Re: [Qemu-devel] [PATCH] win32: replace custom mutex and condition variable with native primitives

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Mon, 3 Apr 2017 18:12:34 +0000
Andrew Baumann <Andrew.Baumann@microsoft.com> wrote:

> > From: Cornelia Huck [mailto:cornelia.huck@de.ibm.com]
> > Sent: Monday, 3 April 2017 7:20
> > 
> > On Fri, 24 Mar 2017 15:01:41 -0700
> > Andrew Baumann <Andrew.Baumann@microsoft.com> wrote:
> > 
> > > From: Andrey Shedel <ashedel@microsoft.com>
> > >
> > > The multithreaded TCG implementation exposed deadlocks in the win32
> > > condition variables: as implemented, qemu_cond_broadcast waited on
> > > receivers, whereas the pthreads API it was intended to emulate does
> > > not. This was causing a deadlock because broadcast was called while
> > > holding the IO lock, as well as all possible waiters blocked on the
> > > same lock.
> > >
> > > This patch replaces all the custom synchronisation code for mutexes
> > > and condition variables with native Windows primitives (SRWlocks and
> > > condition variables) with the same semantics as their POSIX
> > > equivalents. To enable that, it requires a Windows Vista or newer host
> > > OS.
> > >
> > > [AB: edited commit message]
> > > Signed-off-by: Andrew Baumann <Andrew.Baumann@microsoft.com>
> > > ---
> > > The major implication of this patch is that it drops support for
> > > pre-Vista versions of Windows. However, those OSes are past their end
> > > of life, and other OSS projects have dropped support. e.g.; the last
> > > Cygwin release supporting XP was in Jun 2016. It doesn't seem like a
> > > good tradeoff to invest effort in fixing broken code needed to support
> > > them, so hopefully this isn't too controversial.
> > 
> > Just a quick question:
> > 
> > I noticed that this breaks builds on an old fc20-based installation I
> > run some mingw cross builds on (getting an undefined reference to
> > `_imp__TryAcquireSRWLockExclusive@4'). I should probably take that as a
> > trigger to update that installation ;), but wanted to confirm that this
> > is expected.
> 
> Yes, please try updating your mingw headers. I've done x64 cross-builds from Ubuntu 16.04 (WSL) using mingw-w64 4.0.4.

Yes, another, more modern cross-build setup works fine. I just was a
bit surprised that this mingw setup did not go back to Vista level.