Deadlock Avoidance Example

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

Allocation Need Available

A B C A B C A B C

P0 0 1 0 7 4 3 3 3 2

P1 2 0 0 1 2 2

P2 3 0 2 6 0 0

P3 2 1 1 0 1 1

P4 0 0 2 4 3 1

Processes can finish in order < P1, P3, P4, P2, P0 > so system is in a safe state.

Can a request by P1 for (1, 0, 2) be granted?

To determine this, first update table assuming new request has been granted:

Allocation Need Available

A B C A B C A B C

P0 0 1 0 7 4 3 2 3 0

P1 3 0 2 0 2 0

P2 3 0 2 6 0 0

P3 2 1 1 0 1 1

P4 0 0 2 4 3 1

Second, see if there is an order where processes can finish. Yes there is:

< P1, P3, P4, P0, P2 >

Can a request by P4 for (3, 3, 0) be granted?

Can a request by P0 for (0, 2, 0) be granted?