Lock Variable

Question

What is Lock Variable solution to critical section problem?

Does it satisfy all the conditions like Mutual exclusion, Bounded waiting and Progress?

Comments

@Bikram Sir, I was not talking about Peterson's or Dekker's. I was referring to the simplest algo using Lock variable only and nothing else, for which I have written the pseudocode above.

Thanks for all the references.

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@pinaki

yes, i have seen it.. but the thing is we use lock to ensure Mutual exclusion property.

see the definition of lock , it is an object that can only be owned by a single thread at any given time .

so that means no two threads can acquire a same lock at same time , which leads to Mutual exclusion, is not it ?

And there are  2 operations we can perform on a lock:

• acquire: mark the lock as owned by the current thread; if some other thread already owns the lock then first wait until the lock is free. Lock typically includes a queue to keep track of multiple waiting threads.
• release: mark the lock as free (it must currently be owned by the calling thread).

So all it means ME is satisfied using Lock .. infact the purpose of lock is this .

And a good CS problem satisfy all 3 conditions like ME, BW and progress.

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lock variable does NOT guarantee MUTUAL EXCLUSION BOSS. those who are watching, don’t go by this. i think bikram you are making a mistake.

Answer 1

Refer to this PDF: https://cseweb.ucsd.edu/classes/fa05/cse120/lectures/120-l5.pdf

Answer 2

Peterson and Dekker's algo, both solves :

ME, BW and progress these three conditions.

Also progress is satisfied so deadlock is not possible ( bcoz progress done in finite time where as deadlock is infinite waiting).

Reference :

1. https://cs.stackexchange.com/questions/12621/contrasting-peterson-s-and-dekker-s-algorithms ( see 2nd answer , the table)
2. https://cs.stackexchange.com/questions/60235/is-bounded-waiting-ensured-in-given-version-of-dekkers-solution-for-critical-se

Comments

I mistook Dekker's as strict alternation..

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yes Dekker's satisfies all the three properties.

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@Bikram Sir,

In my understanding Lock Variable does not hold Mutual Exclusion and Bounded Waiting it can only hold Progress.

(If_i_am_Wrong)

Please give an example on Lock Variable .

Answer 3

lock  variable solution does not satisfy Mutual exclusion.