DSNPool.inc

<?php
require_once dirname(__FILE__).'/DSN.inc';

class DSNPool
{
    
    
    private $_pool;
    
    private $_currentIndex = -1;
    
    
    public function __construct(Array $dsn_arr)
    {
        $this->_pool = Array();
        foreach ($dsn_arr as $dsn) {
            $this->_pool[] = new DSN($dsn);
        }
        
    }//end constructor
    
    
    public function registerFailureDSN($index = NULL)
    {
        // If there is no index passed in, use the current index
        if (is_null($index)) {
            $index = $this->_currentIndex;
        }
        
        if (isset($this->_pool[$index])) {
            $this->_pool[$index]->setFailure(TRUE);
        }
        
    }//end registerFailureDSN()
    
    
    public function getDSNFromIndex($index = -1)
    {
        // It is unlikely to happen but we reset the current index if the index is invalid
        if (!isset($this->_pool[$index])) {
            $index = -1;
        }
        
        // Set current index
        $this->_currentIndex = $index;
        
        // If index = -1, we just want to reset the current index
        if ($index == -1) {
            return NULL;
        }
        
        return $this->_pool[$index]->getDSN();
        
    }//end getDSNFromIndex()
    
    
    public function getDSN()
    {
        // Get the weight and index arrays of the active DSN objects
        $dsn_weights = $this->_getActiveDSNWeights();
        // Get a weighted random index of the weight array
        $weight_index = $this->_getWeightedRandomIndex($dsn_weights['weights']);
        // Get the pool index from the active weight index
        $index = $weight_index == -1 ? -1 : $dsn_weights['indexes'][$weight_index];
        
        return $this->getDSNFromIndex($index);
        
    }//end getDSN()
    
    
    private function _getActiveDSNWeights()
    {
        $weights = Array();
        $indexes = Array();
        foreach ($this->_pool as $index => $dsn) {
            if ($dsn->getFailure() !== TRUE) {
                $weights[] = $dsn->getWeight();
                $indexes[] = $index;
            }
        }
        
        return Array('weights' => $weights, 'indexes' => $indexes);
        
    }//end _getActiveDSNWeights()
    
    
    private function _getWeightedRandomIndex($weights)
    {
        switch (count($weights)) {
            case 0:
                // The weight array is empty, return -1 to indicate the invalid index
                return -1;
            case 1:
                // The weight array has one element, return the first index
                return 0;
        }
        
        // Get a random index number based on the weights. The bigger the weight of an array element, the bigger chance its index is selected.
        $total_weights = array_sum($weights);
        $random_number = mt_rand(1, $total_weights);
        $n = 0;
        foreach ($weights as $index => $weight) {
            $n += $weight;
            if ($n >= $random_number) {
                break;
            }
        }
        
        return $index;
        
    }//end _getWeightedRandomIndex()
    
    
}//end class


?>