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Operating System TutorialOperating System Tutorial

Source: http://codex.cs.yale.edu/avi/osSource: http://codex.cs.yale.edu/avi/os--book/os7/slidebook/os7/slide--dir/index.htmldir/index.html


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OutlineOutline

Introduction

Process and Threads

Deadlocks and Process Synchronization

Scheduling

Interrupts & System Calls

Memory Management


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What is an Operating System?What is an Operating System?

A program that acts as an intermediarybetween a user of a computer and thecomputer hardware.

Operating system goals:

Execute user programs and make solvinguser problems easier.

Make the computer system convenient touse.

Use the computer hardware in an efficientmanner.


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Four Components of a Computer SystemFour Components of a Computer System


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OperatingOperating--System OperationsSystem Operations

Dual-mode operation allows OS to protectitself and other system components

User mode and kernel mode Mode bit provided by hardware

Provides ability to distinguish when system is running

user code or kernel codeSome instructions designated as privileged, only

executable in kernel mode

System call changes mode to kernel, return from call

resets it to user


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Transition from User to Kernel ModeTransition from User to Kernel Mode


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Process ConceptProcess Concept

Process

a program in execution

process execution must progress in sequentialfashion

A process includes: program counter

stack

data section


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Process Control Block (PCB)Process Control Block (PCB)


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Process State DiagramProcess State Diagram


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CPU Switch From Process to ProcessCPU Switch From Process to Process


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Representation of Process SchedulingRepresentation of Process Scheduling


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Context SwitchContext Switch

When CPU switches to another process,the system must save the state of the old

process and load the saved state for thenew process

Context-switch time is overhead; thesystem does no useful work while switching

Time dependent on hardware support


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Cooperating ProcessesCooperating Processes

Independent process cannot affect or beaffected by the execution of anotherprocess

Cooperating process can affect or beaffected by the execution of anotherprocess

Advantages of process cooperation

Information sharing

Computation speed-up Modularity

Convenience


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ProducerProducer--Consumer ProblemConsumer Problem

Paradigm for cooperating processes,producerprocess produces

information that is consumed by aconsumerprocess

unbounded-bufferplaces no practical limiton the size of the buffer

bounded-bufferassumes that there is a

fixed buffer size


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InterprocessInterprocess Communication (IPC)Communication (IPC)

Mechanism for processes to communicate and tosynchronize their actions

Message system processes communicate with eachother without resorting to shared variables

IPC facility provides two operations:

send(message) message size fixed or variable

receive(message)

If Pand Qwish to communicate, they need to:

establish a communication linkbetween them

exchange messages via send/receive


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ThreadsThreads

A flow of control in a process

has access to entire process (incl. other threads)

potentially parallel execution

minimal state, so low overheads

All threads within a process share the same state and same memory space

use different stack

and can communicate with each other directly, because theyshare the same variables.


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Single and Multithreaded ProcessesSingle and Multithreaded Processes


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BenefitsBenefits

Responsiveness

Resource Sharing

Economy

Utilization of MP Architectures


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ProcessProcess vsvs ThreadThread

Process Thread

Address Space Not Shared Shared

Stack Not Shared Not Shared

Communication IPC Direct

State

Information

Different Same

Context SwitchOverhead

Large Small


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CPU SchedulerCPU Scheduler

Selects from among the processes in memory that areready to execute, and allocates the CPU to one ofthem

CPU scheduling decisions may take place when aprocess:

1. Switches from running to waiting state2. Switches from running to ready state

3. Switches from waiting to ready

4. Terminates Scheduling under 1 and 4 is nonpreemptive

All other scheduling is preemptive


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DispatcherDispatcher

Dispatcher module gives control of the CPU to theprocess selected by the short-term scheduler; this

involves: switching context

switching to user mode

jumping to the proper location in the user program torestart that program

Dispatch latency time it takes for the dispatcher

to stop one process and start another running


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SchedulingScheduling

Optimization Criteria

Max CPU utilization

Min turnaround time Min waiting time

Few Algorithms First Come First Serve

Shortest Job First

Priority based

Round Robin


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Deadlock: Bridge Crossing ExampleDeadlock: Bridge Crossing Example


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Deadlock CharacterizationDeadlock Characterization

Mutual exclusion

Hold and wait

No preemption

Circular wait

Deadlock can arise if four conditions hold simultaneously.

M h d f H dli D dl k


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Methods for Handling DeadlocksMethods for Handling Deadlocks

Ensure that the system will neverenter a deadlockstate.

Allow the system to enter a deadlock state andthen recover.

D dl k P iD dl k P ti


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Deadlock PreventionDeadlock Prevention

Mutual Exclusion

Hold and Wait

Require process to request and be allocated all itsresources before it begins execution

or allow process to request resources only when theprocess has none

No Preemption

Circular Wait

Restrain the ways request can be made.

I H dliI t t H dli


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Interrupt HandlingInterrupt Handling

The operating system preserves the state of theCPU by storing registers and the program counter.

Determines which type of interrupt has occurred: polling

vectoredinterrupt system

Separate segments of code determine what actionshould be taken for each type of interrupt

I t t Ti liI t t Ti li


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Interrupt TimelineInterrupt Timeline

C F ti f I t tCommon F nctions of Interr pts


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Common Functions of InterruptsCommon Functions of Interrupts

Interrupt transfers control to the interrupt serviceroutine generally, through the interrupt vector, whichcontains the addresses of all the service routines.

Interrupt architecture must save the address of theinterrupted instruction.

Incoming interrupts are disabledwhile anotherinterrupt is being processed to prevent a lostinterrupt.

A trapis a software-generated interrupt caused eitherby an error or a user request.

An operating system is interruptdriven.

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