Question

Waiting processes do consume various system resources. Could someone sabotage a system by repeatedly creating processes and making them wait for events that will never happen? What safeguards could be imposed?

Answer 1

Waiting processes do consume various system resources. When system repeatedly create processes and some of them get very low priority resulting to starvation. When two or more processes are in waiting state and having system resources that other process needs to execute then there is a deadlock. So by deadlock and starvation anyone can sabotage a system.

There are some safeguards to prevent from sabotaging a system.
Following are the characteristics of deadlock:

1. Mutual Exclusion: One system resource can be allocated to one process at a time.
2. Hold and Wait: A process is holding one or more than one resources and waiting for other resources which are held by other waiting processes.
3. No Preemption: A resource cannot be taken from a process unless the process releases the resource.
4. Circular Wait: A set of processes are waiting for each other in circular form.

To avoid deadlock any one of the above characteristic must be eliminated.

Eliminate Mutual Exclusion
Mutual exclusion can't be eliminated because there will always be the condition of mutual exclusion in system.

Eliminate Hold and wait
To eliminate Hold and Wait, all required resources can be allocated to the process before the execution. This will lead to low device utilization.

Eliminate No Preemption
Withdraw resources from the process when resources required by other high priority processes only.

Eliminate Circular Wait
Each resource can be assigned with a number. A process can request the resources increasing or decreasing order of numbering.

Eliminating Starvation:
aging : It is the techniques where priority is gradually increased of low priority process over time.

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