Transcript Software Engineering CSCI 3321 Dr. Thomas Hicks Computer Science Department Trinity University Chapter 4 Software Engineering : A Practitioner’s Approach Agile Development & Real Time Systems Dr.

Software Engineering
CSCI 3321
Dr. Thomas Hicks
Computer Science Department
Trinity University
1
Chapter 4
Software Engineering : A Practitioner’s Approach
Agile Development &
Real Time Systems
Dr. Thomas E. Hicks
Computer Science Department
Trinity University
Thanks To Ian Sommerville & Roger Pressman For Much Of The Slide Content
Agile
Development
Lite or Lean Methods
The Manifesto for
Agile Software Development
“We are uncovering better ways of developing software by
doing it and helping others do it. Through this work we
have come to value:
1. Individuals and interactions over processes and tools
2. Working software over
comprehensive documentation
3. Customer collaboration over
contract negotiation
4. Responding to change over following a plan
That is, while there is value in the items on the right, we value
the items on the left more.”
The_Agile_Manifesto_SDMagazine.pdf
Kent Beck et al
“Agility 1,
Everything Else 0”
Tom
Demarco
Politics
Agile Software Development
“Considerable Debate about the benefits and applicability”
• Pro Agile : “Traditional methodologies are a bunch of
stick-in-the-muds who’d rather produce flawless
documentation than a working system that meets
business needs.”
• Pro Traditional: “Lightweight, agile methodologists are a
bunch of glorified hackers who are going to be in for a
heck of a surprise when they try to scale up their toys
into enterprise-wide software”
This methodology risks degenerating
into a religious war.
Pressman
Ivar Jacobson - 1
 “Agility has become today’s buzz word when
considering a modern software process. An agile team
is a nimble team able to appropriately respond to
changes.
 Changes in the software being built, changes in the
team members, changes because of new technology,
changes of all kinds that may have impact upon the
product they build or the project that creates the
product.
Ivar Jacobson – 2
Support for changes should be built-in every
thing we do in software, something we embrace
because it is the heart and soul of software.
 An agile team recognizes that software is developed by
individuals working in teams and that the skills of
those people, their ability to collaborate, is at the core
for the success of the project.”
7 Human Factors Of Agile Software Development
Proponents of the Agile Process emphasize the human factors:
1. Competence – innate talent and overall knowledge of the
process – teach needed info to all team members
2. Common Focus – the agile team will focus the different
talents working on different portions of the project on the
deliverable.
3. Collaboration – quality software requires
the collaboration & communication of
customer & software engineers
4. Decision Making Ability – teams must
be able to make those decisions
necessary to control their destiny
Pressman
7 Human Factors Of Agile Software Development
Proponents of the Agile Process emphasize the human factors:
 Fuzzy-Problem-Solving-Ability – managers realize teams
deal with ambiguity and change – sometimes must accept
the fact that problem solving today will be different than
problem solving tomorrow – maybe use some of same code.
 Mutual Trust & Respect – Agile teams must become what
DeMarco & Lister call “Jelled Teams” – whole greater than
sum of its parts.
 Self Organization – self organized to complete work, meet
deadlines, etc. Moral booster.
Pressman
“There is no substitute
for rapid feedback,
both on the developer
process and on the
product itself”
Martin
Fowler
12 Principles Adopted By The “Agility Conference” 1-4
1. Highest Priority is to satisfy the customer through early
and continuous delivery of valued software.
2. Welcome change requirements even late in the
development. Agile processes harness change for the
customer’s competitive advantage.
3. Deliver working software frequently, from a couple of
weeks to a couple of months, with a preference to the
shorter time scale.
4. Business people, and developers, must
work together daily throughout the project.
12 Principles Adopted By The “Agility Conference” 5-8
5. Build projects around motivated individuals. Give them
the environment and the support they need. Trust them to
get the job done.
6. The most efficient and effective method of conveying
information to and within a development team is face to
face conversation.
7. Working software is the primary measure of progress.
8. Agile processes promote sustainable
development. The sponsors, developers,
users should be able to maintain constant
pace indefinitely.
