[RFC, Fortran] Avoid race on testsuite temporary files

[Yvan Roux <yvan dot roux at linaro dot org>]

Hi,

as it was raised in
https://gcc.gnu.org/ml/gcc-patches/2015-10/msg01540.html we experiment
random failures in gfortran validation when it is run in parallel (-j
8).  The issues occurs because of concurrent access to the same file,
the first two patches fixed some of them by changing the file names
used, but there are still remaining conflicts (6 usages of foo, 8 of
test.dat). This is easy to fix and I've a patch for that, but there is
another issue and I'd like to have your thoughts on it.

There is a little bit more than 1000 testcases which use IO without
explicit file names, ~150 use scratches (a temporary file named
gfortrantmp + 6 extra char is created) and the others, which only
specify the io unit number, use a file named fort.NN with NN the
number of the io unit. We see conflicts on these generated files, as
lot of testcases use the same number, the most used are:

10 => 150
99 => 70
6  => 31
11 => 27
1  => 23

I started to change the testcases to use scratches when it is possible
and before finding that there is that many to fix, and I also had
conflicts on the generated scratch names.  The options I see to fix
that are:

1- Move all these testcases into an IO subdir and change the testsuite
to avoid parallelism in that directory.
2- Use scratches when possible and improve libgfortran file name
generation, I don't know well fortran but is it possible to change the
file name patterns for scratches and io unit files ?
3- Change the io unit numbers used, as it was suggested on irc, but I
find it a bit painful to maintain.

Any comments are welcome.

Thanks
Yvan