- To eliminate deadlocks using resource preemption, we successively preempt some resources from processes and give these resources to other processes until the deadlock cycle is broken.
- In some cases it may be possible to temporarily take a resource away from its current owner and give it to another process. Highly dependent on the nature of the resource. Recovering this way is frequently difficult or impossible.
- Selecting a victim. Which resources and which processes are to be preempted? As in process termination, we must determine the order of preemption to minimize cost.
- Rollback. If we preempt a resource from a process, what should be done with that process? Clearly, it cannot continue with its normal execution; it is missing some needed resource.
- Checkpointing; means that its state is written to a file so that it can be restarted later.
- The checkpoint contains not only the memory image, but also the resource state, that is, which resources are currently assigned to the process.
- When a deadlock is detected, it is easy to see which resources are needed. To do the recovery, a process that owns a needed resource is rolled back to a point in time before it acquired some other resource by starting one of its earlier checkpoints.
- Since, in general, it is difficult to determine what a safe state is, the simplest solution is a total rollback: Abort the process and then restart it.
- Although it is more effective to roll back the process only as far as necessary to break the deadlock, this method requires the system to keep more information about the state of all running processes.
- Starvation. How do we ensure that starvation will not occur? That is, how can we guarantee that resources will not always be preempted from the same process?
Cem Ozdogan
2011-02-14
