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Date: Tue, 14 Sep 2010 18:16:36 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: 1.7.5: Occasional failure of CreatePipe or signal handing due to 	thread-unsafe code in cwdstuff::set
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On Sep 14 18:11, Corinna Vinschen wrote:
> On Sep 14 10:12, Corinna Vinschen wrote:
> > On Sep 13 19:47, John Carey wrote:
> > > Anyway, it looks to me as if overwriting the path in an existing
> > > VistaCwd instance would confuse RtlGetCurrentDirectory_U() and
> > > probably other Win32 API functions.  (It may be that the same is
> > > true for the handle member; I have not tried to find that out.)
> > > Cygwin should probably allocate a new VistaCwd instance,
> > > as does the Win32 SetCurrentDirectory() implementation.
> > 
> > Hmm, I'm still wondering.  In theory we don't have to replace the
> > directory name.  We just have to InterlockedExchange the handle, since
> > we only need to replace the original handle which does not allow
> > sharing-for-delete with our own handle which does.
> > 
> > All other border cases (virtual dir, directory with restricted rights)
> > can be rightfully handled by setting the Win32 CWD to \\?\PIPE\ again.
> > 
> > That's at least worth a try, isn't it?
> 
> I applied the below patch to Cygwin CVS and it appears to work nicely.

Sorry, that wasn't what I was trying to say.  Actually, I'm using this
code just locally for now and put it up here for discussion and for
curious testers.  I intend to apply it only, if we can agree that it's
sufficient.

> The only potential race I can think of is, if another thread of the same
> Cygwin process calls SetCurrentDirectory.  I'm inclined to let this
> situation slip through the cracks since SetCurrentDirectory will already
> mess up a mixed-mode Cygwin process.
> 
> The "wincap.has_transactions ()" is just for testing.  If we can use
> that code, I would replace is with something like
> "wincap.has_messed_up_cwd_handling()" or so.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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