The function <code>run-with-idle-timer</code> has a million and one uses.  The
 following use has vastly improved my life using NTEmacsWithCygwin, for example.

Here's the problem it solves: I frequently want to switch to a buffer named "*Shell*"; I've formed the habit of typing merely <code>* S h e RET</code>, and letting completion complete the buffer name.  However, sometimes there's a buffer lying around named "*Shell Command Output*".  Since that buffer's name shares a common prefix with the name of the buffer to which I want to switch, completion doesn't completely complete :-) the name "*Shell*"; instead it leaves me with "*Shell".  Thus, when I then hit RET, I find myself looking at a new, empty, useless buffer instead of the one I wanted.  Rather than telling completion to honor case (which is annoying on Win32, since the file system is itself case-insensitive), I simply tell Emacs to periodically kill any buffers named "*Shell Command Output*" that it finds lying around (if they're not currently displayed in a window).  The "periodically" part is what run-with-idle-timer does for us.

      (if completion-ignore-case
          (defvar reaper
            (run-with-idle-timer 5 t (lambda ()
                                       (let ((victim (get-buffer "*Shell Command Output*")))
                                         (when (and victim (not (get-buffer-window victim t)))
                                           (message "Killing buffer %s" (buffer-name victim))
                                           (kill-buffer victim)))))
            "idle-timer (see \\[run-with-idle-timer]) that deletes the
      *Shell Command Output* buffer -- that buffer's name is so similar to
      *shell* that completion makes the latter hard to type.  Use
      \\[cancel-timer] to cancel it."))

[new:DrewAdams:2006-01-27 17:28 UTC]
[[Icicles]], IswitchBuffers, and BSBufferSelection all solve this problem in simpler ways. -- DrewAdams

[new]
Yeah, I use IswitchBuffers now. -- EricHanchrow

== Cookbook ==

There are a few steps to set up a function to be repeated every now and again..

* Set up a variable to store the timer object
* Define the function to repeat
* Define functions to start and stop the repetition

<pre>


;; variable for the timer object
(defvar idle-timer-cookbook-timer nil)

;; callback function 
(defun idle-timer-cookbook-callback ()
  (message "I have been called (%s)" (current-time-string)))

;; start functions
(defun idle-timer-cookbook-run-once ()
  (interactive)
  (when (timerp idle-timer-cookbook-timer)
    (cancel-timer idle-timer-cookbook-timer))
  (setq idle-timer-cookbook-timer
          (run-with-idle-timer 1 nil #'idle-timer-cookbook-callback)))

(defun idle-timer-cookbook-start ()
  (interactive)
  (when (timerp idle-timer-cookbook-timer)
    (cancel-timer idle-timer-cookbook-timer))
  (setq idle-timer-cookbook-timer
          (run-with-timer 1 1 #'idle-timer-cookbook-callback)))

;; stop function
(defun idle-timer-cookbook-stop ()
  (interactive)
  (when (timerp idle-timer-cookbook-timer)
    (cancel-timer idle-timer-cookbook-timer))
  (setq idle-timer-cookbook-timer nil))
</pre>
  
== run-with-timer vs run-with-idle-timer ==

These functions are quite similar, the main difference being that <code>run-with-timer</code> will call the callback function repeatedly whereas <code>run-with-idle-timer</code> does so only once (unless you specify the <code>REPEAT</code> parameter, that is)


== Use with Anything ==
'''[[Anything]]''' is a candidate selection framework.

Start with M-x anything-timers, narrow the list by typing some patterns(multiple patterns are space-delimited string),
select with up/down/pgup/pgdown/C-p/C-n/C-v/M-v, choose with enter to cancel,


== Gotchas ==

* Gnu Emacs allows a zero time, XEmacs does not.

----
See EmacsNiftyTricks

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CategoryCode