PHP实现负载均衡的加权轮询方法分析

<?php
// php实现负载均衡的加权轮询（WRR）
class WRR {
  // 每次取100人
  const num = 100;
  // 上次取值时间，秒级时间戳
  public $last_time;
  // 权重 machine=>weight
  public $machines = array(
    'a' => 3, // 0.6
    'b' => 1, // 0.2
    'c' => 1 // 0.2
  );
  // 占比
  public $proportion = array();
  // 用户队列
  public static $user_ids = array();
  public function __construct() {
    // 各机器的占比
    $total = 0;
    foreach ($this->machines as $machine => $weight) {
      $total += $weight;
    }
    $this->proportion['a'] = $this->machines['a'] / $total;
    $this->proportion['b'] = $this->machines['b'] / $total;
    $this->proportion['c'] = $this->machines['c'] / $total;
  }
  public function getUsers() {
    // 用户人数
    $cnt = count(self::$user_ids);
    $a_num = 0;
    $b_num = 0;
    $c_num = 0;
    if ($cnt >= self::num) { // 队列超过100人
      $a_num = round(self::num * $this->proportion['a']);
      $b_num = round(self::num * $this->proportion['b']);
      $c_num = $cnt - $a_num - $b_num;
    } else { // 队列不足100人
      $last_time = $this->last_time; // 上次访问时间
      while (true) {
        $current_time = $this->getMillisecond();
        if (($current_time - $last_time) >= 10) { // 当前时间和上一次取值时间超过10ms
          $a_num = round($cnt * $this->proportion['a']);
          $b_num = round($cnt * $this->proportion['b']);
          $c_num = $cnt - $a_num - $b_num;
          $this->last_time = self::getMillisecond();  // 更新访问时间
          break;
        }
      }
    }
    $a = array_splice(self::$user_ids, 0, $a_num);
    $b = array_splice(self::$user_ids, 0, $b_num);
    $c = array_splice(self::$user_ids, 0, $c_num);
    return array(
      'a' => $a,
      'b' => $b,
      'c' => $c
    );
  }
  // 获取毫秒级时间戳
  public function getMillisecond() {
    list($t1, $t2) = explode(" ", microtime());
    return (float)sprintf('%.0f', (floatval($t1) + floatval($t2)) * 1000);
  }
}
// 测试
$wrr = new WRR();
for ($i = 0; $i < 3; $i++) {// 模拟持续不断的用户请求
  $random = rand(10, 120);
  $user_ids = range(1, $random);
  WRR::$user_ids = $user_ids;
  $users = $wrr->getUsers();
  print_r($users);
}