Bankers Algorithm for Deadlock Avoidance in C with Resource Allocation Graph (RAG)
Bankers Algorithm for Deadlock Avoidance
In the world of computer science and operating systems, managing resources efficiently is a critical aspect. Deadlocks, which occur when two or more processes are unable to proceed because each is waiting for the other to release a resource, can significantly hinder system performance and cause applications to crash.
To tackle this issue, the Bankers Algorithm for deadlock avoidance comes into play. In this article, we will explore the Bankers Algorithm, its implementation in C, and how it uses the Resource Allocation Graph (RAG) to ensure system stability.
What is a Deadlock?
Before diving into the Bankers Algorithm, let’s understand what a deadlock is. A deadlock is a situation in a computer system where two or more processes are unable to proceed because each process is waiting for a resource held by another process. This creates a circular chain of dependencies, leading to a standstill.
Conditions for a Deadlock
For a deadlock to occur, four conditions must be met:
- Mutual Exclusion: Resources can only be held by one process at a time.
- Hold and Wait: A process must hold at least one resource and is waiting for additional resources that are currently being held by other processes.
- No Preemption: Resources cannot be forcibly taken from a process; they must be released voluntarily.
- Circular Wait: A circular chain of processes exists, where each process is waiting for a resource held by another process in the chain.
What is the Bankers Algorithm?
The Bankers Algorithm is a resource allocation and deadlock avoidance algorithm designed to prevent the occurrence of deadlocks in computer systems. It was developed by Edsger W. Dijkstra and takes its name from the concept of a bank that lends resources to processes.
How the Bankers Algorithm Works
The Bankers Algorithm employs a conservative approach to resource allocation. It assumes that all processes will request their maximum resource requirements simultaneously. Based on this assumption, the algorithm checks if the system will remain in a safe state after allocating resources. If the system remains safe, the resources are allocated; otherwise, the request is denied, and the process must wait until sufficient resources are available.
To implement the Bankers Algorithm in C, we need the following data structures:
- Process Control Block (PCB): A PCB contains information about each process, such as its ID, maximum resource needs, allocated resources, and the resources it still needs to complete its execution.
- Resource Allocation Graph (RAG): The RAG represents the allocation of resources to processes and their dependencies.
- Initialization: Before applying the Bankers Algorithm, the system must initialize the following data structures:
- Available Resources: This array contains the total number of available instances of each resource in the system.
- Maximum Resources: This 2D array represents the maximum demand of resources for each process in the system.
- Allocated Resources: This 2D array represents the resources currently allocated to each process.
Safety Algorithm
The Bankers Algorithm uses a safety algorithm to determine whether a system is in a safe state or not. The safety algorithm works as follows:
- Mark all processes as not executed.
- Initialize the Work array with the number of available instances of each resource type.
- Initialize an Finish array to keep track of processes that have finished their execution.
- Find a process whose maximum resource needs are less than or equal to the Work array.
- If such a process is found, add its allocated resources to the Work array and mark the process as finished.
- Repeat steps 4 and 5 until all processes are marked as finished or no process can be found in step 4.
- If all processes are marked as finished, the system is in a safe state and can proceed with resource allocation. Otherwise, the system is in an unsafe state, and resource allocation should be postponed to prevent a potential deadlock.
Conclusion
The Bankers Algorithm is a powerful method for deadlock avoidance in computer systems. By carefully managing resource allocation using the Resource Allocation Graph, the Bankers Algorithm ensures that processes can proceed without the risk of encountering a deadlock. It plays a crucial role in maintaining system stability and preventing applications from crashing due to resource contention.
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