Week 6

Lecture Notes

Semaphores

  • Ben-Ari Ch 6
    • slides: PDF
      • begin: Dining Philosophers
  • Code walk: Dining UPC Philosophers
    • Version 1: busy waiting with upc_lock_attempt()
    • Version 2: deadlocking with upc_lock()

Class exercise

  • The Hungry Birds (handout) PDF
    • split binary semaphores
      • where for binary semaphores s1 and s2: 
          0 <= s1+s2 <= 1
    • technique: pass the baton

Monitors

  • Marc's Lecture Notes: PDF
  • Ben-Ari Ch 7
    • begin slide 146
  • Dr. Seuss on Deadlock:
  • Semaphores vs. Monitors
Semaphore Monitor
wait may or may not block waitC always blocks
signal always has an effect signalC has no effect
if queue is empty
signal unblocks an arbitrary blocked process signalC unblocks the process at the head of the queue
a process unblocked by signal can resume execution immediately a process unblocked by signalC must wait for the signaling process to leave monitor

Midterm Programming Assignment

  • Dining UPC Philosophers PDF
    • Note: version 3 is required (sorry for any confusion!)
      • it can definitely be implemented with busy waiting
      • the challenge is whether it can be implemented without busy waiting!
  • Assigned: Thu, Feb 19
  • Due: Tue, Mar 3, 11:59pm (Tue before Spring break)