Dr. Thomas Hicks Computer Science Department Trinity University 1 Software Engineering CSCI 3321.
-
Upload
noe-henley -
Category
Documents
-
view
217 -
download
0
Transcript of Dr. Thomas Hicks Computer Science Department Trinity University 1 Software Engineering CSCI 3321.
Dr. Thomas HicksComputer Science Department
Trinity University 1
Software EngineeringCSCI 3321
Software Engineering : A Practitioner’s Approach
Agile Development & Real Time Systems
Dr. Thomas E. HicksComputer Science Department
Trinity University
Thanks To Ian Sommerville & Roger Pressman For Much Of The Slide Content
Chapter 4
Agile Development
Lite or Lean Methods
“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 Manifesto for Agile Software Development
Kent Beck et alKent Beck et alThe_Agile_Manifesto_SDMagazine.pdf
“Agility 1, Everything Else 0”
TomTomDemarcoDemarco
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 degeneratingThis methodology risks degenerating
into a religious war. 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 Martin FowlerFowler
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 short-lived
Agile Process develops software iteratively with a heavy emphasis on construction activities
Agile Process delivers multiple ‘software increments’
Agile Process adapts as changes occur
XPExtreme Programming
Extreme Programming (XP)4 Step XP Planning Process
The most widely used agile process, originally proposed
by Kent Beck
XP Planning 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) DesignXP Design
XP Design follows the KIS principleXP Design encourage the use of CRC cards (see Chapter 8)
Class Responsibility Collaborator
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.
Class:
Description:
Responsibility: Collaborator:
Class:
Description:
Responsibility: Collaborator:
Class:
Description:
Responsibility: Collaborator:
Class: FloorPlan
Description:
Responsibility: Collaborator:
incorporates walls, doors and windows
shows position of video cameras
defines floor plan name/type
manages floor plan positioning
scales floor plan for display
scales floor plan for display
Wall
Camera
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) Coding
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
About Extreme Programming (XP) Testing
“Extreme Programming is a
discipline of software
development based on values
of simplicity, communication, feedback, and
courage.”
RonRonJeffriesJeffries
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
ad apt ive cycle planning uses m issio n st at em ent pro ject co nst raint s basic requirem ent s t ime-b ox ed release plan
Requirement s g at hering J A D mini- specs
c omp o nent s implement ed/ t est ed f o cus gro ups f or f eedb ac k f ormal t echnical review s p o st mort ems
s oftw ar e incr ementadj ustm ents f or subsequent cy cles
Release
“I like to listen. I have learned a great deal from
listening carefully. Most people never
listen.”Ernest Ernest
HemingwayHemingway
DSDMDynamic Software
Development Method
Dynamic Systems Development Method - DSDM
DSDMDSDM—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 & Stephen Hawrysh & Jim RuprechtJim 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 allows us to build Software..”
Mike Mike Beetle et al.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
1. Emphasis is on defining “features”
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/software/appdev/story/0,10801,67952,00.html
Real TimeSoftware 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
Real-timecontrol system
ActuatorActuator ActuatorActuator
SensorSensorSensor SensorSensorSensor
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
Dataprocessor
Actuatorcontrol
Actuator
Sensorcontrol
Sensor
Stimulus Response
Real Time DesignHardware & 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 systemrequirements
Partitionrequirements
Hardwarerequirements
Hardwaredesign
Softwarerequirements
Softwaredesign
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.
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)
R-T Systems Design Process – 6 Steps
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 low-level 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
Enabled
do: operateoven
Fullpower
Halfpower
Halfpower
Fullpower
Number
TimerDooropen
Doorclosed
Doorclosed
Systemfault
Start
do: set power = 600
Half powerdo: set power = 300
Set time
do: get numberexit: set time
Disabled
Operation
Timer
Cancel
Waiting
do: display time
Waiting
do: display time
do: display 'Ready'
do: display 'Waiting'
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
Process resourcerequirements
Scheduler
Schedulinginformation
Resourcemanager
Despatcher
Real-timeclock
Processesawaitingresources
Readylist
Interrupthandler
Availableresource
list
Processorlist
Executingprocess
Readyprocesses
Releasedresources
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
Resource manager
Allocate memoryand processor
Scheduler
Choose processfor execution
Despatcher
Start execution on anavailable 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 SystemExample 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
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.
