[PHP知识库] php中单例模式减少内存占用

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[PHP知识库]php中单例模式减少内存占用

1. 普通写法

首先，以一个例子来说明，重复new一个对象的内存占用情况：

<?php

class A {
	function test()
	{
		var_dump("dsfsdflsd");
	}

	function testB()
	{
		$a = ["就是","哈哈哈","哈哈哈哈","哈哈哈哈","就是","哈哈哈","哈哈哈哈","哈哈哈哈","就是","哈哈哈","哈哈哈哈","哈哈哈哈"];
		var_dump($a);
	}
}

$a = new A();
echo "1 ";
var_dump(memory_get_usage());

$a->test();
echo "2 ";
var_dump(memory_get_usage());
$a->testB();
echo "3 ";
var_dump(memory_get_usage());

$b = new A();
echo "4 ";
var_dump(memory_get_usage());

$c = new A();
echo "5 ";
var_dump(memory_get_usage());

$d = new A();
echo "6 ";
var_dump(memory_get_usage());

$e = new A();
echo "7 ";
var_dump(memory_get_usage());

上述例子的执行结果：

从上述结果，很明显的看到，没new 对象，对应的内存使用率随之增长；

2. 普通单例模式写法

现在，使用单例模式：

<?php

class A {
	private static $instance;

	private function __construct()
	{

	}

	public static function getInstance()
	{
		if (!(self::$instance instanceof self)) {
			self::$instance = new self();
		}
		return self::$instance;
	}

	public function test()
	{
		var_dump("dsfsdflsd");
	}

	public function testB()
	{
		$a = ["就是","哈哈哈","哈哈哈哈","哈哈哈哈","就是","哈哈哈","哈哈哈哈","哈哈哈哈","就是","哈哈哈","哈哈哈哈","哈哈哈哈"];
		var_dump($a);
	}

    //克隆方法私有化，防止复制实例
	private function __clone(){}
}

$a = A::getInstance();
echo "1 ";
var_dump(memory_get_usage());

$a->test();
echo "2 ";
var_dump(memory_get_usage());
$a->testB();
echo "3 ";
var_dump(memory_get_usage());

$b = A::getInstance();;
echo "4 ";
var_dump(memory_get_usage());

$c = A::getInstance();;
echo "5 ";
var_dump(memory_get_usage());

$d = A::getInstance();;
echo "6 ";
var_dump(memory_get_usage());

$e = A::getInstance();;
echo "7 ";
var_dump(memory_get_usage());

以下是代码执行结果：
?

?从上述执行结果可以看出，内存占用量一直保持不变，说明使用的是同一对象，没有新增重复对象

3. 并发情况下单例模式

内存仍然保持不变；压力测试命令：ab -n 1000 -c 10 url(-c 并发请求数，-n总请求数)

日志结果（内存使用量0表示new对象之前的内存占用量）：
[2022-02-18 16:24:54] dev.INFO: 16451726941831862993 内存使用量0: 1889832 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:54] dev.INFO: 16451726941831862993 内存使用量1: 1987344 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:54] dev.INFO: 16451726941831862993 内存使用量2: 1987344 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:54] dev.INFO: 16451726941831862993 内存使用量3: 1987344 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:54] dev.INFO: 16451726941831862993 内存使用量4: 1987344 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:54] dev.INFO: 16451726941831862993 内存使用量5: 1987344 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:54] dev.INFO: 16451726941831862993 内存使用量6: 1987344 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:54] dev.INFO: 16451726941831862993 内存使用量7: 1987344 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 16451726951695474085 内存使用量0: 1888920 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 16451726951695474085 内存使用量1: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 16451726951695474085 内存使用量2: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 16451726951695474085 内存使用量3: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 16451726951695474085 内存使用量4: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 16451726951695474085 内存使用量5: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 16451726951695474085 内存使用量6: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 16451726951695474085 内存使用量7: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 1645172695791050071 内存使用量0: 1888920 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 1645172695791050071 内存使用量1: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 1645172695791050071 内存使用量2: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 1645172695791050071 内存使用量3: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 1645172695791050071 内存使用量4: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 1645172695791050071 内存使用量5: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 1645172695791050071 内存使用量6: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 1645172695791050071 内存使用量7: 1986752 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 16451726951046930012 内存使用量0: 1888920 {"api":"/x/x/test2","data":[],"code":0}?
[2022-02-18 16:24:55] dev.INFO: 16451726951046930012 内存使用量1: 1986752 {"api":"/x/x/test2","data":[],"code":0}?