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Date: Thu, 23 May 2013 23:14:58 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: make, PATH & "Win32 error 487"
Message-ID: <20130523211458.GA12260@calimero.vinschen.de>
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References: <alpine DOT LFD DOT 2 DOT 03 DOT 1305230950500 DOT 1918 AT mcs DOT anl DOT gov> <20130523160711 DOT GB25295 AT calimero DOT vinschen DOT de>
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On May 23 18:07, Corinna Vinschen wrote:
> On May 23 10:14, Satish Balay wrote:
> >   [...]
> > - It appears to be related to the huge length of one of the commands - and
> >   length of PATH
> > - I tried it on 3 different machines [with differences in default installed software]
> >   win2008/x64  - breaks when PATH is over 1.5K chars
> >   win2003/x32 - breaks when PATH is over  2K chars
> >   win7/x32    - breaks when PATH is over 20K chars.
> > 
> > Any ideas on how to debug this further to better understand the issue
> > - or workarrounds? This is with latest cygwin [and rebaseall done
> > correctly]
> 
> There's perhaps not much you can do.  First of all, the problem is known
> for a while, but even though we're trying a lot of stuff to make sure
> that fork works, the OS has some funny notions sometimes, which make it
> hard to get fork 100% reliable.
> 
> In this case, there's a subtil difference between the first shell
> started from make, and a forked subshell.  The difference is something
> to do with the size of $PATH which results in a different position of
> the main stack in the forked child process.  This breaks fork because
> fork semantics require to be able to reproduce the parent memory in the
> child process.
> 
> Thanks for the test case.  I'm just investigating what happens exactly,
> and I have a few ideas how we can workaround this problem to make fork
> a bit more reliable in this situation.  This requires some fiddling
> around, so, just stay tuned for a couple of days.

After some experimenting, it looks like I found a surprisingly simple
solution.  I checked in a patch to CVS, and I'm just generating a new
developer's snapshot.  Please try the just uploaded today's snapshot
from http://cygwin.com/snapshots/  Exchanging just the DLL should be
sufficient.  Please report back.

Btw., there's an upper bound for the size of a single environment
variable of about 32K.  Right now, if $PATH reaches this size, forking
any further process fails silently.  I don't know why yet, but as far
as I'm concerned this is no pressing issue.


Corinna

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

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