Subject: bug#70032: 30.0.50; thread-yield inconsistency with macOS GUI and other platforms

From: Daniel Pettersson <[email-masked]>
Date: Wed, 27 Mar 2024 16:44:02 +0100

(make-thread (lambda ()
               (benchmark-progn
                 (dotimes (_ 100000)
                   (thread-yield))))
                   "benchmark-thread")

The thread will finish in less then one second on macOS '-nw' and Linux
(GUI and '-nw') (have not tested on Windows).

On macOS GUI "benchmark-thread" will almost certainly never finish.

The only way that I know to drive the thread forward is to generate
input events, so you need to generate at 100000 input events for it to
finish. With macOS GUI the Main thread does only seam to yield back to
the other thread after an mouse/keyboard event.

* src/nsterm.m: ns_select_1

  /* emacs -nw doesn't have an NSApp, so we're done.  */
  if (NSApp == nil)
    return thread_select (pselect, nfds, readfds, writefds, exceptfds,
			  timeout, sigmask);

  if (![NSThread isMainThread]
      || (timeout && timeout->tv_sec == 0 && timeout->tv_nsec == 0))
    thread_select (pselect, nfds, readfds, writefds,
		   exceptfds, timeout, sigmask);
  else
    {
      struct timespec t = {0, timeout->tv_nsec}; 
      thread_select (pselect, 0, NULL, NULL, NULL, &t, sigmask);
    }

I don't understand Emacs threads well enough but it seams that the
else block is the reason for the main thread not yielding to the
"benchmark-thread" is the Main thread will almost always pselect with
timeout {0, 0}.  But if timeout is not zeroed Emacs becomes extremely
unresponsive (but "benchmark-thread" will finish in the same amount of
time as running emacs with '-nw')

In GNU Emacs 30.0.50 (build 1, aarch64-apple-darwin23.1.0, NS
 appkit-2487.20 Version 14.1.1 (Build 23B81)) of 2023-12-20 built on
 Daniels-Air
Repository revision: 281be72422f42fcc84d43f50723a3e91b7d03cbc
Repository branch: master
Windowing system distributor 'Apple', version 10.3.2487
System Description:  macOS 14.1.1

Configured features:
ACL DBUS GLIB GNUTLS JSON LCMS2 LIBXML2 MODULES NOTIFY KQUEUE NS PDUMPER
PNG RSVG SQLITE3 THREADS TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XIM ZLIB

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

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  minibuffer-regexp-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils time-date subr-x
cl-loaddefs cl-lib rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/ns-win ns-win ucs-normalize mule-util term/common-win tool-bar dnd
fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow
isearch easymenu timer select scroll-bar mouse jit-lock font-lock syntax
font-core term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine 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
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind kqueue cocoa ns
lcms2 multi-tty make-network-process emacs)

Memory information:
((conses 16 38459 8478) (symbols 48 5148 0) (strings 32 13180 1700)
 (string-bytes 1 386239) (vectors 16 10512)
 (vector-slots 8 164949 10278) (floats 8 24 23) (intervals 56 242 3)
 (buffers 992 11))