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Module 4: Deadlocks

20237m

Consider a system with five processes P0 through P4 and have three resource types A, B, C. Resource type A has ten instances, resource type B has five instances, and resource type C has seven instances. Suppose that the following snapshot represents the current state of the system:

Allocation Max Available
A B C A B C A B C
P0 0 1 0 7 5 3 3 3 2
P1 2 0 0 3 2 2
P2 3 0 2 9 0 2
P3 2 1 1 2 2 2
P4 0 0 2 4 3 3

The system is currently in safe state. Suppose now that P1 requests additional resources as (A=1, B=0, C=2). Is this request can be immediately granted? Justify your answer.

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Banker's Request P1 (1,0,2) with Available 3,3,2

Check Need P1 = Max-Alloc = 1,2,2. Request 1,0,2 ≤ Need (1,2,2) and ≤ Available (3,3,2) → pretend allocate: Avail becomes 2,3,0, Alloc P1 becomes 3,0,2.
Check safe: Need remaining: P0 7,4,3, P1 0,2,0, P2 6,0,0, P3 0,1,1, P4 4,3,1. No safe sequence because Avail 2,3,0 insufficient for any Need → request cannot be granted, would lead to unsafe state, P1 must wait.

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PreviousFor a deadlock to occur, each of the necessary conditions must hold. By ensuring that at least one of these conditions cannot hold, we can prevent the occurrence of a deadlock. Give one approach individually to prevent each of these necessary conditions.NextState producer-consumer problem. Give a solution to this problem using semaphore. Justify that your solution guarantees mutual exclusion.
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