Add a simple form of output rate limiting by counting the number of

certain C0 sequences (linefeeds, backspaces, carriage returns) and if it
exceeds a threshold (current default 50/millisecond), start to redraw
the pane every 100 milliseconds instead of making each change as it
comes. Two configuration options - c0-change-trigger and
c0-change-interval.

This makes tmux much more responsive under very fast output (for example
yes(1) or accidentally cat'ing a large file) but may not be perfect on
all terminals and connections - feedback very welcome, particularly
where this change has a negative rather than positive effect (making it
off by default is a possibility).

After much experimentation based originally on a request Robin Lee
Powell (which ended with a completely different solution), this idea
from discussion with Ailin Nemui.

input.c

@@ -908,6 +908,7 @@ input_c0_dispatch(struct input_ctx *ictx)
 	struct screen_write_ctx	*sctx = &ictx->ctx;
 	struct window_pane	*wp = ictx->wp;
 	struct screen		*s = sctx->s;
+	u_int			 trigger;
 
 	log_debug("%s: '%c", __func__, ictx->ch);
 
@@ -919,7 +920,7 @@ input_c0_dispatch(struct input_ctx *ictx)
 		break;
 	case '\010':	/* BS */
 		screen_write_backspace(sctx);
-		break;
+		goto count_c0;
 	case '\011':	/* HT */
 		/* Don't tab beyond the end of the line. */
 		if (s->cx >= screen_size_x(s) - 1)
@@ -936,10 +937,10 @@ input_c0_dispatch(struct input_ctx *ictx)
 	case '\013':	/* VT */
 	case '\014':	/* FF */
 		screen_write_linefeed(sctx, 0);
-		break;
+		goto count_c0;
 	case '\015':	/* CR */
 		screen_write_carriagereturn(sctx);
-		break;
+		goto count_c0;
 	case '\016':	/* SO */
 		ictx->cell.attr |= GRID_ATTR_CHARSET;
 		break;
@@ -951,6 +952,15 @@ input_c0_dispatch(struct input_ctx *ictx)
 		break;
 	}
 
+	return (0);
+
+count_c0:
+	trigger = options_get_number(&wp->window->options, "c0-change-trigger");
+	if (++wp->changes == trigger) {
+		wp->flags |= PANE_DROP;
+		window_pane_timer_start(wp);
+	}
+
 	return (0);
 }
 

options-table.c

@@ -465,6 +465,21 @@ const struct options_table_entry window_options_table[] = {
 	  .default_num = 1
 	},
 
+
+	{ .name = "c0-change-trigger",
+	  .type = OPTIONS_TABLE_NUMBER,
+	  .default_num = 50,
+	  .minimum = 0,
+	  .maximum = USHRT_MAX
+	},
+
+	{ .name = "c0-change-interval",
+	  .type = OPTIONS_TABLE_NUMBER,
+	  .default_num = 100,
+	  .minimum = 1,
+	  .maximum = USHRT_MAX
+	},
+
 	{ .name = "clock-mode-colour",
 	  .type = OPTIONS_TABLE_COLOUR,
 	  .default_num = 4

tmux.1

@@ -2463,6 +2463,24 @@ It may be switched off globally with:
 set-window-option -g automatic-rename off
 .Ed
 .Pp
+.It Ic c0-change-interval Ar interval
+.It Ic c0-change-trigger Ar trigger
+These two options configure a simple form of rate limiting for a pane.
+If
+.Nm
+sees more than
+.Ar trigger
+C0 sequences that modify the screen (for example, carriage returns, linefeeds
+or backspaces) in one millisecond, it will stop updating the pane immediately and
+instead redraw it entirely every
+.Ar interval
+milliseconds.
+This helps to prevent fast output (such as
+.Xr yes 1
+overwhelming the terminal).
+The default is a trigger of 50 and an interval of 100.
+A trigger of zero disables the rate limiting.
+.Pp
 .It Ic clock-mode-colour Ar colour
 Set clock colour.
 .Pp

tmux.h

@@ -811,6 +811,7 @@ struct window_pane {
 
 	int		 flags;
 #define PANE_REDRAW 0x1
+#define PANE_DROP 0x2
 
 	char		*cmd;
 	char		*shell;
@@ -819,6 +820,10 @@ struct window_pane {
 	pid_t		 pid;
 	char		 tty[TTY_NAME_MAX];
 
