You can lock a row in a Postgres table by using "FOR UPDATE" in a SELECT query. The row will stay locked until the transaction is over. For example:
BEGIN;
SELECT *
FROM users
WHERE id = 123
FOR UPDATE; -- 👈
-- at this point, another process can't update user #123 until we're done
UPDATE users
SET name = 'John Smith'
WHERE id = 123;
COMMIT; -- we're done
SELECT *
FROM users
WHERE id = 123
FOR UPDATE; -- 👈
-- at this point, another process can't update user #123 until we're done
UPDATE users
SET name = 'John Smith'
WHERE id = 123;
COMMIT; -- we're done