Recovery from Deadlock in Operating System
Prerequisite – Deadlock Detection And Recovery
When a Deadlock Detection Algorithm determines that a deadlock has occurred in the system, the system must recover from that deadlock. There are two approaches of breaking a Deadlock:
1. Process Termination:
To eliminate the deadlock, we can simply kill one or more processes. For this, we use two methods:
- (a). Abort all the Deadlocked Processes:
Aborting all the processes will certainly break the deadlock, but with a great expense. The deadlocked processes may have computed for a long time and the result of those partial computations must be discarded and there is a probability to recalculate them later.
- (b). Abort one process at a time until deadlock is eliminated:
Abort one deadlocked process at a time, until deadlock cycle is eliminated from the system. Due to this method, there may be considerable overhead, because after aborting each process, we have to run deadlock detection algorithm to check whether any processes are still deadlocked.
2. Resource Preemption:
To eliminate deadlocks using resource preemption, we preempt some resources from processes and give those resources to other processes. This method will raise three issues –
- (a). Selecting a victim:
We must determine which resources and which processes are to be preempted and also the order to minimize the cost.
- (b). Rollback:
We must determine what should be done with the process from which resources are preempted. One simple idea is total rollback. That means abort the process and restart it.
- (c). Starvation:
In a system, it may happen that same process is always picked as a victim. As a result, that process will never complete its designated task. This situation is called Starvation and must be avoided. One solution is that a process must be picked as a victim only a finite number of times.