AggregateCache.php

<?php
/****************************************************************************
 *   Copyright (C) 2005-2008 by Anton E. Lebedevich, Konstantin V. Arkhipov *
 *                                                                          *
 *   This program is free software; you can redistribute it and/or modify   *
 *   it under the terms of the GNU Lesser General Public License as         *
 *   published by the Free Software Foundation; either version 3 of the     *
 *   License, or (at your option) any later version.                        *
 *                                                                          *
 ****************************************************************************/

namespace OnPHP\Core\Cache;

/**
 * A wrapper to multiple cache for workload
 * distribution using CachePeer childs.
 * 
 * @ingroup Cache
**/
class AggregateCache extends BaseAggregateCache
{
	const LEVEL_ULTRAHIGH	= 0xFFFF;
	const LEVEL_HIGH		= 0xC000;
	const LEVEL_NORMAL		= 0x8000;
	const LEVEL_LOW			= 0x4000;
	const LEVEL_VERYLOW		= 0x0001;

	private $levels		= array();

	/**
	 * @return AggregateCache
	**/
	public static function create()
	{
		return new self;
	}

	/**
	 * @return AggregateCache
	**/
	public function addPeer(
		$label, CachePeer $peer, $level = self::LEVEL_NORMAL
	)
	{
		$this->doAddPeer($label, $peer);

		$this->peers[$label]['level'] = $level;

		return $this;
	}

	/**
	 * @return AggregateCache
	**/
	public function setClassLevel($class, $level)
	{
		$this->levels[$class] = $level;

		return $this;
	}

	/**
	 * brain
	**/
	protected function guessLabel($key)
	{
		$class = $this->getClassName();

		if (isset($this->levels[$class])) {
			$classLevel = $this->levels[$class];
		} else {
			$classLevel = self::LEVEL_NORMAL;
		}

		// init by $key, randomness will be restored later
		mt_srand(intval(hexdec(substr(md5($key), 3, 7))));

		$zeroDistances = array();
		$weights = array();

		foreach ($this->peers as $label => $peer) {
			$distance = abs($classLevel - $peer['level']);

			if (!$distance) {
				$zeroDistances[] = $label;
			} else {
				$weights[$peer['level']] = 1 / pow($distance, 2); // BOVM
			}
		}

		if (count($zeroDistances)) {

			$selectedLabel =
				$zeroDistances[mt_rand(0, count($zeroDistances) - 1)];

		} else {

			// weighted random level selection
			$sum = mt_rand() * array_sum($weights) / mt_getrandmax();
			$peerLevel = null;
			foreach ($weights as $level => $weight) {
				if ($sum <= $weight) {
					$peerLevel = $level;
					break;
				} else {
					$sum -= $weight;
				}
			}

			$selectedPeers = array();
			foreach ($this->peers as $label => $peer) {
				if ($peer['level'] == $peerLevel) {
					$selectedPeers[] = $label;
				}
			}

			$selectedLabel = $selectedPeers[mt_rand(0, count($selectedPeers) - 1)];
		}

		if (isset($this->peers[$selectedLabel]['stat'][$class])) {
			++$this->peers[$selectedLabel]['stat'][$class];
		} else {
			$this->peers[$selectedLabel]['stat'][$class] = 1;
		}

		// restore randomness
		mt_srand(
			(int) (
				(int) (microtime(true) << 2)
				* (rand(time() / 2, time()) >> 2)
			)
		);

		return $selectedLabel;
	}
}
?>