12 Principles Adopted By The “Agility Conference” 9-12
9. Continual attention to technical excellence and good
design enhances agility.
10. Simplicity, the art of minimizing the amount of work not
done, is essential.
11. The best architectures, requirements, and designs
emerge from self organizing teams.
12. At regular intervals, the team reflects
on how to become more effective, then
tunes and tunes and adjusts its behavior
accordingly.
Agile  Lite  Less Time Planning  Faster Coding
Agility Software Development Research Tells Us That :
 Effective response to change; rapid and adaptive
 Effective communication among all stakeholders
 Drawing the customer onto the team
 Organizing a team so that it is in control of the work
performed
Yields …
Rapid, incremental
delivery of software
About The Agile Process
Agile Process is driven by customer descriptions
of what is required; these descriptions are called
scenarios
Agile Process recognizes that plans are shortlived
Agile Process develops software iteratively with
a heavy emphasis on construction activities
Agile Process delivers multiple ‘software
increments’
Agile Process adapts as changes occur
XP
Extreme Programming
Extreme Programming (XP)
4 Step XP Planning Process
 The most widely used agile process, originally proposed
by Kent Beck
 XP Planning
1. XP Planning begins with the creation of “user stories”
2. An XP Agile team assesses each story and assigns a
cost
3. These XP Stories are grouped to
for a deliverable increment
4. A commitment is made on delivery
date
About Extreme Programming (XP) Design
XP Design
XP Design follows the KIS principle
XP Design encourage the use of CRC cards (see Chapter 8)
Class Responsibility Collaborator
Clas s :
Clas s :
Descript
ion:
Clas
s:
Descript
ion:
Clas
s :FloorPlan
Descript ion:
Re s pons
ibility:
Descript
ion:
Re s pons ibility:
Re s pons ibility:
Re s pons ibility:
Collaborator :
Collaborator :
Collaborator :
Collaborator :
def ines f loor plan name/ ty pe
manages f loor plan posit ioning
scales f loor plan f or display
scales f loor plan f or display
incorporat es walls, doors and windows
Wall
shows posit ion of v ideo cameras
Camera
For difficult design problems, XP suggests the immediate
creation of “spike solutions”; spikes solutions are an
operational design prototype of the problem area.
XP design encourages “refactoring”; refactoring an
iterative refinement of the internal program design – it is
cleaning up the code after it has been written.
About Extreme Programming (XP) Coding
XP Coding
XP coding recommends the construction of a
unit test for a story before coding commences
XP coding encourages “pair programming” – two
people work together at one computer to complete
code for one story.
About Extreme Programming (XP) Testing
XP Testing
XP testing recommends that all unit tests be
executed daily to encourage regression analysis
(i.e. to make sure code still works after it has been
modified)
“XP testing requires “acceptance tests”, also
called “customer tests” that are defined by the
customer and executed to assess customer visible
functionality
Ron
Jeffries
“Extreme
Programming is a
discipline of
software
development
based on values
of simplicity,
communication,
feedback, and
courage.”
ASD
Adaptive Software
Development
Adaptive Software Development (ASD)
 ASD was originally proposed by Jim Highsmith
 6 Distinguishing Features Of ASD 1-3
1. ASD uses mission-driven planning; accomplish the task
2. ASD partitions the project into components; it is a
component-based focus
3. Uses “time-boxing” – each task associated with a box;
if the project cannot be delivered on time, the work
moves forward to the next task when ~90% of the task is
complete. Although this is not always acceptable, it is
often the case that the last 10% can be completed later.
Adaptive Software Development (ASD)
 ASD was originally proposed by Jim Highsmith
 6 Distinguishing Features Of ASD – 4-6
4. ASD explicitly considers all of risks
5. ASD emphasizes collaboration for requirements
gathering
6. ASD emphasizes “learning” throughout the
process
3 Major Steps of Adaptive Software Development (ASD)
1. Speculation
 Use the customer mission statement, project
constraints, and basic requirements to define sets of
cycles (software releases) for the project.
2. Collaboration
 The collaboration method is central to all of the agile
processes. Using highly motivated people, working
collaboratively together to multiply their talents beyond
individual expectations. Trust is central.
