What the heck is Deadlock?
In an operating system, a deadlock occurs when two or more processes are blocked and waiting for each other to release the resources that they are holding. As a result, none of the processes can proceed, leading to a standstill in the system.
Solutions
To prevent or resolve deadlocks programmatically, several strategies can be employed, including:
Resource Allocation Graph
This algorithm can be used to detect deadlocks in a system. It involves constructing a directed graph, where nodes represent processes, and edges represent resource requests. A cycle in the graph indicates a potential deadlock. Once a deadlock is detected, resources can be released to resolve the deadlock.
Banker's Algorithm
This algorithm is used to ensure that a system is in a safe state, where all processes can complete their execution without deadlocks. The algorithm uses a series of checks to determine if a resource request should be granted or not, based on the current state of the system.
Timeouts
A timeout can be used to prevent a process from waiting indefinitely for a resource. If a process waits for too long, it can be assumed that a deadlock has occurred, and the process can be terminated.
Resource Ordering
This involves defining a global order in which resources can be requested. By enforcing a specific ordering, the system can avoid circular wait conditions that can lead to deadlocks.
Example of Banker's Algorithm
Suppose we have three processes (P1, P2, P3) and three resources (R1, R2, R3). Each process requires a specific set of resources to complete its execution. We can represent the current state of the system in a resource allocation matrix:
| R1 | R2 | R3 | |
| P1 | 1 | 2 | 3 |
| P2 | 3 | 2 | 1 |
| P3 | 1 | 1 | 1 |
We can also represent the maximum amount of resources that each process requires in a maximum resource matrix:
| R1 | R2 | R3 | |
| P1 | 4 | 2 | 4 |
| P2 | 1 | 2 | 1 |
| P3 | 3 | 3 | 3 |
System safe check
To determine if the system is in a safe state, we can use the following steps:
Create a vector called 'Available' that represents the number of available instances of each resource.
Create a matrix called 'Need' that represents the remaining number of instances of each resource that each process requires.
Iterate over each process in the system and check if its resource needs can be satisfied based on the current state of the system. If so, grant the resource to the process and update the 'Available' vector and 'Need' matrix. Repeat this process until all processes have completed execution.
If the system is in a safe state, then all processes can complete their execution without deadlocks. If not, the system should be adjusted to ensure that it is in a safe state.