undo-auto--undoable-change infloop

[Michael Heerdegen <michael_heerdegen@web.de>]

Hello,

does somebody have a guess what is happening here?  After automatically
replacing thousands of matches in a buffer with my el-search, I got a
sluggish Emacs afterwards, after a short pause.  Emacs consumed 100% of
one CPU.  It took me hours to find something, and it seems to be
unrelated to my own code: `undo-auto--undoable-change'.  It seems to
recurse very deep, or to be called extremely often.  I managed to
produce a backtrace, see below.  How is that recursion even possible -
what could be going on?

TIA,

Michael


The backtrace (the first cursor blink afterwards seems to initiate the
problematic behavior):

  (timer-activate [t 25311 13221 560142 nil undo-auto--boundary-timer nil nil 540000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13220 972130 nil undo-auto--boundary-timer nil nil 860000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13220 562017 nil undo-auto--boundary-timer nil nil 682000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13220 175101 nil undo-auto--boundary-timer nil nil 375000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13219 728313 nil undo-auto--boundary-timer nil nil 962000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13219 407621 nil undo-auto--boundary-timer nil nil 486000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13219 71400 nil undo-auto--boundary-timer nil nil 128000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13218 786464 nil undo-auto--boundary-timer nil nil 766000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13218 551162 nil undo-auto--boundary-timer nil nil 891000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13218 258788 nil undo-auto--boundary-timer nil nil 94000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13218 89932 nil undo-auto--boundary-timer nil nil 31000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13217 955384 nil undo-auto--boundary-timer nil nil 756000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13217 847383 nil undo-auto--boundary-timer nil nil 663000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13217 765424 nil undo-auto--boundary-timer nil nil 571000 nil])
  (run-at-time 10 nil undo-auto--boundary-timer)
  (undo-auto--boundary-ensure-timer)
  (undo-auto--undoable-change)
  (timer-activate [t 25311 13207 807483 0.15 blink-cursor-timer-function nil nil 407999 nil])
  (run-at-time 0.15 0.15 blink-cursor-timer-function)
  (run-with-timer 0.15 0.15 blink-cursor-timer-function)
  (blink-cursor--start-timer)
  (blink-cursor-start)

When I redefine `undo-auto--undoable-change' with an empty body, the
problem disappears.  I could not reproduce something similar with normal
query-replace.