 Create Requirements and Mini-Specs.
3. Learning
 Implement and test components
 Technical Reviews
 Focus Group Feedback
Adaptive Software Development
a d a p t i v e c y c l e p l a n ni n g
u se s m i ssi o n st at e m e n t
p r o j e c t c o n st r a i n t s
b a si c r e q u i r e m e nt s
Re q ui r e m e nt s g at h e r i n g
JA D
m i ni - s p e c s
t i m e - b o x e d r el e a se p l a n
Rel e a s e
s o f t w a r e in cr e m e n t
a d j u s t m e n t s f o r s u b s e q u e n t c y c le s
c o m p o n e nt s i m p l e m e nt e d / t e st e d
f o c us g r o up s f o r f eed b ac k
f o r m al t e c h ni c al r ev i e w s
p o st m o r t e m s
Ernest
Hemingway
“I like to listen. I
have learned a
great deal from
listening carefully.
Most people never
listen.”
DSDM
Dynamic Software
Development Method
Dynamic Systems Development Method - DSDM
 DSDM—distinguishing features
 Similar in most respects to XP and/or ASD
 8 Guiding Principles Of DSDM – 1-4
1. Active user involvement is imperative.
2. DSDM teams must be empowered to make
decisions.
3. The focus is on frequent delivery of products.
4. Fitness for business purpose is the essential
criterion for acceptance of deliverables.
Promoted by the DSDM
Consortium (www.dsdm.org)
Dynamic Systems Development Method - DSDM
 8 Guiding Principles Of DSDM 5 - 8
5. Iterative and incremental development is necessary
to converge on an accurate business solution.
6. All changes during development are reversible.
7. Requirements are baselined at a high level
8. Testing is integrated throughout the life-cycle.
Dynamic Systems Development Method
“Our profession goes
through Methodologies
like a 14 year-old goes
through clothing”
Stephen Hawrysh &
Jim Ruprecht
Scrum
Scrum – (rugby match term)
 Developed by Jeff Sutherland in early 1990’s
 Expanded upon by Schwaber and Beedle in 2001
 Scrum—distinguishing features – very “agile like”
1. Scrum has small teams to maximize communication
and minimize costs
2. The Scrum process must be adaptable to business
and technological changes
3. The Scrum process yields software that can be
inspected, adjusted, tested, documented, and built on.
4. The Scrum process partitions the project
into low-coupling partitions, or “packets”.
Scrum (cont)
5. The Scrum process constantly tests and documents as
the project is built.
6. The Scrum process provides the ability to declare the
product “done”
7. Scrum work occurs in “sprints” and is derived from a
“backlog” of existing requirements
8. Scrum meetings are very short and sometimes
conducted without chairs
9. Scrum “demos” are delivered to the
customer with the time-box allocated
Scrum
http://www.controlchaos.com/about/
“Scrum allows us
to build
Software..”
Mike
Beetle et al.
Crystal
Crystal
Proposed by Cockburn and Highsmith
Crystal—distinguishing features
Actually a family of process models that allow
“maneuverability” based on problem
characteristics
Face-to-face communication is emphasized
Suggests the use of “reflection workshops” to
review the work habits of the team
FDD
Feature Driven
Development
Feature Driven Development (FDD)
 Originally proposed by Peter Coad et al as a process
model for OOP
 FDD—distinguishing features
Emphasis is on defining “features”
1.

a feature “is a client-valued function that can be
implemented in two weeks or less.”
