real time operating system based design-1

7/25/2019 Real time operating system based design-1

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UNIT 5UNIT 5

REAL TIME OPERATING SYSTEM (RTOS)

BASED DESIGN-1


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10.1 BASICS OF OS10.1 BASICS OF OS

OS acts as a bridge b/w user applications and task and the underlying

system resources

Primary functions of an OS are:

Make the system convenient to use

Organie and manage the system resources efficiently and correctly

Operating system

architecture


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10.1.1 The Kernel10.1.1 The Kernel

!ore of the operating system

"esponsible for managing system resources and communication

between h/w and other services

#ernel $ System %ibraries & Services

Process management:

Setting memory space for process'

loading process(s code into memory space'

allocating system resources'

scheduling and managing e)ecution of processes' setting up and managing P!*'

+P! and synchroniation'

process termination and deletion


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Primar !emor management:

",M -processes & variables & shared data.

Memory Management nit-MM. of kernel is responsible for :

#eeping track of memory

,llocating and deallocating memory space

File sstem management:

0ile is a collection of related information

1his service of kernel is responsible for :

!reation' deletion and alteration of files

!reation' deletion and alteration of directories

Saving of files in secondary storage memory

Providing automatic allocation of file space

Providing a fle)ible naming convention for the files


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I"O Sstem #$e%ice& management:

"outing +/O re2uests coming from different user application to the

appropriate +/O devices of system

,ccess to +/O devices via ,P+

#ernel maintains the list of all +/O devices of the system-3evice

Manager.

3evice 3river : system calls by which kernel interacts with +/O

3evice Manager is responsible for:

%oading and unloading device drivers

4)changing information' and system specific control signals to and from

devices


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Secon'ar Storage management:

Managing secondary storage memory devices

*ackup medium for programs and data "esponsibilities:

3isk storage allocation

3isk scheduling

0ree disk space management

Protection sstems:

Multiple users with different level of access permissions

+mplementing security policies

Interr()t han'ler


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10.1.1.1 The Kernel S)ace an' User S)ace10.1.1.1 The Kernel S)ace an' User S)ace

Memory space where kernel code is located5kernel space

Memory space where user applications are located 5user space

6irtual memorydemand paging techni2ue

5Swapping act of loading code into and out of main memory

+t happens between main memory and secondary storage memory


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10.1.1.* !onolithic Kernel an' !icro+ernel10.1.1.* !onolithic Kernel an' !icro+ernel

Monolithic kernel :

#ernel services run in kernel space

4ffective utiliation of low level features of underlying system

,ny error or failure in any of the kernel module results in crashing of entire

kernel application

%+78' SO%,"+S' MS93OS


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Microkernel:

Only essential set of OS services into kernel

"est of OS services are implemented in programs called Servers

Mach' 78' Mini) ;


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*enefits of Microkernel approach:

,o-(stness:


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10.* T)es o O)erating sstem10.* T)es o O)erating sstem

/eneral P(r)ose O)erating Sstem#/POS&

#ernel is more generalied and contains all services

1here can be slow responsiveness of an application

Personal !omputers/3esktops system

4): =indows 8P/MS93OS

,eal Time O)erating Sstem#,TOS& 3eterministic timing behavior


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10.* T)es o O)erating sstem10.* T)es o O)erating sstem

,eal Time Kernel

1ask/Process Management

1ask/Process scheduling

1ask/Process synchroniation

4rror/4)ception handling

Memory management +nterrupt handling

1ime management


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Tas+"Process !anagement

TCB contains:

>? 1ask +3@? 1ask State

;? 1ask 1ype

A? 1ask Priority

B? 1ask !onte)t Pointer

C? 1ask Memory Pointers

D? 1ask System "esource Pointers

E? 1ask Pointers

!reates 1!* for a task 3elete 1!*

"ead 1!* for getting state of task

pdate 1!*

Modify 1!* for changing priority of the task


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Tas+"Process Sche'(ling

Tas+"Process Snchroniation

rror"2ce)tion 3an'ling 4rrors occurred during e)ecution of tasks

+nsufficient memory' timeouts' deadlocks' deadline missing' bus error' divide by

ero' etc

#ernel level e)ception$ea'loc+

1ask level e)ceptionTimeo(t

,P+Fet%ast4rror-.=indows !4 "1OS


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!emor !anagement

*%O!# based allocation

0ree *uffer 2ueue Interr()t 3an'ling :

Synchronous and ,synchronous

Synchronousinterrupts occurring in sync with current task -3ivide by Gero.

