bug#1058: 23.0.60; emacs --daemon should not return until socket is ready

[Romain Francoise <romain@orebokech.com>]

Hi Dan, Trent,

Dan Nicolaescu <dann@ics.uci.edu> writes:

> Just curious, what do you get if you do:
> emacs -Q --daemon; while ! ls /tmp/emacs1187/; do sleep 1; done

Yes, the delay is caused by my change to load the init file before
starting the server.

> Unfortunately ATM I don't see an easy way to do that.
> Ideas/patches are certainly welcome.

It's easy to do, but not very clean.  WDYT?


diff --git a/lisp/startup.el b/lisp/startup.el
index 5bd73f9..d9e37be 100644
--- a/lisp/startup.el
+++ b/lisp/startup.el
@@ -1224,7 +1224,8 @@ opening the first frame (e.g. open a connection to an X server).")
   ;; processing all command line arguments to allow e.g. `server-name'
   ;; to be changed before the server starts.
   (when (daemonp)
-    (server-start))
+    (server-start)
+    (daemon-detach-parent))
 
   ;; Run emacs-session-restore (session management) if started by
   ;; the session manager and we have a session manager connection.
diff --git a/src/emacs.c b/src/emacs.c
index f94d2d3..a2842d4 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -235,6 +235,10 @@ int noninteractive1;
 /* Nonzero means Emacs was started as a daemon.  */
 int is_daemon = 0;
 
+/* Pipe used to send exit notification to the daemon parent at
+   startup.  */
+int daemon_pipe[2];
+
 /* Save argv and argc.  */
 char **initial_argv;
 int initial_argc;
@@ -1074,16 +1078,31 @@ main (int argc, char **argv)
   if (argmatch (argv, argc, "-daemon", "--daemon", 5, NULL, &skip_args))
     {
 #ifndef DOS_NT
+      if (pipe (daemon_pipe) == -1)
+	{
+	  fprintf (stderr, "Cannot pipe!\n");
+	  exit (1);
+	}
       pid_t f = fork ();
       int nfd;
       if (f > 0)
-	exit (0);
+	{
+	  char buf[2];
+	  close (daemon_pipe[1]);
+	  /* Wait for the child to close its end of the pipe before
+	     exiting.  */
+	  while (read (daemon_pipe[0], &buf, 1) < 0)
+	    sleep (0.1);
+	  close (daemon_pipe[0]);
+	  exit (0);
+	}
       if (f < 0)
 	{
 	  fprintf (stderr, "Cannot fork!\n");
 	  exit (1);
 	}
 
+      close (daemon_pipe[0]);
       nfd = open ("/dev/null", O_RDWR);
       dup2 (nfd, 0);
       dup2 (nfd, 1);
@@ -2389,6 +2408,16 @@ DEFUN ("daemonp", Fdaemonp, Sdaemonp, 0, 0, 0,
   return is_daemon ? Qt : Qnil;
 }
 
+DEFUN ("daemon-detach-parent", Fdaemon_detach_parent, Sdaemon_detach_parent,
+       0, 0, 0,
+       doc: /* Detach Emacs from its invocation parent if it was started as a daemon.  */)
+  ()
+{
+  if (is_daemon)
+    close (daemon_pipe[1]);
+  return Qt;
+}
+
 void
 syms_of_emacs ()
 {
@@ -2408,6 +2437,7 @@ syms_of_emacs ()
   defsubr (&Sinvocation_name);
   defsubr (&Sinvocation_directory);
   defsubr (&Sdaemonp);
+  defsubr (&Sdaemon_detach_parent);
 
   DEFVAR_LISP ("command-line-args", &Vcommand_line_args,
 	       doc: /* Args passed by shell to Emacs, as a list of strings.