About cyclic objects.

result.txt

$ php test.php 
Array
(
    [a] => 1
    [b] => 1
)
Array
(
    [a] => 1
    [b] => 1
)
Array
(
    [a] => 1
    [b] => 1
)
2 cyclic objects freed
Array
(
)

test.php

<?php
 
class a {}
class b {}
 
$a = new a;
$b = new b;
 
print_r(get_objects_count());
 
// Create circular deps
$a->b = $b;
$b->a = $a;
 
print_r(get_objects_count());
 
// Destroying objects
unset($a, $b);
 
print_r(get_objects_count());
 
// Forces collection of any existing garbage cycles
echo gc_collect_cycles(), " cyclic objects freed\n";
 
print_r(get_objects_count());