Limitando downloads paralelos/simultâneos - Como saber se o download foi cancelado?

<?php

class DownloadObserver
{
  protected $file;
  public function __construct($file) {
    $this->file = $file;
  }

  public function send() {
    // -> note in DB you've started
    readfile($this->file);
  }

  public function __destruct() {
    // download is done, either completed or aborted
    $aborted = connection_aborted();
    // -> note in DB
  }
}

$dl = new DownloadObserver("/tmp/whatever");
$dl->send();