Week 6

• UPC exercises 1.1 — 1.7
  • Assigned: 2/18
  • Due: 2/27

• Exam next Wednesday, March 6
• handout: sample questions from a previous exam
• Review session next Monday, March 4

Semaphores

• Two operations:
  • wait(s)
    • Traditional: P(s)
    • Definition:

       < await (s > 0) s = s - 1; >

  • signal(s)
    • Traditional: V(s)
    • Definition:

       < s = s + 1; >

• wait(s) and signal(s) work the same for binary and counting (general) semaphores
  • binary semaphore: value is always either 1 or 0
  • general semaphore: value is nonnegative

Class exercise

• The Bear and the Honeybees (handout)
  • split binary semaphores
  • technique: pass the baton

• The Water Molecule Problem (handout)
  • solve using counting semaphores
  • solve using a single mutex

Semaphores

• Ben-Ari Ch 6
  • slides: PDF
    • begin slide 105