ITFN 2601 Introduction to Operating Systems

1
ITFN 2601Introduction to Operating Systems

• Lecture 3
• IPC Problems

2
Agenda

• IPC Problems
• Dining Philosophers
• Readers Writers
• Sleeping Barber

3
IPC (Dining Philosophers)

• Multiple processes attempting to obtain multiple
  resources
• Not enough resources to satisfy all requests at
  all times (Wait necessary)
• Why is this relevant?

4
Philosophers Demonstration
5
Philosopher Resolution?

• Patterned locking?
• Take left, then take right?
• Locking the entire find fork area?
• Steal your forks while no one else can
• State Array?
• Track who has forks, who is waiting

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Philosopher Locked Table
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Readers Writers

• Multiple readers can co-exist
• Two people can read the same page
• Multiple writers cannot
• Two people cannot write the same page, they will
  forever be getting in the way
• Writers and readers cannot co-exist
• Cannot read what is not written

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Readers Writers (cont)

• Reader on Reader
• Allow it in
• Reader on Writer
• Writer on Writer
• Must wait for Writer to finish
• Writer on Reader
• Must wait for Reader to finish

9
Sleeping Barber

• How is this different from our sleep/wakeup
  examples?
• Wakeup is issued by a consumer
• Queue size limited
• Customers go to wait-queue if available
• Semaphores offer no count
• Variable to count members of wait-queue

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Summary

• Multiple Resources
• Multiple Consumers
• Must deal w/ these problems using semaphores
  mutex