Question

Consider the following snapshot of a system: 

Using the banker's algorithm, determine whether or not each of the following states is unsafe. If the state is safe, illustrate the order in which the processes may complete. Otherwise, illustrate why the state is unsafe. 

a. Available = (0,2,0,1) 

b. Available = (2, 0, 0, 2)

Answer 1

Let's see the need of each process which is given by max-allocation.

NEED	A	B	C	D
P0	3	1	0	3
P1	1	0	0	1
P2	0	1	0	0
P3	4	2	0	2
P4	1	1	1	3

A) Available=(0, 2,0,1)

Any process can be executed if its need is less than or equal to the available resource.

Here initially, P2's request can be completed.

After executing P2's request, newly available matrix is (3, 3,2,2)

Now, P1's request can be satisfied. Newly available resource matrix is : (5, 3,3,5)

Now rest all processes can be satisfied since their need is less than functional. Thus the given system is in a SAFE state since the processes request can be met in some order.

One of the possible sequence is :

P2->P1->P0->P3->P4

B) Available : (2, 0,0,2)

Initially, P1's request can be satisfied since its need is less than available.

Then newly available resource matrix is :(4, 2,1,2)

Now, P2's request can be satisfied. After executing P2, newly available resource matrix is : (7, 3,3,3)

Now all the process requests can be satisfied since it needs is less than available.

Thus in this second case also, the system is in a SAFE state.

One of the possible executing sequences is :

P1->P2->P0->P3->P4.