bug#21241: 25.0.50; gfilenotify doesn't indicate when limits are reached

bug#21241: 25.0.50; gfilenotify doesn't indicate when limits are reached

[Tassilo Horn]

When acquiring many file/directory watches using file-notify-add-watch
with file-notify--library being gfilenotify, there's no indication when
the limit of watches a user is allowed to place is reached.  You still
get a valid descriptor but the provided callback function won't be
called when the watched file/directory changes.

I've looked at the code and saw that with inotify you'd get an error.
Apparently, gfilenotify (aka glib) also uses inotify on my GNU/Linux box
under the hoods.  At least increasing the inotify limit for user watches
made it work again.

I tried looking at the GFileMonitor API docs.  It seems that
g_file_monitor should return NULL on errors (and I'd count a reached
limit an error), and the fourth parameter should be initialized with the
error.  Emacs calls it with no error parameter:

  monitor = g_file_monitor (gfile, gflags, NULL, NULL);

So I've tried the following:

--8<---------------cut here---------------start------------->8---
diff --git a/src/gfilenotify.c b/src/gfilenotify.c
index 08713a8..2ad2110 100644
--- a/src/gfilenotify.c
+++ b/src/gfilenotify.c
@@ -172,8 +172,9 @@ will be reported only in case of the 'moved' event.  */)
     gflags |= G_FILE_MONITOR_SEND_MOVED;
 
   /* Enable watch.  */
-  monitor = g_file_monitor (gfile, gflags, NULL, NULL);
-  if (! monitor)
+  GError *err = NULL;
+  monitor = g_file_monitor (gfile, gflags, NULL, &err);
+  if (! monitor || err != NULL)
     xsignal2 (Qfile_notify_error, build_string ("Cannot watch file"), file);
 
   Lisp_Object watch_descriptor = make_pointer_integer (monitor);
--8<---------------cut here---------------end--------------->8---

Unfortunately, the err variable won't be set in case the limit is
reached, too.  So it seems that we can't do much from Emacs land and
this should be reported as a glib bug (which I'll do).

Well, one thing we could do was preferring plain inotify over glib's
GFileMonitor when both are available.  On my GNU/Linux box both are
available and configure chose gfilenotify as the default.



In GNU Emacs 25.0.50.3 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.6)
 of 2015-08-12 on thinkpad-t440p
Repository revision: 197f280042a4d901ea94acdf10f1dc544fae4750
Windowing system distributor `The X.Org Foundation', version 11.0.11702000
System Description:	Arch Linux

Configured using:
 `configure 'CFLAGS=-g -ggdb3 -O1''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LC_MONETARY: de_DE.utf8
  value of $LC_NUMERIC: de_DE.utf8
  value of $LC_TIME: de_DE.utf8
  value of $LANG: en_US.utf8
  locale-coding-system: utf-8-unix

Major mode: Group

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Recent messages:
20150812T095021.253> Reading active file via nndraft...
20150812T095021.254> Reading active file via nndraft...done
20150812T095021.254> Reading active file from archive+nnml+archive:sent-postings via nnml...
20150812T095021.254> Opening nnml server on archive+nnml+archive:sent-postings...
20150812T095021.255> Opening nnml server on archive+nnml+archive:sent-postings...done
20150812T095021.255> nnml: Reading incoming mail (no new mail)...done
20150812T095021.255> Reading active file from archive+nnml+archive:sent-postings via nnml...
20150812T095021.256> Reading active file from archive+nnml+archive:sent-postings via nnml...done
20150812T095021.256> Checking new news...done
20150812T095021.257> No news is good news

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bug#21241: 25.0.50; gfilenotify doesn't indicate when limits are reached

[Tassilo Horn]

Here's the glib bug report I've just filed for this issue:

  https://bugzilla.gnome.org/show_bug.cgi?id=753549

Bye,
Tassilo

bug#21241: 25.0.50; gfilenotify doesn't indicate when limits are reached

[Eli Zaretskii]

> From: Tassilo Horn <tsdh@gnu.org>
> Date: Wed, 12 Aug 2015 10:16:54 +0200
> 
> Well, one thing we could do was preferring plain inotify over glib's
> GFileMonitor when both are available.  On my GNU/Linux box both are
> available and configure chose gfilenotify as the default.

I wonder if we should revert our decision to prefer gfilenotify if
available, and instead use it only if there's no other supported
method.  It begins to sound more and more like gfilenotify is more
trouble than it's worth.

bug#21241: 25.0.50; gfilenotify doesn't indicate when limits are reached

[Tassilo Horn]

Eli Zaretskii <eliz@gnu.org> writes:

>> Well, one thing we could do was preferring plain inotify over glib's
>> GFileMonitor when both are available.  On my GNU/Linux box both are
>> available and configure chose gfilenotify as the default.
>
> I wonder if we should revert our decision to prefer gfilenotify if
> available, and instead use it only if there's no other supported
> method.  It begins to sound more and more like gfilenotify is more
> trouble than it's worth.

You mean the other emacs-devel thread where it has been reported that
gfile notifications might get delayed up to 30 seconds?  I haven't seen
that issue here but if it can happen and gfilenotify doesn't provide
some clear benefit over plain inotify, I'd suggest to use the latter by
default when it's available.

