Fix bugs #12447 and #12326 with infloop causes by idle timers, update docs.

 src/keyboard.c (timer_check_2): Move calculation of 'timers' and
 'idle_timers' from here ...
 (timer_check): ... to here.  Use Fcopy_sequence to copy the timer
 lists, to avoid infloops when the timer does something stupid,
 like reinvoke itself with the same or smaller time-out.

 lisp/emacs-lisp/timer.el (run-with-idle-timer)
 (timer-activate-when-idle): Warn against reinvoking an idle timer
 from within its own timer action.

 doc/lispref/os.texi (Idle Timers): Warn against reinvoking an idle timer
 from within its own timer action.

2 files changed, 12 insertions, 0 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index f1ae632267b..8acd12d82a8 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,8 @@
+2012-09-22  Eli Zaretskii  <eliz@gnu.org>
+
+        * os.texi (Idle Timers): Warn against reinvoking an idle timer
+        from within its own timer action.  (Bug#12447)
+
 2012-09-22  Chong Yidong  <cyd@gnu.org>
 
         * frames.texi (Pop-Up Menus): Minor clarification (Bug#11148).
diff --git a/doc/lispref/os.texi b/doc/lispref/os.texi
index 6431ac8bead..68e53c78972 100644
--- a/doc/lispref/os.texi
+++ b/doc/lispref/os.texi
@@ -1864,6 +1864,13 @@ It blocks out any idle timers that ought to run during that time.
 @end itemize
 
 @noindent
+For similar reasons, do not write an idle timer function that sets
+up another idle time (including the same idle timer) with the
+@var{secs} argument less or equal to the current idleness time.  Such
+a timer will run almost immediately, and continue running again and
+again, instead of waiting for the next time Emacs becomes idle.
+
+@noindent
 The correct approach is for the idle timer to reschedule itself after
 a brief pause, using the method in the @code{timer-function} example
 above.