lock_head with ctids

lock_head.sql

    CREATE OR REPLACE FUNCTION lock_head() RETURNS SETOF jobs AS $$                                                                                  
         DECLARE                                                                                                                                          
           unlocked integer;                                                                                                                              
           job jobs%rowtype;                                                                                                                              
         BEGIN                                                                                                                                            
           SELECT id INTO unlocked                                                                                                                        
             FROM jobs                                                                                                                                    
             WHERE locked_at IS NULL                                                                                                               
             AND ctid = any(array(SELECT ctid FROM jobs LIMIT 10))
             LIMIT 1                                                                                                                      
             FOR UPDATE;                                                                                                                                  
           RETURN QUERY UPDATE jobs                                                                                                                       
             SET locked_at = (CURRENT_TIMESTAMP)                                                                                                          
             WHERE id = unlocked AND locked_at IS NULL                                                                                                    
             RETURNING *;                                                                                                                                 
         END;                                                                                                                                             
         $$ LANGUAGE plpgsql;