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Operating System Process Management: Representation, Control, and UNIX SVR4, Study notes of Operating Systems

A chapter from 'operating systems: internals and design principles' discussing process management in operating systems. It covers process representation and control, process states, data structures, and process management in unix svr4. The chapter explains the fundamental task of process management in an operating system, the concepts of process elements and process control blocks, and the execution of processes.

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2016/2017

Uploaded on 04/28/2017

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Chapter 3
Process Description and Control
Operating Systems:
Internals and Design Principles, 6/E
William Stallings
Dave Bremer
Otago Polytechnic, N.Z.
©2008, Prentice Hall
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Chapter 3

Process Description and Control

Operating Systems: Internals and Design Principles, 6/E William Stallings Dave Bremer Otago Polytechnic, N.Z. ©2008, Prentice Hall

Roadmap

  • (^) How are processes represented and controlled by the OS.
  • (^) Process states which characterize the behaviour of processes.
  • (^) Data structures used to manage processes.
  • (^) Ways in which the OS uses these data structures to control process execution.
  • (^) Discuss process management in UNIX SVR4.

Concepts

  • (^) From earlier chapters we saw:
    • (^) Computer platforms consists of a collection of hardware resources
    • (^) Computer applications are developed to perform some task
    • (^) It is inefficient for applications to be written directly for a given hardware platform

Concepts cont…

  • (^) OS provides an interface for applications to use
  • (^) OS provides a representation of resources that can be requested and accessed by application

What is a “process”?

  • (^) A program in execution
  • (^) An instance of a program running on a computer
  • (^) The entity that can be assigned to and executed on a processor
  • (^) A unit of activity characterized by the execution of a sequence of instructions, a current state, and an associated set of system instructions

Process Elements

  • (^) A process is comprised of:
    • (^) Program code (possibly shared)
    • (^) A set of data
    • (^) A number of attributes describing the state of the process

Process Control Block

  • (^) Contains the process elements
  • (^) Created and managed by the operating system
  • (^) Allows support for multiple processes

Trace of the Process

  • (^) The behavior of an individual process is shown by listing the sequence of instructions that are executed
  • (^) This list is called a Trace
  • (^) Dispatcher is a small program which switches the processor from one process to another

Trace from the

processes point of view:

  • (^) Each process runs to completion

Trace from Processors

point of view

Timeout I/O TimeoutTimeout

Two-State Process Model

  • (^) Process may be in one of two states
    • (^) Running
    • (^) Not-running

Queuing Diagram

Etc … processes moved by the dispatcher of the OS to the CPU then back to the queue until the task is competed

Process Creation

  • (^) The OS builds a data structure to manage the process
  • (^) Traditionally, the OS created all processes
    • (^) But it can be useful to let a running process create another
  • (^) This action is called process spawning
    • (^) Parent Process is the original, creating, process
    • (^) Child Process is the new process

Process Termination

  • (^) There must be some way that a process can indicate completion.
  • (^) This indication may be:
    • (^) A HALT instruction generating an interrupt alert to the OS.
    • (^) A user action (e.g. log off, quitting an application)
    • (^) A fault or error
    • (^) Parent process terminating