Process Control Block & Threads and Their Management

Process Control BlockThreads & Their ManagementBy Ujjwal Kumar1149210055CS – V – 2013

Presentation by Ujjwal Kumar

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Process Control Block

or PCB


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Introduction•Each & every process in the Operating

System is represented by a Process Control Block.

•Process Control Block ~ Task Control Block or Task Struct.


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What exactly is PCB?

•It is a Data Structure in the operating system kernel containing the information needed to manage a particular process.

•The PCB is "the manifestation(Visible) of a process in an operating system”


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Source: http://lmgtfy.com/?q=define%3Amanifestation/


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Fig: Process Control Block (PCB)


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What exactly does this diagram mean?


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•Pointers: It contains the address of another process which is present in the ready queue.

• Process State: It contains information about the state of the process i.e.,

• New

• Ready

• Running

• Waiting

• Halted


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•Program Counter: The address of the next instruction to be executed.

• CPU Registers: The registers vary in no.

and type depending on the type of

computer architecture, they include:

• Accumulators, index registers, stack pointers

and general purpose registers


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•CPU scheduling information: This

information includes

▫Process priority

▫Pointer to scheduling queues

▫Other scheduling parameters.

•Memory management information: This

information includes

▫Value of base and limit registers

▫Page tables

▫Segment tables.


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• Accounting information: This information

includes

• Amount of CPU and real time used

• Time limits

• Account numbers

• Job or Process numbers etc.

• I/O status information: This information

includes

• List of I/O devices allocated to the process

• List of open files etc .


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Now we know what exactly the Process Control Block is. But do we know where

the location of PCB is?


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•Contains critical information of processes and hence it must be placed where it is protected from normal user access.

•In many Operating systems, it is placed in the beginning of the kernel stack of the process since that is a convenient protected location.


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Interleaving Execution of

Processes


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Interleaving Execution of Processes•Perception of normal end user:

Process A Process

B

Process C

Process D

Time


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Interleaving Execution of Processes•In reality, this is how the processes are

executed: Process 1Process 2Process 1

Process 2


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Threads & their Management


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Threads

•Definition: In simple words we can say that Threads are light weight processes.

•It is a sequence and not a program because it cannot run on its own so it returns within the program.

•A process is divided into smaller tasks and these tasks are known as threads.

•A basic unit of CPU Utilization.


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Advantages of Threads

•If a process has multiple threads then it will be able to perform more than one single task at the same time.

•Better Throughput.•Makes the program Responsive.


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Types of Threading

•Single Threading•Multi Threading


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Multithreading

•Sometimes several similar tasks have to be performed by the application in order to get the word done.

•This is where the Multithreading comes in.


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Real life examples of Multithreading - I•Web browsers: They have different

threads to do different work.▫One thread will retrieve data from the

remote servers.▫Another one will render the data received

into visual web pages.•Example: Google Chrome, Opera, Firefox

etc.


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Real life examples of Multithreading - II•Word Processors: Different threads in

word processor will do different jobs.▫One will render the text based materials.▫Another one will render graphic based

materials like the images etc.•Example: Microsoft Office


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Benefits of Multithreading

•Responsiveness: The process responds much better while using multithreading as compared to single threaded processes.

•Speed Up: The process is speeded up by using multithreading hence giving a much better experience to the end user.

•Efficient Communication: The threads of a specific process can communicate with each other efficiently because of the shared address space.


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•Utilization in multiprocessor systems: ▫Multithreading can take advantages of a

multiprocessor system.▫Multiple threads can be processed on

multiple cores of the system.


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Implementation of Threads

•Threads are implemented in a system in three different ways. ▫Kernel Level Threads▫User Level Threads▫Hybrid Level Threads


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Kernel Level Threads

•Implemented by the kernel itself.•Management of threads is also done by

the kernel itself.

Process

Threads

Process Table


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User Level Thread

Kernel Space

Thread Table

ThreadProcess

User Space


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User Level Thread

•These type of threads are loaded in the user space and the kernel doesn’t have anything to do with this.

•Threads are managed in user space so each process must have its own private thread table.

•This table consists the information of:▫Program Counter▫Stack Pointer▫Register.


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Acknowledgements

•Sir. Mukesh Kumar Singh•Google.com•Book: OS by Vijay Shukla


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Questions

You can ask any questions you might have in your mind

related to my presentation.

Process Control Block & Threads and Their Management

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