CSE316_OS_Mastry_Quest02_Deadlock_Dominator

Which of the following statements about threads is/are TRUE?

• Thread can only be implemented in kernel space

• Each thread has its own file descriptor table for open files

• All the thread belonging to a process share a common stack

• Thread belonging to a process are by default not protected form each other.

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

• 60

• 70

• 80

• 90

Which of the following statements about deadlock in operating systems are TRUE? (Select all that apply)

• Deadlock occurs when a set of processes are permanently blocked because each process is waiting for a resource held by another process in the set.

• The Hold and Wait condition requires that a process must release all its resources before requesting new ones.

• The Circular Wait condition implies the existence of a circular chain of processes where each process waits for a resource held by the next process in the chain.

• Deadlock can be prevented by ensuring that at least one of the four necessary conditions for deadlock is always violated.

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; b = 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 = 4); (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)

A "Buffer Overflow" attack primarily targets which of the following to gain control of a program's execution flow?

• The Heap

• The Return Address on the Stack

• The Global Data Segment

• The Instruction Register

With respect to deadlocks in an operating system, which of the following statements is/are FALSE? [Select all that apply]   

• Banker’s algorithm is used to prevent deadlocks

• Deadlock formation can be prevented by ensuring that the hold and wait condition is not allowed

• An assignment edge in a resource allocation graph is marked from a process to a resource

• A safe state guarantees that all processes can finish without formation of a deadlock

Consider a system consisting of K instances of a resource R, being shared by 5 processes. Assume that each process requires a maximum of two instances of resource R and a process can request or release only one instance at a time. Further, a process can request the second instance of the resource only after acquiring the first instance. The minimum value of K for the system to be deadlock-free is____.

• 5

• 6

• 7

• 8

Consider the following code for a Two-Process Critical Section solution: // Process Pi flag[i] = true; turn = j; while (flag[j] && turn == j); // CRITICAL SECTION flag[i] = false; This algorithm guarantees?

• Mutual Exclusion

• Progress

• Bounded Waiting.

• Mutual Exclusion only.

A system uses three binary semaphores S1, S2, and S3, all initialized to 1. A single process executes the following sequence:

P(S1), P(S2), V(S2), P(S3), V(S3), P(S2), V(S1)

Assume standard semaphore semantics where:

• ○ P() decreases the semaphore value by 1 and blocks if value becomes negative

• ○ V() increases the semaphore value by 1 and may unblock a waiting process

Which of the following statements are TRUE? (Select all that apply)

• The process will always complete execution without deadlock.

• At some point, the process may block due to S2.

• The final value of S1 will be 1.

• The final value of S3 will always be 1.

In the solution to the Dining Philosophers Problem using semaphores, if all philosophers pick up their left fork simultaneously, a deadlock occurs. Which of the following modifications prevents this deadlock?

• Allow at most n-1 philosophers to sit at the table simultaneously.

• Use an asymmetric solution where odd-numbered philosophers pick the left fork first and even-numbered pick the right.

• Use a monitor to control fork access.

•  All of the above.