Week 4

Critical Sections

• Recap from last week:
  • UPC setup, including ssh keys and script to compile/run
  • Finish up demo of last two versions of UPC temperature programs
  • vim questions? tips/advice?
  • Programming assignment 2 due: next Tue, Feb 17

• Ben-Ari Ch 3
  • slides: PDF
    • begin slide 3.1, p. 50
  • The approaches to enter and exit critical sections were low-level and brittle
    • low-level because: relied on busy-waiting and checking on global variables
    • brittle because: many reasons!
      • processes relied on each other to enter their own CS!
      • hard-coded for a specific number of processes (i.e., 2)! what about for n?

Class Exercise

• More practice with interleavings
  • (Adapted from Problem 2.19 from Andrews's MPD text)
  • mpd-2.19-interleavings.pdf (handout)

Semaphores

• Next we introduce the abstraction of semaphores to control access to CS
• Ben-Ari Ch 6
  • slides: PDF
    • begin slide 6.1, p. 111

• Written HW: Ben-Ari p. 39:
  • Exercises 2, 3, and 4
  • Haven't forgotten that I owe you feedback–sorry!

• UPC Exercises 1.1 through 1.7
• Due: Tue, Feb 17, 11:59pm
• Here's a link: private