Re: [PATCH 1/1] mingw: optionally disable side-band-64k for transport
- Date: Tue, 30 Apr 2019 18:37:06 -0400 (DST)
- From: Johannes Schindelin <Johannes.Schindelin@xxxxxx>
- Subject: Re: [PATCH 1/1] mingw: optionally disable side-band-64k for transport
On Mon, 29 Apr 2019, brian m. carlson wrote:
> On Mon, Apr 29, 2019 at 03:04:36PM -0700, Thomas Braun via GitGitGadget wrote:
> > From: Thomas Braun <thomas.braun@xxxxxxxxxxxxxxx>
> > Since commit 0c499ea60f (send-pack: demultiplex a sideband stream with
> > status data, 2010-02-05) the built-in send-pack uses the side-band-64k
> > capability if advertised by the server.
> > Unfortunately this breaks pushing over the dump git protocol if used
> > over a network connection when using MinGW (but *not* when using
> > mingw-w64).
> > The detailed reasons for this, are courtesy of Jeff Preshing, quoted
> > from https://groups.google.com/d/msg/msysgit/at8D7J-h7mw/eaLujILGUWoJ:
> > MinGW wraps Windows sockets in CRT file descriptors in order to
> > mimic the functionality of POSIX sockets. This causes msvcrt.dll
> > to treat sockets as Installable File System (IFS) handles,
> > calling ReadFile, WriteFile, DuplicateHandle and CloseHandle on
> > them. This approach works well in simple cases on recent
> > versions of Windows, but does not support all usage patterns.
> > In particular, using this approach, any attempt to read & write
> > concurrently on the same socket (from one or more processes)
> > will deadlock in a scenario where the read waits for a response
> > from the server which is only invoked after the write. This is
> > what send_pack currently attempts to do in the use_sideband
> > codepath.
> Since this is a platform-specific issue, can we address this using a
> compile-time constant instead of a config option? It would be better to
> do the right thing automatically in this case and not have to have
> people set a config option. It will also allow us to not to have to
> maintain a config option indefinitely if MinGW becomes more capable in
> the future.
I was really not sure at the time whether this would be fixed in MinGW at
some stage, and with the switch to mingw-w64 (by moving from MSys to MSYS2
as of Git for Windows 2.x) we do not really have any concrete need for it
I just thought that it might benefit somebody (it was my impression that
Hannes Sixt still built his own copy with MSys/MinGW, and we do have a
track record of maintaining certain things even for single users, see e.g.
our insistence on creating the .git/branches/ directory upon `git init`).
But if the consensus is that we do not need this at all anymore, I'll be
just as happy to drop that patch.