Consider the partial program below which includes a main$()$ and threaded runner function that use a semaphore. This program contains a conceptual problem with the way it uses the semaphore, what is it$?$ Identify the problem, and explain why it occurs. Assume all syntax is correct.

Useful Functions:

int sem$\_$init$($sem$\_$t $*$sem$,$ int pshared,

unsigned int count$)$;

int sem$\_$wait$($sem$\_$t $*$sem$)$;

int sem$\_$post$($sem$\_$t $*$sem$)$;

#define NUM$\_$ACTIVE $2/*$ number of threads allowed in critical section at once $*/$

#define NUM$\_$THREADS $5/*$ number of threads total $*/$

sem$\_$t sem,

void$*$ thread$\_$job$($void$)\{$

if $($sem$\_$wait$($&sem$)==-1)\{$

fprintf$($stderr$,$ "Failed to lock!

$")$;

$\}$ else if $($sem$\_$wait$($&sem$)==0)\{$

$//[$do some non$-$critical stuff$]$

$//[$critical section goes here$]$

sem$\_$post$($&sem$)$;

$//[$more non$-$critical stuff$]$

$\}$

$\}$

int main$($void$)\{$

pthread$\_$t tids$[$NUM$\_$THREADS$]$;

sem$\_$init$($&sem, $0,$ NUM$\_$ACTIVE$)$; $//$ initialize semaphore

for $($int i$=0$; i $<$ NUM$\_$THREADS; i$++)$

pthread$\_$create$($&tids$[$i$],$ NULL, thread$\_$ job, NULL$)$;

For $($int i #l O; i L NUM$\_$ THREADS; i$++)$

pthread$\_$join$($tids$[$i$],$ NULL$)$;

$\}$