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From Martin Sebor <>
Subject num_get thread safety tests (was: Re: next steps)
Date Fri, 03 Aug 2007 18:06:46 GMT
[redirected to stdcxx-dev from a private thread]

Travis Vitek wrote:
> As mentioned, I'm already started on the locale tests. I'm actually
> thinking it might make more sense to have the new test
> [] verify the correctness of the output as well
> as the mt safety of the get operations. The existing
> test could remain as-is, or maybe I should just
> roll both the get and put tests into one?

I suppose that would be okay just so long as it's possible to still
exercise one facet without the other. Which I suspect might defeat
your goal of integrating the testing of both facets into the same

The problem with creating a dependency between the two facets is
that a bug in one might prevent the other from ever being tested
or might cause false positives in the other, making debugging the
problem more difficult. At the same time, exercising both of the
facets simultaneously would be valuable in its own right so it
would be nice to be able to do both.

An idea that would let us have it both ways is to integrate the
tests for both (all three when you count numpunct) facets into
the same program, still keeping the option of running them
independently of one another, exercising them all at the same
time by default and, when one fails, invoking the program again
and exercising them independently, one after another. This
approach would involve at least two processes: one to drive and
monitor the tests, and another one or more running the tests
themselves. The infrastructure for this approach has already been
put in place: see the rw_process_create() API in the test driver.
Unfortunately, the tests for the API have been failing on a number
of platforms so there are issues with it that remain to be resolved.

> So here is a quick one for you. The locale facets are all templatized on
> the iterator type. For simplicity I'm thinking that I should just
> instantiate the facets using character pointers instead of the default
> [i,o]streambuf_iterator template. This will avoid testing the stream buf
> iterators in each of the facet tests. Do you have any issues with that?

This approach makes the assumption that the implementations of
the facet specializations for charT* are the same as those for
the streambuf_iterators. This happens to be a safe assumption
to make at the moment but it might change in the future. The
other "issue" with this approach is that the specializations
that are used in the vast majority of cases are those on
the streambuf iterators and not those on pointers.

So I would suggest to roll your own very simple iterator derived
from streambuf_iterator that operates on a plain character buffer.
There should be examples of how to do this in the test suite,
including the test driver itself (see the header rw_streambuf.h).


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