GNU bug report logs - #44638
[PATCH 1/2] autorevert: don't reuse existing watch descriptors

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Michael Albinus <michael.albinus <at> gmx.de>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#44638: closed ([PATCH 1/2] autorevert: don't reuse existing
 watch descriptors)
Date: Thu, 03 Dec 2020 15:02:02 +0000

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Your message dated Thu, 03 Dec 2020 16:01:29 +0100
with message-id <87pn3rc4s6.fsf <at> gmx.de>
and subject line Re: bug#44638: [PATCH 1/2] autorevert: don't reuse existing watch descriptors
has caused the debbugs.gnu.org bug report #44638,
regarding [PATCH 1/2] autorevert: don't reuse existing watch descriptors
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


-- 
44638: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=44638
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Contact help-debbugs <at> gnu.org with problems

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From: Spencer Baugh <sbaugh <at> catern.com>
To: bug-gnu-emacs <at> gnu.org
Cc: Spencer Baugh <sbaugh <at> catern.com>
Subject: [PATCH 1/2] autorevert: don't reuse existing watch descriptors
Date: Sat, 14 Nov 2020 11:54:58 -0500

Previously, when enabling autorevert for a new buffer, we would search
the buffers already registered with autorevert to see if any of them
had the same filename.

This is very slow with a large number of buffers - with 1000, it takes
2 seconds on my system. This 2-second overhead is paid for every new
file opened.

But this is an unnecesary optimization; registering the same file
twice with file-notify has minimal or no overhead, depending on the
implementation.

In fact, file-notify has some baked-in overhead to support registering
the same file twice without problems. For example, inotify on Linux
returns the same inotify watch descriptor when the same file is
registered twice; file-notify adds an additional uniquifying id so
that all watch descriptors are unique in Emacs, even with inotify.

We can rely on file-notify's existing support for handling the same
file being registered twice. We don't need this slow and complex
logic.

With this code deleted, enabling autorevert for a new buffer is
essentially instant even with 1000 buffers.
---
 lisp/autorevert.el | 29 +++++++----------------------
 1 file changed, 7 insertions(+), 22 deletions(-)

diff --git a/lisp/autorevert.el b/lisp/autorevert.el
index 046ea2b5d6..d5bb75c2f1 100644
--- a/lisp/autorevert.el
+++ b/lisp/autorevert.el
@@ -650,30 +650,15 @@ will use an up-to-date value of `auto-revert-interval'."
               (string-match auto-revert-notify-exclude-dir-regexp
 			    (expand-file-name default-directory))
 	      (file-symlink-p (or buffer-file-name default-directory)))
-    ;; Check, whether this has been activated already.
     (let ((file (if buffer-file-name
 		    (expand-file-name buffer-file-name default-directory)
 	          (expand-file-name default-directory))))
-      (maphash
-       (lambda (key _value)
-         (when (and
-                (file-notify-valid-p key)
-                (equal (file-notify--watch-absolute-filename
-                        (gethash key file-notify-descriptors))
-                       (directory-file-name file))
-                (equal (file-notify--watch-callback
-                        (gethash key file-notify-descriptors))
-                       'auto-revert-notify-handler))
-         (setq auto-revert-notify-watch-descriptor key)))
-       auto-revert--buffers-by-watch-descriptor)
-      ;; Create a new watch if needed.
-      (unless auto-revert-notify-watch-descriptor
-        (setq auto-revert-notify-watch-descriptor
-	      (ignore-errors
-		(file-notify-add-watch
-		 file
-                 (if buffer-file-name '(change attribute-change) '(change))
-                 'auto-revert-notify-handler))))
+      (setq auto-revert-notify-watch-descriptor
+	    (ignore-errors
+	      (file-notify-add-watch
+	       file
+               (if buffer-file-name '(change attribute-change) '(change))
+               'auto-revert-notify-handler))))
       (when auto-revert-notify-watch-descriptor
         (setq auto-revert-notify-modified-p t)
         (puthash
@@ -682,7 +667,7 @@ will use an up-to-date value of `auto-revert-interval'."
 	       (gethash auto-revert-notify-watch-descriptor
 		        auto-revert--buffers-by-watch-descriptor))
          auto-revert--buffers-by-watch-descriptor)
-        (add-hook 'kill-buffer-hook #'auto-revert-notify-rm-watch nil t)))))
+        (add-hook 'kill-buffer-hook #'auto-revert-notify-rm-watch nil t))))
 
 ;; If we have file notifications, we want to update the auto-revert buffers
 ;; immediately when a notification occurs. Since file updates can happen very
-- 
2.28.0

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From: Michael Albinus <michael.albinus <at> gmx.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: sbaugh <at> catern.com, 44638-done <at> debbugs.gnu.org
Subject: Re: bug#44638: [PATCH 1/2] autorevert: don't reuse existing watch
 descriptors
Date: Thu, 03 Dec 2020 16:01:29 +0100

Michael Albinus <michael.albinus <at> gmx.de> writes:

> Eli Zaretskii <eliz <at> gnu.org> writes:
>
>>> > auto-revert-test07-auto-revert-several-buffers succeeds.  Running the
>>> > entire test finds 2 failures:
>>> >
>>> >   2 unexpected results:
>>> >      FAILED  auto-revert-test04-auto-revert-mode-dired
>>> >      FAILED  auto-revert-test05-global-notify
>>> >
>>> > Let me know if I can help you more.
>>>
>>> Well, if the same errors happen also w/o that patch, I believe we are
>>> safe to install the patch in master.
>>
>> Yes, I think those tests always failed for me.
>
> Good, so I will install patch 1/2 in master. Likely tomorrow.

Done, closing the bug.

Best regards, Michael.

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