To recover from a deadlock in a system, there are several approaches that can be taken. Here's an explanation of three common recovery methods: recovery through preemption, recovery through rollback, and recovery through killing processes:
(a) Recovery through Preemption: In this approach, the system identifies the resources held by processes involved in the deadlock and forcibly reclaims those resources. The system can preempt resources from one or more processes to break the deadlock. By preempting resources, the system temporarily suspends the affected processes and reallocates the resources to other waiting processes. This allows the system to resolve the deadlock and resume normal operation. Once the deadlock is resolved, the preempted processes can be resumed and allowed to continue their execution.
(b) Recovery through Rollback: In this approach, the system rolls back the state of the processes involved in the deadlock to a previously known safe state. The system maintains checkpoints or snapshots of the process states periodically. When a deadlock is detected, the system identifies the processes involved and rolls back their states to a safe checkpoint. This rollback eliminates the conflicting resource allocations that caused the deadlock. After the rollback, the system can reissue the resource requests from the affected processes in a different order to avoid the deadlock condition. This ensures that the system can recover from the deadlock and continue its normal operation.
(c) Recovery through Killing Processes: In this approach, the system selectively terminates or kills one or more processes involved in the deadlock. The decision on which processes to terminate is based on predefined criteria, such as process priority or resource usage. By killing specific processes, the system releases the resources held by those processes, which can then be used by other processes. This action breaks the circular wait condition and resolves the deadlock. However, it is important to ensure that the terminated processes do not leave the system in an inconsistent or unstable state. Careful consideration is needed to minimize the impact of process termination on system integrity and data consistency.
Each of these recovery methods has its own advantages and trade-offs. The choice of method depends on the specific characteristics of the system, the severity of the deadlock, and the desired system behavior. It's crucial to carefully analyze and implement the chosen recovery method to ensure effective deadlock resolution and system stability.