gistfile1.txt

class Sample
{
    private ?\Closure $callback; // objects own reference

    public function start()
    {
        return $this->callback = $this->poll(...);
    }

    private function poll()
    {
        static $i;

        $i++;
        var_dump($i);
    }
}

class Main
{
    public function __construct(
        private \WeakMap $callbacks = new \WeakMap()
    )
    {}

    public function addCallback(\Closure $callback, ...$args)
    {
        $this->callbacks[$callback] = $args;
    }

    public function run()
    {
        for (;;) {
            foreach ($this->callbacks as $callback => $args) {
                $callback($args);
                unset($callback);
                usleep(100);
            }

            if (count($this->callbacks) < 1) {
                break;
            }
        }
    }
}

$sample = new Sample();
$main = new Main();

$main->addCallback($sample->start());
unset($sample);
$main->run();