[bug#35666] [PATCH 0/2] Build a thread-safe hdf5 library

[Eric Bavier <bavier@cray.com>]

I think this should be fine, though I've not heard of anyone who has relied on this feature.  The "unsupported" part here is that the posix lock used for thread-safety is not hoisted into the higher-level API calls.  So if your colleague is using the C++ interface and expecting thread-safety, they are out of luck.  So the disclaimer is that only the low-level C interface gains thread-safety, and the rest are no better.

Eric Bavier, Scientific Libraries, Cray Inc.

________________________________________
From: Ludovic Courtès <ludovic.courtes@inria.fr>
Sent: Friday, May 10, 2019 08:07
To: Ricardo Wurmus
Cc: Eric Bavier; pgarlick@tourbillion-technology.com; 35666@debbugs.gnu.org
Subject: Re: [bug#35666] [PATCH 0/2] Build a thread-safe hdf5 library

Hi!

Ricardo Wurmus <rekado@elephly.net> skribis:

> Ludovic Courtès <ludo@gnu.org> writes:

[…]

>> It also tells you that, if you insist, you can go ahead and pass
>> ‘--enable-unsupported’, but you’re on your own.
>>
>> We found that Debian chose to pass ‘--enable-unsupported’, and indeed
>> that seems to be saner than providing a variant that does very little,
>> but does it in a thread-safe way.
>
> What other effects does “--enable-unsupported” have?  I see that in
> Fedora “--enable-threadsafe” was removed in 2008 because it’s
> “incompatible with --enable-cxx and --enable-fortran”.

“--enable-unsupported” allows you to force a build that combines C++,
Fortran, and thread-safety.  If you don’t pass that flag, you have to
choose between thread-safety and C++/Fortran¹.  A tough choice!

> Instead they seem to be building different flavours: one with
> --enable-fortran, another with --enable-cxx, yet another with MPI and
> --enable-parallel.

Problem is, my colleagues have code that expects both C++ and
thread-safety (as crazy as it might seem).  They were using the Debian
package until now and hadn’t realized about this.

> Do we have contact to the hdf5 developers to ask what the implications
> of “enable-unsupported” are?

I think it’s a warranty-void kind of flag: by passing it, the user
asserts they understand they’re using a configuration not “officially
supported” by the HDF Group, meaning that if it’s buggy, we’re on our
own.

Thoughts?

Ludo’.

¹ You would think it’s an April fool’s day prank, but it’s not!  We’re
  in May, at least in my timezone.