Operating System Processes: 2nd Grade Telecom

• These are study notes on operating system processes as taught in the 2nd grade of Telecommunications Technology Engineering

Block 1: Operating Systems

• Explores key computer architecture concepts.
• Covers operating systems, processes, memory management, and file systems

Contents Covered

• Introduces operating systems, processes, and threads
• Communication and synchronization mechanisms
• Scheduling algorithms
• Memory and file management

Processes

• Programs in execution are considered processes; these are processing units managed by the operating system.

Topics in the Processes Section

• Process creation
• Process intercommunication
• Synchronization
• Scheduling
• Algorithm mechanism coverage
• Passive wait implementation.

Program vs Process

• A program represents a recipe, while a process represents that recipe in action.
• A process is a unit of processing managed by the OS

Process Table and PCB

• OS maintains a data structure that relies on Processes and Control Blocks
• Segments of the memory image include C+D+S.
• The state of the processor
• File descriptors already opened, PID, user id, and timers.

Process State and CPU

• When a process is running, its state resides in the CPU.
• It exists in the Processes Table's PCB when not running

PCB Information

• Includes identification details like PID, PPID, and user/group IDs.
• Processor State: This captures the process's state.
  • This includes CPU registers like PSW, user/kernel mode, interrupt status, priority, and results.
• Includes PC and SP
• Control State
  • Scheduling for ready and blocked processes
  • Inter-process communications
  • Signals for timing
• Information on CPU time, memory

Memory Table Management

• Controls what memory is allocated to the process
• Includes segment information
  • CS: base address and code amount
  • DS: data variables and static data
  • SS: starting address
  • Permissions
  • Table for memory pages
  • Dynamic Memory Pointer
  • Information on shared memory being used.

I/O Table

• Allocates peripherals and I/O operations.

File Table

• It provides the position in the FILP.
• Info about the directories used
• Access permissions

Example PCB framework from MINIX 1.0

• Example
  • extern struct proc
    • Process registers
      • int p_reg[NR_REGS];
    • Stack pointer
      • int *p_sp;
    • PC and PSW
      • struct pc_psw p_pcpsw;
    • Memory Map
      • struct mem_map p_map[NR_SEGS];
    • Process id - int p_pid;

Basic States of Process

• Execution
• Blocked
• Ready to be executed

Planner Responsibility

• The scheduler chooses the next process to run
• Idle loop for when all processes are idle
  • Keeps CPU going
  • Necessary, prevent errors
  • Saves energy
• Calculate CPU usage
• Basic function for managing memory

Processes are Heirarchical

• Parents, Children, and siblings
• Follow processing life cycle

Life Cycle Includes

• Create
• Execute
• Shutdown
• Has a set of execution types
  • Batch
  • Interactive

Process Management

• PGID
• SID

Processes Inherit information

• Gets variable from creation
• Can use and change values that effect parent and siblings
• IZEN-BALIO table at execution start.
  • int main(int argc, char **argv, char **envp);

Process Setting

• Defaults to parents
• Set via shell command or via API
• Variables are PATH, TERM,HOME, PWD, USER
• Access via command echo $aldagaia and c code getenv("aldagaia")

Multitasking

• Single-tasking does nothing while waiting for Input / output
• CPU Input / Output and parallelism
  • Input / Output system depends on OS.
  • Memory needed to save several states
• Used to increase performance

Multi-tasking Implementation

• Processes Input / Outputs are dependent on the OS, this lets the CPU access a new task
• Provides better performance
• Allows multiple interactive users
• Makes it easier to work on applications that should use multiple threads

Types of Computers

• Multiprogamming via time slicing illusion of concurrency
• Multi-Processor is true concurrency
• Multi-Computer works together (processing is distributed)

Concurrency Purpose

• More usage better of physical resources
• Modular processing increases work force
• Interaction is optimized

Types of Concurrent Processing

• Colleagues
• Independents

Kinds of Interaction

• Share processing power
• Communicate and sync, colleagues

How to handle paralellism and I/O

• I/O devices get interrupts
• An interrupt is addressed by the corresponding memory map.
• OS uses I/O controller for processes to resume from the ready queue

Context Switching

• Caused by interrupt
• Processes' state goes into the PCB
• Interrupt routine executes code
• Scheduler works
• Dispatcher initiates execution depending on the OS scheduler routine

Process Loading

• Executable binary loads into main memory image and the process executes

Process Creation

• Achieved via "fork"
  • Clones a process including the code and information
• The child can be run and modified without disturbing the parent.

