FUNCTION next_task RETURN task.task_id%TYPE
IS
   /* Cursor of all open tasks, assigned and unassigned */
   CURSOR task_cur IS
      SELECT task_id
        FROM task
       WHERE task_status = 'OPEN'
       ORDER BY task_priority, date_entered DESC;

   /* The record for the above cursor */
   task_rec task_cur%ROWTYPE;
   /*
   || An exception for error ORA-00054:
   || "resource busy and acquire with NOWAIT specified"
   */
   record_locked EXCEPTION
   PRAGMA EXCEPTION_INIT (record_locked, -54);
   /* 
   || Variables which determine whether function should continue
   || to loop through the cursor's records.
   */
   found_unassigned_task BOOLEAN := TRUE;
   more_tasks BOOLEAN := TRUE;

   /* The primary key of the unassigned task to be returned */
   return_value task.task_id%TYPE := NULL;
BEGIN
   /* Open the cursor and start up the loop through its records */
   OPEN task_cur;
   WHILE NOT found_unassigned_task AND more_tasks
   LOOP
      /* Fetch the next record. If nothing found, we are done */
      FETCH task_cur INTO task_rec;
      more_tasks := task_cur%NOTFOUND;
      IF more_tasks
      THEN
         /*
         || A record was fetched. Create an anonymous block within
         || the function so that I can trap the record_locked
         || exception and still stay inside the cursor loop.
         */
         BEGIN
            /* Try to get a lock on the current task */
            SELECT task_id INTO return_value
              FROM task
              WHERE task_id = task_rec.task_id
             FOR UPDATE OF task_id NOWAIT;
            /*
            || If I get to this line then I was able to get a lock
            || on this particular task. Notice that the SELECT INTO
            || has therefore already set the function's return value.
            || Now set the Boolean to stop the loop.
            */
            found_unassigned_task := TRUE;
         EXCEPTION
            WHEN record_locked
            THEN
               /* Record was already locked, so just keep on going */
               NULL;
         END;
      END IF;
   END LOOP;
   /*
   || Return the task id. Notice that if an unassigned task was NOT
   || found, I will simply return NULL.
   */
   CLOSE task_cur;
   RETURN return_value;
EXCEPTION
   /*
   || General exception handler for the function: if an error occurred,
   || then close the cursor and return NULL for the task ID.
   */
   WHEN OTHERS 
   THEN
      CLOSE task_cur;
      RETURN NULL;
END;