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Question 1 of 60 Quiz ID: q1

What is the primary purpose of a railway semaphore in the context of concurrent programming?

To control train speed and acceleration

To indicate whether the track ahead is clear or occupied

To communicate with the central train station

To measure the distance between trains

Question 2 of 60 Quiz ID: q2

Who first described the semaphore concept in concurrent programming?

Alan Turing in 1936

Edsger Dijkstra in 1968

Donald Knuth in 1973

Tony Hoare in 1978

Question 3 of 60 Quiz ID: q3

What type of variable is a semaphore?

A boolean variable that can be true or false

A floating-point variable with decimal values

An integer-valued variable that can take only non-negative values

A string variable that stores process names

Question 4 of 60 Quiz ID: q4

How many operations are exactly defined on a semaphore?

One operation

Two operations

Three operations

Four operations

Question 5 of 60 Quiz ID: q5

In the down(S) operation, what happens if S > 0?

The process is suspended

S is incremented by 1

S is decremented by 1

A waiting process is awakened

Question 6 of 60 Quiz ID: q6

What happens in the up(S) operation when there are processes suspended on S?

S is incremented by 1

All suspended processes are awakened

One of the suspended processes is awakened

The semaphore is reset to 0

Question 7 of 60 Quiz ID: q7

What is a critical property of down(S) and up(S) operations?

They can be interrupted by other processes

They are atomic instructions

They must be called in pairs

They can only be used once per process

Question 8 of 60 Quiz ID: q8

What is the requirement for a semaphore's initial value?

It must be exactly 1

It must be exactly 0

It must be non-negative

It can be any integer value

Question 9 of 60 Quiz ID: q9

What is a general semaphore?

A semaphore that can take only values 0 and 1

A semaphore that can take any non-negative value

A semaphore that can take negative values

A semaphore that can take only positive values

Question 10 of 60 Quiz ID: q10

What values can a binary semaphore take?

Any non-negative integer

Only 0 and 1

Only positive integers

Only negative integers

Question 11 of 60 Quiz ID: q11

Which invariant must a semaphore S always satisfy?

S < 0

S >= 0

S = 1

S <= 1

Question 12 of 60 Quiz ID: q12

What does the invariant S = S₀ + #Up(S) - #Down(S) represent?

The relationship between initial value and completed operations

The maximum value the semaphore can reach

The number of processes waiting on the semaphore

The time complexity of semaphore operations

Question 13 of 60 Quiz ID: q13

In the mutual exclusion solution using semaphores, what should be the initial value of semaphore S?

N (number of processes)

Question 14 of 60 Quiz ID: q14

How does the semaphore solution differ from busy-wait approaches?

It uses more memory

It's slower to execute

Suspended processes don't execute instructions in a loop

It can only handle two processes

Question 15 of 60 Quiz ID: q15

In the mutual exclusion proof, what does #CS represent?

Number of critical sections in the program

Number of processes in their critical sections

Number of semaphore operations completed

Number of processes waiting to enter critical sections

Question 16 of 60 Quiz ID: q16

What invariant proves mutual exclusion in the semaphore solution?

#CS + S = 0

#CS + S = 1

#CS - S = 1

#CS * S = 1

Question 17 of 60 Quiz ID: q17

Why cannot the semaphore mutual exclusion solution deadlock with two processes?

Because semaphores prevent all forms of deadlock

Because if both processes are suspended, it contradicts the invariant #CS + S = 1

Because the semaphore automatically resolves conflicts

Because processes alternate in using the critical section

Question 18 of 60 Quiz ID: q18

What ensures no individual starvation in the two-process semaphore solution?

The FIFO ordering of process execution

When one process is suspended and the other exits the critical section, it will wake the suspended process

The automatic process scheduling by the operating system

The alternating execution pattern enforced by semaphores

Question 19 of 60 Quiz ID: q19

What is a blocked-set semaphore?

A semaphore that blocks all processes indefinitely

A semaphore where suspended processes are kept in a set and one unspecified process is awakened

A semaphore that can only be used by a fixed set of processes

A semaphore that blocks after a certain number of operations

Question 20 of 60 Quiz ID: q20

How does a blocked-queue semaphore differ from a blocked-set semaphore?

It can handle more processes

It's faster in execution

Suspended processes are kept in a FIFO queue and awakened in order

It uses less memory

Question 21 of 60 Quiz ID: q21

In a busy-wait semaphore, what happens in the down(S) operation?

The process is immediately suspended

The process loops continuously testing S until it can decrement it

The process is added to a queue

The semaphore value is automatically decremented

Question 22 of 60 Quiz ID: q22

Which type of semaphore can lead to starvation?

Only blocked-queue semaphores

Only binary semaphores

Busy-wait and blocked-set semaphores (for N > 2)

All types of semaphores

Question 23 of 60 Quiz ID: q23

Why is starvation impossible with blocked-queue semaphores?

Because they use more memory

Because processes are awakened in FIFO order

Because they're faster than other types

Because they prevent deadlock

Question 24 of 60 Quiz ID: q24

In the Bill and Ben cafe problem, what is the synchronization requirement?

Bill and Ben must work at the same speed

Bill cannot serve until Ben has made soup, and Ben cannot serve until Bill has made sandwiches

Only one person can work in the kitchen at a time

They must serve customers in a specific order

Question 25 of 60 Quiz ID: q25

In the first solution to the Bill and Ben problem, what are the initial values of the semaphores?

first = 1, second = 1

first = 0, second = 0

first = 1, second = 0

first = 0, second = 1

Question 26 of 60 Quiz ID: q26

In the Bill and Ben problem, what does Bill do in SYNCH 1 in the first solution?

up(first); down(second);

down(first); up(second);

down(second); up(first);

up(second); down(first);

Question 27 of 60 Quiz ID: q27

What does Ben do in SYNCH 2 in the first solution to the Bill and Ben problem?

down(first); up(second);

up(first); down(second);

down(second); up(first);

up(second); down(first);

Question 28 of 60 Quiz ID: q28

What is the main characteristic of the Producer-Consumer problem?

Multiple processes compete for the same resource

One process creates data that another process consumes

Processes must execute in a specific order

All processes must access a shared variable

Question 29 of 60 Quiz ID: q29

What is synchronous communication in the context of the Producer-Consumer problem?

Using a buffer to store multiple data items

When producer and consumer are ready simultaneously, data is sent directly

When all processes run at the same speed

When data is sent at regular time intervals

Question 30 of 60 Quiz ID: q30

What is the purpose of a buffer in asynchronous communication?

To speed up the communication process

To allow flexibility by storing data when sender and receiver are not ready simultaneously

To reduce memory usage

To prevent data corruption

Question 31 of 60 Quiz ID: q31

In the infinite buffer Producer-Consumer solution, why is mutual exclusion not an issue initially?

Because there's only one producer and one consumer

Because the buffer is infinite

Because producer only writes to tail and consumer only reads from head

Because semaphores automatically handle mutual exclusion

Question 32 of 60 Quiz ID: q32

What does the invariant #E = 0 + tail - head represent in the buffer?

The total buffer capacity

The number of elements currently in the buffer

The number of empty slots in the buffer

The difference between production and consumption rates

Question 33 of 60 Quiz ID: q33

What is the initial value of the 'elements' semaphore in the infinite buffer solution?

infinity

N (buffer size)

Question 34 of 60 Quiz ID: q34

What does the consumer do before accessing the buffer in the infinite buffer solution?

up(elements)

down(elements)

Check if tail > head

Lock the buffer

Question 35 of 60 Quiz ID: q35

In the circular buffer solution, how many semaphores are used?

One semaphore

Two semaphores

Three semaphores

Four semaphores

Question 36 of 60 Quiz ID: q36

What is the initial value of the 'spaces' semaphore in the circular buffer solution?

N (buffer size)

Question 37 of 60 Quiz ID: q37

What does the producer do before adding an element to the circular buffer?

down(elements)

down(spaces)

up(elements)

up(spaces)

Question 38 of 60 Quiz ID: q38

In the Dining Philosophers problem, how many philosophers are there?

Three

Four

Five

Six

Question 39 of 60 Quiz ID: q39

How many forks does a philosopher need to eat?

One fork

Two forks

Three forks

All available forks

Question 40 of 60 Quiz ID: q40

What are the synchronization requirements for the Dining Philosophers problem?

Only prevent deadlock

Only ensure mutual exclusion of forks

Only prevent starvation

Mutual exclusion of forks, no deadlock, and no starvation

Question 41 of 60 Quiz ID: q41

Why is philosopher[4] implemented differently from the others in the dining philosophers solution?

Because there are only 4 philosophers

Because it needs to handle the wraparound from fork[4] to fork[0]

Because it's the last philosopher to start eating

Because it uses a different eating strategy

Question 42 of 60 Quiz ID: q42

In the Readers and Writers problem, what is the main constraint?

