SemLock = Semaphore->new (....)  # some where global in the script

if(sem) {
    SemLock->lock()
    sem->lock()
    SemLock->unlock()
}
else {
    SemLock->lock()
    sem= new Semaphore(....)
    sem->lock()
    SemLock->unlock()
}
doStuff()
sem->unlock()