Consider the code below of the two processes $P_1$ and $P_2.$ Which of the following initial values

of $S$ and $Q$ may cause indefinite blocking for one or both processes.

$($a$)S=2,Q=2$

$($b$)S=2,Q=1$

$($c$)S=1,Q=2$

$($d$)S=1,Q=1$

$($e$)$ None of the above

Assume that a semaphore named $"$S$"$ already exists. The result of calling sem$\_$open as shown

below is

#define PERMS $($mode$\_$t$)($S$\_$IRUSR $|$ S$\_$IWUSR $|$ S$\_$IRGRP $|$ S$\_$IROTH$)$

#define FLAGS $(0\_$CREAT$)$

$...$

sem$\_$open $("$S$",$ FLAGS, PERMS, $2)$;

$($a$)$ Changing the permissions on the existing semaphore to PERMS, and setting its value to $2$

$($b$)$ Ignoring PERMS and setting the value of the semaphore is $2$

$($c$)$ Both PERMS and the value $($that is $2)$ will be ignored

$($d$)$ A new semaphore with is created with the same name, and its access permissions are set

to PERMS and its initial value is set to $2$

$($e$)$ None of the above

Which of the following functions is used to remove a named semaphore from the system?

$($a$)$ sem$\_$unlink

$($b$)$ sem$\_$destroy

$($c$)$ sem$\_$close

$($d$)$ None of the above