bug#27670: 25.2; emacs GUI hangs when rxvt is busy displaying logs

[zhanghj]

system: debian 8 stable x86_64
emacs: emacs 25.2

1. Start rxvt-unicode and tmux.
2. Run a test program in tmux, which just prints text(include chinese chars) as 
fast as it can.
3. Start emacs GUI with "emacs -Q". Then open xdisp.c in emacs, and keep
pressing the "down" key.
4. After about 15 seconds, emacs GUI hangs.
5. Kill the test program in 2. Emacs GUI still hangs.




In GNU Emacs 25.2.1 (x86_64-apple-darwin16.5.0, NS appkit-1504.82 Version 
10.12.4 (Build 16E195))
 of 2017-05-01 built on jundemac
Windowing system distributor 'Apple', version 10.3.1504
Configured using:
 'configure --with-ns '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --with-modules --without-makeinfo
 --disable-acl --with-gnutls=no'

Configured features:
NOTIFY LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES

Important settings:
  value of $LANG: zh_CN.UTF-8
  locale-coding-system: utf-8-unix

Major mode: C++/lah

Minor modes in effect:
  highlight-parentheses-mode: t
  company-mode: t
  yas-minor-mode: t
  flycheck-mode: t
  global-hl-line-mode: t
  recentf-mode: t
  irony-mode: t
  auto-insert-mode: t
  global-undo-tree-mode: t
  undo-tree-mode: t
  server-mode: t
  ido-everywhere: t
  which-function-mode: t
  desktop-save-mode: t
  auto-image-file-mode: t
  global-auto-revert-mode: t
  icomplete-mode: t
  delete-selection-mode: t
  display-time-mode: t
  show-paren-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t

Recent messages:
expected expression [2 times]
Wrote /Users/jun/Projects/repo1/vbox_cloud_server2/common/timer_manager.cpp
Reverting buffer ‘main.cpp’.
Type C-c C-c to commit (C-c C-k to cancel).
git finished.
Type C-c C-c to commit (C-c C-k to cancel).
git finished.
Type a prefix key to toggle it. Run ’actions’ with their prefixes. ’?’ for more 
help.
Running git push -v origin master:refs/heads/master
git finished.

Load-path shadows:
/Applications/Emacs.app/Contents/Resources/lisp/emacs-lisp/seq hides 
~/.lisp/lib/seq
/Applications/Emacs.app/Contents/Resources/lisp/emacs-lisp/let-alist hides 
~/.lisp/lib/let-alist

Features:
(shadow sort mail-extr emacsbug sendmail hippie-exp find-file
my-dev-funcs dabbrev misearch multi-isearch wgrep-ag wgrep grep ag
idomenu my-tools magit-bisect magit-key-mode magit esh-var esh-io
esh-cmd esh-opt esh-ext esh-proc esh-arg esh-groups eshell esh-module
esh-mode esh-util ediff-merg ediff-wind ediff-diff ediff-mult ediff-help
ediff-init ediff-util ediff diff-mode log-edit message rfc822 mml
mml-sec password-cache epg epg-config mm-decode mm-bodies mm-encode
mail-parse rfc2231 rfc2047 rfc2045 ietf-drums mm-util help-fns
mail-prsvr mailabbrev mail-utils gmm-utils mailheader pcvs-util add-log
ox-beamer ox-latex ox-html ox-ascii ox-publish ox my-reminder bookmark
pp time-stamp my-flist-body dired-aux conf-mode js sgml-mode json map
make-mode sql view thingatpt highlight-parentheses company-dabbrev-code
company-dabbrev company-irony company-irony-c-headers company yasnippet
irony-completion irony-snippet flycheck-irony irony-diagnostics flycheck
rx dash compile let-alist cc-mode cc-fonts cc-guess cc-menus cc-cmds
cc-styles cc-align cc-engine cc-vars cc-defs org-element org-rmail
org-mhe org-irc org-info org-gnus gnus-util org-docview doc-view subr-x
jka-compr image-mode dired-x dired org-bibtex bibtex org-bbdb org-w3m
ob-ditaa org org-macro org-footnote org-pcomplete pcomplete org-list
org-faces org-entities noutline outline org-version ob-emacs-lisp ob
ob-tangle ob-ref ob-lob ob-table ob-exp org-src ob-keys ob-comint comint
ansi-color ring ob-core ob-eval org-compat org-macs org-loaddefs
format-spec cal-menu calendar cal-loaddefs my-session
solarized-dark-theme solarized-definitions smex hl-line main-init
windmove my-abbrev my-mail my-autoload recentf tree-widget wid-edit
my-fpos my-snippet advice my-completion irony find-func my-skeleton
autoinsert my-dev my-org my-files my-color-theme undo-tree derived
easy-mmode cl-seq cl-macs diff cl helm-autoload bbdb-autoload
prog-modes-autoload emmet-autoload csharp-autoload swift-mode-autoload
go-mode-autoload goodies-autoload evil-autoload expand-region-load
multiple-cursors-load wgrep-autoload iedit-autoload flycheck-autoload
magit-autoload git-modes-autoload irony-autoload company-autoload
yasnippet-autoload autoload-main server ido seq byte-opt gv bytecomp
byte-compile cl-extra help-mode easymenu cconv edmacro kmacro which-func
imenu desktop frameset image-file autorevert filenotify cl-loaddefs
pcase cl-lib icomplete delsel time paren time-date mule-util china-util
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel ns-win ucs-normalize term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cl-generic cham
georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer cl-preloaded nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote kqueue cocoa ns multi-tty
make-network-process emacs)

Memory information:
((conses 16 796382 105831)
 (symbols 48 54736 0)
 (miscs 40 4999 6974)
 (strings 32 91157 14212)
 (string-bytes 1 3461233)
 (vectors 16 64127)
 (vector-slots 8 1928131 81493)
 (floats 8 693 606)
 (intervals 56 14600 1544)
 (buffers 976 197))