Speed-up multiple calls to `org-diary'.

Patch by Matt Lundin

Matt writes:

> The missing piece of the puzzle is integration with "diary" and
> "cal-tex" functions via the org-diary sexp. I have found org-diary to be
> excruciatingly slow when called for anything more than a couple of days.
> I have the following line in my diary file:
>
> &%%(org-diary :timestamp :sexp)
>
> If I try to view 20 or so upcoming days in the diary by typing C-u 20 d
> on a date in the calendar, it can take upwards of 30 seconds to generate
> the diary display. This is of little consequence, since I can, after
> all, simply use the custom agenda command. But I often want to print out
> a nice LaTeX calendar of my appointments with cal-tex-cursor-month. And
> that takes upwards of 50 seconds (see attached elp-results file).
>
> Judging from the elp-results, the culprit seems to be
> org-prepare-agenda-buffers (46 seconds), which is called 31 times (once
> for each day). It seems to me that since org-diary is being called 31
> times in quick succession by the same function (diary-sexp-entry), one
> should only need to call org-prepare-agenda-buffers once.
>
> The only solution I could see to this problem was to add a test to see
> if org-diary had been called less than 1 second ago. Thus, I added the
> variable org-diary-last-run-time and a conditional in org-diary that
> only runs org-prepare-agenda-buffers if org-diary-last-run-time is less
> than 1 second in the past.
>
> With the patch, it now takes appr. 5 seconds to generate the LaTeX
> calendar with cal-tex and org-prepare-agenda-buffers is called only
> once.

lisp/ChangeLog

@@ -1,5 +1,9 @@
 2010-03-29  Carsten Dominik  <carsten.dominik@gmail.com>
 
+	* org-agenda.el (org-diary-last-run-time): New variable.
+	(org-diary): prepare agenda buffers only if last call was some
+	time ago.
+
 	* org-html.el (org-export-html-preprocess): Replace \ref macros
 	with a link.
 	(org-format-org-table-html): Add the label as an anchor.

lisp/org-agenda.el

@@ -4086,6 +4086,8 @@ Needed to avoid empty dates which mess up holiday display."
       (apply 'diary-add-to-list args)
     (apply 'add-to-diary-list args)))
 
+(defvar org-diary-last-run-time nil)
+
 ;;;###autoload
 (defun org-diary (&rest args)
   "Return diary information from org-files.
@@ -4123,8 +4125,14 @@ function from a program - use `org-agenda-get-day-entries' instead."
   (let* ((files (if (and entry (stringp entry) (string-match "\\S-" entry))
 		    (list entry)
 		  (org-agenda-files t)))
+	 (time (org-float-time))
 	 file rtn results)
-    (org-prepare-agenda-buffers files)
+    (when (or (not org-diary-last-run-time)
+	      (> (- time
+		    org-diary-last-run-time)
+		 3))
+      (org-prepare-agenda-buffers files))
+    (setq org-diary-last-run-time time)
     ;; If this is called during org-agenda, don't return any entries to
     ;; the calendar.  Org Agenda will list these entries itself.
     (if org-disable-agenda-to-diary (setq files nil))