是什么使__destruct在如此简单的PHP代码中被两次调用？ [英] What makes __destruct called twice in such a simple PHP code?

问题描述

<?php

class A
{
    static private $_instance = null;

    static public function Init()
    {   
        self::$_instance = new A();
    }   

    function __construct()
    {   
        echo "__construct\n";
    }   

    function __destruct()
    {   
        var_dump(debug_backtrace());
        echo "__destruct\n";
    }   
}
$a = A::Init();

通常，我们应该得到以下输出：（是的。我在2个不同的PHP服务器中得到了这个结果5.2.10-2ubuntu6.10和PHP 5.3.1）

Normally, we should get following output: (Yes. I got this result in 2 different servers with PHP 5.2.10-2ubuntu6.10 and PHP 5.3.1)

__construct
array(1) {
  [0]=>
  array(5) {
    ["function"]=>
    string(10) "__destruct"
    ["class"]=>
    string(1) "A"
    ["object"]=>
    object(A)#1 (0) {
    }
    ["type"]=>
    string(2) "->"
    ["args"]=>
    array(0) {
    }
  }
}
__destruct

但是，在另一台装有CentOS 5.7和PHP 5.2.17的服务器上，我得到了：

But, on another server with CentOS release 5.7 and PHP 5.2.17, I got this :

    __construct
    array(2) {
      [0]=>
      array(7) {
        ["file"]=>
        string(10) "/tmp/1.php"
        ["line"]=>
        int(7)
        ["function"]=>
        string(10) "__destruct"
        ["class"]=>
        string(1) "A"
        ["object"]=>
        object(A)#1 (0) {
        }
        ["type"]=>
        string(2) "->"
        ["args"]=>
        array(0) {
        }
      }
      [1]=>
      array(6) {
        ["file"]=>
        string(10) "/tmp/1.php"
        ["line"]=>
        int(21)
        ["function"]=>
        string(4) "Init"
        ["class"]=>
        string(1) "A"
        ["type"]=>
        string(2) "::"
        ["args"]=>
        array(0) {
        }
      }
    __destruct
    array(1) {
      [0]=>
      array(5) {
        ["function"]=>
        string(10) "__destruct"
        ["class"]=>
        string(1) "A"
        ["object"]=>
        object(A)#2 (0) {
        }
        ["type"]=>
        string(2) "->"
        ["args"]=>
        array(0) {
        }
      }
    }
    __destruct

为什么函数__destruct在这里被两次调用？尤其是第一次。

Why does the function __destruct called twice here? Especially the first time.

我认为配置中可能有一些特殊之处，有什么建议吗？

I think there might be something special in the configuration, any suggestion?

谢谢

==================

==================

PS ：此问题不是由单一设计模式引起的。相同的问题出现在以下代码中：

PS: This problem is not caused by "Singleton design pattern". Same issue appeared with following code :

<?php
class A
{
    function __construct()
    {   
        echo "__construct\n";
    }

    function __destruct()
    {
        var_dump(debug_backtrace());
        echo "__destruct\n";
    }
}
$a = new A(); 

推荐答案

最后我找到了原因。

这可能是PHP 5.2.x中的错误：

It might be a bug in PHP 5.2.x :

如果

zend.ze1_compatibility_mode = On 

上，您会看到 __destruct 两次，当执行我在问题中提供的代码时。

then you can see "__destruct" twice when execute the code I provide in my question.

此问题在其他版本中也有报道： https://bugs.php.net/bug.php?id=29756

This issue has been reported in other versions : https://bugs.php.net/bug.php?id=29756

在我的测试中不影响PHP 5.3。 （PHP 5.3删除了此设置）

Not affect PHP 5.3 in my test. (PHP 5.3 removed this setting)

希望此答案对以后的某些人有用：）

Hope this answer will be helpful for some guys later :)

这篇关于是什么使__destruct在如此简单的PHP代码中被两次调用？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！