Upgrading Perl... Somebody just shoot me and put me out of my misery!

[Ronald F. Guilmette]

In message <17D096510A47C61858D55B19 at atuin.in.mat.cc>, 
Mathieu Arnold <mat at FreeBSD.org> wrote:

>+--On 22 novembre 2013 12:40:07 -0800 "Ronald F. Guilmette"
><rfg at tristatelogic.com> wrote:
>|    1) Change the option in lang/perl5.16:
>|         make -C /usr/ports/lang/perl5.16 config
>| 
>| HUH??  I don't understand this at all.  What exactly is "the option" that
>| we are changing here?  And what does it matter to anything?
>
>Like it is written in the paragraph before, the default option for perl has
>changed, *if* you want to switch from non threaded to threaded, you also
>need to change your perl configuration.

OK, but please help me understand here.  What is it, exactly, that is _now_
being threaded, that wasn't threaded before?

Is it the guts of the Perl interpreter itself?

Is it the Perl programs that get interpreted by the interpreter?

(Part of what is confusing about this is that I was under the impression...
perhaps naive... that Perl was already set up for threads support quite some
long time ago.)