Question

Can anyone explain, how does Livelock occur in case of priority inversion?

Answer 1

Consider two processes A and B both needing an instance of X. Assume priority of A is greater than B. Initially X will be assigned to A due to higher priority of A. But if before X completes execution, priority of B becomes greater than A, A can be put on hold and B can start execution. Now, during execution of B, if priority of A becomes greater, the same cycle continues- two processes trying to make progress but not able to do- livelock.
ref@ https://en.wikipedia.org/wiki/Deadlock#Livelock

Comments

Sir, how can B start its execution, when A is holding X..? Until n unless A is in critical section (holding X), how can B take hold over X? I'm confued >.<

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For that to happen, a rollback mechanism must be there. When a high priority job comes, and a low priority one is holding its required resource, the low priority one would be rolled back.

It is just a possibility.

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Sir, If the lower priority is rolled back , then the resource X will be free and which can be acquired by higher priority process, then where the livelock is..?

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Consider the following scenario:

Suppose process A wants resource X for some amount of time say m. Now, before this time, if this resource is given to B, now the next time A must start from beginning. Again, before m time interval, resource will be given to B. 

Answer 2

I think, as I remember there is low priority process which executing is in critical section and at the same point of time a high priority job comes in ready queue. because of M.E that process can not go into CS so though process high priority but it has to wait unitl Low priority process completes its execution

Comments

Yeah, but i'm not getting, where is livelock in this phenomena.