Re: Warning from libgomp during make check

[Mike Miller]

On Fri, Sep 26, 2014 at 10:22:41 -0700, Rik wrote:
> All,
>
> Is anyone else seeing this warning during the test for imfinfo.m during
> 'make check'?
>
> libgomp: Invalid value for environment variable OMP_NUM_THREADS
>
> I can manually reproduce it outside of 'make check' by doing
>
> ./run-octave -cli -f
> test nproc.cc
> test imfinfo

I don't know that I saw that during the code sprint when I added the
setenv-to-empty-string, but it makes sense.

> The issue seems to be the test code in nproc.cc which is
>
> %!test
> %! c = nproc ("current");
> %! unwind_protect
> %!   old_val = getenv ("OMP_NUM_THREADS");
> %!   new_val = c + 1;
> %!   setenv ("OMP_NUM_THREADS", num2str (new_val));
> %!   assert (nproc ("overridable"), new_val);
> %! unwind_protect_cleanup
> %!   if (! isempty (old_val))
> %!     setenv ("OMP_NUM_THREADS", old_val);
> %!   else
> %!     setenv ("OMP_NUM_THREADS", "");
> %!   endif
> %! end_unwind_protect
>
> At the end of the test, because we don't have unsetenv(), the environment
> variable is cleared to the empty string.  According to the Matlab
> documentation, "setenv (name)" is equivalent to "setenv (name, "")" which
> on a Windows system undefines the variable.  On a UNIX system, however, one
> can have a defined environment variable with an empty value.
>
> Perhaps we should deviate from Matlab here and if the two argument form is
> used, then set the environment variable to whatever value is offered
> including the null string.  But if the number of arguments to the function
> is 1 then we call unsetenv with the name of the variable.

How about keeping setenv the way it is and adding an unsetenv
built-in? This would follow the existing practice of adding standard C
library functions that make sense to have in Octave for completeness,
even if they are not available in Matlab, and keep setenv
Matlab-compatible.

I also think it might be useful to allow setenv (name, "") as it is
now. There might be reasons to want to set an empty value rather than
delete a variable. When I added that cleanup, I wasn't thinking that
it would delete the variable, but that it would set it to an empty
string (which it does) and that OpenMP wouldn't care (but it does).

-- 
mike