bug#51377: Automatically exit server when it has no remaining clients

[Gregory Heytings <gregory@heytings.org>]

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>
> If `save-buffers-kill-emacs' were called after that, the Emacs daemon 
> would be killed, losing the edits to bar.txt.
>

Indeed, you are correct.  Updated patch attached, which also takes care of 
running processes.

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From b699c16bac38923e43992edf27039a5d9bcca4f1 Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Sun, 24 Oct 2021 18:40:39 +0000
Subject: [PATCH] Option to automatically stop Emacs server.

* lisp/server.el (server-stop-automatically): New function.
* doc/emacs/misc.texi (Emacs Server): Document the new function.
Also mention that an Emacs server can be started with emacsclient.
---
 doc/emacs/misc.texi | 11 +++++++++++
 lisp/server.el      | 23 +++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index 5123a716dc..893e5f1843 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -1697,6 +1697,11 @@ Emacs Server
 calls @code{server-start} after initialization and does not open an
 initial frame.  It then waits for edit requests from clients.
 
+@item
+Run the command @code{emacsclient} with the @samp{--alternate-editor=""}
+command-line option.  This starts an Emacs daemon only if no Emacs daemon
+is already running.
+
 @cindex systemd unit file
 @item
 If your operating system uses @command{systemd} to manage startup,
@@ -1763,6 +1768,12 @@ Emacs Server
   emacs --daemon=foo
 @end example
 
+@findex server-stop-automatically
+  If you want to automatically stop the Emacs server when it has no
+clients, no unsaved buffers and no running processes anymore, put the
+expression @code{(server-stop-automatically)} in your init file
+(@pxref{Init File}).
+
 @findex server-eval-at
   If you have defined a server by a unique server name, it is possible
 to connect to the server from another Emacs instance and evaluate Lisp
diff --git a/lisp/server.el b/lisp/server.el
index 6359a76199..944f1a3dce 100644
--- a/lisp/server.el
+++ b/lisp/server.el
@@ -1746,6 +1746,29 @@ server-save-buffers-kill-terminal
 	     (server-delete-client proc)))
 	  (t (error "Invalid client frame")))))
 
+;;;###autoload
+(defun server-stop-automatically ()
+  "Automatically stop server when possible.
+The server is stopped when it has no remaining clients, no remaining
+unsaved buffers, and no running processes with a query-on-exit flag.
+This function is meant to be put in init files."
+  (when (daemonp)
+    (run-with-timer
+     10 2
+     (lambda ()
+       (unless (cdr (frame-list))
+         (when (and
+                (not (memq t (mapcar (lambda (b)
+                                       (and (buffer-file-name b)
+			                    (buffer-modified-p b)))
+                                     (buffer-list))))
+                (not (memq t (mapcar (lambda (p)
+		                       (and (memq (process-status p)
+				                  '(run stop open listen))
+			                    (process-query-on-exit-flag p)))
+		                     (process-list)))))
+           (kill-emacs)))))))
+
 (define-key ctl-x-map "#" 'server-edit)
 
 (defun server-unload-function ()
-- 
2.33.0