Assignment 1 --- Trains - T-106.5600 Concurrent programming

Slides by Jan Lönnberg and Teemu Kiviniemi 

tsim 

Assignment 

Assignment 1 — Trains 

T-106.5600 Concurrent programming 

Jan Lönnberg 

Laboratory of Software Technology 

Helsinki University of Technology 

2nd October 2007 

Jan Lönnberg Assignment 1 — Trains 

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Introduction 

The Story 

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A small railway company wants to automate their train 

control. 

You have been tasked with implementing the train control 

software. 

Proof of concept: write control software for two trains on a 

simulated track. 


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Introduction 

Goal 

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Write a control program for the trains that lets them travel 

between two stations safely. 

Trains must be independent; each train is controlled by a 

separate process. 

You will practise mutual exclusion using semaphores and 

communicating with other concurrently executing programs 

through a prewritten interface. 


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Introduction 

You get: 

tsim 


A simulator called tsim. 

A track with two trains. 

Java interface code for tsim. 

Example control code that drives a train from one station to 

another and back. 

Your task is to: 

Add sensors to the track. 

Write control code that drives two trains back and forth 

between two stations. 


AB

Introduction 

You get: 

tsim 


A simulator called tsim. 

A track with two trains. 

Java interface code for tsim. 

Example control code that drives a train from one station to 

another and back. 

Your task is to: 

Add sensors to the track. 

Write control code that drives two trains back and forth 

between two stations. 


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tsim 

tsim 


Controlling tsim 

Running tsim 


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tsim 

tsim 


The tsim simulator 

tsim is a simple train simulator. 

GUI allows you to: 

Edit tracks and trains. 

Control trains. 

View simulation. 


Running tsim 

Trains can be controlled through an external program. 


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tsim 

Getting tsim 

tsim 



Running tsim 

tsim (and associated code) can be downloaded from the 

assignment page. 

tsim requires a Unix-like system with X (e.g. Linux, 

Windows with Cygwin). 

tsim is preinstalled in Niksula and HUT Computing Centre. 


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tsim 


Controlling tsim with another program 


Running tsim 

External programs can control tsim through a TCP/IP 

socket. 

You write the control code in Java. 

You access tsim through the Java tsim interface (TSim.*), 

which handles TCP/IP communication with tsim. 


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tsim 


Your train controller code (1/2) 


Running tsim 

Control code for each train runs in a separate Java virtual 

machine. 

Your control code communicates with other trains using 

semaphores, which are provided by the Java tsim interface. 

Both trains must be controlled by the same code. 


AB


tsim 


Your train controller code (2/2) 


Running tsim 

Your program must contain a classtrains.Train, an 

instance of which controls one train. 

Two instances oftrains.Train run in two separate Java 

virtual machines, one instance in each virtual machine. 


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tsim (simulator) 

GUI 

User 

Commands 

Events, command results 

Commands 

Events, command results 

tsim 


Java virtual machine 

Java virtual machine 


Running tsim 

tsim Java interface 

TSim.* 

tsim Java interface 

TSim.* 

Wait for events, change switches, set speeds 

Student’s train controller code 

trains.* 

Wait for events, change switches, set speeds 

Student’s train controller code 

trains.* 

Figure: Structure Jan Lönnberg of tsim runtime Assignment 1 configuration 

— Trains 

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tsim 



Running tsim 

Java interface for tsim 

Each train is controlled through class 

TSim.TSimInterface. 

An instance ofTSim.TSimInterface is passed to the 

constructor oftrains.Train. 

The classTSim.TSimInterface provides methods to: 

set the train speed 

set the state of track switches 

load and unload passengers and goods 

get sensor events 

get semaphores 


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tsim 



Running tsim 

Methods of classTSimInterface (1/2) 

public void setSpeed(int speed) 

Set train speed (measured in pixels/second). 

public void setSwitch(int xPos, int yPos, 

int switchPos) 

Set the state of the switch at(xPos, yPos) to 

switchPos (TSimInterface.SWITCH_LEFT or 

TSimInterface.SWITCH_RIGHT). 

public void loadUnload() 

Load and unload passengers and goods. 


