CS 3733 Operating Systems

• Bounded buffer problem
  • Assume a pool of n buffers each of which can contain one item.
  • Use three semaphores: mutex, empty and full.
  • The mutex semaphore is initialized to 1.
  • The empty and full semaphores count the number of empty and full buffers. They are initialized to n and 0.

• Producer-consumer (unbounded)
• Reader-writer problem (4 variations) Consider a shared file in which some processes need to only read, but others may need to update (read and write).
  • Strong reader preference
    No reader will be kept waiting unless a writer has already obtained permission to write. That is, no reader will be kept waiting because a writer is waiting. This problem may have starvation of writers.

  • Strong writer preference - this one is harder
    Once a writer is waiting, it gets to write as soon as possible. That is, new readers must wait if a writer is waiting. This problem may have starvation of readers.

  • Weak reader preference - Readers can continue to get in as long as a reader is reading, but when no one is accessing, the next access is selected on a FIFO basis.

  • Weak writer preference - Readers can continue to get until a writer is next in line.

Skill: Understand the classical synchronization problems.