desktop-auto-save-timeout

desktop-auto-save-timeout

[Eli Zaretskii]

I wonder if the default value of this option (equal to
auto-save-timeout) is TRT.  The latter is used to auto-save our edits,
which are by definition precious, so people are likely to customize it
to small values (I have it at 15 sec).  By contrast, important desktop
changes are relatively rare, and even if some of them are lost, it's
not a disaster, at least not in general.

I've run Emacs 24.3.9x with the default value (which for me means
15sec) for some time, and the results are unpleasant: Emacs becomes
sluggish in its response whenever you look at the screen for more than
the timeout without typing anything.  E.g., start an I-search, then
make a pause to look at the text you found, then type C-s to continue
the search -- it takes a few seconds for Emacs to respond, probably
because the desktop's idle timer invokes desktop-save, which needs to
collect a non-trivial amount of data in a temp buffer, then run that
buffer through md5.  Very annoying.

Why not make the value of this variable nil by default, and let users
who think their desktop configuration is precious customize the
variable to some non-nil value?

Re: desktop-auto-save-timeout

[Juri Linkov]

> I wonder if the default value of this option (equal to
> auto-save-timeout) is TRT.  The latter is used to auto-save our edits,
> which are by definition precious, so people are likely to customize it
> to small values (I have it at 15 sec).  By contrast, important desktop
> changes are relatively rare, and even if some of them are lost, it's
> not a disaster, at least not in general.
>
> I've run Emacs 24.3.9x with the default value (which for me means
> 15sec) for some time, and the results are unpleasant: Emacs becomes
> sluggish in its response whenever you look at the screen for more than
> the timeout without typing anything.  E.g., start an I-search, then
> make a pause to look at the text you found, then type C-s to continue
> the search -- it takes a few seconds for Emacs to respond, probably
> because the desktop's idle timer invokes desktop-save, which needs to
> collect a non-trivial amount of data in a temp buffer, then run that
> buffer through md5.  Very annoying.

I realized now that the right way to implement the desktop auto-saving
is to activate an idle timer only on changes in the window configuration
by window-configuration-change-hook.

The desktop file is mostly about remembering a list of buffers and
windows.  There is no point in auto-saving each time point moves.
This is what web browsers do by auto-saving a list of tabs
only when you open/close a tab.

Re: desktop-auto-save-timeout

[martin rudalics]

 > I realized now that the right way to implement the desktop auto-saving
 > is to activate an idle timer only on changes in the window configuration
 > by window-configuration-change-hook.
 >
 > The desktop file is mostly about remembering a list of buffers and
 > windows.  There is no point in auto-saving each time point moves.
 > This is what web browsers do by auto-saving a list of tabs
 > only when you open/close a tab.

Agreed.  We might lose some window-points and some buffers that have not
been displayed yet in that case but this is no great harm.

martin

Re: desktop-auto-save-timeout

[Juri Linkov]

>> I realized now that the right way to implement the desktop auto-saving
>> is to activate an idle timer only on changes in the window configuration
>> by window-configuration-change-hook.
>>
>> The desktop file is mostly about remembering a list of buffers and
>> windows.  There is no point in auto-saving each time point moves.
>> This is what web browsers do by auto-saving a list of tabs
>> only when you open/close a tab.
>
> Agreed.  We might lose some window-points and some buffers that have not
> been displayed yet in that case but this is no great harm.

This is implemented by this patch.  Not sure whether it fixes a regression or not.

=== modified file 'lisp/desktop.el'
--- lisp/desktop.el	2014-04-27 08:22:11 +0000
+++ lisp/desktop.el	2014-06-05 23:34:41 +0000
@@ -174,7 +174,8 @@ (define-minor-mode desktop-save-mode
   :global t
   :group 'desktop
   (if desktop-save-mode
-      (desktop-auto-save-set-timer)
+      (add-hook 'window-configuration-change-hook 'desktop-auto-save-set-timer)
+    (remove-hook 'window-configuration-change-hook 'desktop-auto-save-set-timer)
     (desktop-auto-save-cancel-timer)))
 
 (defun desktop-save-mode-off ()
@@ -207,13 +208,18 @@ (defcustom desktop-save 'ask-if-new
 
 (defcustom desktop-auto-save-timeout auto-save-timeout
   "Number of seconds idle time before auto-save of the desktop.
+The idle timer activates auto-saving only when window configuration changes.
 This applies to an existing desktop file when `desktop-save-mode' is enabled.
 Zero or nil means disable auto-saving due to idleness."
   :type '(choice (const :tag "Off" nil)
                  (integer :tag "Seconds"))
   :set (lambda (symbol value)
          (set-default symbol value)
-         (ignore-errors (desktop-auto-save-set-timer)))
+         (ignore-errors
+	   (if (and (integerp value) (> value 0))
+	       (add-hook 'window-configuration-change-hook 'desktop-auto-save-set-timer)
+	     (remove-hook 'window-configuration-change-hook 'desktop-auto-save-set-timer)
+	     (desktop-auto-save-cancel-timer))))
   :group 'desktop
   :version "24.4")
 
@@ -1244,7 +1250,7 @@ (defun desktop-auto-save-set-timer ()
   (when (and (integerp desktop-auto-save-timeout)
 	     (> desktop-auto-save-timeout 0))
     (setq desktop-auto-save-timer
-	  (run-with-idle-timer desktop-auto-save-timeout t
+	  (run-with-idle-timer desktop-auto-save-timeout nil
 			       'desktop-auto-save))))
 
 (defun desktop-auto-save-cancel-timer ()

Re: desktop-auto-save-timeout

[Eli Zaretskii]

> From: Juri Linkov <juri@jurta.org>
> Cc: Eli Zaretskii <eliz@gnu.org>,  Juanma Barranquero <lekktu@gmail.com>,  emacs-devel@gnu.org
> Date: Fri, 06 Jun 2014 02:35:42 +0300
> 
> >> I realized now that the right way to implement the desktop auto-saving
> >> is to activate an idle timer only on changes in the window configuration
> >> by window-configuration-change-hook.
> >>
> >> The desktop file is mostly about remembering a list of buffers and
> >> windows.  There is no point in auto-saving each time point moves.
> >> This is what web browsers do by auto-saving a list of tabs
> >> only when you open/close a tab.
> >
> > Agreed.  We might lose some window-points and some buffers that have not
> > been displayed yet in that case but this is no great harm.
> 
> This is implemented by this patch.  Not sure whether it fixes a regression or not.

Thanks.  Since this is a new functionality in Emacs 24.4, I think we
can allow it on the emacs-24 branch.