round robin權重輪循算法php實現代碼

先上代碼，采用php腳本語言

<?php

/* 
 * Copyright (C) FatHong
 */

/* 數據初始化，weight: 權重 */
$hosts['a'] = array('weight' => 5, 'current_weight' => 0, 'count' => 0);
$hosts['b'] = array('weight' => 3, 'current_weight' => 0, 'count' => 0);
$hosts['c'] = array('weight' => 2, 'current_weight' => 0, 'count' => 0);

$result = array();

/* 模擬10次 */
for ($i = 0; $i < 10; $i++) {
  round_robin($hosts, $result);
}

/* 輸出結果 */
print_r($result);

/* round robin 輪循 */
function round_robin(&$hosts, &$result)
{
  $total = 0;
  $best = null;

  foreach ($hosts as $key => $item) {
    $current = &$hosts[$key];
    $weight = $current['weight'];

    $current['current_weight'] += $weight;
    $total += $weight;

    if ( ($best == null) || ($hosts[$best]['current_weight'] < 
                $current['current_weight']) ) 
    {
      $best = $key;
    }
  }

  $hosts[$best]['current_weight'] -= $total;
  $hosts[$best]['count']++;

  $result[] = $best;
}

輸出結果：

Array
(
[0] => a
[1] => b
[2] => c
[3] => a
[4] => a
[5] => b
[6] => a
[7] => c
[8] => b
[9] => a
)

負載均衡的服務器中，其實現算法有種是round-robin權重輪循，就是後端的服務器列表中，給每個服務器標上權重，代表它被采用的機率。

這段代碼把最簡潔的流程剝離出來，沒考慮後端掛起等情況，可以知道它是怎麼實現的，僅供參考.