Execution Modification

• Can be achieved via "exec"
  • Has two phases
    • HUSTE removes current memory allocation
    • KARGA builds the state of a process
• Must keep PID, I/O

Process Timing

• Timing issues of process can be fixed
• A process must wait till the prior exits before starting.

A-Semen life Cycle

• Semeek is a copy and executes
• The atia takes up after the first is done.
• Can deadlock though

Threads

• Threads are known as light-weight processes
• All share an image, execute uniquely
• Each thread has its own
  • PC
  • Stack Pointer
  • Errors
• Share files

Pros and Cons of Threads

• Share memory
• Shorten time in system
• Allow lockstep parallel
• Don't block system easily
• Easy to delegate tasks
  • Needs synchornized Process sync required for intercommunication

Communication

• Communication occurs over calls are used for sending and receiving messages
• Signals, and files are mechanisms
• Sharing leads to conflicts.

Race conditions

• Race conditions need to be addressed for process integrity
• Processes can not simultaneously access critical resources
• Can be solved with flags

Active vs Passive Waiting

Active Waiting means waiting and polling which requires CPU resources Passive Waiting means waiting on the processes to complete.

Classic Issues

• Critical section
• Producer-consuer
• Irkacle-isles arazoa
• Bezero-zerbitzaria

Critical Section Review

• Needs to limit how many process can be in at any given time.
• There must be a mutual exit.
• Must finish in a timely manner

TSL and Sets

• These atomic commands for handling issues of critical process.

Classic IPC problems

• SE needs to do it
• They are called PUA and prevent processing overhead

Atomic Transactions

• Must be done for file or resource security

Production Consumption Review

• Consumers must wait on products.
• Produces must wait on consumers to consume.

Read-Write Review

• Readers consume multiple times while writing must be handled first.

Communication Mechanism

• Intercommunication requires calls and interfaces
• File system usage

Methods of Communication

• Files
• Hodiak (pipes, FIFOs)
• Partial image sharing
• Messages

Synchronized Communication

• Can be handled via messaging, signals
• Has several methods
  • Code management
  • Sempahores

File Sharing

• All processes share files
• The upside is simple processing
• The downside has high processing over head needs synchronization.

Pipes

• Used for temporary or simple code
• Managed by OS - First In First Out

Named vs unamed pipes

• Named are FIFO
• Unmaed are for child/parent only

Datastreams

• Requires 2 hodis

Pipeline Code Example

• Requires std io library for operation

Queue Review

• Code for queue is needed as prior steps can interfere.

Queue Review

• Uses the pipeline

Seinaleaks

• Interrupts that are done in short bursts handled.
  • Kill for interrupt

Handling signals and interrupts

• Can halt signals via code or call another signal interrupt.
  • Pause ()
• Kill (0 exits code

Handling Events

• Hardware, and Software trigger signals with code
• Signal - sends hardware instructions
• Hardware then sends signals to software
• Needs treatment for handling signals
• Called Pause
• Also can delay response

Process Scheduling

• Has several factors
• CPU
• IO
• Time

Goal of Process Scheduling

• Has a variety of goals.
• CPU usage time, and max throughput

Planning

• Has a variety of types.

  • Can be more IO, cpu, etc focused. Process scheduling

• Can be done based on type

• Has a variety of parameters and configuration.

  • Has priority
    • Static,
    • dynamic

• All types of plans have different priorities.

• Lani laburmena

• Can also be randomized

Planning types

• Can mix the different types of scheduling.
• Can also be intermixed for types and kinds of queues Has several methods to prevent deadlock

Time Monitoring

• Needed to limit certain calls.

Time Sharing

• Some processes wait, others do not, each is dependent on one another.

Shared Memory Planning

• Has several levels to maximize performance

Multicore Planning

• Uses all available cores for increased performance

Resource Assignment

• Each section of process is resource intensive to a different extent

Load Balancing

• All different tasks can go to queues

Batch Processing

• Resources assigned to load balance

Lehentasunak

• Different types to assign importance

Round Robin

• Evenly allocates resources Used in network sharing
• Equal Priority

Prioritized

• Has priority over others
• Can be static
• Can be dynamic

Loteria

• Random for fairness
• Uses lotto tickets depending on hardware

Process management

• Can be done