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, 31 insertions, 12 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 6ea40b3f122..b69d4bb7113 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,12 @@
+2012-09-22  Eli Zaretskii  <eliz@gnu.org>
+
+        * 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.
+        (Bug#12447)
+
 2012-09-22  Martin Rudalics  <rudalics@gmx.at>
 
         * window.c (Fsplit_window_internal): Handle only Qt value of
diff --git a/src/keyboard.c b/src/keyboard.c
index 098d3530ef8..8b1113a026a 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -4333,25 +4333,18 @@ decode_timer (Lisp_Object timer, EMACS_TIME *result)
    should be done.  */
 
 static EMACS_TIME
-timer_check_2 (void)
+timer_check_2 (Lisp_Object timers, Lisp_Object idle_timers)
 {
   EMACS_TIME nexttime;
   EMACS_TIME now;
   EMACS_TIME idleness_now;
-  Lisp_Object timers, idle_timers, chosen_timer;
-  struct gcpro gcpro1, gcpro2, gcpro3;
+  Lisp_Object chosen_timer;
+  struct gcpro gcpro1;
 
   nexttime = invalid_emacs_time ();
 
-  /* Always consider the ordinary timers.  */
-  timers = Vtimer_list;
-  /* Consider the idle timers only if Emacs is idle.  */
-  if (EMACS_TIME_VALID_P (timer_idleness_start_time))
-    idle_timers = Vtimer_idle_list;
-  else
-    idle_timers = Qnil;
   chosen_timer = Qnil;
-  GCPRO3 (timers, idle_timers, chosen_timer);
+  GCPRO1 (chosen_timer);
 
   /* First run the code that was delayed.  */
   while (CONSP (pending_funcalls))
@@ -4500,13 +4493,30 @@ EMACS_TIME
 timer_check (void)
 {
   EMACS_TIME nexttime;
+  Lisp_Object timers, idle_timers;
+  struct gcpro gcpro1, gcpro2;
+
+  /* We use copies of the timers' lists to allow a timer to add itself
+     again, without locking up Emacs if the newly added timer is
+     already ripe when added.  */
+
+  /* Always consider the ordinary timers.  */
+  timers = Fcopy_sequence (Vtimer_list);
+  /* Consider the idle timers only if Emacs is idle.  */
+  if (EMACS_TIME_VALID_P (timer_idleness_start_time))
+    idle_timers = Fcopy_sequence (Vtimer_idle_list);
+  else
+    idle_timers = Qnil;
+
+  GCPRO2 (timers, idle_timers);
 
   do
     {
-      nexttime = timer_check_2 ();
+      nexttime = timer_check_2 (timers, idle_timers);
     }
   while (EMACS_SECS (nexttime) == 0 && EMACS_NSECS (nexttime) == 0);
 
+  UNGCPRO;
   return nexttime;
 }