Re: C++ fluency
On May 8, 2:01 am, Jerry Coffin <jcof...@taeus.com> wrote:
In article <e7bb1161-36fe-4e5b-85ec-
3efe895fd...@s16g2000vbp.googlegroups.com>, james.ka...@gmail.com
says...
[ ... ]
I think a better way of characterizing the problem is that
the various latencies are part of the "input". The problem
isn't that the code behaves differently for the same input;
the problem is that the set of input is almost infinite, and
that you usually have no way of controlling it for test
purposes.
I have no problem with that characterization. In fact, I'd
consider it useful in at least one respect -- it tends to
emphasize the similarity between this type of problem, and
some others that prevent testing due to inputs that are too
large to test exhaustively, or even sample meaningfully.
That is, in fact, the reason I used this way of characterizing
it.
(I've vaguely heard of systems for small, embedded
processors, where you could control the timing of external
events, but I've never actually seen one. And of course,
you have absolutely no control over when Windows or Unix
does a context switch.)
(And I'd simply love it if someone could prove me wrong
about the above.)
In both cases, you can exercise some control. That's rarely of
much use though.
As you said (or at least implied) elsethread, to be useful,
testing has to progress from the complexity of the code itself
toward something that's ultimately so simple we trust it
without testing.
That's really the key for just about everything.
In the case of attempting to demonstrate subtle thread
synchronization problems, the progression is in the opposite
direction -- even when a problem is quite obvious, getting it
to manifest itself within a reasonable period of time is often
quite difficult, and the code to do so substantially more
complex than the original code, or a corrected version
thereof.
Yes. I know I found a threading bug in the g++ implementation
of std::string (bug number 21334). I found it by code review.
I know it is there. But I don't know how to reliably reproduce
it; in fact, it requires a set of coincidences in the timing
that I don't think it's ever actually been triggered. But it's
an error, none the less.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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