[Development] Incorporating Intel Threading Building Blocks into Qt? (Was: Evolving Qt's multithreading API)

[Thiago Macieira]

On quinta-feira, 28 de fevereiro de 2013 18.35.23, Sze Howe Koh wrote:
> On 23 February 2013 00:16, Thiago Macieira <thiago.macieira at intel.com> 
wrote:
> > On sexta-feira, 22 de fevereiro de 2013 19.26.06, Sze Howe Koh wrote:
> >> Actually, I just realized that the open-source "flavour" of TBB is
> >> licensed under GPLv2 (http://threadingbuildingblocks.org/Licensing).
> >> Doesn't that mean that Qt TBB, if it were to become reality, can't be
> >> licensed under the LGPL?
> > 
> > It's GPLv2+exceptions:
> > 
> > The source code of Threading Building Blocks is distributed under version
> > 2
> > of the GNU General Public License, with the so-called "runtime exception,"
> > 
> > as follows (or see any header or implementation file):
> >    As a special exception, you may use this file as part of a free
> >    software
> >    library without restriction.  Specifically, if other files instantiate
> >    templates or use macros or inline functions from this file, or you
> >    compile
> >    this file and link it with other files to produce an executable, this
> >    file does not by itself cause the resulting executable to be covered by
> >    the GNU General Public License.  This exception does not however
> >    invalidate any other reasons why the executable file might be covered
> >    by
> >    the GNU General Public License.
> > 
> > I believe it's the same exception as the one in GNU libstdc++
> 
> Apparently, one legal team out there came to the conclusion that, if a
> non-GPL project incorporates TBB, someone with access to the project's
> source could then re-release the whole project under GPL, even if it
> was proprietary [1]

"Some legal team" does not help, of course. But I did a little more digging 
and it looks like the exception is not like libstdc++'s. The one there is a 
MUCH longer text. It's also not the short text found in GNU classpath.

Moreover, I've just noticed it says "you may use this file as part of a free 
software library". That means if you're not doing a free software library, it 
does not apply.

> It sounds a bit far-fetched to me, but it would probably be prudent
> for us to get an official response from Digia's legal team before we
> go ahead, right?

Yup.

Bit I can also check with Intel's legal team what the intention was. They may 
not give a legal opinion, but the people behind TBB might be able to say what 
their intention was.

Also note that TBB is available under a commercial license too.

> So, TBB is the shiniest at the moment, as it can replace all of
> QtConcurrent's functionality and more. I'm happy to set up the project
> to Qt-ify TBB, if people think it's a good idea and if we get a legal
> green light.
-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
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