Question

How do you use the Banker’s Algorithm to detect deadlock? How do you use the Banker’s Algorithm to detect an unsafe state?

Answer 1

these data structures used in algorithm to detect deadlock:  
Available- A vector of length m indicates the number of available resources of each type.
Allocation- An n*m matrix defines the number of resources of each type currently allocated to a process. Column represents resource and resource represent process.
Request- An n*m matrix indicates the current request of each process. If request[i][j] equals k then process Pi is requesting k more instances of resource type Rj.
We treat rows in the matrices Allocation and Request as vectors, we refer them as Allocationi and Requesti.

Steps to detect deadlock:

Let Work and Finish be vectors of length m and n respectively. Initialize Work= Available. For i=0, 1, …., n-1, if Requesti = 0, then Finish[i] = true; otherwise, Finish[i]= false.
Find an index i such that both
a) Finish[i] == false
b) Requesti <= Work
If no such i exists go to step 4.
Work= Work+ Allocationi
Finish[i]= true
Go to Step 2.
If Finish[i]== false for some i, 0<=i<n, then the system is in a deadlocked state.
Moreover, if Finish[i]==false the process Pi is deadlocked.
now, if a system is deadlocked then it is in unsafe state