GATEverse — GATE CSE previous year questions

Consider the following two threads $\mathrm{T} 1$ and $\mathrm{T} 2$ that update two shared variables $\mathrm{a}$ and $\mathrm{b}$ . Assume that initially $\mathrm{a}=\mathrm{b}=1$ . Though context switching between threads can happen at any time, each statement of $\mathrm{T} 1$ or $\mathrm{T} 2$ is executed atomically without interruption. $\begin{gathered}\mathrm{T} 1 \\ \mathrm{a}=\mathrm{a}+1; \\ \mathrm{~b}=\mathrm{b}+1;\end{gathered}$ $\quad$ $\begin{gathered}\mathrm{T} 2 \\ \mathrm{b}=\mathrm {2 * b}; \\ \mathrm{a}=\mathrm 2 * {a}; \end{gathered}$ Which one of the following options lists all the possible combinations of values of a and b after both T1 and T2 finish execution?

(A)

$(\mathrm{a}=4, \mathrm{~b}=4) ;(\mathrm{a}=3, \mathrm{~b}=3) ;(\mathrm{a}=4, \mathrm{~b}=3)$

(B)

$(\mathrm{a}=3, \mathrm{~b}=4) ;(\mathrm{a}=4, \mathrm{~b}=3) ;(\mathrm{a}=3, \mathrm{~b}=3)$

(C)

$(\mathrm{a}=4, \mathrm{~b}=4) ;(\mathrm{a}=4, \mathrm{~b}=3) ;(\mathrm{a}=3, \mathrm{~b}=4)$

(D)

$(\mathrm{a}=2, \mathrm{~b}=2) ;(\mathrm{a}=2, \mathrm{~b}=3) ;(\mathrm{a}=3, \mathrm{~b}=4)$