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ASSIGNMENT-3

1. Compare: Producer-Consumer problem with Reader Writer problemAns:

Producer-Consumer Problem:

The consumer producer problem (also known as the bounded-buffer problem) is aclassical example of a multi-process synchronization problem.

The problem describes two processes, the producer and the consumer, who share acommon, fixed-size buffer used as a queue.

The producer's job is to generate a piece of data, put it into the buffer and start again.At the same time, the consumer is consuming the data (i.e., removing it from the

buffer) one piece at a time. The problem is to make sure that the producer won't try to

add data into the buffer if it's full and that the consumer won't try to remove data from

an empty buffer.

Reader-Writer Problem:An object is shared among many threads, each belonging to one of two classes:

Readers: read data, never modify it Writers: read data and modify it. Using a single lock on the data object is overly restrictive Want many readers reading the object at once Allow only one writer at any point Correctness criteria Each read or write of the shared data must happen within a critical section. Guarantee mutual exclusion for writers. Allow multiple readers to execute in the critical section at once.

2. Write a solution for writer priority of reader writer problemAns: Semaphore Solution: Writers have Priority

int readcount, writecount = 0;

semaphore rsem, wsem = 1; //

semaphore x,y,z = 1; //

void reader(){

while(1){wait(z);

wait(rsem);

wait(x);

readcount++;

if (readcount==1)

wait(wsem);

signal(x);

signal(rsem);

void writer(){

while(1){wait(y);

writecount++;

if (writecount==1)

wait(rsem);

signal(y);

wait(wsem);

doWriting();

signal(wsem);

http://en.wikipedia.org/wiki/Process_(computing)http://en.wikipedia.org/wiki/Synchronization_(computer_science)http://en.wikipedia.org/wiki/Buffer_(computer_science)http://en.wikipedia.org/wiki/Queue_(data_structure)http://en.wikipedia.org/wiki/Queue_(data_structure)http://en.wikipedia.org/wiki/Buffer_(computer_science)http://en.wikipedia.org/wiki/Synchronization_(computer_science)http://en.wikipedia.org/wiki/Process_(computing)

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signal(z);

doReading();

wait(x);

readcount--;

if (readcount==0)

signal(wsem);

signal(x);

}

}

wait(y);

writecount--;

if (writecount==0)

signal(rsem);

signal(y);

}

}

3. Explain drawbacks of Dekkers algorithmAns: The drawbacks ofDekkers Algorithm are:

It is limited to two processes and makes use ofbusy waiting instead of processsuspension where use of busy waiting suggests that processes should spend a minimum

of time inside the critical section.

Modern operating systems provide mutual exclusion primitives that are more generaland flexible than Dekker's algorithm.

Many modern CPUs execute their instructions in an out-of-order fashion. This algorithmwon't work on SMP machines equipped with these CPUs without the use ofmemory

barriers.

In many languages, it is legal for a compiler to detect that the flag variablesflag[0] and flag[1] are never accessed in the loop. It can then remove the writes to those

variables from the loop, using a process called Loop-invariant code motion. It would

also be possible for many compilers to detect that the turn variable is never modified by

the inner loop, and perform a similar transformation, resulting in a potential infinite

loop. If either of these transformations is performed, the algorithm will fail, regardless ofarchitecture.

4. compare android OS with windowsAns: ANDROID OPERATING SYSTEM

There are four officially released Versions of Android:

1. Froyo2. Ginderbread3. Honeycomb4.

Ice cream Sandwich5. Jelly beans [announced recently ]

PROS of Android OS:

