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GATE | Quiz for Sudo GATE 2021 | Question 10
  • Last Updated : 14 Dec, 2020

Consider the following system there are total 12 instances of resources A, 10 instances of resources B and 11 instances of resources C:

Process   Allocation        Maximum           
          A  B  C           A  B  C         
P0        0  2  3           3  3  6         
P1        2  4  2           2  5  3
P2        3  1  2           3  5  3
P3        5  2  2           6  5  4

If Banker’s algorithm is applied for deadlock avoidance this system is in safe state. Which of the following option will be permitted with additional request?

Note – This question is multiple select questions (MSQ).
(A) Request: P3 – 1 instance of A, 2 instances of B, 3 instances of C
(B) Request: P2 – 1 instance of A, 2 instances of B, 3 instances if C
(C) Request: P1 – 1 instance of A, instances of B, 3 instances of C
(D) Request: P0 – 1 instance of A, 2 instances of B, 3 instances of C


Answer: (A) (B) (D)

Explanation: Currently, the system is in the safe state. When addition requests are made:
Available Instances are

A B C
2 1 2

Request: P3 – 1 instance of A, 2 instances of B, 3 instances of C
Need matrix:

A B C
3 1 3
0 1 1
0 4 1
2 5 5

Since 2 instances of A, 1 instance of B, 2 instances of C.
System is in safe state and start processing from P1.
Request: P2 – 1 instance of A, 2 instances of B, 3 instances of C
Need matrix:



A B C
3 1 3
0 1 1
1 6 4
1 3 2

Since 2 instances of A, 1 instance of B, 2 instances of C.
System is in safe state and start processing from P1.
Request: P1 – 1 instance of A, 2 instances of B, 3 instances of C
Need matrix:

A B C
3 1 3
1 3 4
0 4 1
1 3 2

The system is unsafe. Since 2 instances of A, 1 instance of B, 2 instances of C.
Request: P0 – 1 instance of A, 2 instances of B, 3 instances of C
Need matrix:

A B C
3 3 6
0 1 1
0 4 1
1 3 2

Since 2 instances of A, 1 instance of B, 2 instances of C.
System is in safe state and start processing from P1.

So, request of option (C) will not be permitted.

Option (A), (B), and (D) are correct.


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