Concurrent Programming 8893
Assignment 3

1. (Text 5.6 p. 256 (b) only) Dining Philosophers One solution to the dining philosophers problem, in which the philosophers are modeled as in Philosopher.java and eat with chopsticks as in Chopstick.java, is to use a waiter to control access to the chopsticks. Each phiolosopher will request permission to eat before trying to pick up his chopsticks, and will inform the waiter when he is finished eating.

   You are to implement the assign3_Waiter class as a monitor, with public methods as follows:

   • assign3_Waiter(int Num) -- Constructor. Num is the number of philosophers at the table.
   • void request(int seat) -- The philosopher at position seat (0 ≤ seat < Num) request permission to eat. This should block until it is safe for him to eat.
   • void done(int seat) -- The philosopher at position seat calls this to indicate that he is finished eating.

   Be sure to specify the monitor invariant in comments in your code. Your solution should avoid starvation without relying on the fairness of the monitor locks. Submit assign3_Waiter.java Don't include main -- I'll make my own.

2. For their post-graduation party a group of students wish to share a seemingly endless, but possibly slow arriving, supply of beer. They hire a runner to fetch the beer (in kegs) and a bartender to ensure that it is dispensed in an orderly fashion. When a student is ready for a new glass of beer, she will approach the bartender, and, if there is some in the keg, he will pour it for her. If the keg is empty she will wait until it is replaced with a full keg. The runner fetches kegs one at a time and, when he arrives back at the bar, he signals the bartender that he is ready. When the current keg is empty the bartender allows the runner to install the new keg. The runner then leaves to fetch a new keg, and the bartender continues to serve students.

   The students drink at varying rates, so, in the interest of fairness, they instruct the bartender to keep track of the number of glasses of beer served to each student, and, when more than one student is waiting to be served, to serve the student who has had the fewest glasses.

   The more astute among the students (i.e., those who have taken concurrent programming), recognize this as a conditional synchronization problem and set out to simulate the interaction in a Java program. They model the students and runner as in Student.java, and Runner.java.

   Implement the assign3_Bartender class using Java monitors. The class must have public methods as follows:

   • assign3_Bartender(int kegSize, int numStudents) -- constructor. The arguments are the number of glasses in a keg and the number of drinking students.
   • void getBeer(int id) -- called by the students and blocks until the student's glass is filled, and
   • void installNewKeg() -- called by the runner and blocks until the old keg is consumed and the new keg is installed.

   Be sure to specify the monitor invariant in comments in your code. Submit assign3_Bartender.java. Don't include a main -- I'll put yours and mine together to make my own party.

Last modified: Tue 2004.03.09 at 08:57 NST by Dennis Peters