How reliable is __destruct?

Question

Are there situations in which this method would not be called?

I'm thinking to store a important variable into a persistent cache just before the cache object gets destroyed. This variable is used many times in the page so I wouldn't like to update the cache with it every time the variable changes...

Answer 1

Let's have a class:

class A {
    public function __construct(){
        echo "Construct\n";
    }

    public function __destruct(){
        echo "Destruct\n";
    }
}

And test code:

$test = new A();
die( "Dead\n");  // Will output Construct; dead; Destruct

$test = new A();
throw new Exception("Blah\n"); // Construct, Fatal error (no destruct)

$test = new A();
require_once( 'invalid_file.php'); // Construct, Fatal error (no destruct)

So basically: there are situations (fatal errors) when destructor won't be called.

Ah and this question has the same answer as this one: When will __destruct not be called in PHP? (+/-)

Answer 2

It is called as soon as there are no more references to that particular object, or during the shutdown sequence. The manual also states destructors are called when scripts are terminated with exit().

Aside from the issue pointed out by TimWolla, I am not aware of any problems with PHP destructors.

Answer 3

It seems there at least was a problem using Windows: https://github.com/WoltLab/WCF/blob/ff7e6ed381f2ccab7f51220f97087921133b2237/wcfsetup/install/files/lib/system/WCF.class.php#L122

I don't know whether this is still relevant.