,synchronous

not in sync with currently e)ecuting task


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3ar' real time :

"1OS strictly adhere to the timing constraint

Missing deadlinecatastrophic results-data lose. A late answer is a wrong answer

,ir bag control system H ,nti lock brake system-,*S.


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Tas+s Process an' Threa'sTas+s Process an' Threa's

Tas+ : Program in e)ecution and all related information maintained

by OS for the program? #6OB&

Process : Program or part of it in e)ecution' it re2uires various system

resources

Str(ct(re o )rocess: !oncurrent e)ecution of tasks


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Process states an' state TransitionProcess states an' state Transition

Process 4ie Ccle

Create' state

,ea' state

,(nning state

Bloc+e' state Com)lete' state

State Transition


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Process states an' state TransitionProcess states an' state Transition

728or+s

,A$9

PN$ -*%O!#43.

$4A9-process is sleeping.

SUSPN$ !icroC"OSII

$O,!ANT -!"4,143.

,A$9

,UNNIN/ 8AITIN/

INT,,UPT$


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T3,A$ST3,A$S

Primitive that can e)ecute code

Single se2uential flow of control within a process

%ight weight process

!emor organiation o a )rocess an' its threa's


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!U4TIT3,A$IN/!U4TIT3,A$IN/

*etter memory utiliation

Speeds up e)ecution

of process

!P utiliation


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T3,A$ STAN$A,$ST3,A$ STAN$A,$S

POS+8 1hreads:

Portable Operating System +nterface

%ibraryPthreads -creation and management functions in 5!I.

int pthreadJcreate-pthreadJt KnewJthreadJ+3'

const pthreadJattrJt Kattribute'void K -KstartJfunction. -void K.'

void Karguments.L

int pthreadJoin-pthreadJt newJthread' void K KthreadJstatus.L

"eturn value of N5successI


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2am)le 12am)le 1

includepthread?hQ

includestdlib?hQincludestdio?hQ

void KnewJthread-void KthreadJargs.

R

int i' Lfor-$NL BL &&.

R

printf-5NNNNL i&&. L //sleep-.' delay-.

T

return 7%%L

T


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2am)le 1#cont'&2am)le 1#cont'&

int main-void.

Rint i'L

pthreadJt tcbL

if -pthreadJcreate - Htcb' 7%%' newJ thread' 7%%..

R

printf-54rror in creating new threadnI.Lreturn 9>L

T

for-$NL BL &&.

R

printf-5hello an in main threadnI.Lfor-i$NL i>NNNNL i&&.L

T


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if -pthreadJoin -tcb' 7%% . .

Rprintf-54rror in thread oinnI.L

return 9>L

T

return 9>LT


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Threa' Termination :

>? 7atural termination -returnorpthread_exit().@? 0orced termination -pthread_cancel() .


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8in ;* Threa's8in ;* Threa's

1hreads supported by =indows operating system

%ibrary=in ;@ ,P+


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8in ;* Threa's8in ;* Threa's

GetCurrenthread(void)

GetCurrenthread!d(void) GethreadPriorit"(void)

#ethreadPriorit"($A%&' hhread, int n Priorit")


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2am)le2am)le

includewindows?hQ

includestdio?hQ""Chil' Threa'

void !hild1hread-void.

R

char iLfor -i$NL i$>NL &&i.

