bug#12430: Glitches caused by addition of psec to timers

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> > Wouldn't it be better to leave timers at their previous size of 8, and
>> > instead allow the usecs element be a floating-point number?
>> I doubt there's code out there that depends on the size of
>> this structure, so adding fields to it should be safe.
> But NOT adding fields is even safer, no?

In general, yes, but not if it is replaced by modifying another field.
And since the danger that we're trying to avoid is vanishingly small,
I'd rather not worry about it.  If/when someone bumps into a package
that breaks because of it, we will see what to do.

> I will remember that when I write a hard-realtime application in
> Emacs Lisp.

Nanoseconds are real.  Think about it: if the eldoc timer is always late
by a nanosecond each time, over your whole lifetime this might add up to
your wasting a measurable amount of your life waiting unnecessarily.
Do you really want to die cursing those wasted nanoseconds?
I didn't think so,


        Stefan