Main Ideas For Today

• Readers/Writers Problem
• Dining Philosophers Problem
• Sleeping Barber Problem
• Traffic Control Problem

Reading Assignment For Today

• Operating Systems: A Modern Perspective: Chapter 8, In the Hanger, pp 197-203.
  Read this again and study the examples!
• Operating Systems: A Modern Perspective: Chapter 8, Exercises 9, 10, 11.
  Read the exercises and understand the questions posed.

Discussion Assignments

Due Date: 6:00 am

Group B
Group A

Web Sites Related to Today's Topic

Getting Started With POSIX Threads

This page provides an introduction to posix threads. Written by Tom Wagner, Don Towsley at University of Massachusetts at Amherst. NOTE: That the syntax for the Semaphores used on this page is not exactly the same as what we are using.

Sample Code For Today's Class

• tcreate.c - Example of thread creation using p-threads in c (from class 5).
• terror.c - Example that demonstrates a race condition and the critical section problem.
• tlockfix.c - Example that shows how locks can be used to fix the terror.c program.
• tsemfix.c - Example that shows how semaphores can be used to fix the terror.c program.
• SleepBarber.c - Example that uses semaphores to solve the sleeping barber problem.

Project Assigned Today

Due Date: 4/27/00


1. Barber Shop Expansion:¹

   The barber from SleepBarber.c has achieved wild success because he is always well rested and perky. The customers love that. With his success came more and more customers and consequently more money. To better serve his growing number of customers the barber is going to expand. In the expansion he is going to add 2 more barber chairs (with narcoleptic barbers) and a cashier. Expand the code in SleepBarber.c to handle this expansion.

   • Be sure that each barber only services one customer at a time.
   • After a customer's hair is cut they must visit the cashier to pay.
   • The sleepiness in this place is contagious so the the cashier also sleeps when there is no one waiting to pay and must be woken by a customer who needs to pay.
   
   
2. Cookie-Bakers Problem:²

   A small cookie making company called "Deadlock Cookies" consists of 3 cookie chefs and 1 assistant. Each chef has a supply of one of 3 ingredients necessary to make cookies:

   • Chef 1 has a supply of dough.
   • Chef 2 has a supply of chocolate chips.
   • Chef 3 has a supply of nuts.
   The assistant has an infinite supply of all three items.

   To start the cookie making process the assistant will place a ration of each of two ingredients on the counter. The chef who has the third ingredient will take those two ingredients and begin making a batch of cookies. In the mean time the assistant randomly selects 2 more items and places them on the counter. This process should repeat until 10 batches of cookies have been made.

2. This problem is a knock-off of the "Cigarette-Smokers Problem" from "Operating Sytems Concepts, Fifth Ed." by Silberschatz and Galvin (Addison Wesley, 1998).