Consider a system with seven processes A through G and six resources R through…
2016
Consider a system with seven processes A through G and six resources R through W. Resource ownership is as follows :
process A holds R and wants T
process B holds nothing but wants T
process C holds nothing but wants S
process D holds U and wants S & T
process E holds T and wants V
process F holds W and wants S
process G holds V and wants U
Is the system deadlocked ? If yes, ______ processes are deadlocked.
- A.
No
- B.
Yes, A, B, C
- C.
Yes, D, E, G
- D.
Yes, A, B, F
Attempted by 80 students.
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Correct answer: C
Answer: Yes — processes D, E and G are deadlocked.
Reason:
Key allocations and requests:
A holds R and requests T.
B holds nothing and requests T.
C holds nothing and requests S.
D holds U and requests S and T.
E holds T and requests V.
F holds W and requests S.
G holds V and requests U.
Identify the circular waits that form the deadlock:
D is waiting for T, which is held by E.
E is waiting for V, which is held by G.
G is waiting for U, which is held by D.
Conclusion:
The three processes D, E and G form a closed cycle of waiting, so they are deadlocked.
Number of deadlocked processes: 3.
Other processes (A and B) are blocked waiting for T held by E but are not part of the deadlock cycle; C and F request S which is currently free, so they are not deadlocked.
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