round robin权重轮循算法php实现代码

先上代码，采用php脚本语言

    <?php

    /* 
     * Copyright (C) FatHong
     */

    /* 数据初始化，weight: 权重 */
    $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();

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

    /* 输出结果 */
    print_r($result);

    /* round robin 轮循 */
    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;
    }

输出结果：

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

负载均衡的服务器中，其实现算法有种是round-robin权重轮循，就是后端的服务器列表中，给每个服务器标上权重，代表它被采用的机率。

这段代码把最简洁的流程剥离出来，没考虑后端挂起等情况，可以知道它是怎么实现的，仅供参考.