Add new --timeout flag to emacsclient

* lib-src/emacsclient.c (DEFAULT_TIMEOUT): New constant.
(timeout): New static variable.
(longopts, shortopts, decode_options, print_help_and_exit): Add new
flag --timeout.
(set_socket_timeout, check_socket_timeout): New helper functions.
(main): Display a status message or exit after Emacs has not responded
for a while, depending on above new --timeout flag.  (Bug#50849)

* doc/emacs/misc.texi (emacsclient Options):
* doc/man/emacsclient.1: Document the above new option.
* etc/NEWS: Announce it.

2 files changed, 14 insertions, 4 deletions

diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index df74577592a..d8ad0bee34f 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -2089,6 +2089,13 @@ all server buffers are finished.  You can take as long as you like to
 edit the server buffers within Emacs, and they are @emph{not} killed
 when you type @kbd{C-x #} in them.
 
+@item -w
+@itemx --timeout=@var{N}
+Wait for a response from Emacs for @var{N} seconds before giving up.
+If there is no response within that time, @command{emacsclient} will
+display a warning and exit.  The default is @samp{0}, which means to
+wait forever.
+
 @item --parent-id @var{id}
 Open an @command{emacsclient} frame as a client frame in the parent X
 window with id @var{id}, via the XEmbed protocol.  Currently, this
diff --git a/doc/man/emacsclient.1 b/doc/man/emacsclient.1
index e5d1bbe09ae..83c8a366f8b 100644
--- a/doc/man/emacsclient.1
+++ b/doc/man/emacsclient.1
@@ -1,5 +1,5 @@
 .\" See section COPYING for conditions for redistribution.
-.TH EMACSCLIENT 1 "2021-11-05" "GNU Emacs" "GNU"
+.TH EMACSCLIENT 1 "2022-09-05" "GNU Emacs" "GNU"
 .\" NAME should be all caps, SECTION should be 1-8, maybe w/ subsection
 .\" other params are allowed: see man(7), man(1)
 .SH NAME
@@ -87,9 +87,12 @@ Use TCP configuration file FILENAME for communication.
 This can also be specified via the EMACS_SERVER_FILE environment variable.
 .TP
 .B \-n, \-\-no-wait
-Return
-immediately without waiting for you to "finish" the buffer in Emacs.
-If combined with --eval, this option is ignored.
+Return immediately without waiting for you to "finish" the buffer in
+Emacs.  If combined with --eval, this option is ignored.
+.TP
+.B \-w, \-\-timeout=N
+How long to wait, in seconds, for Emacs to respond before giving up.
+The default is 0, which means to wait forever.
 .TP
 .B \-nw, \-t, \-\-tty
 Open a new Emacs frame on the current terminal.