====== Week 7 ======

~~NOTOC~~

===== From Semaphores to Monitors =====

**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 |

  * Class participation with monitors:
    * The One-Lane Bridge problem:<code text>
Cars coming from the north and south arrive at a 
one-lane bridge. Cars heading in the same direction 
can cross the bridge at the same time, but cars 
heading in opposite directions cannot.</code>
    * can we find a way to be safe, fair, and efficient?
    * {{onelanebridgemonitor2026.pdf|PDF}} (with thanks to Charlie Hughes!)

===== Monitors in Java =====

  * Java case study (starter code for Assign 4)
    * starter code for Assign 4  (for //**after**// the break)
    * this version deadlocks! 
    * you will use two different approaches to fix:
      * synchronized methods
      * synchronized code blocks \\ \\


===== 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)