R

printf-54)ecuting !hild 1hread: !ounter $ VdnI' i.L

Sleep-BNN.L

T

T


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2am)le#cont'&2am)le#cont'&

""Primar Threa'

int main-int argc' charK argvWX.R

L

T


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2am)le#cont'&2am)le#cont'&

""Primar Threa'

for-i$NL i$>NLi&&.R

printf-54)ecuting main thread: !ounter$VdnI'i.L

Sleep-BNN.L

Treturn NL

T


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6a%a Threa's6a%a Threa's

1hreads supported by ava programming language

Packageava?lang

import ava?lang?KL

public class My1hreade)tends 1hread

R

public void run-.

R

System?out?println-5


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6a%a Threa's6a%a Threa's

My1hread?start-.

"eady state My1hread?yield-.

6oluntarily gives up e)ecution of thread

"eady state

My1hread?sleep->NN.

0orces to sleep for the duration mentioned

Suspend mode and again back "eady state


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Threa' )reem)tionThrea' )reem)tion

Preempting currently running thread

=hy preemptionY 1hread conte)t switching

User 4e%el Threa'

>? 7o kernel/OS support

@? Process

multiple user level thread

OS treat as a single thread

processhas to schedule each thread

Kernel 4e%el Threa'

>? OS treat as separate threads

@? Scheduling is done by OS


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T3,A$ BIN$IN/ !O$4S

!antoOne !o'el

>? Solaris Freen 1hreads

@? F7 Portable 1hread

OnetoOne !o'el>? =indows 8P/71/@NNN

@? %inu) 1hreads

!anto!an !o'el

>? =indows 71/@NNN

@? 1hread0ibre


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!(lti)rocessing an' !(ltitas+ing!(lti)rocessing an' !(ltitas+ing

!U4TIP,OCSSIN/ :

4)ecuting multiple processes simultaneously Multiprocessor systemsmultiple !Ps

!U4TIP,O/,A!!IN/ :

Multiple programs in memory

niprocessor systemsswitching !P among the processes

Multitaskingability of !P to hold multiple programs in memory and switch

!P

+llusion of multiple tasks e)ecuting parallelly


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CONT


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T)es o !(ltitas+ingT)es o !(ltitas+ing

COOP,ATI7 !U4TITASKIN/:

!urrent 4)ecuting process has to release !P voluntarily Process can hold !P as much as it wants

P,!PTI7 !U4TITASKIN/:

4very process gets a chance to e)ecute

=hen and how much timeYYY

NONP,!PTI7 !U4TITASKIN/:

Process can e)ecute until it terminates O" enters *locked/=aiting state O"

waiting for an +/O or system resource


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Tas+ Sche'(lingTas+ Sche'(ling

+t forms the basis of multitasking

3etermining which task/process has to be e)ecuted at a given point of time Sche'(ler : kernel service / application that implements the scheduling

algorithm

"unning "eady

Pre9emptive

*locked/=aiting "eady

Priority based

pre9emptive

"unning *locked/=aiting

Pre9emptive /

non pre9emptive

"unning !ompleted

Pre9emptive /

non pre9emptive /

cooperative


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Factors to -e consi'ere' '(ring selection oFactors to -e consi'ere' '(ring selection o

Sche'(ling algorithm " criterionSche'(ling algorithm " criterionCPU UTI4I=ATION:

+t should be high

Measure of how much percentage !P is being ultilied

T3,OU/3PUT:

7o of process e)ecuted per unit time

+t should be high

TU,NA,OUN$ TI!:

,mount of time taken be a process for completing its e)ecution

1ime waiting for memory & time in ready 2ueue & time spend for +/O & time

spent for e)ecution


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Factors to -e consi'ere' '(ring selection oFactors to -e consi'ere' '(ring selection o

Sche'(ling algorithm " criterionSche'(ling algorithm " criterion8AITIN/ TI!:

,mount of time spend in "eady 2ueue waiting for !P

+t should be minimal

,SPONS TI!:

1ime between submission of a process and the first response

+t should be least


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7ario(s >UUS in OS7ario(s >UUS in OS

6OB >UU:

,ll process in the system

,A$9 >UU:

