please answer fast and I will rate you high, thank you!!!

8. (25 Points) Jim plans to test out a new idea using a very low-cost wireless station that he can install outside his dorm room window. users can upload or download their MP3-encoded songs from their laptops, anytime, anywhere on campus. However, the cheap wireless technology he's acquired is half-duplex: all users can either upload or download--never both at once. The following questions investigate your ability to help Jim in particular ways. (8.1) (7 Points): Jim intends to test out the basic idea, with just two users, of whom only one can upload or download one song at a time. To impress him, you whip out the following simple semaphore-based synchronization code that only works for two users, along with an explanation of why it works correctly: upload 3 download () {