key > $resourcePosition)
            {
                $collect = true;
            }

            if ($collect && !in_array($value, $results))
            {
                $results []= $value;
            }
            if (count($results) == $requestedCount || count($results) == $this->_targetCount)
            {
                return $results;
            }
        }

        foreach ($this->_positionToTarget as $key => $value)
        {
            if (!in_array($value, $results))
            {
                $results []= $value;
            }

            if (count($results) == $requestedCount || count($results) == $this->_targetCount)
            {
                return $results;
            }
        }

        return $results;
    }

    public function __toString()
    {
        return sprintf(
            '%s{targets:[%s]}',
            get_class($this),
            implode(',', $this->getAllTargets())
        );
    }

    private function _sortPositionTargets()
    {
        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
    }

}

class Flexihash_Exception extends Exception
{
}

$hash = new Flexihash();
$targets=array(
    "192.168.1.1:11011",
    "192.168.1.1:11012",
    "192.168.1.1:11013",
    "192.168.1.1:11014",
    "192.168.1.1:11015",
);
$hash->addTargets($targets);
for ($i=0; $i < 25; $i++) {
    $resource = sprintf("format %d",$i);
    var_dump($resource." --> ".$hash->lookup($resource));
}

string(30) "format 0 --> 192.168.1.1:11015"
string(30) "format 1 --> 192.168.1.1:11015"
string(30) "format 2 --> 192.168.1.1:11015"
string(30) "format 3 --> 192.168.1.1:11015"
string(30) "format 4 --> 192.168.1.1:11011"
string(30) "format 5 --> 192.168.1.1:11011"
string(30) "format 6 --> 192.168.1.1:11011"
string(30) "format 7 --> 192.168.1.1:11011"
string(30) "format 8 --> 192.168.1.1:11012"
string(30) "format 9 --> 192.168.1.1:11013"
string(31) "format 10 --> 192.168.1.1:11013"
string(31) "format 11 --> 192.168.1.1:11011"
string(31) "format 12 --> 192.168.1.1:11012"
string(31) "format 13 --> 192.168.1.1:11011"
string(31) "format 14 --> 192.168.1.1:11014"
string(31) "format 15 --> 192.168.1.1:11014"
string(31) "format 16 --> 192.168.1.1:11014"
string(31) "format 17 --> 192.168.1.1:11014"
string(31) "format 18 --> 192.168.1.1:11012"
string(31) "format 19 --> 192.168.1.1:11012"
string(31) "format 20 --> 192.168.1.1:11013"
string(31) "format 21 --> 192.168.1.1:11012"
string(31) "format 22 --> 192.168.1.1:11012"
string(31) "format 23 --> 192.168.1.1:11014"
string(31) "format 24 --> 192.168.1.1:11012"