Well, at least it seems that THIS issue is considered to be a bug also
by one glib developer so chances are good that it'll be fixed
eventually.  But of course it may take some time until a fixed version
is distributed to all users and until then users will have to learn the
hard way why notifications don't work [1].

Bye,
Tassilo

[1] I've been working on magit-filenotify.el which automatically
    refreshes the magit status buffer when something in the git
    repository changes, and at some point it just didn't work anymore
    (no notifications) for repositories I've started working on later
    while it still worked for those I've had opened earlier.  Well, that
    way I've at least learned about inotify limits and how to change
    them... :-)

bug#21241: 25.0.50; gfilenotify doesn't indicate when limits are reached

[Eli Zaretskii]

> From: Tassilo Horn <tsdh@gnu.org>
> Cc: 21241@debbugs.gnu.org
> Date: Wed, 12 Aug 2015 15:27:26 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Well, one thing we could do was preferring plain inotify over glib's
> >> GFileMonitor when both are available.  On my GNU/Linux box both are
> >> available and configure chose gfilenotify as the default.
> >
> > I wonder if we should revert our decision to prefer gfilenotify if
> > available, and instead use it only if there's no other supported
> > method.  It begins to sound more and more like gfilenotify is more
> > trouble than it's worth.
> 
> You mean the other emacs-devel thread where it has been reported that
> gfile notifications might get delayed up to 30 seconds?

That, and this bug, and also the fact that it simply doesn't work on
Windows (no notifications come in), although the corresponding glib
tests all pass.  There's also bug#20417, and I think someone also
complained about gfilenotify on OS X.

> Well, at least it seems that THIS issue is considered to be a bug also
> by one glib developer so chances are good that it'll be fixed
> eventually.

Let's hope it will be.

bug#21241: 25.0.50; gfilenotify doesn't indicate when limits are reached

[Michael Albinus]

Eli Zaretskii <eliz@gnu.org> writes:

>> > I wonder if we should revert our decision to prefer gfilenotify if
>> > available, and instead use it only if there's no other supported
>> > method.  It begins to sound more and more like gfilenotify is more
>> > trouble than it's worth.
>> 
>> You mean the other emacs-devel thread where it has been reported that
>> gfile notifications might get delayed up to 30 seconds?
>
> That, and this bug, and also the fact that it simply doesn't work on
> Windows (no notifications come in), although the corresponding glib
> tests all pass.  There's also bug#20417, and I think someone also
> complained about gfilenotify on OS X.

I would also agree to favor inotify when available.

On OS X (better: on systems which have defined HAVE_NS), we should
disable gfilenotify, because the Glib main loop won't be used (ns_select
is used rather than xg_select).

Best regards, Michael.

bug#21241: 25.0.50; gfilenotify doesn't indicate when limits are reached

[Paul Eggert]

[-- Attachment #1: Type: text/plain, Size: 485 bytes --]

Michael Albinus writes:

> I would also agree to favor inotify when available.

Let's give that a try, then.  I installed the attached patch as master commit 
200c2b10faf298bf65e8b6dbd0cb9ef00b2f95d6.

> On OS X (better: on systems which have defined HAVE_NS), we should
> disable gfilenotify, because the Glib main loop won't be used (ns_select
> is used rather than xg_select).

configure.ac was trying to do that, but there was a typo.  Should also be fixed 
in the attached patch.

[-- Attachment #2: 0001-Default-to-inotify-instead-of-gfile.patch --]
[-- Type: text/x-diff, Size: 3697 bytes --]

From 3f9999c2c0b0eb96c7e7e83fd5dd97da4ca301d1 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Fri, 14 Aug 2015 18:20:35 -0700
Subject: [PATCH] Default to inotify instead of gfile

* configure.ac (with_file_notification): Fix typo that
prevented suppression of file notification if HAVE_NS.
(NOTIFY_OBJ): Prefer inotify to gfile if both exist and
with_file_notification is 'yes' (Bug#21241).
* etc/NEWS: Mention this.
---
 configure.ac | 34 ++++++++++++++++------------------
 etc/NEWS     |  4 ++++
 2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/configure.ac b/configure.ac
index 16d4484..9f8089f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -365,7 +365,7 @@ AC_ARG_WITH([file-notification],[AS_HELP_STRING([--with-file-notification=LIB],
     * ) AC_MSG_ERROR(['--with-file-notification=$withval' is invalid;
 this option's value should be 'yes', 'no', 'gfile', 'inotify' or 'w32'.
 'yes' is a synonym for 'w32' on MS-Windows, for 'no' on Nextstep,
-otherwise for the first of 'gfile' or 'inotify' that is usable.])
+otherwise for the first of 'inotify' or 'gfile' that is usable.])
     ;;
    esac
    with_file_notification=$val
@@ -2674,7 +2674,7 @@ NOTIFY_SUMMARY=no
 
 dnl FIXME?  Don't auto-detect on NS, but do allow someone to specify
 dnl a particular library.  This doesn't make much sense?
-if test "${HAVE_ns}" = yes && test ${with_file_notification} = yes; then
+if test "${HAVE_NS}" = yes && test ${with_file_notification} = yes; then
   with_file_notification=no
 fi
 
