function DatabaseQueue::claimItem

File

core/lib/Drupal/Core/Queue/DatabaseQueue.php, line 116

Class

DatabaseQueue

Default queue implementation.

Namespace

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) {
        try {
            $item = $this->connection
                ->queryRange('SELECT data, created, item_id FROM {' . static::TABLE_NAME . '} q WHERE expire = 0 AND name = :name ORDER BY created, item_id ASC', 0, 1, [
                ':name' => $this->name,
            ])
                ->fetchObject();
        } catch (\Exception $e) {
            $this->catchException($e);
        }
        // If the table does not exist there are no items currently available to
        // claim.
        if (empty($item)) {
            return FALSE;
        }
        // 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 = $this->connection
            ->update(static::TABLE_NAME)
            ->fields([
            '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;
        }
    }
}