A request from Process P1 arrives for (0, 4, 2, 0). Should the request be grante
ID: 3685447 • Letter: A
Question
A request from Process P1 arrives for (0, 4, 2, 0). Should the request be granted? How would I answer this question if I do not know what is available or the allocation?
1 5 2 0
sequence process allocation claim needs available
P0
0 0 1 2
0 0 1 3
0 0 0 1
1 5 6 4
P1
1 0 0 0
1 9 5 0
0 9 5 0
3 9 12 11
P2
1 3 5 3
2 3 5 6
1 0 0 3
2 8 11 7
P3
0 0 3 2
0 5 5 2
0 5 2 0
1 5 5 2
P4
0 1 1 4
0 7 5 6
0 6 4 2
2 9 12 11
A) Fill in the needs column.
B) Is the system in a safe state ?_________Yes__________________________
Show a sequence ( if above is yes) __P3 P0 P2 P4 P1____________
C) A request from Process P1 arrives for (0, 4, 2, 0)
Should the request be granted? ____________
sequence process allocation claim needs available
P0
0 0 1 3
P1
1 9 5 0
P2
2 3 5 6
P3
0 5 5 2
P4
0 7 5 6
(use to calculate the answer to part C)
P0
0 0 1 2
0 0 1 3
0 0 0 1
1 5 6 4
P1
1 0 0 0
1 9 5 0
0 9 5 0
3 9 12 11
P2
1 3 5 3
2 3 5 6
1 0 0 3
2 8 11 7
P3
0 0 3 2
0 5 5 2
0 5 2 0
1 5 5 2
P4
0 1 1 4
0 7 5 6
0 6 4 2
2 9 12 11
Explanation / Answer
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
2)
Yes, there exist several sequences that satisfy safety requirements (e.g.P0, P2, P1, P3, P4 )
3)
Pretend that the allocation can be made since the Available matrix is (1, 5, 2, 0), and it will now change to (1, 1, 0, 0). The next step is to find the safe sequence of processes. Alloc for P1 becomes (1,4,2,0) and Need for P1 becomes (0, 3, 3, 0).
One possible safe sequence is: P0, P2, P3, P1, P
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