round robin权重轮循算法实现
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。
-----------------------------------------------
小编hx注解：
附执行时，每个key的变化，就比较好理解了。
每次执行时current_weight加上weight，如果当前current_weight>=weight则命中，把命中的减去所有weight(本例中是10)，然后不断循环。
Array
(
[a] => Array
(
[weight] => 5
[current_weight] => -5
[count] => 1
)
[b] => Array
(
[weight] => 3
[current_weight] => 3
[count] => 0
)
[c] => Array
(
[weight] => 2
[current_weight] => 2
[count] => 0
)
)
Array
(
[a] => Array
(
[weight] => 5
[current_weight] => 0
[count] => 1
)
[b] => Array
(
[weight] => 3
[current_weight] => -4
[count] => 1
)
[c] => Array
(
[weight] => 2
[current_weight] => 4
[count] => 0
)
)
Array
(
[a] => Array
(
[weight] => 5
[current_weight] => 5
[count] => 1
)
[b] => Array
(
[weight] => 3
[current_weight] => -1
[count] => 1
)
[c] => Array
(
[weight] => 2
[current_weight] => -4
[count] => 1
)
)
Array
(
[a] => Array
(
[weight] => 5
[current_weight] => 0
[count] => 2
)
[b] => Array
(
[weight] => 3
[current_weight] => 2
[count] => 1
)
[c] => Array
(
[weight] => 2
[current_weight] => -2
[count] => 1
)
)
Array
(
[a] => Array
(
[weight] => 5
[current_weight] => -5
[count] => 3
)
[b] => Array
(
[weight] => 3
[current_weight] => 5
[count] => 1
)
[c] => Array
(
[weight] => 2
[current_weight] => 0
[count] => 1
)
)
Array
(
[a] => Array
(
[weight] => 5
[current_weight] => 0
[count] => 3
)
[b] => Array
(
[weight] => 3
[current_weight] => -2
[count] => 2
)
[c] => Array
(
[weight] => 2
[current_weight] => 2
[count] => 1
)
)
Array
(
[a] => Array
(
[weight] => 5
[current_weight] => -5
[count] => 4
)
[b] => Array
(
[weight] => 3
[current_weight] => 1
[count] => 2
)
[c] => Array
(
[weight] => 2
[current_weight] => 4
[count] => 1
)
)
Array
(
[a] => Array
(
[weight] => 5
[current_weight] => 0
[count] => 4
)
[b] => Array
(
[weight] => 3
[current_weight] => 4
[count] => 2
)
[c] => Array
(
[weight] => 2
[current_weight] => -4
[count] => 2
)
)
Array
(
[a] => Array
(
[weight] => 5
[current_weight] => 5
[count] => 4
)
[b] => Array
(
[weight] => 3
[current_weight] => -3
[count] => 3
)
[c] => Array
(
[weight] => 2
[current_weight] => -2
[count] => 2
)
)
Array
(
[a] => Array
(
[weight] => 5
[current_weight] => 0
[count] => 5
)
[b] => Array
(
[weight] => 3
[current_weight] => 0
[count] => 3
)
[c] => Array
(
[weight] => 2
[current_weight] => 0
[count] => 2
)
)
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