Cancellable register_shutdown_function

demo.php

<?php
/**
 * @author Alexey Kopytko
 * @license MIT license
 */

include 'register_cancellable_shutdown_function.php';

$first = register_cancellable_shutdown_function(function () {
	echo "This function is never called\n";
});

$second = register_cancellable_shutdown_function(function () {
	echo "This function is going to be called\n";
});

cancel_shutdown_function($first);

register_cancellable_shutdown_function.php

<?php
/**
 * @author Alexey Kopytko
 * @license MIT license
 */

function register_cancellable_shutdown_function($callback)
{
        return new cancellable_shutdown_function_envelope($callback);
}

function cancel_shutdown_function(cancellable_shutdown_function_envelope $envelope)
{
	$envelope->cancel();
}

final class cancellable_shutdown_function_envelope
{
        private $callback;

        public function __construct($callback)
        {
                $this->callback = $callback;
                register_shutdown_function(function () {
                        $this->callback && call_user_func($this->callback);
                });
        }

        public function cancel()
        {
                $this->callback = false;
        }
}