UGC NET CSE | July 2016 | Part 2 | Question: 37

Question

Suppose there are $4$ processes in execution with $12$ instances of a Resource $R$ in a system.

The maximum need of each process and current allocation are given below :

$\begin{array}{|c|c|c|} \hline \textbf{Process} & \textbf{Max Need} & \textbf{Current} \\  & & \textbf{Allocation} \\\hline \text{$P_1$} & \text{8} & \text{3} \\\hline \text{$P_2$} & \text{9} & \text{4} \\\hline  \text{$P_3$} & \text{5} & \text{2} \\\hline \text{$P_4$} & \text{3} & \text{1} \\\hline \end{array}$

With reference to current allocation, is system safe? If so, what is the safe sequence?

• A. No
• B. Yes, $P_1P_2P_3P_4$
• C. Yes, $P_4P_3P_1P_2$
• D. Yes, $P_2P_1P_3P_4$

Answer 1

• P1  holds  3 resources
• P2 holds 4  resources
• P3 holds 2  resources
• P4 holds 1  resource

Total 3+4+2+1 = 10 resources are allocated and 12-10=2 resources are free

• P1 requires maximum 8 resources; It needs 8-3 =5 more tapes
• P2 requires maximum 9 resources; It needs 9-4 =5 more tapes
• P3 requires maximum 5 resources; It needs5-2 =3 more tapes
• P4 requires maximum 3 resources; It needs 3-1 = 2 more tapes

  
We can allocate 2 free resources to P4. 

P4 will complete execution and release all its resources. Now total 3 resoucres are free. 

We can allocate 3 free resources to P3.

P3 will complete execution and release all its resources. Now total 5 resoucres are free. 

We can allocate 5 free resources to P1.

P1 will complete execution and release all its resources. Now total 8 resoucres are free. 

We can allocate 5 free resources to P2.

P2 will complete execution and release all its resources. 


System is in safe state.!!!

The sequence is P4P3P1P2

Answer C

Answer 2

C option answer