,ll process ready for e)ecution and waiting for !P

$7IC >UU:

,ll process waiting for an +/O device


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Non )reem)ti%e Sche'(lingNon )reem)ti%e Sche'(ling

irst co*e irst #erve(C#) + ! scheduling ,llocate !P based on the order in which they enter "eady 2ueue

1icketing "eservation system

2am)le 1

1hree Process with +3s P>'P@'P; with estimated completion time >N'B'D milliseconds

respectively enters ready 2ueue in the order P>' P@' P;? !alculate waiting timeand turn around time for each process and also average waiting time and turn

around time-,ssume no +/O waiting for the processes.

2am)le *

!alculate waiting time and turn around time for each process and also average waiting

time and turn around time-,ssume no +/O waiting for the processes. for the

above e)ample if process enters the "eady ueue in the order P@' P>' P;


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'ast co*e irst #erve('C#) + '! scheduling

2am)le 1


respectively enters ready 2ueue in the order P>' P@' P;? -,ssume only P> is

present in the "eady 2ueue when the scheduler picks it up and P@' P; entered"eady 2ueue after that.? 7ow a new process PA with estimated completion time

Cms enters the "eady 2ueue after Bms of scheduling P>? calculate the waiting

time and turn around time?


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#hortest -ob irst #cheduling

2am)le 1


respectively enters ready 2ueue together? calculate the waiting time and turn

around time for each process and also average waiting time and turn around

time?2am)le *

!alculate the waiting time and turn around time for each process and also average

waiting time and turn around time for the above e)ample if a new process PA

with estimated completion time @ms enters the "eady ueue after @ms of

e)ecution of P@?&isadvantage.

Starvation

!annot predict ne)t shortest process in the "eady 2ueue for scheduling


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Priorit" based #cheduling

=indows !4 -N9@BB priority numbers.

2am)le 1


and priorities N';'@ -N highest priority and ; lowest priority. respectively enters

ready 2ueue together? calculate the waiting time and turn around time for eachprocess and also average waiting time and turn around time?

2am)le *

!alculate the waiting time and turn around time for each process and also average

waiting time and turn around time for the above e)ample if a new process PA

with estimated completion time Cms and priority > enters the "eady ueue after

Bms of e)ecution of P>?

&isadvantage.

Starvation -1ackled by ,F+7F.


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Preem)ti%e Sche'(lingPreem)ti%e Sche'(ling

Pree*ptive #- #cheduling+ #hortest /e*aining i*e(#/)

2am)le 1


respectively enters ready 2ueue together? , new process PA enters with

estimated completion time @ms enters the "eady 2ueue after @ms? calculate thewaiting time and turn around time for each process and also average waiting

time and turn around time?


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/ound /obin (//) #cheduling

42ual chance to all

0irst Process in the "eady 2ueue is selected for e)ecution

+t is e)ecuted for pre9defined time

,nd ne)t process is selected when the previous process pre9defined time elapses

or process completes


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/ound /obin (//) #cheduling i*ple*entation for /012 in" #

includert)B>tny?hQ

int counterNL

int counter>L

obN -. JtaskJN R

osJcreateJtask ->.L

while->. R

counterN&&L

T

T

ob> -. JtaskJ> R

while->. R

counter>&&L

T

T

void func (void) _tas3_tas3_id

24 tas3s


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/012 in" // #cheduling in #5A/ CA/& /A&/

Creating the tas+s

void checkJcardJtask -void. JtaskJ>

R

T

void processJcardJtask -void. JtaskJ@

R

T

void checkJserialJioJtask -void. JtaskJ;

RT

void processJserialJdataJtask -void. JtaskJA

R

T

Chec3 presence of cardProcess data received fro* card6pdate displa"Chec3 serial port for co**and

and data

Process data received fro* serial

port


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Sche'(ling o the tas+s

void startupJtask -void. JtaskJN

R

osJcreateJtask ->.L

osJcreateJtask [email protected] -;.L

osJcreateJtask -A.L

osJdeleteJtask -N.L

T


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void checkJcardJtask -void. JtaskJ>

Rwhile->.

