A deadlock is a situation in an operating system where two or more processes are waiting for each other to release resources, resulting in a frozen system. To detect and resolve deadlocks, various algorithms have been proposed. Here, we will describe one of the most widely used deadlock detection algorithms in operating systems, the Banker's Algorithm.
The Banker's Algorithm is a resource allocation algorithm that ensures that a set of processes do not deadlock by checking whether a safe state exists. The algorithm considers the resources that are currently available, the maximum resources each process may require, and the resources currently being held by each process. If a process requests a resource that cannot be granted without causing a deadlock, the request is denied.
The Banker's Algorithm operates in two phases:
1. Resource Request
2. Resource Allocation
Resource Request: In this phase, a process requests a set of resources. The request is either granted or denied based on the state of the system.
Resource Allocation: In this phase, the requested resources are granted to the process if the system remains in a safe state. If the grant of the requested resources results in a deadlock, the request is denied.
The algorithm uses a set of data structures to keep track of the state of the system:
1. Available: An array that keeps track of the number of available resources of each type.
2. Max: A matrix that describes the maximum resources required by each process for completion.
3. Allocation: A matrix that describes the resources currently allocated to each process.
4. Need: A matrix that describes the resources still needed by each process to complete. The Need matrix is calculated by subtracting the Allocation matrix from the Max matrix.
To determine if a request can be granted, the Banker's Algorithm checks if the requested resources can be safely granted without resulting in a deadlock. A safe state exists if there exists a sequence of processes such that every process can complete its execution without causing a deadlock.
The Banker's Algorithm checks for a safe state by simulating the allocation of resources to processes. The algorithm starts by assuming that all resources are available and then goes through a series of steps:
1. Select a process that can be completed.
2. Allocate the necessary resources to the selected process.
3. Update the state of the system by marking the allocated resources as not available, updating the Allocation matrix, and updating the Need matrix.
4. Repeat the process until either all processes have completed or no process can be completed.
If all processes have completed, then the system is in a safe state, and the request can be granted. If no process can be completed, then the system is in an unsafe state, and the request is denied.
Example:
Consider a system with five processes and three resource types. The state of the system is as follows:
Available = [3, 3, 2]
Max = [[7, 5, 3], [3, 2, 2], [9, 0, 2], [2, 2, 2], [4, 3, 3]]
Allocation = [[0, 1, 0], [2, 0, 0], [3, 0, 2], [2, 1, 1], [0, 0, 2]]
Need = [[7, 4, 3], [1, 2, 2], [6, 0, 0], [0, 1, 1], [4, 3, 1]]
A process P1 requests [1, 0, 2] resources.
The Banker's Algorithm checks if the request can be safely granted by simulating the allocation of resources. First, the Available array is updated to reflect the requested resources:
Available = [2, 3, 0]
Next, the algorithm checks if a process can be completed by comparing the Need matrix and the Available array. A process can be completed if the resources in the Need matrix are less than or equal to the resources in the Available array. In this example, no process can be completed, so the request cannot be granted. The system is in an unsafe state, and the request is denied.
In conclusion, the Banker's Algorithm is a powerful tool for deadlock detection in operating systems. It provides a systematic approach to ensuring that a set of processes does not deadlock by checking if a safe state exists before granting a resource request. The algorithm operates in two phases: resource request and resource allocation, and it uses data structures to keep track of the state of the system, including the Available array, the Max matrix, the Allocation matrix, and the Need matrix. By simulating the allocation of resources and checking for a safe state, the Banker's Algorithm can prevent deadlocks and ensure the efficient use of resources in an operating system.
