UNIT 2 and UNIT 3 (2 Mark Answer)

8/13/2019 UNIT 2 and UNIT 3 (2 Mark Answer)

1/14

UNIT 2 and UNIT 3

Part - A

1. What is a thread?

A thread otherwise called a lightweight process (LWP) is a basic unit o !PU utili"ation#it co$prises o a thread id# a progra$ counter# a register set and a stac%& It shares with

other threads belonging to the sa$e process its code section# data section# and operating

s'ste$ resources such as open iles and signals&

2. What are the benefits of multithreaded programming?

The beneits o $ultithreaded progra$$ing can be bro%en down into our $aor

categories

*esponsi+eness

*esource sharing

,cono$'

Utili"ation o $ultiprocessor architectures

3.Compare user threads and kernel threads.

User threads Kernel threads

User threads are supported abo+e the %ernel and arei$ple$ented b' a thread librar' at the user le+el

ernel threads are supported directl' b' the operating s'ste$

Thread creation . scheduling are done in the userspace# without %ernel inter+ention& Thereore the' areast to create and $anage

Thread creation# scheduling and $anage$ent are done b' theoperating s'ste$& Thereore the' are slower to create .$anage co$pared to user threads

/loc%ing s'ste$ call will cause the entire process tobloc%

I the thread peror$s a bloc%ing s'ste$ call# the %ernel canschedule another thread in the application or e0ecution


2/14

4.Define thread cancellation target thread.

The thread cancellation is the tas% o ter$inating a thread beore it has co$pleted& Athread that is to be cancelled is oten reerred to as the target thread& 1or e0a$ple# i

$ultiple threads are concurrentl' searching through a database and one thread returns the

result# the re$aining threads $ight be cancelled&

!.What are the different "a#s in "hich a thread can be cancelled?

!ancellation o a target thread $a' occur in two dierent scenarios

Asynchronous cancellation:ne thread i$$ediatel' ter$inates the target thread

is called as'nchronous cancellation&

Deferred cancellation:The target thread can periodicall' chec% i it should

ter$inate# allowing the target thread an opportunit' to ter$inate itsel in an

orderl' ashion&

$.Define C%U scheduling.

!PU scheduling is the process o switching the !PU a$ong +arious processes& !PU

scheduling is the basis o $ultiprogra$$ed operating s'ste$s& /' switching the !PU

a$ong processes# the operating s'ste$ can $a%e the co$puter $ore producti+e&

&.What is preempti'e and nonpreempti'e scheduling?

Under nonpree$pti+e scheduling once the !PU has been allocated to a process# the

process %eeps the !PU until it releases the !PU either b' ter$inating or switching to the

waiting state&


3/14

Pree$pti+e scheduling can pree$pt a process which is utili"ing the !PU in between its

e0ecution and gi+e the !PU to another process&

(.What is a Dispatcher?

The dispatcher is the $odule that gi+es control o the !PU to the process selected b' the

short-ter$ scheduler& This unction in+ol+es

witching conte0t

witching to user $ode

4u$ping to the proper location in the user progra$ to restart that progra$&

).What is dispatch latenc#?

The ti$e ta%en b' the dispatcher to stop one process and start another running is %nown

as dispatch latenc'&

56&What are the +arious scheduling criteria or !PU scheduling7

The +arious scheduling criteria are

!PU utili"ation

Throughput

Turnaround ti$e

Waiting ti$e

*esponse ti$e

11.Define throughput?


4/14

Throughput in !PU scheduling is the nu$ber o processes that are co$pleted per unit

ti$e& 1or long processes# this rate $a' be one process per hour8 or short transactions#

throughput $ight be 56 processes per second&

12.What is turnaround time?

Turnaround ti$e is the inter+al ro$ the ti$e o sub$ission to the ti$e o co$pletion o

a process& It is the su$ o the periods spent waiting to get into $e$or'# waiting in theread' 9ueue# e0ecuting on the !PU# and doing I:&

13.Define race condition.

When se+eral process access and $anipulate sa$e data concurrentl'# then theoutco$e o the e0ecution depends on particular order in which the access ta%es place is

called race condition& To a+oid race condition# onl' one process at a ti$e can $anipulate

the shared +ariable&

14.What is critical section problem?

