PHP：析构函数vs register_shutdown_function [英] PHP: destructor vs register_shutdown_function

问题描述

我有一个PHP类，可以动态创建PNG图像并将其发送到浏览器。 PHP手册说我需要确保在结束时调用 imagedestroy 函数来释放内存。现在，如果我没有使用类，我会有这样的代码：

I have a PHP class that creates a PNG image on the fly and sends it to browser. PHP manual says that I need to make sure that imagedestroy function is called at end to release the memory. Now, if I weren't using a class, I would have some code like this:

function shutdown_func() 
{
    global $img;
    if ($img)
        imagedestroy($img);
}
register_shutdown_function("shutdown_func");

但是，我相信我班级的适当位置是打电话给 imagedestroy 在类'析构函数中。

However, I believe that appropriate place for my class would be to place a call to imagedestroy in class' destructor.

我没有发现析构函数是否以与关闭函数相同的方式被调用？例如，如果用户在浏览器中按下STOP按钮，则执行停止。

I failed to find out if destructors get called the same way shutdown functions does? For example, if execution stops when user presses the STOP button in browser.

注意：无论你在答案中写什么，请指向一些文章或手册页（URL）支持它。

Note: whatever you write in your answer, please point to some article or manual page (URL) that supports it.

推荐答案

我刚用Apache测试过，PHP用作Apache模块。我创建了一个这样的无限循环：

I just tested with Apache, PHP being used as Apache module. I created an endless loop like this:

<?php
class X
{
    function __destruct()
    {
        $fp = fopen("/var/www/htdocs/dtor.txt", "w+");
        fputs($fp, "Destroyed\n");
        fclose($fp);
    }
};

$obj = new X();
while (true) {
    // do nothing
}
?>

这是我发现的：

• 在Firefox中按STOP按钮不会停止此脚本


• 如果我关闭Apache，则析构函数不会被调用


• 当它到达PHP max_execution_time并且destuctor没有被调用时它停止

然而，执行此操作：

<?php
function shutdown_func() {
    $fp = fopen("/var/www/htdocs/dtor.txt", "w+");
    fputs($fp, "Destroyed2\n");
    fclose($fp);
}
register_shutdown_function("shutdown_func");

while (true) {
    // do nothing
}
?>

调用shutdown_func。所以这意味着类destuctor不如关闭函数那么好。

shutdown_func gets called. So this means that class destuctor is not that good as shutdown functions.

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