The Banker's Algorithm is a resource allocation and deadlock avoidance algorithm used in operating systems to ensure the safe and efficient allocation of resources. The algorithm is based on the concept of a safe state, which is a state in which it is guaranteed that no deadlocks will occur. The Banker's Algorithm operates in two phases: the resource request phase and the resource allocation phase.
The resource request phase is initiated when a process requests a set of resources. During this phase, the operating system checks to see if the request can be granted without putting the system into an unsafe state. If the request can be granted, the algorithm moves on to the resource allocation phase.
The resource allocation phase is where the requested resources are granted to the process. The operating system ensures that the resources are allocated in a way that ensures the system remains in a safe state. If the system would become unsafe if the resources were granted, the request is denied.
The Banker's Algorithm uses the following information to determine if a resource request can be granted:
Available: An array of the available resources in the system.
Max: A matrix that represents the maximum number of resources that each process may request.
Allocation: A matrix that represents the resources that have been allocated to each process.
Need: A matrix that represents the remaining resources needed by each process to complete its task.
The Banker's Algorithm uses the following steps to determine if a resource request can be granted:
Calculate the Need matrix: The Need matrix is calculated by subtracting the Allocation matrix from the Max matrix.
Check for a safe state: The operating system checks to see if there is a safe state by using the Need and Available arrays. A safe state is a state in which there exists a sequence of processes such that for each process, the sum of its allocated resources plus the resources it can still request is less than or equal to the resources available.
Grant or deny the request: If the request can be granted without putting the system into an unsafe state, the resources are granted to the process. If the request would put the system into an unsafe state, the request is denied.
The Banker's Algorithm is an efficient algorithm for ensuring the safe allocation of resources and avoiding deadlocks. It is particularly useful in systems where multiple processes compete for limited resources, such as computer systems, banking systems, and transportation systems.
Example of the Banker's Algorithm:
Suppose we have a system with three processes and three resources. The maximum number of resources each process may request is represented by the following matrix:
P0 P1 P2
R0 [ 7, 5, 3 ] R1 [ 3, 2, 2 ] R2 [ 9, 0, 2 ]
The resources that have been allocated to each process are represented by the following matrix:
P0 P1 P2
R0 [ 0, 1, 0 ] R1 [ 2, 0, 0 ] R2 [ 3, 0, 2 ]
The available resources in the system are represented by the following array:
[ 3, 3, 2 ]
The first step is to calculate the Need matrix by subtracting the Allocation matrix from the Max matrix. The Need matrix is:
P0 P1 P2
R0 [ 7, 4, 3 ] R1 [ 1, 2, 2 ] R2 [ 6, 0, 0 ]
Next, the operating system will use the Need and Available arrays to check for a safe state. A safe state exists if there exists a sequence of processes such that for each process, the sum of its allocated resources plus the resources it can still request is less than or equal to the resources available.
Suppose process P0 requests 2 units of resource R1 and 1 unit of resource R2. The operating system will check if granting this request would put the system into an unsafe state. To do this, the operating system will check if the Available array minus the requested resources is less than or equal to the Need array for each process. In this case, the Available array minus the requested resources is [1, 1, 1]. The Need array for each process is [7, 4, 3] for P0, [1, 2, 2] for P1, and [6, 0, 0] for P2.
Since the Available array minus the requested resources is less than or equal to the Need array for each process, the operating system can grant the request. The Allocation matrix will now be updated to [2, 2, 3] for P0, [2, 0, 0] for P1, and [3, 0, 2] for P2. The Available array will be updated to [1, 1, 1].
The Banker's Algorithm can be used to prevent deadlocks by checking for a safe state before granting a resource request. If a safe state does not exist, the request will be denied, and the system will not enter into a deadlocked state.
In conclusion, the Banker's Algorithm is a valuable tool for ensuring the safe and efficient allocation of resources in operating systems. It uses the concept of a safe state to avoid deadlocks, and it operates in two phases: the resource request phase and the resource allocation phase. The algorithm is based on the availability of resources, the maximum resources each process may request, and the resources that have been allocated to each process. By using the Banker's Algorithm, operating systems can prevent deadlocks and ensure the efficient allocation of resources.
