GNU bug report logs - #49496
28.0.50; process-tests/fd-setsize-no-crash/make-network-process hangs on Cygwin

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Ken Brown <kbrown <at> cornell.edu>
Subject: bug#49496: closed (Re: bug#49496: 28.0.50; process-tests/fd-setsize-no-crash/make-network-process
 hangs on Cygwin)
Date: Fri, 09 Jul 2021 20:44:02 +0000

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Your bug report

#49496: 28.0.50; process-tests/fd-setsize-no-crash/make-network-process hangs on Cygwin

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 49496 <at> debbugs.gnu.org.

-- 
49496: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=49496
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

[Message part 2 (message/rfc822, inline)]

From: Ken Brown <kbrown <at> cornell.edu>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 49496-done <at> debbugs.gnu.org
Subject: Re: bug#49496: 28.0.50;
 process-tests/fd-setsize-no-crash/make-network-process hangs on Cygwin
Date: Fri, 9 Jul 2021 16:42:36 -0400

On 7/9/2021 2:18 PM, Eli Zaretskii wrote:
> Yes, OK.  But please explain there in a comment why we skip that, with
> a reference to this bug.

Done.  Closing.

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From: Ken Brown <kbrown <at> cornell.edu>
To: bug-gnu-emacs <at> gnu.org
Subject: 28.0.50; process-tests/fd-setsize-no-crash/make-network-process hangs
 on Cygwin
Date: Fri, 9 Jul 2021 14:01:33 -0400

The hang can actually be triggered by evaluating the following, extracted from 
the test in the subject:

(setq socket-name "/tmp/socktest/socket")
(delete-file socket-name)
(make-network-process :name "server"
                      :server 10
                      :buffer nil
                      :service socket-name
                      :family 'local
                      :coding 'no-conversion
                      :noquery t)
(make-network-process :name "client"
		      :service socket-name
		      :family 'local
		      :coding 'no-conversion
		      :noquery t)

The reason for the hang is that Cygwin does a blocking handshake in 
accept/connect to exchange credentials.  This can hang in certain situations in 
which connect is called before a listening socket is ready to accept connections.

It is possible to work around this problem by disabling the credential exchange 
as in the following patch:

diff --git a/src/process.c b/src/process.c
index b8c3e4ecfb..01548c8ab5 100644
--- a/src/process.c
+++ b/src/process.c
@@ -3355,6 +3355,12 @@ connect_network_socket (Lisp_Object proc, Lisp_Object 
addrinfos,
 	      xerrno = EMFILE;
 	      continue;
 	    }
+#ifdef CYGWIN
+	  /* Avoid possible hang in connect/accept.  */
+	  if (family == AF_LOCAL && p->socktype == SOCK_STREAM
+	      && setsockopt (s, SOL_SOCKET, SO_PEERCRED, 0, 0) < 0)
+	    report_file_error ("Cannot disable credential exchange", Qnil);
+#endif
 	}
        if (p->is_non_blocking_client && ! (SOCK_NONBLOCK && socket_to_use < 0))

But this seems too drastic just to fix a potential problem that doesn't seem to 
occur in practice, but only in the contrived situation of 
process-tests/fd-setsize-no-crash/make-network-process.  So my preference is to 
simply skip that test on Cygwin.

OK?

In GNU Emacs 28.0.50 (build 9, x86_64-pc-cygwin, GTK+ Version 3.22.28, cairo 
version 1.17.4)
 of 2021-07-09 built on moufang2
Repository revision: 68276f6d30bbdc09cc26fb49d7f0c3aa4bce35f2
Repository branch: master
Windowing system distributor 'The Cygwin/X Project', version 11.0.12011000
Configured using:
 'configure 'CFLAGS=-g -O0''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LCMS2 LIBOTF LIBXML2 M17N_FLT MODULES NOTIFY GFILENOTIFY PDUMPER PNG
RSVG SOUND THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM GTK3 ZLIB

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