GATE CSE Operating System PYQs & Answers — Page 5

Questions 41–50 of 65. Imported answers require independent review unless marked reviewed.

Consider a computer system with multiple shared resource types, with one instance per resource type. Each instance can be owned by only one process at a time. Owning and freeing of resources are done by holding a global lock (L). The following scheme is used to own a resource instance:

function OwnResource(Resource R) Acquire lock L // a global lock if R is available then Acquire R Release lock L else if R is owned by another process P then Terminate P, after releasing all resources owned by P Acquire R Restart P Release lock L end if end if end function

Which of the following choice(s) about the above scheme is/are correct?

Your answerSelect all correct options. You can choose more than one.

The scheme ensures that deadlocks will not occur.

The scheme may lead to live-lock.

The scheme may lead to starvation.

The scheme violates the mutual exclusion property.

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Consider the following pseudocode, where S is a semaphore initialized to 5 in line#2 and counter is a shared variable initialized to 0 in line#1. Assume that the increment operation in line#7 is not atomic.

int counter = 0;

Semaphore S = init(5);

void parop(void)

{

wait(S);

counter++;

signal(S);

} If five threads execute the function parop concurrently, which of the following program behavior(s) is/are possible?

Your answerSelect all correct options. You can choose more than one.

The value of counter is 5 after all the threads successfully complete the execution of parop.

The value of counter is 1 after all the threads successfully complete the execution of parop.

The value of counter is 0 after all the threads successfully complete the execution of parop.

There is a deadlock involving all the threads.

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Consider allocation of memory to a new process. Assume that none of the existing holes in the memory will exactly fit the process’s memory requirement. Hence, a new hole of smaller size will be created if allocation is made in any of the existing holes. Which one of the following statements is TRUE?

Your answerChoose one option.

The hole created by first fit is always larger than the hole created by next fit.

The hole created by worst fit is always larger than the hole created by first fit.

The hole created by best fit is never larger than the hole created by first fit.

The hole created by next fit is never larger than the hole created by best fit.

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Consider the following statements about process state transitions for a system using preemptive scheduling.

I. A running process can move to ready state.

II. A ready process can move to running state.

III. A blocked process can move to running state.

IV. A blocked process can move to ready state.

Which of the above statements are TRUE?

Your answerChoose one option.

I, II, and III only

II and III only

I, II, and IV only

I, II, III, and IV

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Each of a set of

processes executes the following code using two semaphores a and b initialized to 1 and 0, respectively. Assume that count is a shared variable initialized to 0 and not used in CODE SECTION P.

Diagram for Computer Science and Information Technology question 34

What does the code achieve?

Your answerChoose one option.

It ensures that no process executes CODE SECTION Q before every process has finished CODE SECTION P.

It ensures that at most two processes are in CODE SECTION Q at any time.

It ensures that all process execute CODE SECTION P mutually exclusively.

It ensures that at most

processes are in CODE SECTION P at any time.

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Consider the following five disk access requests of the form (request id, cylinder number) that are present in the disk scheduler queue at a given time. (P, 155), (Q, 85), (R, 110), (S, 30), (T, 115) Assume the head is positioned at cylinder 100. The scheduler follows Shortest Seek Time First scheduling to service the requests. Which one of the following statements is FALSE?

Your answerChoose one option.

T is serviced before P.

Q is serviced after S, but before T.

The head reverses its direction of movement between servicing of Q and P.

R is serviced before P.

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Consider the following set of processes, assumed to have arrived at time 0. Consider the CPU scheduling algorithms Shortest Job First (SJF) and Round Robin (RR). For RR, assume that the processes are scheduled in the order

Process
Burst time (in ms)	8	7	2	4

If the time quantum for RR is 4 ms, then the absolute value of the difference between the average turnaround times (in ms) of SJF and RR (round off to 2 decimal places) is ______.

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The following C program is executed on a Unix/Linux system:

#include <unistd.h>

int main()

{

int i;

for (i=0; i<10; i++)

if (i%2 == 0) fork();

return 0;

}

The total number of child processes created is __________.

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Consider three concurrent processes P1, P2 and P3 as shown below, which access a shared variable D that has been initialized to 100.

P1	P2	P3
⋮	⋮	⋮
D = D + 20	D = D − 50	D = D + 10
⋮	⋮	⋮

The processes are executed on a uniprocessor system running a time-shared operating system. If the minimum and maximum possible values of D after the three processes have completed execution are X and Y respectively, then the value of Y − X is ______________.

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Consider the following snapshot of a system running

concurrent processes. Process

is holding

instances of a resource R,

. Assume that all instances of R are currently in use. Further, for all

, process

can place a request for at most

additional instances of R while holding the

instances it already has. Of the

processes, there are exactly two processes

and

such that

. Which one of the following conditions guarantees that no other process apart from

and

can complete execution?

Your answerChoose one option.

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GATE CSE Operating System PYQs

Question 43

Question 46

Question 11

Question 12

Question 34

Question 35

Question 50

Question 17

Question 23

Question 39