OS Semaphore

Question

Consider the methods used by process $P_{1}$ and P2 for accessing their critical sections whenever needed, as given below. The initial values shared Boolean variables, $\mathrm{S}_{1}$ and $\mathrm{S}_{2}$ are random assigned..
\begin{tabular}{|l|l|}
\hline Method used by $\mathrm{P}_{1}$ & Method used by $\mathrm{P}_{2}$ \\
\hline do & do \\
\hline 1 & 1 \\
\hline flag $[/]=$ True;
\[
S_{1}=S_{2}
\] & flag $[j]=$ True;
\[
S_{1}=S_{2}+1 ;
\] \\
\hline & \\
\hline & \\
\hline ) while(1); & ) while(1): \\
\hline
\end{tabular}

For the program to guarantee mutual exclusion, the predicate P and Q in the while loop should be
a.
$\mathbf{P}$ : Flag $[J]=$ true and $\mathrm{S}_{1}!=\mathrm{S}_{2}$
Q : Flag $[t]=$ true and $\mathrm{S}_{1}==\mathrm{S}_{2}$
b.
$\mathbf{P}:$ Flag $[\eta]=$ true and $\mathrm{S}_{1}==\mathrm{S}_{2}$
$\mathbf{Q}:$ Flag $[t]=$ true and $\mathrm{S}_{1}!=\mathrm{S}_{2}$
$\mathbf{P}$ : Flag $[t]=$ true and $\mathrm{S}_{1}!=\mathrm{S}_{2}$
c.

Q : Flag $[\lambda]=$ true and $\mathrm{S}_{1}=-\mathrm{S}_{2}$
$\mathbf{P}$ : Flag $[t]=$ true and $\mathrm{S}_{1}==\mathrm{S}_{2}$
d. $\mathbf{Q}$ : Flag $[J]=$ true and $\mathrm{S}_{1}!=\mathrm{S}_{2}$

Comments

is it B??

Answer 1

Correct Answer is A.

Comments

Opt A will disobey mutual exclusion

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yes bro you are right...answer should be A..

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What is the problem with ans D?

Answer 2

Correct Ans should be Opt B