!onsider a s'ste$ consists o ;n; processes& ,ach process has seg$ent o code called a

critical section# in which the process $a' be changing co$$on +ariables# updating a

table# writing a ile& When one process is e0ecuting in its critical section# no other processcan allowed to e0ecute in its critical section&

1!.What are the re*uirements that a solution to the critical section problem must

satisf#?

The three re9uire$ents are


5/14


6/14

boolean te$p > a8

a > b8

b > te$p8

?

1(.What is semaphores?

A se$aphore ;@ is a s'nchroni"ation tool which is an integer +alue that# apart ro$

initiali"ation# is accessed onl' through two standard ato$ic operations8 wait and signal&

e$aphores can be used to deal with the n-process critical section proble$& It can be alsoused to sol+e +arious s'nchroni"ation proble$s&

The classic deinition o ;wait@

wait ()

=

while (>6)

8

--8

?

The classic deinition o ;signal@

signal ()

=

BB8

?


7/14

1).Define bus# "aiting and spinlock.

When a process is in its critical section# an' other process that tries to enter itscritical section $ust loop continuousl' in the entr' code& This is called as bus' waiting

and this t'pe o se$aphore is also called a spinloc%# because the process while waiting

or the loc%&

2-. o" can "e sa# the /irst Come /irst 0er'ed scheduling algorithm is non

preempti'e?

nce the !PU has been allocated to a process# that process %eeps the !PU until it

releases the !PU# either b' ter$inating or b' re9uesting I:& o we can sa' the 1irst!o$e 1irst er+ed scheduling algorith$ is non pree$pti+e&

21.What is "aiting time in C%U scheduling?

Waiting ti$e is the su$ o periods spent waiting in the read' 9ueue& !PU scheduling

algorith$ aects onl' the a$ount o ti$e that a process spends waiting in the read'9ueue&

22. What is esponse time in C%U scheduling?


8/14

*esponse ti$e is the $easure o the ti$e ro$ the sub$ission o a re9uest until the

irst response is produced& *esponse ti$e is a$ount o ti$e it ta%es to start responding#

but not the ti$e that it ta%es to output that response&

23. Differentiate long term scheduler and short term scheduler

The long-ter$ scheduler or ob scheduler selects processes ro$ the ob pool and

loads the$ into $e$or' or e0ecution&

The short-ter$ scheduler or !PU scheduler selects ro$ a$ong the process that

are read' to e0ecute# and allocates the !PU to one o the$&

24. Write some classical problems of s#nchroniation?

The /ounded-/uer Proble$

The *eaders-Writers Proble$

The Cining Philosophers Proble$

2!. When the error "ill occur "hen "e use the semaphore?

i& When the process interchanges the order in which the wait and signal operations on

the se$aphore $ute0&

ii& When a process replaces a signal ($ute0) with wait ($ute0)&

iii& When a process o$its the wait ($ute0)# or the signal ($ute0)# or both&

2$.What is utual +clusion?


9/14

A wa' o $a%ing sure that i one process is using a shared $odiiable data# the other

processes will be e0cluded ro$ doing the sa$e thing& ,ach process e0ecuting the shared

data +ariables e0cludes all others ro$ doing so si$ultaneousl'& This is called $utuale0clusion&

2&.Define the term critical regions?

!ritical regions are s$all and inre9uent so that s'ste$ through put is largel' unaectedb' their e0istence& !ritical region is a control structure or i$ple$enting $utual

e0clusion o+er a shared +ariable&

2(.What are the dra"backs of monitors?

5&


10/14

A two di$ensional chart that plots the acti+it' o a unit on the D-a0is +ersus the ti$e on

the E-a0is& The chart 9uic%l' represents how the acti+ities o the units are seriali"ed&

31.Define deadlock.

A process re9uests resources8 i the resources are not a+ailable at that ti$e# the process

enters a wait state& Waiting processes $a' ne+er again change state# because the

resources the' ha+e re9uested are held b' other waiting processes& This situation is calleda deadloc%&

32.What is the se*uence in "hich resources ma# be utilied?

Under nor$al $ode o operation# a process $a' utili"e a resource in the ollowing

se9uence

*e9uest I the re9uest cannot be granted i$$ediatel'# then the re9uesting process

$ust wait until it can ac9uire the resource&

Use The process can operate on the resource&

*elease The process releases the resource&

33.What are conditions under "hich a deadlock situation ma# arise?

