Resource Allocation Graph (RAG) in Operating
System
As Banker’s algorithm using some kind of table like allocation, request, available all
that thing to understand what is the state of the system. Similarly, if you want to
understand the state of the system instead of using those table, actually tables are
very easy to represent and understand it, but then still you could even represent the
same information in the graph. That graph is called Resource Allocation Graph
(RAG).
So, resource allocation graph is explained to us what is the state of the system in
terms of processes and resources. Like how many resources are available, how
many are allocated and what is the request of each process. Everything can be
represented in terms of the diagram. One of the advantages of having a diagram is,
sometimes it is possible to see a deadlock directly by using RAG, but then you might
not be able to know that by looking at the table. But the tables are better if the
system contains lots of process and resource and Graph is better if the system
contains less number of process and resource.
We know that any graph contains vertices and edges. So RAG also contains vertices
and edges. In RAG vertices are two type –
1. Process vertex – Every process will be represented as a process
vertex.Generally, the process will be represented with a circle.
2. Resource vertex – Every resource will be represented as a resource vertex. It is
also two type –
Single instance type resource – It represents as a box, inside the box, there
will be one dot.So the number of dots indicate how many instances are present
of each resource type.
Multi-resource instance type resource – It also represents as a box, inside
the box, there will be many dots present.
Now coming to the edges of RAG.There are two types of edges in RAG –
