Re: [PATCH] libstdc++: Allow std::condition_variable waits to be cancelled [PR103382]

[Jonathan Wakely <jwakely.gcc@gmail.com>]

On Tue, 7 Dec 2021 at 21:52, Florian Weimer wrote:
>
> * Jonathan Wakely:
>
> > On Tue, 7 Dec 2021, 21:20 Florian Weimer via Libstdc++, <libstdc++@gcc.gnu.org>
> > wrote:
> >
> >  * Jonathan Wakely via Libstdc:
> >
> >  > If necessary we could keep the terminate-on-cancellation behaviour as
> >  > _ZNSt18condition_variable4waitERSt11unique_lockISt5mutexE@GLIBCXX_3.4.11
> >  > and export the new behaviour as @@GLIBCXX_3.4.30, although this patch
> >  > doesn't do that.
> >
> >  Note that if this fix escapes into the wild and then you have to make
> >  the symbol version change, you will break newer applications.  In a few
> >  cases in glibc, we proactively added aliases at a different symbol
> >  version, but with the same implementation (at first).
> >
> > To be safe, we probably should preserve the old behaviour for the old
> > version of the symbol. If we decide that the new behaviour is always
> > preferable, we could change that later by making the old symbol an
> > alias for the new. If we don't decide that, we'll be glad we made it a
> > separate symbol.
>
> On the other hand, with separate versions, it's possible to reintroduce
> the old behavior at a later date, as a bugfix.  It's not strictly
> necessary to do that work upfront.  It's just nice to have this option.

Ah yes, a new symbol version gives us more flexibility in every direction.

> > I'll see if I can get it working with two versioned symbols. We don't
> > actually do that in libstdc++ currently, we only have a single version
> > of every symbol.
>
> Ping me if you want to discuss options. 8->

Thanks. I'll try it and let you know how I get on.

> Out of curiosity—do you support building libstdc++ (the shared object)
> with a different compiler than the included GCC?

No. Even using a different GCC is unsupported. I know of two people
who've tried using clang, for reasons. But it's unsupported.

You can use the installed libstdc++ headers and libs with other
non-GCC compilers, but not other versions of GCC. But you can't build
it with anything except the GCC built from the same revision of the
source tree.