R

if-card is present.

osJsendJsignal [email protected]

T

void processJcardJtask -void. JtaskJ@

Rwhile->.

R

osJwait>-#JS+F.L

TT


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void checkJserialJioJtask -void. JtaskJ;

Rwhile->.

R

if-data is received.

osJsendJsignal -A.

T

void processJserialJdataJtask -void. JtaskJA

R

while->.

RosJwait>-#JS+F.L

T

T


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/ound /obin (//) #cheduling

2am)le 1

1hree Process with +3s P>'P@'P; with estimated completion time C'A'@

milliseconds respectively enters ready 2ueue together +7 1'P@'P;? calculate the waiting time and turn around time

for each process and also average waiting time and turn around

time using "" algorithm with 1ime slice $@ms?


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Priorit" 7ased #cheduling

2am)le 1

1hree Process with +3s P>'P@'P; with estimated completion time >N'B'D

milliseconds and priorities >';'@ -N highest priority and ; lowest

priority. respectively enters ready 2ueue together? , new process

PA with estimated completion time Cms and priority N enters the

"eady ueue after Bms of e)ecution of P>? calculate the waiting

time and turn around time for each process and also average

waiting time and turn around time?


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Threa's Processes an' Sche'(lingThrea's Processes an' Sche'(ling

Process 1

includewindows?hQ

includestdio?hQ

void 1ask-void.

Rwhile->.

R

//Perform task e)ecution time $D?B units

Sleep->D?B.L

//"epeat 1ask

T


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Process 1

void main-void.

R

3=O"3 idL


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Threa's Processes an' Sche'(lingThrea's Processes an' Sche'(ling

Process *

includewindows?hQ

includestdio?hQ

void 1ask-void.

Rwhile->.

R

//Perform task e)ecution time $>N units

Sleep-B.L

//"epeat 1ask

T


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Process *

void main-void.

R

3=O"3 idL


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Process *

Set1hreadPriority-h1hread'

1


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I$4 P,OCSS#TASK&

void +dleJProcess -void.

R

//simple wait doing nothing

=hile->.L

T


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Tas+ Comm(nicationTas+ Comm(nication

7ased on the degree of interaction.

1. Coo)erating )rocesses

*. Com)eting )rocesses

!ooperation through sharing-through some shared resources.

!ooperation through communication-communicate for synchroniation.Share' !emor:

=rite and read data from

from memory


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Tas+ Comm(nicationTas+ Comm(nication

!*ple*enting #hared 5e*or".

1. Pi)es:

!lient9server architecture

Pipe server and pipe client

nidirectional and bidirectional

Microsoft =indows support two types of Pipes:

,nonymous Pipes -unnamed and unidirectional.

7amed Pipes -named and unidirectional or bidirectional.


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!emor !a))e' O-?ects!emor !a))e' O-?ects

Shared memory techni2ue

Createile5apping($A%&' hile, 'P#C6/!8_A/!76#

lpile5appingAttributes, &9/& flProtect, &9/&

dw5axi*un#i:e$igh,&9/&dw5axi*un#i:e'ow,'PC#/lp%a*e)

5ap;iewfile( $A%&' hile5appingb


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=include>stdio?h@

=include>windows?h@

void *ain()

$A%&' hile5apB

'P#/ h5ap;iewB

hile5ap Createile5apping( ($A%&') D2, %6'',

PAG_/A&9/!, E, EFEEE, 0(*e*or"*appedob


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h5ap;iew ('P#/) 5ap;iewfile (hile5ap, !'_5AP_9/!, E,E,E)B

!f(%6''h5ap;iew)

printf(ailed. rror codeHdIn,Get'astrror())B

returnB

J

else

printf(;irtual Address is Hd, h5ap;iew)B

J

6n*ap;iewfile(h5ap;iew)BClose$andle(hile5ap)B

J


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!essage Passing!essage Passing

