Operating Systems (H)

1.
Consider two threads T1 and T2 which execute the following code concurrently, accessing shared variables a, b, and c:
Initialization
int a = 4;
int b = 0;
int c = 0;
Thread 1

if (a < 0) { c = b - a; } else { c = b + a; }

Thread 2

b = 10; a = -3;

What are the possible values for variable c after both threads complete? Assume that reads and writes of the variables are atomic

4, 7, 13, 14

4, 7, 13, 11, 14, -3

Both threads are blocked.

2. The time interval between the time of submission and completion of the job is called:

Throughput

Waiting time

Response time

Turnaround time

3. A program in execution is called:

CPU

Process

Memory

Function

4. CPU burst time indicates the time, the process needs the CPU. Consider the following processes with their respective CPU burst times (in milliseconds). Process P1 with CPU burst time 10ms, Process P2 with CPU burst time 5 ms, and Process P3 with CPU burst time 5 ms. Based on a FCFS scheduling scheme, if the processes arrived in the order: P1, P2, P3 at time t=0, which is the average waiting time?

5/3

30/3

25/3

10/3

5.
Consider the following system snapshot using data structures in the Bankerâ€™s algorithm, with resources A, B, C, and D, and process P0 to P4:

Using the Bankerâ€™s algorithm:

How many resources of type A, B, C, and D are there?

A-11; B-22; C-21; D-17

A-9; B-13; C-10; D-11

A-3; B-2; C-1; D-1

A-6; B-11; C-9; D-10

6.
Consider the following system snapshot using data structures in the Bankerâ€™s algorithm, with resources A, B, C, and D, and process P0 to P4:

Using the Bankerâ€™s algorithm:

If a request from process P4 arrives for additional resources of (1,1,0,0) can the Bankerâ€™s algorithm grant the request immediately?

There are no available resources for this request, thus, this request cannot be granted.

It is impossible to deal with this request, since the system is already in an unsafe state.

There are available resources for this request, but the system will transit to an unsafe state after granting this request.

There are available resources for this request and the system will transit to a safe state after granting this request.

7.
Consider the following system snapshot using data structures in the Bankerâ€™s algorithm, with resources A, B, C, and D, and process P0 to P4:

Using the Bankerâ€™s algorithm:

Which is the sequence of the processes to get the system in a safe state?

P0, P3, P4, P1, P2

P0, P2, P4, P1, P3

P0, P1, P4, P2, P3

P0, P1, P2, P3, P4

8. Consider the following resource allocation graph:

Is the system in a deadlock state?

No, although we have a cycle in the graph, it does not imply that the system is in a deadlock state.

Since there is a cycle in the graph, then we have a deadlock.

We cannot infer that the system is in a deadlock state by observing this graph.

The system is in a deadlock state after observing the resource allocation graph.

9.
We need to use semaphores to synchronize processes A, B, C, and D so that A completes before any other process (B, C, or D) starts, and B completes before C or D may execute, but C and D may execute concurrently.

Which of the following statements implement the above-mentioned requirement?

semaphore S1 = 1; S2 = 0;
    //Process A:
    ----------
    acquire(S1);
    - do work of A
    release(S1);
    //Process B:
    ----------
    acquire(S2);
    - do work of B
    release(S2);
    //Process C:
    ----------
    acquire(S2);
    - do work of C
    //Process D:
    ----------
    acquire(S2);
    - do work of D

semaphore S1 = 0; S2 = 0;
    //Process A:
    ----------
    - do work of A
    release(S1);
    //Process B:
    ----------
    acquire(S1);
    - do work of B
    release(S2);
    release(S2);
    //Process C:
    ----------
    acquire(S2);
    - do work of C
    //Process D:
    ----------
    acquire(S2);
    - do work of D

semaphore S1 = 1; S2 = 1;
    //Process A:
    ----------
    acquire(S1);
    - do work of A
    //Process B:
    ----------
    acquire(S1);
    - do work of B
    release(S2);
    release(S2);
    //Process C:
    ----------
    release(S2);
    - do work of C
    //Process D:
    ----------
    release(S2);
    - do work of D

semaphore S1 = 0; S2 = 0;
    //Process A:
    ----------
    acquire(S1);
    - do work of A
    release(S1);
    //Process B:
    ----------
    acquire(S2);
    - do work of B
    release(S2);
    //Process C:
    ----------
    acquire(S2);
    - do work of C
    release(S2);
    //Process D:
    ----------
    acquire(S2);
    - do work of D
    release(S2); 

10.
Suppose that a process executes the following code:

/initialization section/ semaphore S_a = 0; semaphore S_b = 0; /logic section/ acquire(S_a); - access resource R_a release(S_a); acquire(S_b); - access resource R_b release (S_b);

Assume that the system has one resource of type R_a and one resource of type R_b. How would you change the code so that it provides mutually exclusive access to R_a and R_b?

Replace only the initialization section with:

semaphore S_a = 1; semaphore S_b = 1;

Replace only the logic section with:

acquire(S_a);
acquire(S_b);
    - access resource R_a
    - access resource R_b
release(S_b);
release(S_a);

There is no change in the code to provide mutual exclusion.

Replace only the initialization section with:

semaphore S_a = 1; semaphore S_b = 0;

Operating Systems (H)

2. The time interval between the time of submission and completion of the job is called:

3. A program in execution is called:

5. Consider the following system snapshot using data structures in the Bankerâ€™s algorithm, with resources A, B, C, and D, and process P0 to P4: Using the Bankerâ€™s algorithm: How many resources of type A, B, C, and D are there?

7. Consider the following system snapshot using data structures in the Bankerâ€™s algorithm, with resources A, B, C, and D, and process P0 to P4: Using the Bankerâ€™s algorithm: Which is the sequence of the processes to get the system in a safe state?

8. Consider the following resource allocation graph: Is the system in a deadlock state?

9. We need to use semaphores to synchronize processes A, B, C, and D so that A completes before any other process (B, C, or D) starts, and B completes before C or D may execute, but C and D may execute concurrently. Which of the following statements implement the above-mentioned requirement?

5.
Consider the following system snapshot using data structures in the Bankerâ€™s algorithm, with resources A, B, C, and D, and process P0 to P4:

Using the Bankerâ€™s algorithm:

How many resources of type A, B, C, and D are there?

7.
Consider the following system snapshot using data structures in the Bankerâ€™s algorithm, with resources A, B, C, and D, and process P0 to P4:

Using the Bankerâ€™s algorithm:

Which is the sequence of the processes to get the system in a safe state?

8. Consider the following resource allocation graph:

Is the system in a deadlock state?

9.
We need to use semaphores to synchronize processes A, B, C, and D so that A completes before any other process (B, C, or D) starts, and B completes before C or D may execute, but C and D may execute concurrently.

Which of the following statements implement the above-mentioned requirement?