2. Uses a feature template

<action> the <result> <by | for | of | to> a(n)
<object>
3. A features list is created and “plan by feature” is
conducted
4. Design and construction merge in FDD
Feature Driven Development
Agile
Modeling
Agile Modeling
 Originally proposed by Scott Ambler
 Suggests a set of agile modeling principles
1. Model with a purpose
2. Use multiple models
3. Travel light
4. Content is more important than representation
5. Know the models and the tools you use to
create them
6. Adapt locally
Computer World
Computer World Link
http://www.computerworld.com/softwaretopics/soft
ware/appdev/story/0,10801,67952,00.html
Real Time
Software Design
Real-time Software Design
Real-time Software Design
is designing embedded software
systems whose behaviour is
subject to timing constraints
Real Time
Systems
Real-time systems
 Real-time systems are used to monitor and
control their environment
 Real-time systems inevitably are associated with
hardware devices
 Sensors: Collect data from the system
environment
 Actuators: Change (in some way) the
system's environment
 Time is critical. Real-time systems
MUST respond within specified
times
Real-time Definitions
 A real-time system is a software system where
the correct functioning of the system depends on
the results produced by the system and the time
at which these results are produced
 A ‘soft’ real-time system is a system whose
operation is degraded if results are not produced
according to the specified timing requirements
 A ‘hard’ real-time system is a system whose
operation is incorrect if results are not produced
according to the timing specification
Stimulus &
Responses
Stimulus/Response Systems
 Given a stimulus, the system must produce a response
within a specified time
 Periodic Stimuli: Stimuli which occur at predictable time
intervals
 For example, a temperature sensor may be polled 10
times per second
 Aperiodic stimuli: Stimuli which occur at unpredictable
times
 For example, a system power failure may trigger an
interrupt which must be processed by the system
Architectural Considerations
 Because of the need to respond to timing
demands made by different stimuli/responses, the
system architecture must allow for fast switching
between stimulus handlers
 Timing demands of different stimuli are different
so a simple sequential loop is not usually
adequate
 Real-time systems are usually designed as
cooperating processes with a real-time executive
controlling these processes
A Real-time System Model
Sensor
Sensor
Sensor
Sensor
Sensor
Sensor
Real-time
control system
Actuator
Actuator
Actuator
Actuator
Real Time
System Elements
Real-time System Elements
 Sensors control processes
 Collect information from sensors. May buffer
information collected in response to a sensor
stimulus
 Data processor
 Carries out processing of collected information
and computes the system response
 Actuator control
 Generates control signals for the actuator
Sensor/Actuator Processes
Sensor
Actuator
Stimulus
Sensor
control
Response
Data
processor
Actuator
control
Real Time Design
Hardware & Software
Real-time System Design – 2 Stages
 Real-time system engineers must design both the
hardware and the software associated with
system.
 Real-time system engineers then partition
functions to either hardware or software
 Design decisions should be made on the basis
on non-functional system requirements
 Hardware delivers better performance but
potentially longer development and less scope
for change
Hardware & Software Design
Establish system
requirements
Partition
requirements
Software
requir ements
Hardware
requirements
Software
design
Hardware
design
R-T Systems Design Process – 6 Steps
1. The first step in the R-T design process is to
identify the stimuli to be processed and the
required responses to these stimuli
2. The second step in the R-T design process is to
identify the timing constraints for each stimulus
and response
3. The third step in the R-T design process is to
aggregate the stimulus and response
processing into concurrent processes. A
process may be associated with each class of
stimulus and response.
R-T Systems Design Process – 6 Steps
 The fourth step in the R-T design process is to
design algorithms for each concurrent process.
These must meet the given timing requirements
 The fifth step in the R-T design process is to
design a scheduling system which will ensure that
processes are started in time to meet their
deadlines
 The sixth step in the R-T design process is to
integrate the real-time executive with an operating
system (if necessary)
Real Time
Timing Constraints
Timing Constraints
 Meeting timing constraints may require extensive
simulation and experiment to ensure that these
are met by the system
 Meeting timing constraints may mean that certain
design strategies such as object-oriented design
cannot be used because of the additional
overhead involved
 Meeting timing constraints may mean that lowlevel programming language features have to be
used for performance reasons
Real Time
State Machines
State Machine Modelling
 The effect of a stimulus in a real-time system may
trigger a transition from one state to another.
 Finite state machines can be used for modelling
real-time systems.
 However, FSM models lack structure. Even simple
systems can have a complex model.
