====== Week 6 ======

~~NOTOC~~


===== Lecture Notes =====

**Semaphores**

  * Ben-Ari Ch 6
    * slides: {{slides.pdf|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) {{ the_hungry_birds.pdf |PDF}}
    * split binary semaphores
      * where for binary semaphores s1 and s2: <code text>
  0 <= s1+s2 <= 1 </code>
    * technique: pass the baton

**Monitors**

  * Marc's Lecture Notes: {{ cs377-monitors.pdf |PDF}}
  * Ben-Ari Ch 7
    * begin slide 146
  * Dr. Seuss on Deadlock:
    * [[zax|The Zax]]
  * 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 {{diningupcphils.pdf |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)