A deadloc% situation can arise i the ollowing our conditions hold si$ultaneousl' in a

s'ste$

5&


11/14

Ceadloc%s can be described $ore precisel' in ter$s o a directed graph called a s'ste$

resource allocation graph& This graph consists o a set o +ertices H and a set o edges ,&The set o +ertices H is partitioned into two dierent t'pes o nodes8 P the set consisting

o all acti+e processes in the s'ste$ and * the set consisting o all resource t'pes in thes'ste$&

3!.Define re*uest edge and assignment edge.

A directed edge ro$ process Pi to resource t'pe * is denoted b' Pi*8 it

signiies that process Pi re9uested an instance o resource t'pe * and is currentl' waiting

or that resource& A directed edge ro$ resource t'pe * to process Pi is denoted b'*Pi# it signiies that an instance o resource t'pe has been allocated to a process Pi& A

directed edge Pi* is called a re9uest edge& A directed edge *Pi is called an

assign$ent edge&

3$.What are the methods for handling deadlocks?

The deadloc% proble$ can be dealt with in one o the three wa's

Use a protocol to pre+ent or a+oid deadloc%s# ensuring that the s'ste$ will ne+er

enter a deadloc% state&

Allow the s'ste$ to enter the deadloc% state# detect it and then reco+er&

Ignore the proble$ all together# and pretend that deadloc%s ne+er occur in the

s'ste$&

3&.Define deadlock pre'ention.

Ceadloc% pre+ention is a set o $ethods or ensuring that at least one o the our

necessar' conditions li%e $utual e0clusion# hold and wait# no pre-e$ption and circular


12/14

wait cannot hold& /' ensuring that that at least one o these conditions cannot hold# the

occurrence o a deadloc% can be pre+ented&

3(.Define deadlock a'oidance.

An alternati+e $ethod or a+oiding deadloc%s is to re9uire additional inor$ation

about how resources are to be re9uested& ,ach re9uest re9uires the s'ste$ consider the

resources currentl' a+ailable# the resources currentl' allocated to each process# and theuture re9uests and releases o each process# to decide whether the could be satisied or

$ust wait to a+oid a possible uture deadloc%&

3).What are a safe state and an unsafe state?

A state is sae i the s'ste$ can allocate resources to each process in so$e orderand still a+oid a deadloc%& A s'ste$ is in sae state onl' i there e0ists a sae se9uence& A

se9uence o processes P5#P2#J&PnK is a sae se9uence or the current allocation state i#

or each Pi# the resource that Pi can still re9uest can be satisied b' the current a+ailableresource plus the resource held b' all the P# with i& i no such se9uence e0ists# then the

s'ste$ state is said to be unsae&

4-.What is banker6s algorithm?

/an%er@s algorith$ is a deadloc% a+oidance algorith$ that is applicable to aresource-allocation s'ste$ with $ultiple instances o each resource t'pe& The two

algorith$s used or its i$ple$entation are

Safety algorithm:The algorith$ or inding out whether or not a s'ste$ is in a sae state&


13/14

Resource-request algorithm:i the resulting resource-allocation is sae# the transaction is

co$pleted and process Pi is allocated its resources& I the new state is unsae Pi $ust wait

and the old resource-allocation state is restored&

41.Define logical address and ph#sical address.

An address generated b' the !PU is reerred as logical address& An address seen b' the

$e$or' unit that is the one loaded into the $e$or' address register o the $e$or' isco$$onl' reerred to as ph'sical address&

42.What is logical address space and ph#sical address space?

The set o all logical addresses generated b' a progra$ is called a logical address space8

the set o all ph'sical addresses corresponding to these logical addresses is a ph'sicaladdress space&

43.What is the main function of the memor#5management unit?

The runti$e $apping ro$ +irtual to ph'sical addresses is done b' a hardwarede+ice called a $e$or' $anage$ent unit (


14/14

4!.Differentiate deadlock and star'ation.

A set o processes is in deadloc% state when e+er' process in the set is waiting or

an e+ent that can be caused onl' b' the other process in the set&

tar+ation or indeinite bloc%ing is a situation where processes wait indeinitel' within

the se$aphore&

*ead $ore !522 - P,*ATINM DT,

UNIT 2 and UNIT 3 (2 Mark Answer)

Documents

Transcript of UNIT 2 and UNIT 3 (2 Mark Answer)