Hello,
It is my opinion that you should not close a port which you have not opened.
OsX  allows different programs to open one serial communications port, which
means that
the system knows how many times a particular port was opened. I think it
also assigns separate buffers
every time an open statement is executed, but then again, I never got to see
the Os X source code...
What you are trying to do right now, is to make your program as bulletproof
as possible, so why
not keep track of your luggage yourself, rather then depend on something you
can't control?

It will not ?unleash? a demon, it is already there - a.k.a. the mess fairy.
Best regards, Kris