ISRO CSE 2014 | Question: 68

Question

What is the minimum number of resources required to ensure that deadlock will never occur, if there are currently three processes $P_1, P_2$ and $P_3$ running in a system whose maximum demand for the resources of same type are 3, 4, and 5 respectively.

• A. 3
• B. 7
• C. 9
• D. 10

Answer 1

consider the worst case all processes holding just one resource less than their completion(max need)

P1=2

P2=3

P3=4

TOTAL RESOURCE =9  now one more resource will ensure that any one of these process will execute and release all its resources

hence 9+1=10 resources will ensure there will not be deadlock hence ans is D

Comments

what will be the ans if the condition changed to "deadlock always occur"....????

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deadlock may or may not occur when the resources are less than 10... i think deadlock always occur we cannot say as it depends on the allocation of resources...for example consider 2 resources if these two resources are allocated to p1..and no resources are allocated to p2,p3...there is no deadlock...but no process completes also.

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? i did not get after 9 , how u wrote total resources =10

plz explain

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it is just a case when resources becomes 10  there is no deadlock

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beacuse for maximum no for happing dead lock if  we provided resource

p1=2

p2=3

p3=4

2+3+4=9 means if we have 9 process so there is chance that deadlock may happen thats why min no will be 10 resource we can ensure that there will no deadlock

Answer 2

Short trick for these kind of questions-

subtract 1 from "all" max demands,like

3-1 = 2

4-1= 3

5-1 = 4

add all of them = 2+3+4 = 9

then add 1 to it 9+1 =10 so answer is D

Answer 3

Option D will right option for it.

We have processes like P1,P2 and P3 now assign each one of them 2,3 and 4 units.This is condition for deadlock if we assign one more unit to any one of the processes then deadlock will be broken .Therefore minimum resourses required is 10.