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Module 4: Deadlocks

20227m

A single processor system has three resource types X, Y and Z, which are shared by three processes. There are 5 units of each resource type. Consider the following scenario, where the column 'alloc' denotes the number of units of each resource type allocated to each process, and the column request denotes the number of units of each resource type requested by a process in order to complete execution. Find the process that will finish first and last.

alloc<br>X Y Z Request<br>X Y Z
P0 1 2 1 1 0 3
P1 2 0 1 0 1 2
P2 2 2 1 1 2 0
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Resource allocation X,Y,Z (5 each) alloc vs request

Total allocated: X=5(1+2+2),Y=4(2+0+2),Z=3(1+1+1) → Available =5-allocated = X0,Y1,Z2 initially? Actually given no available row, compute: assume total 5 each → Avail = Total - sumAlloc = X0,Y1,Z2. Need calc Need=Request.
Check P1 Need 0,1,2 ≤ Avail 0,1,2 → P1 can finish first, release 2,0,1 → Avail 2,1,3. Then P0 Need 1,0,3 ≤ Avail 2,1,3 → P0 finishes last? Let's simulate order P1→P0→P2 gives finish first P1, last P0/P2 depending. Detailed safe sequence P1,P2,P0 => first P1, last P0.

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