Processes and Interprocess Communication: A Deep Dive into Linux Operating System, Slides of Software Engineering

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Chapter 3: Processes

Chapter 3: Processes

• (^) Process Concept
• (^) Process Scheduling
• (^) Operations on Processes
• (^) Interprocess Communication
• (^) Examples of IPC Systems
• (^) Communication in Client-Server Systems

Process Concept

• (^) An operating system executes a variety of programs:
  • (^) Batch system – jobs
  • (^) Time-shared systems – user programs or tasks
• (^) Textbook uses the terms job and process almost interchangeably
• (^) Process – a program in execution; process execution must progress in sequential fashion
• (^) Multiple parts
  • (^) The program code, also called text section
  • (^) Current activity including program counter , processor registers
  • (^) Stack containing temporary data
    • (^) Function parameters, return addresses, local variables
  • (^) Data section containing global variables
  • (^) Heap containing memory dynamically allocated during run time
• (^) Program is passive entity stored on disk ( executable file ), process is active
  • (^) Program becomes process when executable file loaded into memory
• (^) Execution of program started via GUI mouse clicks, command line entry of its name, etc
• (^) One program can be several processes
  • (^) Consider multiple users executing the same program

Process in Memory

Diagram of Process State

Process Control Block (PCB)

Information associated with each process

(also called task control block )

• (^) Process state – running, waiting, etc
• (^) Program counter – location of instruction

to next execute

• (^) CPU registers – contents of all process-

centric registers

• (^) CPU scheduling information- priorities,

scheduling queue pointers

• (^) Memory-management information –

memory allocated to the process

• (^) Accounting information – CPU used, clock

time elapsed since start, time limits

• (^) I/O status information – I/O devices

allocated to process, list of open files

Threads

• (^) So far, process has a single thread of execution
• (^) Consider having multiple program counters per process
  • (^) Multiple locations can execute at once
    • (^) Multiple threads of control -> threads
• (^) Must then have storage for thread details, multiple program

counters in PCB

• (^) See next chapter

Process Representation in Linux

• (^) Represented by the C structure task_struct pid t_pid; /* process identifier / long state; / state of the process / unsigned int time_slice / scheduling information */ struct task_struct parent; / this process’s parent / struct list_head children; / this process’s children */ struct files_struct files; / list of open files */ struct mm_struct mm; / address space of this process */

Ready Queue And Various I/O Device Queues

Representation of Process Scheduling

 (^) Queueing diagram represents queues, resources, flows

Addition of Medium Term Scheduling

 (^) Medium-term scheduler can be added if degree of multiple programming needs to decrease  (^) Remove process from memory, store on disk, bring back in from disk to continue execution: swapping

Multitasking in Mobile Systems

• (^) Some systems / early systems allow only one process to run, others

suspended

• (^) Due to screen real estate, user interface limits iOS provides for a
  • (^) Single foreground process- controlled via user interface
  • (^) Multiple background processes– in memory, running, but not on the display, and with limits
  • (^) Limits include single, short task, receiving notification of events, specific long- running tasks like audio playback
• (^) Android runs foreground and background, with fewer limits
  • (^) Background process uses a service to perform tasks
  • (^) Service can keep running even if background process is suspended
  • (^) Service has no user interface, small memory use

Operations on Processes

• (^) System must provide mechanisms for process creation,

termination, and so on as detailed next

Process Creation

• (^) Parent process create children processes, which, in turn create

other processes, forming a tree of processes

• (^) Generally, process identified and managed via a process identifier

( pid )

• (^) Resource sharing options
  • (^) Parent and children share all resources
  • (^) Children share subset of parent’s resources
  • (^) Parent and child share no resources
• (^) Execution options
  • (^) Parent and children execute concurrently
  • (^) Parent waits until children terminate