3. SEQUENTIAL MODELS
A model in which instructions are executed one at a time.
Computer perform each step in specific order.
Program is divided into multiple tasks.
Computer programs set up in story form Beginning , Middle and End
All the tasks in program are in one file.
All tasks are interdependent.
Ex: Let A, B, C and D are four tasks. Then B starts only after
completing task A. Then after finishing the task B the C
starts and so on….
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4. CONCURRENCY
Two tasks are said to be concurrent if they occur within the
same time interval.
They do not mean that the tasks are executing at the same
instance.
They might be executing at the same hour but at different
period of interval.
EX: A and B are two concurrent tasks means- A might execute
for some fraction of seconds then B might execute for some
fraction of seconds. Again the task A execute, so on.......
Concurrent tasks can execute in
MULTIPROCESSING ENVIRONMENT.
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a SINGLE
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or
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5. CONCURRENCY
Single Processing Environment:
Context Switching :
It is a process of storing and restoring the execution state so
that multiple processes can share the same processor in a given
period of time.
Multiprocessing Environment:
Depends on No. of FREE Processors.
Developer deals with following challenges:
1. Software Development
2. Software Deployment
3. Software maintenance
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6. SOFTWARE DEVELOPMENT
It happens from developing device drivers to large scale Ntire applications.
Its size and scope vary to large extent. So, challenges are in
creating multiprocessing and multithreading applications.
Carried out in various phases [ SDLC].
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7. SOFTWARE DEVELOPMENT
SDLC ACTIVITIES
DESCRIPTION
Requirement
specification
Agreement between developer and the client. What s/w
must do and Constrains are specified.
Design
Specifications are model using s/w design. It determines
the INTERNAL STRUCTURE.
2 approaches- architectural design and detailed design.
Implementation
Detailed design is translated to the programming code.
Testing and
Evaluation
Exercising s/w in order to uncover the errors and improve
the quality of s/w.
Maintenance
After delivery of s/w.
Modifications are done to correct errors, to improve
performance.
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8. SOFTWARE DEVELOPMENT METHODOLOGY
S/W
DEVELOPMENT
METHODOLOGIES
DESCRIPTION
CORE ACTIVITIES
Agile
Part of functionality is delivered
at some time interval
Planning, requirement analysis,
design, implementation,
testing and documentation
Build and Fix
s/w is build and modifications
are done many times as needed
Build initial version, modify as
per customer’s requirements,
At each iteration developer
inform the client about time
required. Client selects the
desire feature
Requirement gathering,
specification, architectural
design, implementation and
integration, delivery
s/w developed in increments.
Integrated module by module
Requirement gathering,
specification, architectural
design, build loop
Extreme
Programming
Incremental
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9. SOFTWARE DEVELOPMENT METHODOLOGY
S/W
DEVELOPMENT
METHODOLOGIES
Object Oriented
DESCRIPTION
Objects are identified and with
them s/w is designed
At each iteration prototype of the
Rapid prototyping system is developed.
Interaction with client.
Spiral
Structured
Waterfall
CORE ACTIVITIES
Requirement gathering, OO
analysis, OO design,
implementation and integration
Rapid prototyping, specifications,
design, implementation,
integration, maintenance,
retirement.
Iterative model like incremental.
Emphasis on risk analysis and
verification at each phase
Planning, risk analysis,
evaluation
Top down approach.
Requirement analysis, design,
Implementation, testing,
development.
c/as linear sequential model
Rrq. Gathering and specification,
design, imple, integration,
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maintenance, retirement
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10. CHALLENGES OF S/W DEVELOPMENT
1) S/W Decomposition:
-> WBS & Architectural Artifacts (AAs)
-> Decomposition is written in form of PROBLEM & SOLUTION
CHALLENGES OF S/W DECOMPOSITION:
1) multiple ways to rep[resent a problem and its solution
2) making sure that decomposition is complete and correct.
-> Finding right model for decomposition.
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11. CHALLENGES OF S/W DEVELOPMENT
2) Task To Task Communication:
-> IPC ?
-> Managing IPC:
POSIX support six basic mechanisms to
accomplish communication between processes.
1) Files with lock and unlock facility
2) Pipes
3) Shared Memory
4) Message Queues
5) Semaphore (use variables)
6) Sockets
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12. CHALLENGES OF S/W DEVELOPMENT
3) Concurrent Access To Data Or Resources By
Multiple Tasks Or Agents:
Three commonly occurring problems while executing the instructions
concurrently:->
1) Data race: When two or more tasks are attempting to update the
data resource at the same time, the race condition occurs which is called
as data race.
2) Deadlock: It is a situation in which two or more tasks are waiting
for the other to finish so that they can acquire the resources.
3) Indefinite postponement: In this one or more tasks are waiting
for some event or condition to occur and if that condition or event never
occurs.
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13. CHALLENGES OF S/W DEVELOPMENT
4) Identifying Relationship Between Concurrently
Executing Tasks:
Four basic relationships
1) Start to Start
2) Finish to Start
3) Start to Finish
4) Finish to Finish
5) Controlling resource contention between tasks
6) Determining sufficient no. of processes or threads
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14. CHALLENGES OF S/W DEVELOPMENT
7 & 8) Finding reliable and reproducible debugging and
testing
-> Testing & debugging in sequential model.
-> Difficult to produce exact content of parallel or concurrent tasks
because of OS-scheduling policies,
dynamic workload,
process or thread priorities etc.
-> Multiprocessing and multithreaded applications are nondeterministic in nature.
That is recreation of the same sequence of events of these
type of applications in order to test or debug the program is
NOT POSSIBLE AT ALL.
-> Finding the right debugger or profiler
* state of the kernel process and system calls.
* attach or detach a process or thread.
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15. CHALLENGES OF S/W DEVELOPMENT
9) Communicating the designs having multiprocessing
components.
-> UML (Unified Modeling Language)
-> System Architecture (Structural Diagrams):
1) Component diagram: Represent the dependencies
and organization among a set of physical modules.
2) Deployment diagram: shows runtime
configuration of processing nodes, hardware and
software components in a system.
-> Behavioral Diagrams:
1) State diagram
2) Sequence diagram
3) Activity diagram
4) Collaboration diagram
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16. CHALLENGES OF S/W DEVELOPMENT
10) Implementing multiprocessing and multithreading in
C++.
-> C++ does not include any keyword primitives for
parallelism.
-> How can we implement the multiprocessing or
multithreading applications using C++? (By using libraries)
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17. NEW LIBRARIES FOR C++ DEVELOPERS
1) System Libraries:
-> Provides by O.S. itself
-> Ex: POSIX thread Library.
It contains the set of system calls that support parallelism.
-> POSIX ( Portable O. S. Interface for Unix)
* POSIX threads
* POSIX spawn function
* The exec() family of functions
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18. PROCESSOR ARCHITECTURE CHALLENGES
Four popularly used multi-core architectures1) Opteron
2) Cell
3) UltraSparc T1
4) Intel Core-2
-> These different architectures translate to different sets of compiler
switches and directives.
-> For this, it is necessary that the developer must be familiar with the use of
compiler and linker specific features.
-> In some cases multiple types of compilers needed to generate single
executable program.
-> But for taking the advantage of particular architecture we can make the
s/w non-portable.
-> So, taking most advantage of Multicore architecture without affecting
the portability of the s/w application is the real challenge of processor
architecture.
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