The banker’s algorithm is a resource allocation and deadlock avoidance algorithm that tests for safety by simulating the allocation for predetermined maximum possible amounts of all resources, then makes an “s-state” check to test for possible activities, before deciding whether allocation should be allowed to continue.

Following Data structures are used to implement the Banker’s Algorithm:

Let ‘n’ be the number of processes in the system and ‘m’ be the number of resources types.

Available :

It is a 1-d array of size ‘m’ indicating the number of available resources of each type.
Available[ j ] = k means there are ‘k’ instances of resource type Rj
Max :

It is a 2-d array of size ‘n*m’ that defines the maximum demand of each process in a system.
Max[ i, j ] = k means process Pi may request at most ‘k’ instances of resource type Rj.
Allocation :

It is a 2-d array of size ‘n*m’ that defines the number of resources of each type currently allocated to each process.
Allocation[ i, j ] = k means process Pi is currently allocated ‘k’ instances of resource type Rj
Need :

It is a 2-d array of size ‘n*m’ that indicates the remaining resource need of each process.
Need [ i, j ] = k means process Pi currently need ‘k’ instances of resource type Rj
for its execution.

Need [ i, j ] = Max [ i, j ] – Allocation [ i, j ]

Allocationi specifies the resources currently allocated to process Pi and Needi specifies the additional resources that process Pi may still request to complete its task.

 

example：

Suppose t0   A has 8  B has 6   C has 4

Allocation   Max  Available

p0   02 2         7 7 7     0  2  0

p1    5 2 2       5 4 5

p3   3 0 0        4  5  1

the need will be

p0    7 5 5

p1    0 2 3

p2   1 5 1

First work=[0 2 0]

we cannot find any NEEDi<WORK

then it is unsafe now