+	u_int		 changes;
+	struct event	 changes_timer;
+	u_int		 changes_redraw;
+
 	int		 fd;
 	struct bufferevent *event;
 
@@ -1963,6 +1968,7 @@ void		 window_destroy_panes(struct window *);
 struct window_pane *window_pane_find_by_id(u_int);
 struct window_pane *window_pane_create(struct window *, u_int, u_int, u_int);
 void		 window_pane_destroy(struct window_pane *);
+void		 window_pane_timer_start(struct window_pane *);
 int		 window_pane_spawn(struct window_pane *, const char *,
 		     const char *, const char *, struct environ *,
 		     struct termios *, char **);
@@ -1981,7 +1987,6 @@ int		 window_pane_visible(struct window_pane *);
 char		*window_pane_search(
 		     struct window_pane *, const char *, u_int *);
 char		*window_printable_flags(struct session *, struct winlink *);
-
 struct window_pane *window_pane_find_up(struct window_pane *);
 struct window_pane *window_pane_find_down(struct window_pane *);
 struct window_pane *window_pane_find_left(struct window_pane *);

tty.c

@@ -661,7 +661,7 @@ tty_write(
 
 	if (wp->window->flags & WINDOW_REDRAW || wp->flags & PANE_REDRAW)
 		return;
-	if (!window_pane_visible(wp))
+	if (!window_pane_visible(wp) || wp->flags & PANE_DROP)
 		return;
 
 	for (i = 0; i < ARRAY_LENGTH(&clients); i++) {

window.c

@@ -61,6 +61,7 @@ struct window_pane_tree all_window_panes;
 u_int	next_window_pane_id;
 u_int	next_window_id;
 
+void	window_pane_timer_callback(int, short, void *);
 void	window_pane_read_callback(struct bufferevent *, void *);
 void	window_pane_error_callback(struct bufferevent *, short, void *);
 
@@ -648,6 +649,8 @@ window_pane_destroy(struct window_pane *wp)
 {
 	window_pane_reset_mode(wp);
 
+	event_del(&wp->changes_timer);
+
 	if (wp->fd != -1) {
 		bufferevent_free(wp->event);
 		close(wp->fd);
@@ -764,6 +767,43 @@ window_pane_spawn(struct window_pane *wp, const char *cmd, const char *shell,
 	return (0);
 }
 
+void
+window_pane_timer_start(struct window_pane *wp)
+{
+	struct timeval	tv;
+
+	tv.tv_sec = 0;
+	tv.tv_usec = 1000;
+
+	evtimer_del(&wp->changes_timer);
+	evtimer_set(&wp->changes_timer, window_pane_timer_callback, wp);
+	evtimer_add(&wp->changes_timer, &tv);
+}
+
+void
+window_pane_timer_callback(unused int fd, unused short events, void *data)
+{
+	struct window_pane	*wp = data;
+	struct window		*w = wp->window;
+	u_int			 interval, trigger;
+
+	interval = options_get_number(&w->options, "c0-change-interval");
+	trigger = options_get_number(&w->options, "c0-change-trigger");
+
+	if (wp->changes_redraw++ == interval) {
+		wp->flags |= PANE_REDRAW;
+		wp->changes_redraw = 0;
+
+	}
+
+	if (trigger == 0 || wp->changes < trigger) {
+		wp->flags |= PANE_REDRAW;
+		wp->flags &= ~PANE_DROP;
+	} else
+		window_pane_timer_start(wp);
+	wp->changes = 0;
+}
+
 /* ARGSUSED */
 void
 window_pane_read_callback(unused struct bufferevent *bufev, void *data)