php LRU 模拟redis LRU淘汰过期的key

原创

mzh9112 2021-08-13 01:02:23 博主文章分类：redis ©著作权

文章标签 redis php LRU 页面置换 json 文章分类 PHP 后端开发

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LRU是最近最少使用页面置换算法(Least Recently Used),也就是首先淘汰最长时间未被使用的页面

* LRU_Cache.php

<?php
/**
 * Created by PhpStorm.
 * User: mingzhanghui
 * Date: 1/10/2020
 * Time: 14:40
 */

class LRU_Cache
{
    /** @var array */
    private $map;

    /** @var int */
    private $cap = 0;

    /**
     * LRU_Cache constructor.
     * @param $size int
     */
    public function __construct($size) {
        $this->map = array();
        $this->cap = $size;
    }

    /**
     * @param $key string
     * @param $value mixed
     */
    public function setValue($key, $value) {
        // 如果存在，则向队尾移动，先删除，后追加
        if (isset($this->map[$key])) {
            unset($this->map[$key]);
        }
        // 长度检查, 超长则删除首元素
        if (count($this->map) >= $this->cap) {
            array_shift($this->map);
        }
        // 队尾追加元素
        $this->map[$key] = $value;
    }

    /**
     * @param $key
     * @return mixed|null
     */
    public function getValue($key) {
        $ret = null;
        if (isset($this->map[$key])) {
            $ret = $this->map[$key];
            // 移动到队尾
            unset($this->map[$key]);
            $this->map[ $key ] = $ret;
        }
        return $ret;
    }

    /**
     * @return false|string
     */
    public function __toString() {
        return json_encode($this->map);
    }
}

测试代码:

* index.php

<?php
/**
 * Created by PhpStorm.
 * User: mingzhanghui
 * Date: 1/10/2020
 * Time: 14:50
 */
include "LRU_Cache.php";

$cache = new LRU_Cache(5);
$cache->setValue("01", "a");
$cache->setValue("02", "b");
$cache->setValue("03", "c");
$cache->setValue("04", "d");
$cache->setValue("05", "e");
printf("%s\n", $cache);

$cache->setValue("06", "f");
printf("%s\n", $cache);

$cache->setValue("03", "g");
printf("%s\n", $cache);

$cache->setValue("07", "h");
printf("%s\n", $cache);

$cache->setValue("01", "xxx");
printf("%s\n", $cache);

php index.php

{"01":"a","02":"b","03":"c","04":"d","05":"e"}
{"02":"b","03":"c","04":"d","05":"e","06":"f"}
{"02":"b","04":"d","05":"e","06":"f","03":"g"}
{"04":"d","05":"e","06":"f","03":"g","07":"h"}
{"05":"e","06":"f","03":"g","07":"h","01":"xxx"}

缓存中始终5个元素始终淘汰array首个元素，查询或者设置key，会使对应的KeyValuePair到array末尾