Add FOR UPDATE to the query.
FOR UPDATE prevents the rows retrieved by the SELECT statement from being modified or deleted by other transactions until the current transaction ends. Other transactions that attempt UPDATE, DELETE, or SELECT FOR UPDATE of these rows will be blocked until the current transaction ends.
$set: IF TRUE, FOR UPDATE will be added to the query, if FALSE then it won't.
QueryConditionInterface: The called object.
includes/ database/ select.inc, line 535
- Interface definition for a Select Query object.
public function forUpdate($set = TRUE);