Only one reader can access the database at a time

Only one writer can access the database at a time

Readers can access simultaneously, but only one writer can write with no active readers

Writers have priority over readers

Question 43 of 60 Quiz ID: q43

What is wrong with the first Readers and Writers solution that uses only semaphore rw?

It allows multiple writers simultaneously

It doesn't allow multiple readers simultaneously

It causes deadlock

It's too complex

Question 44 of 60 Quiz ID: q44

What does the variable 'nr' represent in the improved Readers and Writers solution?

Number of writers currently writing

Number of readers currently reading

Number of readers waiting

Number of read operations completed

Question 45 of 60 Quiz ID: q45

When does the first reader execute down(rw) in the Readers and Writers solution?

Always before reading

Only when nr == 1 (it's the first reader)

Only when nr == 0

Never, only writers use down(rw)

Question 46 of 60 Quiz ID: q46

When does the last reader execute up(rw) in the Readers and Writers solution?

Always after reading

Only when nr == 1

Only when nr == 0 (it was the last reader)

Never, only writers use up(rw)

Question 47 of 60 Quiz ID: q47

Under what circumstances is the Readers and Writers solution unfair?

When there are more readers than writers

When writers can be starved by a continuous stream of readers

When readers have to wait for writers

It's always fair

Question 48 of 60 Quiz ID: q48

In the Sleeping Barber problem, what happens when a customer arrives and the waiting room is full?

The customer waits outside the barbershop

The customer comes back later

The customer wakes the barber immediately

The customer joins a queue outside

Question 49 of 60 Quiz ID: q49

What does the barber do when the waiting room is empty?

Closes the barbershop

Goes home

Daydreams (sleeps)

Cleans the shop

Question 50 of 60 Quiz ID: q50

What does the 'customers' semaphore represent in the Sleeping Barber solution?

Total number of customers served

Number of customers currently waiting

Maximum number of customers allowed

Number of customers that have arrived

Question 51 of 60 Quiz ID: q51

What is the purpose of the 'cutting' semaphore in the Sleeping Barber problem?

To control access to the scissors

To coordinate the customer-barber interaction during the haircut

To count the number of haircuts completed

To measure the time spent cutting hair

Question 52 of 60 Quiz ID: q52

What does the 'barber' semaphore signify in the Sleeping Barber solution?

Whether the barber is sleeping or awake

The barber's availability to start cutting hair

The number of barbers in the shop

The barber's skill level

Question 53 of 60 Quiz ID: q53

What type of relationship does the Sleeping Barber problem illustrate?

Producer-Consumer relationship

Reader-Writer relationship

Client-Server relationship

Master-Slave relationship

Question 54 of 60 Quiz ID: q54

What is a rendezvous in the context of the Sleeping Barber problem?

A scheduled appointment time

A point where customer and barber wait for each other to arrive

The physical meeting place in the barbershop

A payment transaction

Question 55 of 60 Quiz ID: q55

What is the main difference between blocked-set and blocked-queue semaphores in terms of fairness?

Blocked-set is always fair, blocked-queue can cause starvation

Both are equally fair

Blocked-queue guarantees FIFO fairness, blocked-set can cause starvation for N > 2

Neither provides any fairness guarantees

Question 56 of 60 Quiz ID: q56

In semaphore implementations, what does 'atomic' mean for the down(S) and up(S) operations?

They use atomic data types

They cannot be interrupted or interleaved with other instructions

They operate on single bits

They are the smallest possible operations

Question 57 of 60 Quiz ID: q57

What is the key advantage of using semaphores over busy-waiting solutions?

Semaphores are faster to execute

Semaphores use less memory

Suspended processes don't waste CPU cycles in busy-wait loops

Semaphores prevent all types of deadlock

Question 58 of 60 Quiz ID: q58

In the Producer-Consumer problem with circular buffer, what prevents the producer from overwriting unread data?

The 'elements' semaphore

The 'spaces' semaphore

The head and tail pointers

The buffer size limit

Question 59 of 60 Quiz ID: q59

What is the main purpose of the 'mutex' semaphore in concurrent programming?

To count resources

To provide mutual exclusion for critical sections

To signal between processes

To implement producer-consumer relationships

Question 60 of 60 Quiz ID: q60

Which semaphore definition provides the strongest guarantee against starvation?

Busy-wait semaphore

Blocked-set semaphore

Blocked-queue semaphore

Binary semaphore

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