How can we make sure that $)$ will be executed before $S2()$ in the following two threads?

Semaphore sync $=0$;

Th$1$:

Th$2$ :

$(1)(2)$

S$1()$ ;

S$2()$;

$(4)$

$(1)$ empty

$(2)$ sem$\_$wait$($sync$)$;

$(3)$ sem$\_$post$($sync$)$;

$(4)$ empty

$(1)$ empty

$(2)$ sem$\_$post$($sync$)$;

$(3)$ sem$\_$wait$($sync$)$;

$(4)$ empty

$(1)$ sem$\_$wait$($sync$)$;

$(2)$ sem$\_$wait$($sync$)$;