Sensors & Actions Of A Burglar Alarm SystemExample Of A Monitoring System
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
Stimulus/Response Timing requirementsPower fail interrupt The switch to backup power must be completed
within a deadline of 50 ms.Door alarm Each door alarm should be polled twice per
second.Window alarm Each window alarm should be polled twice per
second.Movement detector Each movement detector should be polled twice
per second.Audible alarm The audible alarm should be switched on within
1/2 second of an alarm being raised by a sensor.Lights switch The lights should be switched on within 1/2
second of an alarm being raised by a sensor.Communications The call to the police should be started within 2
seconds of an alarm being raised by a sensor.Voice synthesiser A synthesised message should be available
within 4 seconds of an alarm being raised by asensor.
A Burglar Alarm System’s Timing Requirements
A Burglar Alarm System’s Architecture Diagram
Lighting controlprocess
Audible alarmprocess
Voice synthesizerprocess
Alarm systemprocess
Power switchprocess
Building monitorprocess
Communicationprocess
Door sensorprocess
Movementdetector process
Window sensorprocess
560Hz
60Hz400Hz 100Hz
Power failureinterrupt
Alarmsystem
Building monitor
Alarmsystem
Alarm system
Alarm system
Detector status Sensor status Sensor status
Room number
Alert message
Room number
Room number
Building_monitor process 1 }
// See http://www.software-engin.com/ for links to the complete Java code for this// example
class BuildingMonitor extends Thread {
BuildingSensor win, door, move ;
Siren siren = new Siren () ;Lights lights = new Lights () ;Synthesizer synthesizer = new Synthesizer () ;DoorSensors doors = new DoorSensors (30) ;WindowSensors windows = new WindowSensors (50) ;MovementSensors movements = new MovementSensors (200) ;PowerMonitor pm = new PowerMonitor () ;
BuildingMonitor(){
// initialise all the sensors and start the processessiren.start () ; lights.start () ;synthesizer.start () ; windows.start () ;doors.start () ; movements.start () ; pm.start () ;
A Burglar Alarm System’s
Sample Code
Building_monitor process 2
public void run (){
int room = 0 ;while (true){
// poll the movement sensors at least twice per second (400 Hz)move = movements.getVal () ;// poll the window sensors at least twice/second (100 Hz)win = windows.getVal () ;// poll the door sensors at least twice per second (60 Hz)door = doors.getVal () ;if (move.sensorVal == 1 | door.sensorVal == 1 | win.sensorVal == 1)
{// a sensor 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 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
Thermostatprocess
Sensorprocess
Furnacecontrol process
Heater controlprocess
500Hz
500Hz
Thermostat process500Hz
Sensorvalues
Switch commandRoom number
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 CollectionAnother 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 MonitoringAnother Control System Example
DisplayProcess
dataSensor data
bufferSensorprocess
Sensoridentifier and
value
Processedflux level
Sensors (each data flow is a sensor value)
A Ring Buffer
Consumerprocess
Producerprocess
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.
Java implementation of a ring buffer 1
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 () ;
} // putA Circular Buffer
Sample Code
Java implementation of a ring buffer 2
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 Code
Software EngineeringCSCI 3342
Dr. Thomas E. HicksComputer Science Department
Trinity University
Textbook: Software EngineeringBy Roger Pressman
Textbook: Software EngineeringBy Ian Sommerville
Special Thanks To WCB/McGraw-Hill & Addison Wesley For Providing Graphics Of Some Of Text Book Figures For Use In This
Presentation.