OS Process synchronization

When several processes access the same data concurrently and the outcome of the execution depends on the particular order in which the access takes place is called ________
a) dynamic condition
b) race condition
c) essential condition
d) critical condition

• a

• b

• c

• d

Which of the following option is suitable when a process is executing in its critical section, then no other processes can be executing in their critical section

A. mutual exclusion
B. critical exclusion
C. synchronous exclusion
D. d asynchronous exclusion

• a

• b

• c

• d

A semaphore is a shared integer variable that can not

A. drop below zero
B. be more than zero
C. drop below one
D. that cannot be more than one

• a

• b

• c

• d

All processes share a semaphore variable mutex, initialized to 1. Each process must execute wait(mutex) before entering the critical section and signal(mutex) afterward.
Suppose a process executes in the following manner.

signal(mutex); .

.... critical section .....

wait(mutex);

• a deadlock will occur
  

• processes will starve to enter critical section
  

• several processes maybe executing in their critical section
  

• all of the mentioned

Consider the methods used by processes P1 and P2 for accessing their critical sections whenever needed, as given below. The initial values of shared boolean variables S1 and S2 are randomly assigned.

Method used by P1 : while(S1==S2);

Critical section

S1 = S2;  

Method used by P2 :

while(S1!=S2);

Critical section S2 = not(S1);

Which of the following statements describes properties achieved?

• Mutual exclusion but not progress
  

• Progress but not mutual exclusion
  

• Neither mutual exclusion nor progress
  

• Both mutual exclusion and progress

What are the two kinds of semaphores?
a) mutex & counting
b) binary & counting
c) counting & decimal
d) decimal & binary

• a

• b

• c

• d

At a particular time of computation the value of a counting semaphore is 7.Then 20 P operations and 15 V operations were completed on this semaphore. The resulting value of the semaphore is?

a) 42
b) 2
c) 7
d) 12

• a

• b

• c

• d

he program follows to use a shared binary semaphore T.

Process A

int Y;

A1: Y = X*2;

A2: X = Y;

signal(T);  

Process B

int Z;

B1: wait(T);

B2: Z = X+1;

X = Z;

T is set to 0 before either process begins execution and, as before, X is set to 5.
Now, how many different values of X are possible after both processes finish executing?

• one

• two

• three

• four

Consider the following set of processes, with the arrival times and the CPU-burst times given in milliseconds (GATE-CS-2004)

  Process   Arrival Time    Burst Time

    P1          0              5

    P2          1              3

    P3          2              3

    P4          4              1

 

What is the average turnaround time for these processes with the preemptive shortest remaining processing time first (SRPT) algorithm ?

• 5.50

• 5.75

• 6.00

• 6.25

In Priority Scheduling a priority number (integer) is associated with each process. The CPU is allocated to the process with the highest priority (smallest integer = highest priority). The problem of, Starvation? low priority processes may never execute, is resolved by __________.

a) Terminating the process.

b) Aging

c) Mutual Exclusion

d) Semaphore

• a

• b

• c

• d