DEADLOCK

A system contains three programs and each requires three tape units for its operation. The minimum number of tape units which the system must have such that deadlocks never arise is

• 6

• 7

• 8

• 9

Consider a system having m resources of the same type. These resources are shared by 3 processes A, B, C which have peak time demands of 3, 4, 6 respectively. The minimum value of m that ensures deadlock will never occur is

• 11

• 12

• 13

• 14

Which of the following is not a necessary condition for deadlock?

• Mutual Exclusion

• Reentrancy

• Hold and wait

• No pre-emption

In which of the following four necessary conditions for deadlock processes claim exclusive control of the resources they require?

• no preemption

• mutual exclusion

• circular wait

• hold and wait

A total of 9 units of a resource type available, and given the safe state shown below, which of the following sequence will be a safe state?

Process Used Max

A 2 7

B 1 6

C 2 5

D 1 4

• (P4, P1, P3, P2)

• (P4, P2, P1, P3)

• (P4, P2, P3, P1)

• (P3, P1, P2, P4)

Consider a system with 3 processes that share 4 instances of the same resource type. Each process can request a maximum of K instances. Resource instances can be requested and released only one at a time. The largest value of K that will always avoid deadlock is _______ .

• 1

• 2

• 3

• 4

Which of the following is NOT a valid deadlock prevention scheme?

• Release all resources before requesting a new resource

• Number the resources uniquely and never request a lower numbered resource than the last one requested

• Never request a resource after releasing any resource

• Request and all required resources be allocated before execution.

A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?

• -2

• -1

• 1

• 2

At a particular time of computation, the value of a counting semaphore is 10. Then 12 P operations and “x” V operations were performed on this semaphore. If the final value of semaphore is 7, x will be:

• 8

• 9

• 10

• 11

What is the name of the technique in which the operating system of a computer executes several programs concurrently by switching back and forth between them?

• Partitioning

• Multi-tasking

• Windowing

• Paging