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From: Eric Blake <ebb9@byu.net>
Subject:  Re: cygwin 1.7.0-28: Broken pipe signal broken?
Date: Mon, 25 Aug 2008 15:50:17 +0000 (UTC)
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Christopher Faylor <cgf-use-the-mailinglist-please <at> cygwin.com> writes:

> >The parallel make is hit and miss; I've seen make go for quite some time
> >without failures.  I'm also seeing occasional failures with gcc -pipe.
> >But it looks like I've finally stumbled on a 100% reproducible testcase,
> >in the m4 testsuite.  /home/eblake/m4/build/src/m4 is a self-built m4 from
> >the latest m4.git; when I replace that string with /bin/m4, I don't see
> >the failure, so it might be something added in m4.git since m4 1.4.10b
> >that tickles the behavior; I'm still trying to set up a decent debugging
> >session to catch that.  I'll continue trying to trim it down even further,

I tried.  But it proved very difficult.  Even adding a usleep(0) in the code 
made it go away, so I couldn't even figure out how to attach a debugger in time 
to see the bug in action; it was definitely a form of data race between writing 
data to a pipe and calling exit(), where the mere call to usleep(0) was enough 
to avoid the race.

> 
> I don't understand how this is a useful test case.  I obviously don't
> have the /home/eblake/m4/build/src/m4.  I looked on sourceware and there
> is no file there either.

Yes, that file was only on my machine; sorry that I made it so hard for you.  I 
suppose you could have built your own m4 from scratch from m4.git, but that's 
asking too much from a STC.

> 
> Have you tried the latest snapshot?  I made a grasp-in-the-dark change
> there.

Whatever you did made a difference.  Everything I've tried with a self-built 
cygwin1.dll with your change has worked without issues, where it was previously 
failing, including my (private) m4 build that was showing the problem every 
single test run.

-- 
Eric Blake




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