Add a limit on image count and size.

image-grid.c

@@ -60,7 +60,12 @@ TAILQ_HEAD(image_placements, image_placement);
 /* Placements owned by one grid. */
 struct image_store {
 	struct image_placements		 placements;
+	TAILQ_ENTRY(image_store)	 entry;
 };
+TAILQ_HEAD(image_stores, image_store);
+
+/* All current placements. */
+static struct image_stores image_stores = TAILQ_HEAD_INITIALIZER(image_stores);
 
 /* A shared placements copied when duplicating lines. */
 struct image_copy_map {
@@ -175,6 +180,7 @@ image_draw_span(struct image_backend *backend, struct tty *tty,
 	struct image_rect	 rect;
 
 	rect.image = span->placement->image;
+	image_touch(rect.image);
 	rect.src_x = span->source_x + start - span->x;
 	rect.src_y = span->source_y;
 	rect.sx = end - start;
@@ -265,6 +271,7 @@ image_store_get(struct grid *gd)
 	if (gd->images == NULL) {
 		gd->images = xcalloc(1, sizeof *gd->images);
 		TAILQ_INIT(&gd->images->placements);
+		TAILQ_INSERT_TAIL(&image_stores, gd->images, entry);
 	}
 	return (gd->images);
 }
@@ -293,6 +300,7 @@ image_placement_create(struct grid *gd, struct image *im)
 	TAILQ_INIT(&plmt->spans);
 	TAILQ_INSERT_TAIL(&store->placements, plmt, entry);
 	image_ref(im);
+	image_touch(im);
 	return (plmt);
 }
 
@@ -440,6 +448,32 @@ image_grid_remove(struct grid *gd, u_int x, u_int y, u_int sx, u_int sy)
 	image_store_prune(gd->images);
 }
 
+/* Remove a placement and all of its spans. */
+static void
+image_remove_placement(struct image_placement *plmt)
+{
+	struct image_span	*span, *span1;
+
+	TAILQ_FOREACH_SAFE(span, &plmt->spans, placement_entry, span1)
+		image_span_free(span);
+	image_placement_free(plmt);
+}
+
+/* Remove every placement for an image. */
+void
+image_grid_remove_all(struct image *im)
+{
+	struct image_store	*store;
+	struct image_placement	*plmt, *next;
+
+	TAILQ_FOREACH(store, &image_stores, entry) {
+		TAILQ_FOREACH_SAFE(plmt, &store->placements, entry, next) {
+			if (plmt->image == im)
+				image_remove_placement(plmt);
+		}
+	}
+}
+
 /* Free all spans on a grid line. */
 void
 image_grid_free_line(struct grid *gd, struct grid_line *gl)
@@ -464,6 +498,7 @@ image_grid_free(struct grid *gd)
 {
 	if (gd->images != NULL) {
 		image_store_prune(gd->images);
+		TAILQ_REMOVE(&image_stores, gd->images, entry);
 		free(gd->images);
 		gd->images = NULL;
 	}
@@ -973,6 +1008,7 @@ image_grid_get_at(struct grid *gd, u_int x, u_int y, struct image **im,
 	if (found == NULL)
 		return (-1);
 	*im = found->placement->image;
+	image_touch(*im);
 	*src_x = found->source_x + x - found->x;
 	*src_y = found->source_y;
 	return (1);

image.c

@@ -26,13 +26,19 @@
 
 #include "tmux.h"
 
+/* Maximum number of images and total bytes. */
+#define IMAGE_MAX_IMAGES 1000
+#define IMAGE_MAX_BYTES (1024 * 1024 * 1024)
+
 /* An image. */
+TAILQ_HEAD(image_list, image);
 struct image {
 	u_int			 id;
 	u_int			 references;
 	struct image_geom	 geom;
 
 	struct image		*parent;
+	struct image_list	 children;
 	u_int			 order_id;
 
 	/*
@@ -46,10 +52,19 @@ struct image {
 	u_char			*pixels;
 
 	RB_ENTRY(image)		 entry;
+	TAILQ_ENTRY(image)	 all_entry;
+	TAILQ_ENTRY(image)	 child_entry;
 };
 RB_HEAD(images, image);
 static struct images images = RB_INITIALIZER(&images);
 
+/* All images, most recently used first. */
+static struct image_list all_images = TAILQ_HEAD_INITIALIZER(all_images);
+
+/* Number of images and size. */
+static u_int image_count;
+static size_t image_size;
+
 /* Next image ID. */
 static u_int image_next_id;
 
@@ -65,6 +80,18 @@ image_cmp(struct image *a, struct image *b)
 }
 RB_GENERATE_STATIC(images, image, entry, image_cmp);
 
