Add a couple of helper functions, and flush imsgs on exit.

client.c

@@ -223,20 +223,7 @@ client_exit_message(void)
 static void
 client_exit(void)
 {
-	struct client_file	*cf;
-	size_t			 left;
-	int			 waiting = 0;
-
-	RB_FOREACH (cf, client_files, &client_files) {
-		if (cf->event == NULL)
-			continue;
-		left = EVBUFFER_LENGTH(cf->event->output);
-		if (left != 0) {
-			waiting++;
-			log_debug("file %u %zu bytes left", cf->stream, left);
-		}
-	}
-	if (waiting == 0)
+	if (!file_write_left(&client_files))
 		proc_exit(client_proc);
 }
 

file.c

@@ -477,6 +477,26 @@ file_push(struct client_file *cf)
 	free(msg);
 }
 
+/* Check if any files have data left to write. */
+int
+file_write_left(struct client_files *files)
+{
+	struct client_file	*cf;
+	size_t			 left;
+	int			 waiting = 0;
+
+	RB_FOREACH (cf, client_files, files) {
+		if (cf->event == NULL)
+			continue;
+		left = EVBUFFER_LENGTH(cf->event->output);
+		if (left != 0) {
+			waiting++;
+			log_debug("file %u %zu bytes left", cf->stream, left);
+		}
+	}
+	return (waiting != 0);
+}
+
 /* Client file write error callback. */
 static void
 file_write_error_callback(__unused struct bufferevent *bev, __unused short what,

proc.c

@@ -18,6 +18,7 @@
 
 #include <sys/types.h>
 #include <sys/queue.h>
+#include <sys/socket.h>
 #include <sys/uio.h>
 #include <sys/utsname.h>
 
@@ -45,6 +46,8 @@ struct tmuxproc {
 	struct event	  ev_sigusr1;
 	struct event	  ev_sigusr2;
 	struct event	  ev_sigwinch;
+
+	TAILQ_HEAD(, tmuxpeer) peers;
 };
 
 struct tmuxpeer {
@@ -58,6 +61,8 @@ struct tmuxpeer {
 
 	void		(*dispatchcb)(struct imsg *, void *);
 	void		 *arg;
+
+	TAILQ_ENTRY(tmuxpeer) entry;
 };
 
 static int	peer_check_version(struct tmuxpeer *, struct imsg *);
@@ -190,6 +195,7 @@ proc_start(const char *name)
 
 	tp = xcalloc(1, sizeof *tp);
 	tp->name = xstrdup(name);
+	TAILQ_INIT(&tp->peers);
 
 	return (tp);
 }
@@ -207,6 +213,10 @@ proc_loop(struct tmuxproc *tp, int (*loopcb)(void))
 void
 proc_exit(struct tmuxproc *tp)
 {
+	struct tmuxpeer	*peer;
+
+	TAILQ_FOREACH(peer, &tp->peers, entry)
+	    imsg_flush(&peer->ibuf);
 	tp->exit = 1;
 }
 
@@ -297,6 +307,7 @@ proc_add_peer(struct tmuxproc *tp, int fd,
 	event_set(&peer->event, fd, EV_READ, proc_event_cb, peer);
 
 	log_debug("add peer %p: %d (%p)", peer, fd, arg);
+	TAILQ_INSERT_TAIL(&tp->peers, peer, entry);
 
 	proc_update_event(peer);
 	return (peer);
@@ -305,6 +316,7 @@ proc_add_peer(struct tmuxproc *tp, int fd,
 void
 proc_remove_peer(struct tmuxpeer *peer)
 {
+	TAILQ_REMOVE(&peer->parent->peers, peer, entry);
 	log_debug("remove peer %p", peer);
 
 	event_del(&peer->event);
@@ -325,3 +337,27 @@ proc_toggle_log(struct tmuxproc *tp)
 {
 	log_toggle(tp->name);
 }
+
+pid_t
+proc_fork_and_daemon(int *fd)
+{
+	pid_t	pid;
+	int	pair[2];
+
+	if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, pair) != 0)
+		fatal("socketpair failed");
+	switch (pid = fork()) {
+	case -1:
+		fatal("fork failed");
+	case 0:
+		close(pair[0]);
+		*fd = pair[1];
+		if (daemon(1, 0) != 0)
+			fatal("daemon failed");
+		return (0);
+	default:
+		close(pair[1]);
+		*fd = pair[0];
+		return (pid);
+	}
+}

server.c

@@ -156,35 +156,22 @@ int
 server_start(struct tmuxproc *client, int flags, struct event_base *base,
     int lockfd, char *lockfile)
 {
-	int		 pair[2];
-	sigset_t	 set, oldset;
-	struct client	*c = NULL;
-	char		*cause = NULL;
+	int		  fd;
+	sigset_t	  set, oldset;
+	struct client	 *c = NULL;
+	char		 *cause = NULL;
 
 	sigfillset(&set);
 	sigprocmask(SIG_BLOCK, &set, &oldset);
 
 	if (~flags & CLIENT_NOFORK) {
-		if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, pair) != 0)
-			fatal("socketpair failed");
-
-		switch (fork()) {
-		case -1:
-			fatal("fork failed");
-		case 0:
-			break;
-		default:
+		if (proc_fork_and_daemon(&fd) != 0) {
 			sigprocmask(SIG_SETMASK, &oldset, NULL);
-			close(pair[1]);
-			return (pair[0]);
+			return (fd);
 		}
-		close(pair[0]);
-		if (daemon(1, 0) != 0)
-			fatal("daemon failed");
 	}
-
-	server_client_flags = flags;
 	proc_clear_signals(client, 0);
+	server_client_flags = flags;
 
 	if (event_reinit(base) != 0)
 		fatalx("event_reinit failed");
@@ -213,7 +200,7 @@ server_start(struct tmuxproc *client, int flags, struct event_base *base,
 	if (server_fd != -1)
 		server_update_socket();
 	if (~flags & CLIENT_NOFORK)
-		c = server_client_create(pair[1]);
+		c = server_client_create(fd);
 	else
 		options_set_number(global_options, "exit-empty", 0);
 

tmux.h

@@ -1899,6 +1899,7 @@ struct tmuxpeer *proc_add_peer(struct tmuxproc *, int,
 void	proc_remove_peer(struct tmuxpeer *);
 void	proc_kill_peer(struct tmuxpeer *);
 void	proc_toggle_log(struct tmuxproc *);
+pid_t	proc_fork_and_daemon(int *);
 
 /* cfg.c */
 extern int cfg_finished;
@@ -2389,6 +2390,7 @@ void	 file_write(struct client *, const char *, int, const void *, size_t,
 	     client_file_cb, void *);
 void	 file_read(struct client *, const char *, client_file_cb, void *);
 void	 file_push(struct client_file *);
+int	 file_write_left(struct client_files *);
 void	 file_write_open(struct client_files *, struct tmuxpeer *,
 	     struct imsg *, int, int, client_file_cb, void *);
 void	 file_write_data(struct client_files *, struct imsg *);