Operating System :Deadlock :

Question

We know that whenever a process needs i/o time it goes to block/wait state. At that time cpu is idle and it can run other processes. What happens during the deadlock ? In which state do the processes go, so that the cpu freezes ? If all the processes during deadlock, go into block state then why does the cpu freezes ? The cpu should stay idle, but it should not freeze . Can anyone clarify ?

Comments

Please correct me if i am wrong.

For a process to run on CPU it must have the resources requested,until then it will be waiting in ready queue.Now,a deadlock between 2 processes will occur if they are holding resources that both of them require and unwilling to release until they are executed.Now,if all the processes are in a deadlock then no other process will running on CPU that's why the CPU remains idle.Here the point to be noted is that the processes will remain in ready queue rather than in the block queue.If not all the processes are in deadlock then the processes whose resources are allocated will run on CPU.

Answer 1

For starters, all the processes going in a deadlock simultaneously, is a very very rare occurrence, at least on the CPUs our generation is used to. In fact its so rare that major names in the market, like Windows and Ubuntu, do not have any deadlock resolving mechanism at all. The ultimate solution is that the user gets frustrated and restarts the system.

But still, if a condition occurs wherein all the processes are in deadlock, then CPU goes in an idle state (as there is no process to execute) and its same as what we call as freezing or "hang". After some time, if one of the processes is killed the deadlock may be resolved and the system starts running again. But if one the process stuck in deadlock is of kernel type, the only solution is a total restart.$^{[1]}$

Also, there may be the case wherein not all, but only a few processes are in a deadlock. In that case, the CPU may be (in fact is) used by other processes. Its one of those moments when one of our application (say Chrome becomes unresponsive) while rest of the applications are running well and good.

Comments

NO, you are going wrong somewhere or misinterpreting something. May I have the source from where you are quoting the above scenario. Lemme have a look first.

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I was going through rabindrababu Ravula'r videos... He described the scenario... What I am confused is whether the processes end up in ready queue or not.. If you could describe please

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Also I saw somewhat similar answer in this post, https://gateoverflow.in/46833/difference-between-deadloack-%26-spinlock
The answer posted by Varun Taneja on 25th february, 2018.