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tsim 



Running tsim 

Methods of classTSimInterface (2/2) 

public SensorEvent getSensor() 

Waits for a sensor event from the train. 

public Semaphore getSemaphore(int s) 

Create a semaphore with starting values. 

The semaphore is shared with all other trains on the track; 

the nthSemaphore object created by each train 

corresponds to the same semaphore. 

Parametersspecifies the the initial value of the semaphore 

(if the semaphore is not already created) 


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tsim 



Running tsim 

ClassSensorEvent 

ASensorEvent is generated when the train enters or 

exits a sensor square. It has the following methods: 

public int getXpos() 

Return the X position of the sensor. 

public int getYpos() 

Return the Y position of the sensor. 

public int getStatus() 

Return the status of the sensor: 

SensorEvent.ACTIVE if the train has entered the sensor 

square or 

SensorEvent.INACTIVE if the train has left the sensor 

square 


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tsim 



Running tsim 

ClassSemaphore 

public void acquire() 

Acquires the semaphore (P operation). 

public void release() 

Releases the semaphore (V operation). 

public boolean tryAcquire() 

Acquires the semaphore if possible. 

Returnstrue if the semaphore was acquired. 


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Running tsim 

tsim 



Running tsim 

Starting tsim with the controller code (1/2) 

tsim/run.sh 

˜jlonnber/tsim/run.sh in Niksula or HUT-CC. 

The command starts tsim and two Java virtual machines to 

control the trains. 


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Running tsim 

tsim 



Running tsim 

Starting tsim with the controller code (2/2) 

Option-speedupFactor can be used to 

speed up the simulation (default is 1.0). Your controller 

code must behave correctly when the default acceleration 

is used and with any speed-up factor up to 15.0. 

Alternative scripttsim/run-log.sh activates logging in 

both simulator and Java interface, producing a lot of 

information that can aid testing and debugging. 

More command-line options are described on the 

assignment web page. 


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Running tsim 

Editing a track with tsim 

tsim 


tsim/tsim.sh 


Running tsim 

˜jlonnber/tsim/tsim.sh in Niksula or 

HUT-CC. 


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Doing the assignment 

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Group size: 1–2 students. 

Grading does not depend on group size. 

Grade: 0 (fail), 3 (pass), 5 (pass with honours). 

Submission 

Deadline is 2007-10-22 23:59. 

Submit a tar.gz archive containing: 

Control code source. 

Track with added sensors. 

There will be one extra round for re-submissions or late 

submissions (grade: 0 (fail) or 1 (pass)). 


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Coding style 

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The program must be written in Java, and should have a 

clear and simple structure. 

Explanatory comments are required for code that is not 

self-explanatory to a programmer fluent in Java. 

English for variable names, method names, comments and 

reports is recommended. 

Cryptic method and variable names may not be used. 


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tsim 


Instructions and requirements 

Full instructions will be on the course home page. 

Include a report explaining: 

The reasoning behind your solution. 

Measures you have taken to ensure your solution is correct 

Any unexpected behaviour you may have encountered 

during testing and how you have investigated and resolved 

it. 

The instructions on the course web page are the 

authoritative description of the assignment. 


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tsim 


Questions and clarifications 

Technical questions and clarification requests should be 

sent to the course newsgroup: 

opinnot.tik.rinnakkaisohjelmointi 

Clarifications (if any) will be posted to the newsgroup. 


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Tips 

tsim 


Read the instructions thoroughly. 

Test your code well, with different speed-up factors. 

Follow the newsgroup. 

Start working now. 


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Conclusion 

tsim 


Conclusion 

Assignment is intended to help learn mutual exclusion 

using semaphores. 

These slides and the full assignment instructions are 

available on the course web page. 

Questions? 


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Assignment 1 --- Trains - T-106.5600 Concurrent programming

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