Question

Q1. Solve the following problem of Deadlock avoidance. Allocate the resources such that all the process are executed safe and no deadlock is occur.

Total instances of a resource=10

Process	Has	Maximum
P1	2	4
P2	2	7
P3	3	9
Free

Answer 1

Solution:

Given data

Process	Has	Maximum Needed	Remaining Needs After Allocation
P1	2	4	4-2=2
P2	2	7	7-2=5
P3	3	9	9-3=6

Here we know that total number of resources available are 10

So Total number of resources which are free = total resources - sum(allocated resources)

i.e Available resources = 10 - (2+2+3) = 3

Available Resources

3

Here available resources are 3.

For avoiding deadlock we need to allocate the resources whose needs are meeting with the available resources.

So from the given processes P1 requires 2 resources,P2 requires 5 resources where as P3 requires 6 resources.

Here available resources are 3 so we can allot the 2 resources needed for process P1.

i.e

Available Resources after alloting to process P1

3-2=1

Now assume process p1 has completed that means it will relase all its resouces i.e 4 will be added to available resources.

Available Resources after completion of P1

Prev Available + P1 releases resources = 1 + 4 = 5

Now we have available resources as 5. Since P1 is completed the remaining processes are P2,P3 which requires 5 and 6 resources to complete the execution.

Here process P2 requires 5 resources and the available resources also 5 so we can allot those resources to process P2.

i.e

Available Resources after alloting to process P2

5 - 5 = 0

Now P2 has all needed resources so it will complete its execution and will release the resources it has i.e 7.

Available Resources after completion of P2

Prev Available + P2 releases resources = 0 + 7 = 7

Till now P1,P2 are executed safely without any deadlock.

Now the final remaining process is P3 which requires 6 more resources to execute . Here available resources are 7 so assign 6 resources to process P3.

Available Resources after alloting to process P3

7 - 6 =1

Since all needed resources allocated P3 will completer its execution and releases the resources.

Available Resources after completion of P3

Prev Available + P3 releases resources = 1 + 9 = 10

Final Available resources after completion of all processes should equal to total instance of resources i.e 10

Available Resources after completion of All processes

10

Here P1,P2,P3 executed without any deadlock. So the system is in safe state and the safe sequence is P1,P2,P3.

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