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CS604 3rd Assignment solution
Consider the following snapshot of a system:
Allocation Max Available
A B C D A B C D A B C D
P0 0 0 1 2 0 0 1 2 1 5 2 0
P1 1 0 0 0 1 7 5 0
P2 1 3 5 4 2 3 5 6
P3 0 6 3 2 0 6 5 2
P4 0 0 1 4 0 6 5 6


Answer the following questions using the banker’s algorithm:

(a) what is the content of the matrix Need?
(b) Is the system in a safe state?
(c) If a request from process P1 arrives for (0, 4, 2, 0), can the request be granted
immediately?

SOLUTION
(a) Need = Max - Allocation
Need
A B C D
P0 0 0 0 0
P1 0 7 5 0
P2 1 0 0 2
P3 0 0 2 0
P4 0 6 4 2

(b) The system is in a safe state. For example: P0, P1, P3, P4, is a safe sequence.
(c) After satisfying P1 request, the system becomes the following state.
Allocation Max Need Available
A B C D A B C D A B C D A B C D
P0 0 0 1 2 0 0 1 2 0 0 0 0 1 1 0 0
P1 1 4 2 0 1 7 5 0 0 3 3 0
P2 1 3 5 4 2 3 5 6 1 0 0 2
P3 0 6 3 2 0 6 5 2 0 0 2 0
P4 0 0 1 4 0 6 5 6 0 6 4 2
By using the safety algorithm, the system is still in a safe state and P0, P2, P1, P3, P4 is a
safe sequence.
http://ping.fm/08e8G
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