@@ -2694,22 +2694,7 @@ case $with_file_notification,$opsys in
     fi ;;
 esac
 
-dnl g_file_monitor exists since glib 2.18.  G_FILE_MONITOR_EVENT_MOVED
-dnl has been added in glib 2.24.  It has been tested under
-dnl GNU/Linux only.  We take precedence over inotify, but this makes
-dnl only sense when glib has been compiled with inotify support.  How
-dnl to check?
-case $with_file_notification,$NOTIFY_OBJ in
-  gfile, | yes,)
-    EMACS_CHECK_MODULES([GFILENOTIFY], [gio-2.0 >= 2.24])
-    if test "$HAVE_GFILENOTIFY" = "yes"; then
-       AC_DEFINE(HAVE_GFILENOTIFY, 1, [Define to 1 if using GFile.])
-       NOTIFY_OBJ=gfilenotify.o
-       NOTIFY_SUMMARY="yes -lgio (gfile)"
-    fi ;;
-esac
-
-dnl inotify is only available on GNU/Linux.
+dnl inotify is available only on GNU/Linux.
 case $with_file_notification,$NOTIFY_OBJ in
   inotify, | yes,)
     AC_CHECK_HEADER(sys/inotify.h)
@@ -2723,6 +2708,19 @@ case $with_file_notification,$NOTIFY_OBJ in
     fi ;;
 esac
 
+dnl g_file_monitor exists since glib 2.18.  G_FILE_MONITOR_EVENT_MOVED
+dnl has been added in glib 2.24.  It has been tested under
+dnl GNU/Linux only.
+case $with_file_notification,$NOTIFY_OBJ in
+  gfile,* | yes,)
+    EMACS_CHECK_MODULES([GFILENOTIFY], [gio-2.0 >= 2.24])
+    if test "$HAVE_GFILENOTIFY" = "yes"; then
+       AC_DEFINE(HAVE_GFILENOTIFY, 1, [Define to 1 if using GFile.])
+       NOTIFY_OBJ=gfilenotify.o
+       NOTIFY_SUMMARY="yes -lgio (gfile)"
+    fi ;;
+esac
+
 case $with_file_notification,$NOTIFY_OBJ in
   yes,* | no,* | *,?*) ;;
   *) AC_MSG_ERROR([File notification '$with_file_notification' requested but requirements not found.]) ;;
diff --git a/etc/NEWS b/etc/NEWS
index f131981..bbcdc0c 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -43,6 +43,10 @@ or by sticking with Emacs 24.4.
 If gnustep-config is not available, the old heuristics are used.
 
 ---
+** 'configure' now prefers inotify to gfile for file notification,
+unless gfile is explicitly requested via --with-file-notification='gfile'.
+
+---
 ** The configure option '--with-pkg-config-prog' has been removed.
 Use './configure PKG_CONFIG=/full/name/of/pkg-config' if you need to.
 
-- 
2.1.0

bug#21241: 25.0.50; gfilenotify doesn't indicate when limits are reached

[Tassilo Horn]

Paul Eggert <eggert@cs.ucla.edu> writes:

>> I would also agree to favor inotify when available.
>
> Let's give that a try, then.  I installed the attached patch as master
> commit 200c2b10faf298bf65e8b6dbd0cb9ef00b2f95d6.

FWIW, all my file-notification needs are still satisfied with inotify as
`file-notify--library', and now I also get an error when I run out of
allowed used watches.  So from my side, feel free to close this report
as gfilenotify's broken behavior is glib's bug, not ours.

Bye,
Tassilo

bug#21241: 25.0.50; gfilenotify doesn't indicate when limits are reached

[Paul Eggert]

Tassilo Horn wrote:
> So from my side, feel free to close this report
> as gfilenotify's broken behavior is glib's bug, not ours.

Thanks for checking; closing the bug.

bug#21241: 25.0.50; gfilenotify doesn't indicate when limits are reached

[Michael Albinus]

Tassilo Horn <tsdh@gnu.org> writes:

> So I've tried the following:
>
> diff --git a/src/gfilenotify.c b/src/gfilenotify.c
> index 08713a8..2ad2110 100644
> --- a/src/gfilenotify.c
> +++ b/src/gfilenotify.c
> @@ -172,8 +172,9 @@ will be reported only in case of the 'moved' event.  */)
>      gflags |= G_FILE_MONITOR_SEND_MOVED;
>  
>    /* Enable watch.  */
> -  monitor = g_file_monitor (gfile, gflags, NULL, NULL);
> -  if (! monitor)
> +  GError *err = NULL;
> +  monitor = g_file_monitor (gfile, gflags, NULL, &err);
> +  if (! monitor || err != NULL)
>      xsignal2 (Qfile_notify_error, build_string ("Cannot watch file"), file);
>  
>    Lisp_Object watch_descriptor = make_pointer_integer (monitor);

For the records, I've committed a modified version of this patch. It
returns the error message from g_file_monitor, if present.

Best regards, Michael.