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Date: 8 Nov 2001 10:55:42 -0500
Message-ID: <20011108155542.19905.qmail@lizard.curl.com>
From: Jonathan Kamens <jik AT curl DOT com>
To: cygwin-developers AT cygwin DOT com
Subject: Debugging problem in peek_pipe in select.cc

I'm trying to debug why "make -j2" continues to hang for us
occasionally even after cgf's recent fix to the code in this area.

After deploying a cygwin1.dll with his fix, I ran two builds in a row
which both hung.  I didn't get much useful information out of them, so
I set things up to be able to debug better in case of future hangs,
and then started running builds.

I ran a whole bunch of builds over several days and none of them
hung.  Finally, one of them hung, and then one of my coworkers killed
and restarted it before I could debug it :-).

Shortly after that, I finally got another build to hang, and I'm
looking at that one now.  Here's the current roadblock preventing me
from understanding what's going on....

I attached to a hung process.  The top of its stack trace in thread 1
looks like this:

  #0  0x77f67a5b in ?? ()
  #1  0x61053b08 in peek_pipe (s=0x24aeee4, ignra=0, guard_mutex=0x1dc)
      at /u/jik/cygwin-cvs/src/winsup/cygwin/select.cc:453
  #2  0x61053eba in fhandler_pipe::ready_for_read (this=0x61544920, fd=6, 
      howlong=4294967295, ignra=0)
      at /u/jik/cygwin-cvs/src/winsup/cygwin/select.cc:512
  #3  0x61062b97 in _read (fd=6, ptr=0x24aeff2, len=1)
      at /u/jik/cygwin-cvs/src/winsup/cygwin/syscalls.cc:315
  #4  0x6108cbce in read (fd=6, buf=0x24aeff2, cnt=1)
      at /u/jik/cygwin-cvs/src/newlib/libc/syscalls/sysread.c:15

Line 453 of select.cc is a call to PeekNamedPipe.  According to the
MSDN documentation for PeekNamedPipe, it never hangs.  So, thinking
that frame 0 must be the PeekNamedPipe invocation, I typed "frame 0"
and then "finish" in a "gdb -nw" window (running inside an ssh session
to the Windows servers), and now it's hung.  How can that be?  I don't
get it.

^C has no effect at this point, so I can't get get to stop the process
and tell me where it is now.

Any suggestions?

  jik