Guess what $counter is!

Destructy.php

<?php

function timer(callable $fn, $name, $freq=50000)
{
    $start = microtime(true);
	$start_mem = memory_get_usage(true);
	$things = [];
	for ($i = 0; $i < $freq; $i++)
	{
		$things[] = $fn();
	}
	$end_mem = memory_get_usage(true);
	print_r(sprintf("%s took %s seconds and %s bytes\n", $name, microtime(true) - $start, $end_mem - $start_mem));
}

$counter = 0;

class Destructy
{
    public function __destruct()
    {
        global $counter;
        $counter++;
    }
}

timer(function() {
    $a = new Destructy();
    $b = new Destructy();
    $a->foo = 'hey';
    $b->bar = 'there';
    unset($a);
    unset($b);
}, 'two variables');

echo "counter is now $counter\n";

timer(function() {
    $a = new Destructy();
    $b = new Destructy();
    $a->foo = $b;
    $b->bar = $a;
    unset($a);
    unset($b);
}, 'two variables with references to each other');

echo "counter is now $counter\n";
gc_collect_cycles();
echo "counter is now $counter\n";