BEGIN;
SELECT stuff ... FOR UPDATE;
    fetches `stuff` and prevents (via a lock) other connections from messing with row(s).
work with `stuff`.
UPDATE the rows SELECTed (or a subset of them)
COMMIT;

(autocommit=1)
UPDATE Queue... WHERE ... LIMIT...  -- Grab row for self
SELECT ... WHERE ...           -- Make sure I got it, and fetch id
if got it     -- Perhaps someone else got it
then
    BEGIN;
    work on application things
    COMMIT;
endif
DELETE FROM Queue WHERE ...   -- remove from queue