A simple implementation of the Weighted Round-Robin Scheduling in PHP ( PHP >= 5.3 )

PHP Weighted Round Robin Scheduling

<?php

/**
 * @author Alexis Gruet
 * 
 * A simple implementation of the Weighted Round-Robin Scheduling in PHP 5.3+
 * 
 * The weighted round-robin scheduling is designed to better handle servers with different 
 * processing capacities. Each server can be assigned a weight, an integer value that 
 * indicates the processing capacity. Servers with higher weights receive new connections 
 * first than those with less weights, and servers with higher weights get more connections 
 * than those with less weights and servers with equal weights get equal connections.
 * 
 * Note : 
 *  composer     is required 
 *  array_column is required - use ./composer.phar require rhumsaa/array_column:~1.1 
 *  predis       is required - use ./composer.phar require predis/predis:~0.7.3
 *  
 *  
 * $aProvider represents an array of partners with their associated weights. 
 * 
 * For example, the partners, 1, 2 and 3, have the weights, 4, 3, 2 
 * respectively, a scheduling sequence will be 1 1 2 1 2 3 1 2 3 in a scheduling 
 * period (mod sum(w(provider))).
 * 
 * Useful when you want to send smartly balanced traffic to a remote api or something else
 * 
 * @see http://kb.linuxvirtualserver.org/wiki/Weighted_Round-Robin_Scheduling
 */

const __I__  = 'round-robin-dispatch-i';
const __CW__ = 'round-robin-dispatch-cw';

require __DIR__ . '/../vendor/autoload.php';

$c = new \Pimple;

/**
 * Registering predis
 */
$c[ 'predis' ] = (function () {
	return new Predis\Client( array(
		'scheme' => 'tcp',
		'host'   => '127.0.0.1',
		'port'   => '6379'
	));
});

/**
 * A list of partners with their associated weights
 */
$aProvider = array(
	0 => array( 
		'provider' => 'partner1',   
		'weight'   => 4 ),
	1 => array( 
		'provider' => 'partner2', 
		'weight'   => 3 ),
	2 => array( 
		'provider' => 'partner3', 
		'weight'   => 2 )
);

/**
 * A simple array used for stats
 */
$aStats = array(
	'partner1'   => 0,
	'partner2'   => 0,
	'partner3'   => 0,
);

/**
 * Weighted round robin algorithm
 */
$wrr = function() use( $c, $aProvider ) {
	
	$n  = count( $aProvider );
	$i  = $c[ 'predis' ]->exists( __I__ )  ? $c[ 'predis' ]->get( __I__ )   : -1;
	$cw = $c[ 'predis' ]->exists( __CW__ ) ? $c[ 'predis' ]->get( __CW__ )  : 0;
	
	/**
	 * greatest common divisor of all provider weights;
	 */
	$gcd = function() use ( $aProvider ) {
		$gcd = function ( $a, $b ) use ( &$gcd ) {
			return $b ? $gcd( $b, $a % $b ) : $a;
		};
		return array_reduce( array_column( $aProvider, 'weight' ), $gcd );
	};
	
	/**
	 * get the max weight across the whole providers
	 */
	$max = array_reduce( $aProvider, function( $v, $w ) {
		return max( $v, $w[ 'weight' ] );
	}, -9999999 );
	
	/**
	 * get the weight of a specific provider
	 */
	$w = function( $provider ) use ( $aProvider ) {
		return $aProvider[ $provider ][ 'weight' ];
	};
	
	while( 1 ) {
		
		$i = ( $i + 1 ) % $n; $c[ 'predis' ]->set( __I__, $i );
		if ( $i == 0 ) {
			 $cw = $cw - $gcd(); $c[ 'predis' ]->set( __CW__, $cw );
			 if ( $cw <= 0 ) {
			 	$cw = $max; $c[ 'predis' ]->set( __CW__, $cw );
			 	if ( $cw == 0 ) {
			 		return NULL;
			 	}
			 }
		}
		if ( $w( $i ) >= $cw ) {
			return $aProvider[ $i ];
		}
	}
};

for ( $k=1;$k<=100;$k++ ) {
	
	$current = $wrr();
	
	echo  '----------------------'       		     . PHP_EOL;
	echo  'Iteration       :: ' . $k    		     . PHP_EOL;
	echo  'Will be sent to :: ' . $current[ 'provider' ] . PHP_EOL;
	
	$aStats[ $current[ 'provider' ] ]++;
	
	//sleep( 1 );
}

echo  PHP_EOL;
echo  PHP_EOL;
echo  'Statistics' . PHP_EOL;
echo  '---------------------------------------' . PHP_EOL;
print_r( $aStats );