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Subject: |
28.0.50; process-tests/fd-setsize-no-crash/make-network-process hangs on Cygwin |
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Date: |
Fri, 9 Jul 2021 14:01:33 -0400 |
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User-agent: |
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 |
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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--- Begin Message ---
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Subject: |
Re: bug#49496: 28.0.50; process-tests/fd-setsize-no-crash/make-network-process hangs on Cygwin |
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Date: |
Fri, 9 Jul 2021 16:42:36 -0400 |
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User-agent: |
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 |
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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