3ifference between shared memory and message passing

,mount of data transferred

Speed

1. !essage @(e(e

0+0O

send(%a*e of the process to which *essage is to be sent, *essage)

receive(%a*e of the process fro* which *essage is be sent,

*essage)

Synchronous

Z 4nters waiting state

,synchronous

Z 7o waiting for acceptance


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!essage @(e(e

Post5essage($9%& h9nd, 6!% 5sg, 9PA/A5 wPara*,

'PA/A5 lPara*)

Posthread5essage(&9/& idhread, 6!% 5sg, 9PA/A5

wPara*, 'PA/A5 lPara*)

#end5essage($9%& h9nd, 6!% 5sg, 9PA/A5 wPara*,'PA/A5 lPara*)

Create5sgKueue('PC9#/ lps:%a*e, 'P5#GK66P!%#

lpptions)


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t"pedef 5#GK66P!%#_#

&9/& dw#i:eB

&9/& dwlagsB

&9/& dw5ax5essagesB

&9/& cb5ax5essagesB

7' b/eadAccessB

JB


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!essage @(e(e

pen5sgKueue()

9rite5sgKueue($A%&' h5sgK, 'P;!& lp7uffer, &9/&

cb&ata#i:e, &9/& dwi*eut, &9/& dwlags)

Z dwlags5#GK66_5#GA'/

/ead5sgKueue($A%&' h5sgK, 'P;!& lp7uffer, &9/&

cb7uffer#i:e, 'P&9/& lp%u*berf7"tes/ead, &9/&

dwi*eut, &9/& pwlags)

Get5sgKueue!nfo($A%&' h5sgK, 'P5#GK66!% lp!nfo)


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!ailBo2!ailBo2

,lternate form of Message 2ueue

!reation and Subscribing

Mailbo) server and mailbo) client


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SignallingSignalling

Primitive way of communication between processes

Signals do not carry any data

4g "18B> 1iny OS

osJsendJsignal

osJwait


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,emote Proce'(re Call # ,PC& an' Soc+ets,emote Proce'(re Call # ,PC& an' Soc+ets

"emote +nvocation or "emote +nvocation Method-"M+.

!lient Server applications and heterogeneous environments

Server and client

Synchronous-*locking.

,synchronous

,uthentication

-34S' ;34S.

Sockets-+741' 7+8.

Stream Socket

3atagram Socket


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Tas+ SnchroniationTas+ Snchroniation

Multiple processessharing system resources H variables

Shared memory -write and read.

ne)pected results

,ct of making the processes aware of the access of shared resources by

each process to avoid conflicts

>? "acing

@? 3eadlock

;? 3ining Philosophers Problem

A? Producer9consumer/bounded buffer problem

B? "eaders =riters problem

C? Priority inversion


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1. ,acing1. ,acing

includewindows?hQ

includestdio?hQ

char *ufferW>NX$R>'@';'A'B'C'D'E'['>NTL

short int counter$NL

void ProcessJ,-void. R

int iL

for-i$NL iBL i&&. R

if-*ufferWiX QN.counter&&L

T

T


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1. ,acing1. ,acing

void ProcessJ*-void. R

int L

for-$NL BL &&. R

if-*ufferWX QN.

counter&&LT

T


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1. ,acing1. ,acing

int main-.

R

3=O"3 idL

!reate1hread-7%%'N'

-%P1


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1. ,acing1. ,acing

mov ea) ' dword ptr Webp9AXL

add ea)'>L

mov dword ptr Webp9AX ' ea)L


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1. ,acing1. ,acing

Multiple process compete each other to access and manipulate

shared data concurrently-incorrect results. Sol(tion:

Make access and modification of shared variables mutually

e)clusive


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*. $ea'loc+*. $ea'loc+

7one of the processes can e)ecute

C 'i i i $ 'l +


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Con'itions a%oring $ea'loc+Con'itions a%oring $ea'loc+

!ombined occurrence of all the four condition-Coff*an!onditions.

