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Consider a system with twelve magnetic tape drives and three processes $P_1, P_2$ and $P_3$. process $P_1$ requires maximum ten tape drives, process $P_2$ may need as many as four tape drives and $P_3$ may need upto nine tape drives. Suppose that at time $t_1$, process $P_1$ is holding five tape drives, process $P_2$ is holding two tape drives and process $P_3$ is holding three tape drives, At time $t_1$, system is in:

  1. safe state
  2. unsafe state
  3. deadlocked state
  4. starvation state
in Operating System by Veteran
edited by | 2.6k views

3 Answers

+3 votes
Best answer

System is in UNSAFE state

  • P1  holds  5 tapes
  • P2 holds 2  tapes
  • P3 holds 3  tapes

Total 10 tapes are allocated and 12-10=2 tapes are free

  • P1 requires maximum 10 tape drives; It needs 10-5 =5 more tapes
  • P2 may need as many  as 4tape drives. It needs 4-2=2 more tapes.
  • P3 may need as many as 9 tape drives. It needs 9-3=6 more tapes.

We can allocate 2 free tapes to P2.

P2 will complete execution and release all its resources including 4 tapes.

Even if we allocate 4 tapes to P1 or P3 they cannot complete execution because P1 nees 5 more taps while P3 needs 6 more tapes.

System is in unsafe state.!!!

by Boss
selected by
+3 votes

At time T1
Maximum need P1  P2  P3
10 4 9
Allocated P1  P2  P3
5 2 3
Total tape drives = 12
Available tape drives = 12-(Allocated tape drives)
= 12 - (10)=2
Need  P1  P2  P3
5 2 6
So process P2 needs 2 tap drives and we have available 2.
So P2 satisfies is need at t1 After this Available becomes 4
So we can see neither P1 nor P3 need satisfies so system no longer becomes 
safe and System goes to unsafe state at time t1

by Boss
0 votes

System is unsafe .


Processes Used Max Need
P1 5 10 5
P2 2 4 2
P3 3 9 6

Now Available A=12-(5+3+2)=2

Anew=2,With Anew we can only fulfil the desire of P2

Now Anew=2+2=4

Anew=4::: With Anew=4 we are totaly unable to fulfill the need of P1 and P3.So there is no sequence exist by which we can say system in safe.

by Boss
@Paras+Nath Suppose we had $11$ tape drives instead of $12$, then there would be a deadlock?
if we had 11 tape drives then we hav only 1 available resource....and we are not able fulfil need of any process....I think in this condition we still in deadlock!!

correct me if im wrong...
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