Critical Section

Question

Please explain why bounded waiting is not satisfied...?

Comments

I don't know which book this question is from, but it doesn't seem a good book. How many grammatical mistakes are there in this question? It is always better to study from good books.

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whats the starting values of flag[i] and flag[j] ?? i think i should be mentioned ...rt

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yes, we should take them as false.

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@arjun sir: answer should be -:it satisfies Mutual exclusion and bounded wait but no progress.Am i right?

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no bounded wait guarantee rt?

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sir isn't it similar to strict alteration ? so i guess bounded wait is satisfied 

https://gateoverflow.in/39600/gate2016-2-48

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No, it is not. There is no need to "alterate" here. i.e. say Process $P_i$ can just repeat any number of times.

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sir, progress not satisfied because-:

Process $P_{1}$ have to wait for process $P_{0}$ to execute its  critical section(set flag[0]=false) inorder to execute its $(P_{1}'s)$ critical section..

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boundedwait not satisfied because-:

once process $P_{0}$ executed its critical section, $P_{0} $can again make request and CAN successfully execute critical section as many times it wants

Am i right sir?

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some typo?

And will deadlock always cause "no progress"?

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updated.

sir if there is Progress, then it is definetly Deadlock free,i mean

$\text{progress }\rightarrow \text{No deadlock}$

https://www.cse.iitb.ac.in/~cs744/references/CS347-04-process-sync.pdf

But i am not sure about converse.

Answer 1

only mutual exclusion is satisfied here. Consider below situation: Initially critical section is free. Now, Lets Process Pi executes its 1st statement flag[i] = true and got preempted. Then Lets Process Pj comes and tries to execute its own while statement and as this condition is true for Pi, the process Pj keeps on busy waiting. This waiting is for Pi which is not inside in Critical section which is still free. So, process Pj can not be able to make any progress for a outside process which is not in critical section. Hence, progress is not satisfied. Now, let say, continuing as per the above situation, process Pj also preemptes after few time. Till that, Pi not comes back yet. Now, say process Pi comes and wants to execute its own while part which is also becomes true becoz of process Pj made flag[j]=true. In this situation, Process Pi is also waiting and its own progress hampers becoz of a process which is outside of critical section. Remember, Critical section is still free. So, based on the above cases, these 2 process are in deadlock while mutual exclusion condition can be still satisfied only as one process can enter in CS alone. So, correct is (A), along with that the full answer is only ME is satisfied with deadlock.

Answer 2

Ans is (D)

here mutual exclusion and progress both are guranteed.

bounded waiting is also guranteed. As per Operating System Concepts by Galvin, "There exists a bound on the number of times that other processes are allowed to enter their critical sections after  a process has made a request to enter its critical section and before that request is granted."

in option A they are talking about m/e only so A is wrong.

in option B they said m/e and b/w are guranteed only. means they indirectly saying progress is not guranteed. so B is wrong.

in C they said progress is satisfied only. so C also wrong.

in D they said m/e and progress guranteed. Here they didnt mention anything negative about b/w so we can not think b/w is not satisfying. therefore D is correct.

I hope you got my point.