3escribed by 4 F !offman in >[D>

Mutual 4)clusion

Only one process can hold a resource at a time


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$ea'loc+ 3an'ling$ea'loc+ 3an'ling

Ignore $ea'loc+s :

,ssume system design is deadlock free

!ost of removing a deadlock is large

4): 7+8

$etect an' ,eco%er $ea'loc+s : 7ac3 up cars techni2ue

OS keeps a resource graph in m/y

pdating the graph

1erminate the process or preempt the

resource

$ 'l + 3 'li$ 'l + 3 'li


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A%oi' $ea'loc+s :

,voiding by careful resource allocation techni2ues

4): 1raffic %ight mechanisms to avoid traffic ams

Pre%ent $ea'loc+s :7egating one of the four conditions

Mutual 4)clusion

Process should re2uest and be allocated all resource before e)ecution

,llocate resource only if the process does not hold resource currently 7o "esource Preemption

"elease resources if re2uest made by a process cannot be fulfilled

pdate the resource list

"eschedule processes when it gets its old resources and new resource

$ 'l + 3 'li$ 'l + 3 'li


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4i%eloc+ an' $ea'loc+s

Star%ation

; Th $i i Phil h P -l; Th $i i Phil h P -l


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;. The $ining Philoso)hers Pro-lem;. The $ining Philoso)hers Pro-lem

0ive philosophers - n.

4ating '


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1hree different scenarios:

Scenario 1:

+nvolve in brainstorming together and try to eat together

!ircular chain

Starvation and deadlock



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Scenario *:

,ll philosophers start brainstorming together

"ace condition-une)pected results.



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Scenario ;:

Philosophers brainstorming together and trying to eat together

%ivelock and starvation

; Th $i i Phil h P -l; The $ining Philoso)hers Pro-lem


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Sol(tions:

"ound "obin

+mposing rules in accessing the forks by philosophers

Philosopher ac2uires a semaphore - mute). before picking up ant fork

P ' C "B ' ' B P -l Pro'(cer Cons(mer"Bo(n'e' B(er Pro-lem


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. Pro'(cerCons(mer"Bo(n'e' B(er Pro-lem. Pro'(cerCons(mer"Bo(n'e' B(er Pro-lem

1wo process concurrently access a shared buffer with fi)ed sie

1hread/Process producing dataProducer hread+Process

1hread/Process consuming dataConsu*er hread+Process

3ue to lack of synchroniation:

7uffer overrun

7uffer underDrun

%ead to inaccurate data and data loss

Pro'(cer Cons(mer"Bo(n'e' B(er Pro-lem Pro'(cer Cons(mer"Bo(n'e' B(er Pro-lem


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includewindow?hQ

includestdio?hQ

define 7 @N

int bufferW7XL

6oid producerJthread-void.R

int )L

while-true.R

for-)$NL )7L )&&.R

bufferW)X$rand-.V>NNNL

printf-5Produced:*ufferWVdX$VdI' )' bufferW)X.L

[email protected]

T

T

T



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6oid consumerJthread-void.R

int y$N' valueL

while-true.R

for-y$NL y7L y&&.R

value$bufferWyXL

printf-5!onsumed:*ufferWVdX$VdI' y' value.L

[email protected]

T

T

T



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int main-.

R

3=O"3 threadJidL

!reate1hread-7%%'N'

-%P1


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ISSUS:

>? Producer thread is scheduled more fre2uently than consumer thread

@? !onsumer thread is scheduled more fre2uently than Producer thread

SO4UTIONS:

>? Sleep and wake9up

5 ,ea'ers 8riters Pro-lem5 ,ea'ers 8riters Pro-lem


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5. ,ea'ers8riters Pro-lem5. ,ea'ers8riters Pro-lem

Processes competing for limited shared resources

*anking system

Multiple processes read data concurrentlyno impact

Multiple processes read and write data concurrentlyimpact

Priorit In%ersion Priorit In%ersion


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. Priorit In%ersion. Priorit In%ersion

unlocked


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Priorit InheritancePriorit Inheritance


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Priorit InheritancePriorit Inheritance

