Destructable.php

<?php

namespace Drupal\destructable_test;

use Drupal\Core\DestructableInterface;
final class Destructable implements DestructableInterface {
  
  /**
   * Semaphore filename.
   *
   * @var string
   */
  protected string $semaphore;
  
  /**
   * Set the destination for the semaphore file.
   *
   * @param string $semaphore
   *   Temporary file to set a semaphore flag.
   */
  public function setSemaphore(string $semaphore) : void {
    $this->semaphore = $semaphore;
  }
  
  /**
   * {@inheritdoc}
   */
  public function destruct() {
    sleep(3);
    file_put_contents($this->semaphore, 'ran');
  }

}