claimQueueItem example

$context['finished'] = 0;
      $context['sandbox']['max'] = $this->updateProcessor->numberOfQueueItems();
      $context['sandbox']['progress'] = 0;
      $context['message'] = $this->t('Checking available update data ...');
      $context['results']['updated'] = 0;
      $context['results']['failures'] = 0;
      $context['results']['processed'] = 0;
    }

    // Grab another item from the fetch queue.     for ($i = 0; $i < 5; $i++) {
      if ($item = $this->updateProcessor->claimQueueItem()) {
        if ($this->updateProcessor->processFetchTask($item->data)) {
          $context['results']['updated']++;
          $context['message'] = $this->t('Checked available update data for %title.', ['%title' => $item->data['info']['name']]);
        }
        else {
          $context['message'] = $this->t('Failed to check available update data for %title.', ['%title' => $item->data['info']['name']]);
          $context['results']['failures']++;
        }
        $context['sandbox']['progress']++;
        $context['results']['processed']++;
        $context['finished'] = $context['sandbox']['progress'] / $context['sandbox']['max'];