Deadlines

Lab 2: Trainspotting (Part II)

In this assignment, you will implement a variation of the program to control the two trains that uses monitors rather than semaphores.

Choice of programming language

In this assignment you must use Java.

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Assignment

Your assignment is to adapt the program that controls the trains from the Lab 1 to use monitors instead of semaphores.

Requirements

• All the requirements from the first assignment are also demanded here except that now we use monitors instead of semaphores.

• You should use monitors that have explicit locks and condition variables. That is, you must use the java.util.concurrent.locks package from Java 5, not synchronized methods, to implement your monitor.

• You should not use the tryLock() method of the Lock interface. If you need such functionality, you have to implement it yourself in your monitor.

• Waiting in your monitors should be realised using condition variables. Locks should be held locked only for short moments.

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Getting started

Use the same project for the previous. Copy Lab1.java to Lab2.java, renaming the class, and change Main.java to use Lab2 instead of Lab1. You do not need to change the map file.

Tips and Tricks

To give you some hints, you should think that each track is represented by a monitor. The monitor will have, at least , the following interface:

public void enter()
public void leave()

where enter() is called by a train when entering a single track and leave() when a train leaves a single or double track.

Submission

In your submission, you should clearly explain the following items:

• What is the purpose of each method in the monitor?
• How many conditional variables, if any, are needed in your solution? Justify your answer.

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