 The UML includes notations for defining state
machine models
Microwave Oven State Machine
Full
power
Full power
do: set power
= 600
Timer
Waiting
do: display
time
Half
power
Number
Full
power
Half
power
do: operate
oven
Door
closed
Timer
Door
open
Half power
do: set power
= 300
Operation
Set time
do: get number
exit: set time
Door
closed
Disabled
do: display
'Waiting'
Cancel
Start
Enabled
do: display
'Ready'
System
fault
Waiting
do: display
time
Real Time
Programming
Real-time Programming & Languages
 Hard-real time systems may have to programmed
in assembly language to ensure that deadlines
are met
 Languages such as C allow efficient programs to
be written but do not have constructs to support
concurrency or shared resource management
 Ada as a language designed to support real-time
systems design so includes a general purpose
concurrency mechanism
Java As a Real-time Language
 Java supports lightweight concurrency (threads and
synchronized methods) and can be used for some soft
real-time systems
 Java 2.0 is not suitable for hard RT programming or
programming where precise control of timing is required
1. Not possible to specify thread execution time
2. Uncontrollable garbage collection
3. Not possible to discover queue sizes for shared
resources
4. Variable virtual machine implementation
5. Not possible to do space or timing analysis
Real Time
Executives
Real-time Executives
 Real-time executives are specialized operating
systems which manage the processes in the RTS
 Real-time executives are responsible for
process management and resource (processor
and memory) allocation
 Real-time executives may be based on a
standard RTE kernel which is used unchanged or
modified for a particular application
 Real-time executives do not include facilities
such as file management
14
R-T Executive Components
 Real-time clock
 Provides information for process scheduling.
 Interrupt handler
 Manages aperiodic requests for service.
 Scheduler
 Chooses the next process to be run.
 Resource manager
 Allocates memory and processor resources.
 Dispatcher
 Starts process execution.
R-T Non-stop System Components
 Configuration manager
 Responsible for the dynamic reconfiguration of the
system software and hardware. Hardware modules
may be replaced and software upgraded without
stopping the systems
 Fault manager
 Responsible for detecting software and hardware
faults and taking appropriate actions (e.g. switching to
backup disks) to ensure that the system continues in
operation
Real-time Executive Components
Scheduling
information
Real-time
clock
Interrupt
handler
Scheduler
Process resource
requirements
Processes
awaiting
resources
Ready
processes
Ready
list
Available
resource
list
Resour ce
manager
Released
resources
Processor
list
Despatcher
Executing
process
Real Time
Process Priority &
Servicing
R-T Process Priority
 The processing of some types of stimuli must
sometimes take priority
 Interrupt level priority. Highest priority which is
allocated to processes requiring a very fast
response
 Clock level priority. Allocated to periodic
processes
 Within these, further levels of priority may be
assigned
R-T Interrupt Servicing
 Control is transferred automatically to a
pre-determined memory location
 This location contains an instruction to jump to
an interrupt service routine
 Further interrupts are disabled, the interrupt
serviced and control returned to the interrupted
process
 Interrupt service routines MUST be short,
simple and fast
R-T Periodic Process Servicing
 In most real-time systems, there will be several
classes of periodic process, each with different
periods (the time between executions),
execution times and deadlines (the time by
which processing must be completed)
 The real-time clock ticks periodically and each
tick causes an interrupt which schedules the
process manager for periodic processes
 The process manager selects a process which
is ready for execution
Real Time
Process Management
R-T Process Management
 Concerned with managing the set of concurrent
processes
 Periodic processes are executed at pre-specified
time intervals
 The executive uses the real-time clock to
determine when to execute a process
 Process period - time between executions
 Process deadline - the time by which processing
must be complete
R-T Process Management
Scheduler
Choose process
for execution
Resource manager
Allocate memory
and processor
Despatcher
Start execution on an
available processor
Process Switching
 The scheduler chooses the next process to be
executed by the processor. This depends on a
scheduling strategy which may take the process
priority into account
 The resource manager allocates memory and a
processor for the process to be executed
 The dispatcher takes the process from ready list,
loads it onto a processor and starts execution
Real Time
Scheduling Strategies
R-T Scheduling Strategies
 Non pre-emptive scheduling
 Once a process has been scheduled for execution, it
runs to completion or until it is blocked for some
reason (e.g. waiting for I/O)
 Pre-emptive scheduling
 The execution of an executing processes may be
stopped if a higher priority process requires service
 Scheduling algorithms
 Round-robin
 Rate monotonic
 Shortest deadline first
Real Time
Monitoring & Control
Systems
Monitoring & Control Systems
 Monitoring & control systems are an important
class of real-time systems
 Monitoring & control systems continuously check
sensors and take actions depending on sensor
values
 Monitoring systems examine sensors and
report their results
 Control systems take sensor values and
control hardware actuators
Real Time
Monitoring Systems
Burglar Alarm
Designing A Burglar Alarm System
Example Of A Monitoring System
 A system is required to monitor sensors on doors
and windows to detect the presence of intruders in
a building
 When a sensor indicates a break-in, the system
switches on lights around the area and calls police
automatically
 The system should include provision for operation
without a mains power supply
Sensors & Actions Of A Burglar Alarm System
Example Of A Monitoring System
 Sensors
 Movement detectors, window sensors, door sensors.