Open Source Linux based System Custom ROMs High reliability Integrated Java and Flash

http://en.wikipedia.org/wiki/Busy_waitinghttp://en.wikipedia.org/wiki/CPUhttp://en.wikipedia.org/wiki/Symmetric_multiprocessinghttp://en.wikipedia.org/wiki/Memory_barrierhttp://en.wikipedia.org/wiki/Memory_barrierhttp://en.wikipedia.org/wiki/Loop-invariant_code_motionhttp://en.wikipedia.org/wiki/Infinite_loophttp://en.wikipedia.org/wiki/Infinite_loophttp://www.latesthub.org/tag/ice-cream-sandwichhttp://www.latesthub.org/tag/ice-cream-sandwichhttp://en.wikipedia.org/wiki/Infinite_loophttp://en.wikipedia.org/wiki/Infinite_loophttp://en.wikipedia.org/wiki/Loop-invariant_code_motionhttp://en.wikipedia.org/wiki/Memory_barrierhttp://en.wikipedia.org/wiki/Memory_barrierhttp://en.wikipedia.org/wiki/Symmetric_multiprocessinghttp://en.wikipedia.org/wiki/CPUhttp://en.wikipedia.org/wiki/Busy_waiting

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Dedicated App library, i.e., Google Play Wireless app installation Good security [No antivirus needed]

Cons of Android OS:

Still Under Development

WINDOWS OPERATING SYSTEM

Windows is a very old operating system since year 1985. Windows 1 was the first

operating system by Microsoft, after then they released many updated version of Windows like:

Windows 95 [year - 1995] Windows 98 [year - 1998] Windows 2000 [year - 2000] Windows XP [2001] Windows Vista [year - 2006] Windows 7 [year - 2009] Windows 8 [year - 2012]

Pros of Windows:

Large user baseBillion of peoples are used to Windows, so there are manyprograms for various fields over internet.

Better User InterfaceIt takes less time for a newbie to learn windowsfunctioning.

Its an old operating system, so large amount of fixes for various bugs will beavailable easily over internet.

Cons of Windows:

Not open source [so you need to buy license] Less secured as compared to Linux , you need an external antivirus to secure

windows

From Windows 95 to windows 7, Microsoft fixed many bugs and improved a lotbut still it is not as reliable as linux is.

Both of the operating system is best for the mobile and pc users but there are some factorsthat can distinguish android from the windows.

1. GadgetsWindows does not have the wide range of the Google gadgets that android provide to its

user, more specifically mobile users.

2. PricingAndroid is expensive than the pure licensed window operating system by Microsoft

because of the additional feature and compatibility with almost every hardware and software

http://www.latesthub.org/what-is-windows-8-advantages/7659http://www.latesthub.org/what-is-windows-8-advantages/7659

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application brand.

3. Largest ComputingAndroid offers the large range of applications and smart phone application to its users. It

provides specific installations and setups for the Google chromes that Microsoft windows

doesnt.

iOS

6.0

Android

4.1

Window

s Phone

8

Window

s Phone

7.8

Apps 650,000+ 600,000+100,000

+

100,000

+

Multitaskingyes

limitedyes

yes

limited

yes

limited

Widgets no yesexpandable

Live Tiles

expandable

Live Tiles

Expandable storage no yes yes yes

Multi-core

processorsyes yes yes yes

High-res displays yes yes yes yes

File manager no yes no no

Drag and drop file

management

no

requires iTunes

yesno

requires Zune

no

requires ZuneIntelligent voice

assistantyes

yes

with Google

Now

no no

Sideloading apps Cydiayes

many outletsno no

Centralized

notifications

yes

drop-down pane

yes

drop-down

pane

no no

Flash support no yes ? ?

Native screenshots yes yes no no

Offline mapsno

paid appsyes yes

no

only Lumias

Core Darwin LinuxWindow

s NT

Window

s CE 7

USB Host

limited

via Camera

Connection Kit

yes ? ?

Parameters

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5. Give the solution for reader writer problem with the help of monitor and messagepassing.

6. compare: semaphore, msg passing & monitorSEMAPHORES

Processes need toshare Memory

It is a shared variablethat can be accessedanywhere in the

program.

No connectionbetween the

semaphore and data

being controlled.

Inconvenient to use.

MONITORS

Processes need toshare Memory

It is a programminglanguage constructthat has protected

data that can be

accessed only by

process inside the

monitor.

The procedures inthe monitor are in

direct contact with

the data.

MESSAGE PASSING

Processes neednot share

Memory.

It consists of dataencapsulated intomessages that are

transferred

between the

sender and

intended recipient.

The sender andreceiver have

access to the

message.