Deadlocks

Question

Consider a system with processes P0_, P1,P2, . . . .  P99, P100, each process requires maximum of 4 resources. System has allocated 2 resources to each process. The minimum number of resources should release such that above system is deadlock free is _____

Comments

@Nitish, I wonder there should be some logic behind preempting a Process. Unless it is Priority? Or Time Slots or Their order of arrival. How is it possible that without any valid reason a random process is Preempted??You only think for yourself. How can we Preempt a process without a prior discretion??Coz if u see there has gotta be solid base behind it. I don't find any logic in this question.

Answer 1

For a system to be deadlock free ,

Sum of max need of processes < No. of processes + No. of resources ........ (i)

here System has allocated 2 resources to each process , and Total number of process = 101

so max need of processes = 101 * 2 = 202

let number of resources = R

so from (i) we get, 202 < 101 + R

101 < R

that means the minimum number of resources  should be 102 .

Comments

Sir answer should be 102?
there are 101 process thus

202<101+r

101<r

r=102?

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But the max request is 4 for each process then why cann't the total max request be 404 Instead of 202

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If we give 3 resources to each process, then still they can be in a deadlock = total 303 resources allocated 

But if 1 more resource is given, then one of the processes will complete its execution and release the resources held by it and all the other processes need will be satisfied = 303+1                                                     =304 resources will ensure no deadlock 

Since 202 has already been allocated so we need 304-202 = 102 minimum resources ( the question asks about minimum)

 

Answer 2

System needs to release just 2 resources (and no less) to enter a safe state. This will allow one of the processes to complete and free all 4 resources it was using. Clearly, a safe sequence exists now.

(These 4 resources will help complete 2 more processes, and so on…)

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Comments

I too got the answer as 2 but solution says its 68!

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@arjun sir plz check??

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The two resources given may get allocated to two different processes.