Question

Consider the following snapshot of a system:  
Allocation Max Available ABCD ABCD ABCD P0 1121 2233 2212 P1 2122 5445 P2 3010 3121 P3 1001 2311 P4 2000 3221
Answer the following questions using the banker`s algorithm:
a) Illustrate that the system is in a safe state by demonstrating an order in which the processes may complete. Give the Available matrix after completion of each process.

Answer 1

The given inputs are -

Now , Need = Max - allocation

We can show that the state given is a safe state by showing that it is possible for each process to acquire its maximum resources and then terminate.

1. P0 acquires 1 A, 1 B, 1 C and 2 D resources, achieving its maximum
   • [available resource: <2 2 1 2> - <1 1 1 2> = <1 1 0 0>]
   • The system now still has 1 A, 1 B, no C and no D resource available
2. P0 terminates, returning 2 A, 2 B, 3 C and 3 D resources to the system
   • [available resource: <1 1 0 0 > + <2 2 3 3> = <3 3 3 3>]
   • The system now has 3 A, 3 B, 3 C and 3 D resources available
3. P1 acquires 3 A, 3 B, 2 C and 3 D resources, achieving its maximum
   • [available resource: <3 3 3 3> - <3 3 2 3> = <0 0 1 0>]
   • The system now still has no A, no B, 1 C and no D resource available
4. P1 terminates, returning 5 A, 4 B, 4 C and 5 D resources to the system
   • [available resource: <0 0 1 0> + <5 4 4 5> = <5 4 5 5>]
   • The system now has 5 A, 4 B, 5 C and 5 D resources available
5. P2 acquires 0 A, 1 B, 1 C and 1 D resources, achieving its maximum
   • [available resource: <5 4 4 5> - <0 1 1 1> = <5 3 3 4>]
   • The system now still has 5 A, 3 B, 3 C and 4 D resource available
6. P2 terminates, returning 3 A, 1 B, 2 C and 1 D resources to the system
   • [available resource: <5 3 3 4 > + <3 1 2 1> = <8 4 5 5>]
   • The system now has 8 A, 4 B, 5 C and 5 D resources available
7. P3 acquires 1 A, 3 B, 1 C and 0 D resources, achieving its maximum
   • [available resource: <8 4 5 5 > - <1 3 1 0> = <7 1 4 5>]
   • The system now still has 7 A, 1 B, 4 C and 5 D resource available
8. P3 terminates, returning 2 A, 3 B, 1 C and 1 D resources to the system
   • [available resource: <7 1 4 5> + <2 3 1 1> = <9 4 5 6>]
   • The system now has 9 A, 4 B, 5 C and 6 D resources available
9. P4 acquires 1 A, 2 B, 2 C and 1 D resources, achieving its maximum
   • [available resource: <9 4 5 6> - <1 2 2 1> = <8 2 3 5>]
   • The system now still has 8 A, 2 B, 3 C and 5 D resource available
10. P4 terminates, returning 3 A, 2 B, 2 C and 1 D resources to the system
    • [available resource: <8 2 3 5> + <3 2 2 1> = <11 4 5 6>]
    • The system now has 11 A, 4 B, 5 C and 6 D resources available
11. Because all processes were able to terminate, this state is safe.