 50 window sensors, 30 door sensors and 200
movement detectors
 Voltage drop sensor
 Actions
 When an intruder is detected, police are called
automatically.
 Lights are switched on in rooms with active sensors.
 An audible alarm is switched on.
 The system switches automatically to backup power
when a voltage drop is detected.
Real Time
System Design
The 5 Step R-T System Design Process
1. Identify stimuli and associated responses
2. Define the timing constraints associated with
each stimulus and response
3. Allocate system functions to concurrent
processes
4. Design algorithms for stimulus processing and
response generation
5. Design a scheduling system which ensures that
processes will always be scheduled to meet
their deadlines
Stimuli To Be Processed - A Burglar Alarm System
 Power failure
 Generated aperiodically by a circuit monitor.
When received, the system must switch to
backup power within 50 ms
 Intruder alarm
 Stimulus generated by system sensors.
Response is to call the police, switch on
building lights and the audible alarm
A Burglar Alarm System’s Timing Requirements
Stimulus/Response
Power fail interrupt
Door alarm
Window alarm
Movement detector
Audible alarm
Lights switch
Communications
Voice synthesiser
Timing requirements
The switch to backup power must be comp leted
within a deadline of 5 0 ms .
Each door alarm should be polled twice per
second.
Each window alarm should be polled twice per
second.
Each mo vement detector should be polled twice
per second.
The audible alarm should be switched on within
1/2 second of an alarm being raised by a sensor.
The lights should be switched on within 1/2
second of an alarm b eing raised by a sensor.
The call to the police should be started within 2
seconds of an alarm being raised by a sensor.
A synthesised message should be available
within 4 seconds of an alarm being raised by a
sensor.
A Burglar Alarm System’s Architecture Diagram
400Hz
60Hz
Movement
detector process
100Hz
Door sensor
process
Detector status
Window sensor
process
Sensor status
Sensor status
560Hz
Alar m system
Communication
process
Building monitor
process
Power failure
interrupt
Power switch
process
Building monitor
Alarm system
process
Room number
Alarm
system
Alarm
system
Audible alarm
process
Room number
Alert message
Alarm system
Room number
Lighting control
process
Voice synthesizer
process
// See http://www.software-engin.com/ for links to the complete Java code f or this
// example
class BuildingMonitor extends Thread {
BuildingSensor win, door, move ;
Siren
siren = new Siren () ;
Lights lights = new Lights () ;
Synthesizer synthesizer = new S ynthesizer () ;
DoorSensors doors = new D oorSensors (30) ;
WindowSensors windows = new W indowSensors (50) ;
MovementSensors movements = new MovementSensors (200) ;
PowerMonitor pm = new Po werMonitor () ;
BuildingMonitor()
{
// initialise all the sensors and start the processes
siren.start () ; lights.start () ;
synthesizer.start () ; windows.start () ;
doors.start () ; movements.start () ; pm.start () ;
}
A Burglar Alarm
System’s
Building_monitor process 1
Sample Code
public void run ()
{
int room = 0 ;
while (t rue)
{
// poll the movement sensors at least twice per second (400 Hz)
move = movements.getVal () ;
// poll the window s ensors at least twice/second (100 Hz)
win = windows.getVal () ;
// poll the door sensors at least twice per second (60 H z)
door = doors.getVal () ;
if (move.sensorVal == 1 | door.sensorVal == 1 | win.sensorVal == 1)
{
// a s ensor has indicated an intruder
if (move.sensorVal == 1)
room = move.room ;
if (door.sensorVal == 1)
room = door.room ;
