Default queue implementation.


Expanded class hierarchy of SystemQueue

Related topics

1 string reference to 'SystemQueue'
DrupalQueue::get in modules/system/
Returns the queue object for a given name.


modules/system/, line 198
Queue functionality.

View source
class SystemQueue implements DrupalReliableQueueInterface {

   * The name of the queue this instance is working with.
   * @var string
  protected $name;
  public function __construct($name) {
    $this->name = $name;
  public function createItem($data) {

    // During a Drupal 6.x to 7.x update, drupal_get_schema() does not contain
    // the queue table yet, so we cannot rely on drupal_write_record().
    $query = db_insert('queue')
      'name' => $this->name,
      'data' => serialize($data),
      // We cannot rely on REQUEST_TIME because many items might be created
      // by a single request which takes longer than 1 second.
      'created' => time(),
    return (bool) $query
  public function numberOfItems() {
    return db_query('SELECT COUNT(item_id) FROM {queue} WHERE name = :name', array(
      ':name' => $this->name,
  public function claimItem($lease_time = 30) {

    // Claim an item by updating its expire fields. If claim is not successful
    // another thread may have claimed the item in the meantime. Therefore loop
    // until an item is successfully claimed or we are reasonably sure there
    // are no unclaimed items left.
    while (TRUE) {
      $item = db_query_range('SELECT data, item_id FROM {queue} q WHERE expire = 0 AND name = :name ORDER BY created, item_id ASC', 0, 1, array(
        ':name' => $this->name,
      if ($item) {

        // Try to update the item. Only one thread can succeed in UPDATEing the
        // same row. We cannot rely on REQUEST_TIME because items might be
        // claimed by a single consumer which runs longer than 1 second. If we
        // continue to use REQUEST_TIME instead of the current time(), we steal
        // time from the lease, and will tend to reset items before the lease
        // should really expire.
        $update = db_update('queue')
          'expire' => time() + $lease_time,
          ->condition('item_id', $item->item_id)
          ->condition('expire', 0);

        // If there are affected rows, this update succeeded.
        if ($update
          ->execute()) {
          $item->data = unserialize($item->data);
          return $item;
      else {

        // No items currently available to claim.
        return FALSE;
  public function releaseItem($item) {
    $update = db_update('queue')
      'expire' => 0,
      ->condition('item_id', $item->item_id);
    return $update
  public function deleteItem($item) {
      ->condition('item_id', $item->item_id)
  public function createQueue() {

    // All tasks are stored in a single database table (which is created when
    // Drupal is first installed) so there is nothing we need to do to create
    // a new queue.
  public function deleteQueue() {
      ->condition('name', $this->name)



Contains filters are case sensitive
Namesort descending Modifiers Type Description Overrides
SystemQueue::$name protected property The name of the queue this instance is working with.
SystemQueue::claimItem public function Claim an item in the queue for processing. Overrides DrupalQueueInterface::claimItem
SystemQueue::createItem public function Add a queue item and store it directly to the queue. Overrides DrupalQueueInterface::createItem
SystemQueue::createQueue public function Create a queue. Overrides DrupalQueueInterface::createQueue
SystemQueue::deleteItem public function Delete a finished item from the queue. Overrides DrupalQueueInterface::deleteItem
SystemQueue::deleteQueue public function Delete a queue and every item in the queue. Overrides DrupalQueueInterface::deleteQueue
SystemQueue::numberOfItems public function Retrieve the number of items in the queue. Overrides DrupalQueueInterface::numberOfItems
SystemQueue::releaseItem public function Release an item that the worker could not process, so another worker can come in and process it before the timeout expires. Overrides DrupalQueueInterface::releaseItem
SystemQueue::__construct public function