Book Chapter 1
Concurrency: introduction 1
©Magee/Kramer 2nd Edition
Concurrency
State Models and Java Programs
Jeff Magee and Jeff Kramer
Concurrency: introduction 2
©Magee/Kramer 2nd Edition
What is a Concurrent Program?
A sequential program has a
single thread of control.
A concurrent program has
multiple threads of control
allowing it perform multiple
computations in parallel and to
control multiple external
activities which occur at the
same time.
Concurrency: introduction 3
©Magee/Kramer 2nd Edition
Concurrent and Distributed Software?
Interacting,
concurrent software
components of a
system:
single machine ->
shared memory
interactions
multiple machines ->
network interactions
Communication
Network
Concurrency: introduction 4
©Magee/Kramer 2nd Edition
Why Concurrent Programming?
Performance gain from multiprocessing hardware
parallelism.
Increased application throughput
an I/O call need only block one thread.
Increased application responsiveness
high priority thread for user requests.
More appropriate structure
for programs which interact with the environment, control
multiple activities and handle multiple events.
Concurrency: introduction 5
©Magee/Kramer 2nd Edition
Do I need to know about concurrent programming?
Concurrency is widespread but error prone.
♦ Therac – 25 computerised radiation therapy machine
Concurrent programming errors contributed to accidents
causing deaths and serious injuries.
♦ Mars Rover
Problems with interaction between concurrent tasks
caused periodic software resets reducing availability for
exploration.
Concurrency: introduction 6
©Magee/Kramer 2nd Edition
a Cruise Control System
♦ Is the system safe?
♦ Would testing be sufficient to discover all errors?
When the car ignition is
switched on and the on
button is pressed, the
current speed is recorded
and the system is enabled:
it maintains the speed of
the car at the recorded
setting.
Pressing the brake,
accelerator or off button
disables the system.
Pressing resume re-enables
the system.
buttons
Concurrency: introduction 7
©Magee/Kramer 2nd Edition
models
A model is a simplified representation of the real world.
Engineers use models to gain confidence in the adequacy
and validity of a proposed design.
♦ focus on an aspect of interest – concurrency
♦ model animation to visualise a behaviour
♦ mechanical verification of properties (safety & progress)
Models are described using state machines, known as
Labelled Transition Systems LTS. These are described
textually as finite state processes (FSP) and displayed
and analysed by the LTSA analysis tool.
Concurrency: introduction 8
©Magee/Kramer 2nd Edition
modeling the Cruise Control System
LTSA Animator to step through
system actions and events.
engineOn
speed
engineOff
0 1
LTS of the process
that monitors speed.
Later chapters will explain how
to construct models such as this
so as to perform animation and
verification.
Concurrency: introduction 9
©Magee/Kramer 2nd Edition
programming practice in Java
Java is
♦ widely available, generally accepted and portable
♦ provides sound set of concurrency features
Hence Java is used for all the illustrative examples, the
demonstrations and the exercises. Later chapters will
explain how to construct Java programs such as the
Cruise Control System.
“Toy” problems are also used as they
exemplify particular aspects of
concurrent programming problems!
Concurrency: introduction 10
©Magee/Kramer 2nd Edition
course objective
This course is intended to provide a sound
understanding of the concepts, models and practice
involved in designing concurrent software.
The emphasis on principles and concepts provides a
thorough understanding of both the problems and the
solution techniques. Modeling provides insight into
concurrent behavior and aids reasoning about particular
designs. Concurrent programming in Java provides the
programming practice and experience.
Concurrency: introduction 11
©Magee/Kramer 2nd Edition
Book
Concurrency:
State Models &
Java Programs,
2nd Edition
Jeff Magee &
Jeff Kramer
WILEY
1st
edition
Concurrency: introduction 12
©Magee/Kramer 2nd Edition
Course Outline
2. Processes and Threads
3. Concurrent Execution
4. Shared Objects & Interference
5. Monitors & Condition Synchronization
6. Deadlock
7. Safety and Liveness Properties
8. Model-based Design
9. Dynamic systems
10. Message Passing
11. Concurrent Software Architectures
Concepts
Models
Practice
12. Timed Systems
13. Program Verification
14. Logical Properties
The main basic
Advanced topics …
Concurrency: introduction 13
©Magee/Kramer 2nd Edition
Web based course material
http://www.wileyeurope.com/college/magee
Java examples and demonstration programs
State models for the examples
Labelled Transition System Analyser (LTSA) for
modeling concurrency, model animation and model
property checking.
Concurrency: introduction 14
©Magee/Kramer 2nd Edition
Summary
Concepts
we adopt a model-based approach for the design and
construction of concurrent programs
Models
we use finite state models to represent concurrent behavior.
Practice
we use Java for constructing concurrent programs.
Examples are used to illustrate the concepts, models and
demonstration programs.