if (win.sensorVal == 1 )
room = win.room ;
lights.on (room) ; siren.on () ; synthesizer.on (room) ;
break ;
}
}
lights.shutdown () ; siren.shutdown () ; synthesizer.shutdown () ;
windows.shutdown () ; doors.shutdown () ; movements.shutdown () ;
} // run
} //BuildingMonitor
A Burglar Alarm
System’s
Building_monitor
process 2
Sample Code
Real Time
Control Systems
Temperature Control
Control Systems
 A burglar alarm system is primarily a monitoring system. It
collects data from sensors but no real-time actuator control
 Control systems are similar but, in response to
sensor values, the system sends control signals
to actuators
 An example of a monitoring and control system is
a system which monitors temperature and
switches heaters on and off
A Temperature Control System
500Hz
Sensor
process
Sensor
values
500Hz
Thermostat
process
500Hz
Switch command
Room number
Heater control
process
Thermostat process
Furnace
control process
Data Acquisition Systems
 Data Acquisition Systems collect data from
sensors for subsequent processing and analysis.
 Data collection processes and processing
processes may have different periods and
deadlines.
 Data collection may be faster than processing
e.g. collecting information about an explosion.
 Circular or ring buffers are a mechanism for
smoothing speed differences.
Nuclear Reactor Data Collection
Another Control System Example
 A system collects data from a set of sensors
monitoring the neutron flux from a nuclear
reactor.
 Flux data is placed in a ring buffer for later
processing.
 The ring buffer is itself implemented as a
concurrent process so that the collection and
processing processes may be synchronized.
Nuclear Reactor Flux Monitoring
Another Control System Example
Sensors (each data flow is a sensor value)
Sensor
process
Sensor
identifier and
value
Processed
flux level
Sensor data
buffer
Process
data
Display
A Ring Buffer
Producer
process
Consumer
process
Mutual Exclusion
 Producer processes collect data and add it to
the buffer. Consumer processes take data from
the buffer and make elements available
 Producer and consumer processes must be
mutually excluded from accessing the same
element.
 The buffer must stop producer processes
adding information to a full buffer and consumer
processes trying to take information from an
empty buffer.
class CircularBuffer
{
int bufsize ;
SensorRecord [] store ;
int numberOfEntries = 0 ;
int front = 0, back = 0 ;
CircularBuffer (int n) {
bufsize = n ;
store = new SensorRecord [bufsize] ;
} // CircularBuffer
synchronized void put (SensorRecord rec ) throws InterruptedException
{
if ( numberOfEntries == bufsize)
wait () ;
store [back] = new SensorRecord (rec.sensorId, rec.sensorVal) ;
back = back + 1 ;
if (back == bufsize)
back = 0 ;
numberOfEntries = numberOfEntries + 1 ;
notify() ;
} // put
A Circular Buffer
Sample
Java implementation
of a ring buffer 1 Code
synchronized SensorRecord get () throws InterruptedException
{
SensorRecord result = new SensorRecord (-1, -1) ;
if (numberOfEntries == 0)
wait () ;
result = store [front] ;
front = front + 1 ;
if (front == bufsize)
front = 0 ;
numberOfEntries = numberOfEntries - 1 ;
notify() ;
return result ;
} // get
} // CircularBuffer
A Circular Buffer
Sample
Java implementation
of a ring buffer 2 Code
Software Engineering
CSCI 3342
Dr. Thomas E. Hicks
Computer Science Department
Trinity University
Textbook: Software Engineering
By Roger Pressman
Textbook: Software Engineering
By Ian Sommerville
Special Thanks To WCB/McGraw-Hill & Addison Wesley For
Providing Graphics Of Some Of Text Book Figures For Use In This
Presentation.