Transcript Aug16_2010 - Computer Science

CSCI 6900: Design, Implementation, and Verification of
Concurrent Software
Eileen Kraemer
August 16th, 2010
The University of Georgia
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My background…
 at UGA since 1998
 except for a one-year sabbatical at Michigan State (2007-2008)
 dept. head since July of 2008
 professor at Washington University in St. Louis (1995-1998)
 grad student in the College of Computing at Georgia Tech (19891995)
 worked in industry (banking software) and taught part-time at
(Oglethorpe University) (1986-1989)
 taught high school science (Biology, Chemistry, Physics), while
attending Polytechnic University (Farmingdale, NY and Brooklyn, NY)
for MS in CS (1980-1985)
 undergrad degree in Biology, Hofstra University, Hempstead, NY
(1976-1980)
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My research interests
 Concurrent Software <> Cognitive Psychology
 Designing, implementing and debugging concurrent
software are difficult tasks.
 How do people think about concurrent systems and
software?
 What do they find difficult? What is easy?
 What strategies do expert/ successful programmers
employ?
 Can these strategies be successfully taught to and
used by less experience / less successful
programmers?
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Concurrent Software <> Cognitive Psychology, cont’d.
 What types of tools and techniques can be developed to
help people be more successful in:
 specifying concurrent software?
 modeling concurrent software?
 implementing concurrent software?
 testing concurrent software?
 debugging concurrent software?
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Other research interests & projects
 Smartphone Intervention for Pediatric Transplant patients
 Evaluation of web site effectiveness
 User interfaces for biological databases
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About the course …
 Mondays, 2:30 – 3:20 in Boyd 306
 Student presentations
 Tues/Thurs: 2:00 -3:15 in Dawson 379
 EK will lecture &/or demo
 Course website:
 www.cs.uga.edu/~eileen/6900
Details to appear soon
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What you will be expected to do
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Read papers (10-20)
Present papers (1- 2)
Read textbook
Design concurrent software
Use and create models of concurrent software (FSP, etc.)
Implement concurrent software (Java, C++/Pthreads/Ace wrappers)
Verify concurrent software
 download & install LTSA tool and demo programs
 Install and use other software, as needed
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Book
Concurrency:
State Models &
Java Programs,
2nd Edition
Jeff Magee &
Jeff Kramer
WILEY
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The textbook has a website:
www.doc.ic.ac.uk/~jnm/book/
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Concurrency
State Models and Java Programs
Jeff Magee
and
Jeff Kramer
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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 that occur at the
same time.
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Concurrent and Distributed Software?
Interacting,
concurrent software
components of a
system:
single machine ->
shared memory
interactions
multiple machines ->
network interactions
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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 that interact with the environment, control
multiple activities and handle multiple events.
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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.
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a Cruise Control System
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.
buttons
 Is the system safe?
Pressing the brake,
accelerator or off button
disables the system.
Pressing resume re-enables
the system.
 Would testing be sufficient to discover all errors?
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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
 animate model 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.
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modeling the Cruise Control System
LTSA Animator to step through
system actions and events.
eng ineOn
0
1
eng ineOff
speed
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.
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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!
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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.
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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
Advanced topics …
9. Dynamic systems
The main basic
Concepts
Models
Practice
12. Timed Systems
10. Message Passing
13.
Program Verification
11. Concurrent Software Architectures
14.
Logical Properties
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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.
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