MadeEasy Subject Test: Operating System - Process Synchronization

Question

I don't know how to check for bounde wait. How does it fails. please explain taking this question as example.

Comments

S1=3 ,S2=2 S3=1

In Bounded waiting there must be bound on process to get a chance to enter into CS

If we execute three process at a time all are entering and make S1=0.

If we execute second opearation i.e)S2 only two process are entering and one is struct. // S2=0

Execute third opeartion S3 only one process enter the CS other is struct here.

When executed process leave the CS it is not allowed immediately because S1=0 and make S3=1.

whichever process is strct at S3 i.e)is allowed.

So we can say there is bound to get chance.

Ex:p1,p2,p3(arriving order)

P1(CS),P2(strck on S2) and P3(struck on S1)

after sequence is P2 (enter Cs) follwed by P3....

---

ok..thanks for explaining :)

---

Consider a process does P(s1) and then P(s2) now another process comes and it goes repeatedly in CS section, so bounded wait should also not be satisfied, right???

But progress should be satisfied, I think, bcoz only those process that want to enter CS take part in decision and when no process is in CS other process is not denied.

---

@Vijaycs

If you closely observe it is same as lock variable with constraints of a semaphore. Since S2 and S3 will not affect over here. Whatever the value has been assigned to S3 and S2 only one process can enter into the critical section.

---

What is the explaination given by ME for D)...?

---

They didn't give any explaination :D

 I think it should not be bounded waiting, but if we think like the code isn't present within 'while(true)' , then the waiting is necessarily bounded. So my doubt is whether we should consider while(true) by ourselves or not?

---

If while (True) is not there, there is no need to assume.

---

then it's bounded waiting. m I right?

---

Yes ..

---

Even if "While(true)" is there, still it would satisfy bounded waiting

---

If while was used then no bounded wait, otherwise bounded wait satisfied, progress is stasfied anyway while used or not same for mutual exclusion.

---

@Rahul. Could you explain that if while was used, why the bounded wait be dissatisfied?

---

Consider a situation Process1 comes and does P(s1) and p(s2) and then another process comes and repeatedly goes in CS and during that if process1 tries it is blocked.

---

So you are keeping out Process 1 out of race. Thats not BW def.

BW says that when processes are competing, if it happens that any process never gets a resource then BW is hampered.

Now, where does your situation fit here?

---

Basically , process 1 is blocked on S3. SO, when other process get out, Process 1 will be signalled.

---

Bounded wait says when a process wants to enter CS it can be denied only a finite no. Of times or we can say there is a bound on other processes entering CS.

---

Yes signlling is done and that is why progress is satisfied.

---

Your 2nd def is incorrect. See this https://gateoverflow.in/39719/gate-2016-1-50#c75224

Let me check for 1st def and tell you.

---

@Rahul. The situation which you have put forth is quite a possible scenario. So, you are true. If while is there BW may not be satisfied.

But I still doubt. The reason is if queue is maintained for blocked processes on S3, then it would surely satisfy BW

---

We can't assume queue is there. Anyway here BW is not satisfied.

If we use queue then order of execution becomes sequential i.e. first come first served. Which is not required always.

---

Yes, ur right. The short term scheduler woul decide which to schedule once any blcoked process is unblocked and not necessarily in FCFS. Anyways, thanks for explanation :)

---

I think D is right Option , obviously Mutual exclusion is guaranteed.

---

its guranted. Could you tell why its not?

---

Why mutual exclusion not valid? Suppose I take 3 process runs in parallel all decreases S1 value from 3 to 0,then 2 process decrease S2 value 2 to 0 and S3 is 1 only so only one process can down all S1 and S2 and S3 value to 0 and enter CS.Other process will be looping before CS.

---

I see now... Mutual exclusion is gaurantee.

---

Sushant pls explain how mutual exclusion is guaranteed..

---

Had S3>=2 then more than 2 processes could enter the CS. But, S3=1 which implies only 1 process can enter CS. Simple.

---

How bounded waiting is satisfied?

---

plz explain progress in this question

---

plz explain progress on this question

Answer 1

bounded waiting is satisfied as  each process has bounded wait of atmost of 2 process(at worst case)..even if a process comes out of cs and again wishes for CS then it has bounded wait of atmost 2 process ..hence bounded waiting satisfied