public function AdvancedQueue::claimItem in Advanced Queue 7

Claim an item in the queue for processing.

Parameters

$lease_time: How long the processing is expected to take in seconds, defaults to an hour. After this lease expires, the item will be reset and another consumer can claim the item. For idempotent tasks (which can be run multiple times without side effects), shorter lease times would result in lower latency in case a consumer fails. For tasks that should not be run more than once (non-idempotent), a larger lease time will make it more rare for a given task to run multiple times in cases of failure, at the cost of higher latency.

Return value

On success we return an item object. If the queue is unable to claim an item it returns false. This implies a best effort to retrieve an item and either the queue is empty or there is some other non-recoverable problem.

Overrides DrupalQueueInterface::claimItem

File

./advancedqueue.queue.inc, line 77

Class

AdvancedQueue

Extended queue.

Code

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) {
    $data = array(
      ':created' => time(),
      ':name' => $this->name,
    );
    $item = db_query_range('SELECT item_id, item_key, created, uid, title, data FROM {advancedqueue} q WHERE status = -1 AND expire = 0 AND name = :name AND created <= :created ORDER BY created ASC', 0, 1, $data)
      ->fetchObject();
    if ($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('advancedqueue')
        ->fields(array(
        'status' => ADVANCEDQUEUE_STATUS_PROCESSING,
        '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;
    }
  }
}