X-Recipient: archive-cygwin@delorie.com X-SWARE-Spam-Status: No, hits=-1.8 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,TW_MK,TW_YG,T_TO_NO_BRKTS_FREEMAIL X-Spam-Check-By: sourceware.org MIME-Version: 1.0 In-Reply-To: References: <00c301cb3b22$ae416800$0ac43800$@gmail.com> <4C65A83F.4010608@redhat.com> <4C65AA3A.70303@redhat.com> Date: Fri, 13 Aug 2010 13:56:30 -0700 Message-ID: Subject: Re: Broken process substitution From: Daniel Colascione To: cygwin@cygwin.com Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-IsSubscribed: yes Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Delivered-To: mailing list cygwin@cygwin.com On Fri, Aug 13, 2010 at 1:44 PM, Daniel Colascione wrote: > On Fri, Aug 13, 2010 at 1:25 PM, Eric Blake wrote: >> Then again, cat should exist until something causes the input side of >> its pipe to declare EOF; so I guess there's no race in this example >> after all. =A0Rather, it looks like a limitation in cygwin1.dll. =A0I do= n't >> know why bash is unable to duplicate the output end of the pipe to the >> echo process, unless cygwin's /dev/fd handling doesn't work on pipes. >> But that's highly likely that you are dealing with yet another one of >> cygwin's pipe handling shortfalls. > > Would these shortfalls also explain why this script doesn't do what > I'd expect (that is, output "hello" and exit)? It just hangs right now > --- this is the ps output: Actually, the seemingly-equivalent version below works fine. Maybe there was a race between the cygpath's starting to read the fifo and the last line starting to write to it. The *real* bug seems to be triggered by the following commands: #!/bin/sh cd /tmp mkfifo blah ( echo hello > blah )& cat blah On other systems (OS X and Linux), that just outputs "hello", then both processes exit. On Cygwin, the writer is blocked indefinitely and has to be SIGKILLed --- even if a reader then starts. And the reader acts as if there were no writer at all. -------- #!/bin/bash set -e tmpdir=3D$(mktemp -dt cygfilter-XXXXXX) function cleanup() { rm -rf "$tmpdir" } trap cleanup 0 mkfifo "$tmpdir/f-out" mkfifo "$tmpdir/f-err" cygpath -u -f- < "$tmpdir/f-out"& cygpath -u -f- < "$tmpdir/f-err" >&2 & "$@" >"$tmpdir/f-out" 2>"$tmpdir/f-err" -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple