Analysis of destructor __destruct and garbage collection mechanism in PHP

Destructor
Executed when a object becomes garbage or when the object is explicitly destroyed.
The destructor provided in PHP5 is destruct, which corresponds to the constructor methodconstruct.

Garbage Collection - GC (Garbage Collector)
In PHP, when there is no variable pointing to this object, the object becomes garbage, and PHP will destroy it in memory .
This is PHP's GC (Garbage Collector) garbage disposal mechanism. Garbage collection can prevent memory overflow.
When a PHP thread ends, all memory space currently occupied will be destroyed, and all objects in the current program will also be destroyed.

destruct() destructor is executed when the garbage object is recycled.
The destructor is automatically called by the system, and can also be called explicitly, but do not do this.

As shown in the program below, all objects are destroyed before the program ends. The destructor was called.

<?php
class Person {
	public function destruct(){
		echo &#39;析构函数现在执行了 <br />&#39;;
		echo &#39;这里一般用来设置、关闭数据库、关闭文件等收尾工作&#39;;
	}}$p = new Person();for($i = 0; $i < 5; $i++){
	echo "$i <br />";}
	?>

Program running results:

0 1 2 3 4 析构函数现在执行了 
这里一般用来设置、关闭数据库、关闭文件等收尾工作

When the object is not pointed to, the object is destroyed.

<?php
class Person {
	public function destruct(){
		echo &#39;析构函数现在执行了 <br />&#39;;
	}
}

$p = new Person();
$p = null; // 析构函数在这里执行了
$p = "abc"; // 一样的效果
for($i = 0; $i < 5; $i++){
	echo "$i <br />";
}
?>

Program running result:

析构函数现在执行了 
0 
1 
2 
3 
4

In the above example, we set $p to empty or give $p a string, In this way, the object pointed to by $p becomes a garbage object. PHP garbage destroys this object.

php unset variable

<?php
class Person {
	public function destruct(){
		echo &#39;析构函数现在执行了 <br />&#39;;
	}
}

$p = new Person();
$p1 = $p;

unset($p);
echo &#39;现在把 $p 被销毁了，对象是否也被销毁了呢？ <br />&#39;;

for($i = 0; $i < 5; $i++){
	echo "$i <br />";
}

echo &#39;现在再把 $p1 也销毁掉,即已经没有指向对象的变量了<br />&#39;;
unset($p1); // 现在没有指向对象的变量了,析构函数在这里执行了
?>

Program execution result:

现在把 $p 被销毁了，对象是否也被销毁了呢？
0 
1 
2 
3 
4 
现在再把 $p1 也销毁掉,即已经没有指向对象的变量了
析构函数现在执行了

unset destroys the variable pointing to the object, not the object.

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