Re: [TCLCORE] TIP 233 inquiry, from long in the past

[Kevin K. <kev...@gm...>]

[Adding a cc: to tcl-core so that we don't have to repeat the discussion
there.]

On Tue, May 13, 2025 at 4:32 PM Andreas Kupries <and...@gm...>
wrote:

> Harald asked me today about
>
> https://core.tcl-lang.org/tips/doc/trunk/tip/233.md
>
> which virtualized Tcl's sense of wall clock time.
>
> Given that the work was done 21 years ago I do not remember anymore
> the purpose behind the reasons stated in the TIP.
>
> While I am pretty sure that this was asked for by a customer of
> ActiveState, I do not truly remember which, and what use they had for
> this feature.
>
> My mind seems to be thinking Cisco, but also throws out Synopsys.
> Both are sensible possibilities (Network and other simulation stuff).
>
> As the TIP's link to the reference implementation,
> https://sourceforge.net/p/tcl/patches/393,
>
> references you as owner of that patch/ticket, I hope that you may also
> remember things about this feature, beyond my own recollection.
>
> This topic has come up because this virtual time interferes with
> current efforts towards monotonic time for the core.


What I recall about the ticket was what I posted on tcl-core a few days
ago. I understood what virtual time was about - allowing a production
script to run in simulated time rather than real time, while continuing to
interact with real I/O devices.  (It's also used in some highly secure
systems to avoid certain timing-dependent covert channels for data
exfiltration.)

I never knew the details of the intended application - you and Jeff were
under an NDA with the customer, and were not at liberty to disclose them.
My name was on the ticket, because I was the maintainer of the time system
at the time.  I allowed it in primarily because it had no effect on a build
that didn't use it.  The TIP was approved at a time when we were not
extremely formal about the process. My reasoning was "it's something an
ActiveState customer needs, and can't be done without surgery on the Core -
and this particular surgery is relatively minimal, since the functionality
is activated only by invoking an unusual API."

I never knew the identity of the customer, and as far as I know, nobody
else has ever demanded virtualization of the clock.

-- 
73 de ke9tv/2, Kevin