Banker's Algorithm
Introduction
The Banker’s Algorithm is a fundamental deadlock avoidance algorithm developed by Edsger Dijkstra. It is designed to allocate limited resources among multiple processes while ensuring that the system remains in a safe state and avoids deadlock. The algorithm gets its name from the concept of a banker managing customer loans — just as a banker must ensure that lending resources to a customer will not lead to insolvency, the operating system must ensure that granting a resource request will not lead to deadlock.
In modern operating systems, multiple processes often compete for limited resources such as CPU cycles, memory, disk space, and network connections. Without proper coordination, processes could enter a deadlock state, where none of them can proceed because they are waiting for each other to release resources. The Banker’s Algorithm prevents this by carefully analyzing the current state of resource allocation and future needs before deciding whether to grant a request.
A virtual lab simulation of the Banker’s Algorithm will help students understand how resource allocation works, why deadlock occurs, and how to prevent it through structured decision-making.
Why We Need Synchronization
In a multi-process environment, the need for synchronization arises when multiple processes compete for shared resources. Without proper management, several critical problems can occur:
1. Deadlock
Deadlock occurs when two or more processes hold resources and wait for each other to release them, leading to a state where none of the processes can make progress.
Example:
- Process A holds Resource 1 and waits for Resource 2.
- Process B holds Resource 2 and waits for Resource 1.
- Neither process can proceed → Deadlock
2. Starvation
Starvation happens when a low-priority process waits indefinitely because higher-priority processes continuously acquire resources.
Example:
- Process A continuously acquires the CPU because it has a higher priority.
- Process B, with a lower priority, never gets a chance to execute → Starvation
3. Resource Hoarding
A process may hold resources longer than needed, preventing other processes from accessing them and leading to reduced system efficiency.
Example:
- Process A acquires memory blocks and holds them even after completing execution → Resource hoarding
4. Race Condition
A race condition occurs when multiple processes attempt to modify shared resources simultaneously, leading to unpredictable behavior.
Example:
- Process A and Process B both update a shared counter at the same time → Final value may be corrupted → Data inconsistency
5. Unsafe State
An unsafe state occurs when a system’s resource allocation allows the possibility of deadlock, even if it hasn't occurred yet.
Example:
- If granting a resource request leaves the system with insufficient resources to fulfill future needs → Unsafe state
Example of Banker's Algorithm in an Operating System
Let’s consider a scenario where multiple processes in an operating system are competing for limited resources without using the Banker's Algorithm for resource allocation. This example highlights the problems that can arise due to the lack of proper coordination and deadlock prevention.
Scenario:
A system has three types of resources:
- CPU cycles
- Memory blocks
- Disk I/O slots
There are 3 processes (P1, P2, P3) competing for these resources.
The maximum demand, allocated resources, and available resources are as follows:
Maximum Demand Matrix:
| Process | CPU | Memory | Disk |
|---|---|---|---|
| P1 | 7 | 5 | 3 |
| P2 | 3 | 2 | 2 |
| P3 | 9 | 0 | 2 |
Allocated Resources Matrix:
| Process | CPU | Memory | Disk |
|---|---|---|---|
| P1 | 0 | 1 | 0 |
| P2 | 2 | 0 | 0 |
| P3 | 3 | 0 | 2 |
Available Resources:
- CPU = 5
- Memory = 4
- Disk = 3
Need Matrix:
| Process | CPU | Memory | Disk |
|---|---|---|---|
| P1 | 7 | 4 | 3 |
| P2 | 1 | 2 | 2 |
| P3 | 6 | 0 | 0 |
Why We Need the Banker’s Algorithm
The Banker’s Algorithm introduces structured resource management using the following components:
- Available Vector – Tracks the number of currently available resources.
- Maximum Matrix – Tracks the maximum demand of each process.
- Allocation Matrix – Tracks the resources currently allocated to each process.
- Need Matrix – Tracks the remaining resources needed by each process to complete execution.
How the Banker’s Algorithm Prevents These Issues:
| Problem | How Banker’s Algorithm Fixes It |
|---|---|
| Deadlock | Evaluates future state before granting a request. |
| Starvation | Ensures fair allocation through the need matrix. |
| Resource Hoarding | Releases unused resources after process completion. |
| Unsafe State | Grants requests only if the system remains in a safe state. |
| Lost Update | Ensures exclusive access to resources while updating. |
Conclusion
The Banker’s Algorithm provides a structured approach to prevent deadlock, starvation, and unsafe states by evaluating the current state, future demands, and available resources before granting requests. Through a virtual lab simulation, students can observe how resource conflicts are resolved and how stable resource allocation is maintained using the Banker’s Algorithm.