1
GATE CSE 2024 Set 1
+2
-0.66

Consider the following two threads T1 and T2 that update two shared variables a and b. Assume that initially $a = 1$ and $b = 1$. Though context switching between threads can happen at any time, each statement of T1 or T2 is executed atomically without interruption.

T1:
$a = a + 1$;
$b = b + 1$;

T2:
$b = 2 * b$;
$a = 2 * a$;

Which one of the following options lists all the possible combinations of values of a and b after both T1 and T2 finish execution?

A

$(a = 4, b = 4); (a = 3, b = 3); (a = 4, b = 3)$

B

$(a = 3, b = 4); (a = 4, b = 3); (a = 3, b = 3)$

C

$(a = 4, b = 4); (a = 4, b = 3); (a = 3, b = 4)$

D

$(a = 2, b = 2); (a = 2, b = 3); (a = 3, b = 4)$

2
GATE CSE 2024 Set 1
Numerical
+2
-0.66

Consider the following code snippet using the fork() and wait() system calls. Assume that the code compiles and runs correctly, and that the system calls run successfully without any errors.

int x = 3;
while(x > 0) {
fork();
printf("hello");
wait(NULL);
x--;
}

The total number of times the printf statement is executed is _______

3
GATE CSE 2023
+2
-0.67

Consider the two functions incr and decr shown below.


incr() {
wait(s);
X = X+1;
signal(s);
}

decr() {
wait(s);
X = X-1;
signal(s);
}



There are 5 threads each invoking incr once, and 3 threads each invoking decr once, on the same shared variable X. The initial value of X is 10.

Suppose there are two implementations of the semaphore s, as follows:

I-1: s is a binary semaphore initialized to 1.

I-2: s is a counting semaphore initialized to 2.

Let V1, V2 be the values of X at the end of execution of all the threads with implementations I-1, I-2, respectively.

Which one of the following choices corresponds to the minimum possible values of V1, V2, respectively?

A
15, 7
B
7, 7
C
12, 7
D
12, 8
4
GATE CSE 2020
+2
-0.67
Each of a set of n processes executes the following code using two semaphores a and b initialized to 1 and 0, respectively. Assume that count is a shared variable
What does the code achieve?
A
It ensures that all processes execute CODE SECTION P mutually exclusively.
B
It ensures that at most two processes are in CODE SECTION Q at any time.
C
It ensures that no process executes CODE SECTION Q before every process has finished CODE SECTION P.
D
It ensures that at most n-1 processes are in CODE SECTION P at any time.
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