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Introduction
As the Banker's algorithm uses some type of tables such as allocation, request, available all that item to comprehend what the condition of the system is. Similarly, if we want to comprehend the system's status, instead of using tables, we could also display the same information in a graph. This graph is known as the Resource Allocation Graph (RAG). The resource allocation graph explains the system's condition in terms of processes and resources. Such as how many resources are available, how many are assigned, and what each process's requirement is.
One advantage of having a picture is that it is sometimes feasible to notice a stalemate immediately by using Resource Allocation Graph in Operating System, which one may not detect by looking at the table. However, tables are preferable if the system has many processes and resources, whereas graphs are preferable if the system contains a small number of processes and resources.
Resource Allocation Graph in Operating System
The resource allocation graph is a graphical representation of a system's status.
A resource allocation graph displays which process holds which resource and which process is waiting for a specific resource type. It's a straightforward tool for illustrating potential deadlocks among interacting processes, showing resource allocation and process requests.
As the name implies, the resource allocation graph contains all of the information about all of the processes holding some resources or waiting for some resources.
It also contains information on all instances of all resources, whether they are accessible or in use by the processes.
Types of Vertices in RAG
In RAG vertices are two types –
1. Process vertex
A process vertex represents a process or task in the system. It denotes a unit of execution or activity that requires access to resources to perform its function. Processes can be anything from software threads to physical operations in a manufacturing environment. These vertices typically indicate the tasks or activities that need to be performed within the system.
2. Resource vertex
A resource vertex represents a resource that processes may need to access or utilize in order to complete their tasks. Resources can be anything from CPU time, memory, or network bandwidth in a computing system to physical tools or materials in a manufacturing setting. These vertices denote the entities that are being shared among different processes and are essential for those processes to progress or complete.
It also has two types :
Single instance type resource: It is represented as a box with one dot within.
As a result, the number of dots indicates how many instances of each resource type are present.
Multi-resource instance type resource: It is also represented as a box with multiple dots within.
Now, coming to the edges of the Resource Allocation Graph(RAG).
Types of Edges are there in RAG
In RAG, there are two kinds of edges:
1. Assign Edge -If you have previously assigned a resource to a process, this is called Assign edge.
2. Request Edge - This indicates that in the future, the process may require some resources to finish the execution, which is referred to as the request edge.
As a result, if a process uses a resource, an arrow is drawn from the resource node to the process node.
If a process requests a resource, an arrow is drawn from the process node to the resource node.
If RAG contains a cycle, the system is in deadlock; otherwise, it is not.
Example
Consider a simple scenario where we have two processes (P1 and P2) and three resources (R1, R2, and R3). Here's how the Resource Allocation Graph (RAG) might look in this scenario:
Process Vertices:
P1
P2
Resource Vertices:
R1
R2
R3
Now, let's add edges to represent the relationships between processes and resources:
P1 requires R1 and R2 to execute, so there are edges from P1 to R1 and R2.
P2 requires R2 and R3 to execute, so there are edges from P2 to R2 and R3.
This configuration might look something like this:
R1
|
|
P1
/ \
/ \
R2 R3
\ /
\ /
P2
In this graph:
Process P1 is waiting for resources R1 and R2.
Process P2 is waiting for resources R2 and R3.
Resources R1 and R3 are currently free and not allocated to any process.
Characteristics of RAG
Pictorial representation-RAG is a visual depiction of a system's states.
Deadlock detection: Using RAG, we can quickly determine whether the system is in deadlock or not.
Resources Information –RAG holds all of the information about resources and their instances, whether they are free or in use by other processes.
Processes Information: RAG informs us about the processes, such as which process holds which resource and which resource it is demanding.
Advantages of RAG
It is pretty effective in detecting deadlocks.
The Banker's Algorithm makes extensive use of it.
It's a graphical depiction of a system.
A quick peek at the graph may sometimes tell us if the system is in deadlock or not.
Understanding resource allocation using RAG takes less time.
Disadvantages of RAG
RAG is beneficial when there are fewer procedures and resources.
When dealing with a large number of resources or processes, it is preferable to keep data in a table than a RAG.
When there are a vast number of resources or processes, the graph becomes challenging to interpret and very complex.
A Resource Allocation Graph (RAG) is a directed graph used to represent the allocation of resources to processes in a system.
How to check deadlock in Resource Allocation Graph?
Deadlock occurs if the Resource Allocation Graph contains a cycle involving processes and resources, indicating that resources are waiting indefinitely.
How to convert Resource Allocation Graph to wait-for graph?
To convert, Resource Allocation Graph to wait-for graph you need to replace resource nodes with direct edges from each process to the process holding the resource, indicating waiting relationships between processes.
Conclusion
In this blog, we learned about Resource Allocation graphs. We have covered the basic idea of the Resource Allocation Graph. Further, we saw the types of vertices and edges in the Resource Allocation Graph. We have also witnessed the Advantages and Disadvantages of the Resource Allocation Graph. On the other hand, learning never ceases, and there is always more to learn. So, keep learning and keep growing.
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