%ow priority task accessing shared resource re2uested by high priority

task temporarily inherits the priority of high priority task from themoment high priority task raises the re2uest

,nd when the resource is released priority is set back to original value


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Priorit CeilingPriorit Ceiling


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Priorit CeilingPriorit Ceiling

Priority is associated with each shared resource

Priority $ priority of highest priority task using the resource

!eiling priority

*oosting the priority of low priority task to ceiling priority

,nd the priority is reset after it releases shared resource


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Tas+ Snchroniation Techni@(esTas+ Snchroniation Techni@(es


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Tas+ Snchroniation Techni@(esTas+ Snchroniation Techni@(es

,voiding conflicts in resource access

4nsuring proper se2uence of operation across processes

!ommunicating between the processes

C,ITICA4 SCTION:

!ode memory area holding program instructions for accessing shared

resource

Mutual e)clusion

1 !(t(al 2cl(sion thro(gh B(s 8aiting " S)in 4oc+1. !(t(al 2cl(sion thro(gh B(s 8aiting " S)in 4oc+


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1. !(t(al 2cl(sion thro(gh B(s 8aiting " S)in 4oc+1. !(t(al 2cl(sion thro(gh B(s 8aiting " S)in 4oc+

%ock variable for implementing mutual e)clusion

%ock$ $ >in critical section

%ock $ $ Nnot in critical section

//inside main thread

bool b0lagL //lock variable

b0lag$0,%S4L

//inside child threa

if-b0lag $ $0,%S4.

b0lag$1"4L

*. !(t(al 2cl(sion thro(gh Slee) 8a+e()*. !(t(al 2cl(sion thro(gh Slee) 8a+e()


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*. !(t(al 2cl(sion thro(gh Slee) 8a+e()*. !(t(al 2cl(sion thro(gh Slee) 8a+e() !P is busy checking the lock to see whether they can proceed

7ot feasible in embedded systems-power consumption. Sleep H =ake up mechanisms

Process in critical section new process accessing critical section will

goto #leep process owning critical section wakeup the new process

when it lives the critical section

2? #e*aphore .

Process which wants to access shared resource first should ac2uire

system obect to indicate other processes that the shared resource is

currently ac2uired by it

"esource


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C i i l S i Obj


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Critical Section Objects:

!nitiali:eCritical#ection('PC/!!CA'_#C!%lpCritical#ection)

nterCritical#ection('PC/!!CA'_#C!%lpCritical#ection) 9ait Lueue

r"nterCritical#ection('PC/!!CA'_#C!%lpCritical#ection)

'eaveCritical#ection('PC/!!CA'_#C!%lpCritical#ection)

&eletenterCritical#ection('PC/!!CA'_#C!%lpCritical#ection)

$7IC $,I7,S$7IC $,I7,S


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$7IC $,I7,S$7IC $,I7,S *ridge between OS and hardware

,bstracts hardware from user applications 4stablish connectivity' initialie hardware and transfer data

=i9fi module' 0ile systems' Storage device interfaces

Protocols different

4ach hardware need a uni2ue driver component

$7IC $,I7,S$7IC $,I7,S


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$7IC $,I7,S 7,73 0lash memory7,73 0lash 3river

*uilt in drivers or Onboard drivers

loaded during booting

kept in",M

+nstallable driversloaded on need basis

3O8 TO C3OOS AN ,TOS3O8 TO C3OOS AN ,TOS


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O8 O C OOS N OSFUNCTIONA4 ,>UI,!NTS:

Processor support Memory re2uirements- "OM HH ",M .

"eal91ime !apabilities

#ernel and interrupt latency-latency minimal.

+P! and task synchroniation Modulariation support

Support for 7etworking and !ommunication

3evelopment %anguage support

3O8 TO C3OOS AN ,TOS3O8 TO C3OOS AN ,TOS


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NONFUNCTIONA4 ,>UI,!NTS:

!ustom developed or off the shelf !ost

3evelopment and debugging tools availability

4ase of use

real time operating system based design-1

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