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.