+/* Record use of an image and its parents. */
+void
+image_touch(struct image *im)
+{
+	for (; im != NULL; im = im->parent) {
+		if (TAILQ_FIRST(&all_images) != im) {
+			TAILQ_REMOVE(&all_images, im, all_entry);
+			TAILQ_INSERT_HEAD(&all_images, im, all_entry);
+		}
+	}
+}
+
 /* Find an image by its ID. */
 struct image *
 image_find(u_int id)
@@ -82,6 +109,76 @@ image_get_id(struct image *im)
 	return (im->id);
 }
 
+/* Remove an image and children. */
+static void
+image_remove_all(struct image *im)
+{
+	struct image *child;
+
+	image_ref(im);
+	while ((child = TAILQ_FIRST(&im->children)) != NULL)
+		image_remove_all(child);
+	image_grid_remove_all(im);
+	image_free(im);
+}
+
+/* Find the oldest image. */
+static struct image *
+image_find_oldest(struct image *keep, size_t size)
+{
+	struct image *im, *parent;
+
+	TAILQ_FOREACH_REVERSE(im, &all_images, image_list, all_entry) {
+		if (image_size + size > IMAGE_MAX_BYTES && im->parent != NULL)
+			continue;
+		for (parent = keep; parent != NULL; parent = parent->parent) {
+			if (parent == im)
+				break;
+		}
+		if (parent == NULL)
+			return (im);
+	}
+	return (NULL);
+}
+
+/* Is there enough space for this image? */
+static int
+image_can_add(size_t size)
+{
+	if (image_count >= IMAGE_MAX_IMAGES)
+		return (0);
+	if (image_size + size > IMAGE_MAX_BYTES)
+		return (0);
+	return (1);
+}
+
+/* Check limits and remove images if needed. */
+static int
+image_check_limits(struct image *keep, size_t size)
+{
+	struct image	*oldest;
+	struct client	*c;
+
+	if (size > IMAGE_MAX_BYTES)
+		return (-1);
+	if (image_can_add(size))
+		return (0);
+
+	TAILQ_FOREACH(c, &clients, entry)
+		image_tty_free(&c->tty);
+	while (!image_can_add(size)) {
+		oldest = image_find_oldest(keep, size);
+		if (oldest == NULL)
+			break;
+		image_remove_all(oldest);
+	}
+	TAILQ_FOREACH(c, &clients, entry)
+		server_redraw_client(c);
+	if (!image_can_add(size))
+		return (-1);
+	return (0);
+}
+
 /* Allocate an image and assign a unique ID. */
 static struct image *
 image_alloc(struct image_geom *ig, size_t stride, u_char *pixels)
@@ -103,7 +200,9 @@ image_alloc(struct image_geom *ig, size_t stride, u_char *pixels)
 	im->stride = stride;
 	im->size = (ig->src_h - 1) * stride + ig->src_w * 4;
 	im->pixels = pixels;
+	TAILQ_INIT(&im->children);
 	RB_INSERT(images, &images, im);
+	image_count++;
 	return (im);
 }
 
@@ -122,6 +221,7 @@ image_create_with_parent(struct image *parent, struct image_geom *ig,
     size_t stride, u_char *pixels)
 {
 	struct image	*im;
+	size_t		 size = 0;
 
 	if (ig->src_w == 0 || ig->src_h == 0)
 		return (NULL);
@@ -138,12 +238,22 @@ image_create_with_parent(struct image *parent, struct image_geom *ig,
 	if (ig->scaled_width <= 0 || ig->scaled_height <= 0)
 		return (NULL);
 
+	if (parent == NULL)
+		size = (ig->src_h - 1) * stride + ig->src_w * 4;
+	if (image_check_limits(parent, size) != 0)
+		return (NULL);
+
 	im = image_alloc(ig, stride, pixels);
 	im->parent = parent;
-	if (parent != NULL) {
+	if (parent == NULL)
+		image_size += im->size;
+	else {
 		im->order_id = parent->order_id;
+		TAILQ_INSERT_TAIL(&parent->children, im, child_entry);
 		image_ref(parent);
 	}
+	TAILQ_INSERT_HEAD(&all_images, im, all_entry);
+	image_touch(im);
 	return (im);
 }
 
@@ -164,10 +274,15 @@ image_free(struct image *im)
 		fatalx("invalid image reference %u", im->id);
 	if (--im->references == 0) {
 		RB_REMOVE(images, &images, im);
-		if (im->parent == NULL)
+		TAILQ_REMOVE(&all_images, im, all_entry);
+		image_count--;
+		if (im->parent == NULL) {
+			image_size -= im->size;
 			free(im->pixels);
-		else
+		} else {
+			TAILQ_REMOVE(&im->parent->children, im, child_entry);
 			image_free(im->parent);
+		}
 		free(im);
 	}
 }

regress/image-sixel-limits.sh

@@ -0,0 +1,76 @@
+#!/bin/sh
+
+# Check image quotas, last use order, copied grids and released image slots.
+
+PATH=/bin:/usr/bin
+TERM=screen
+export TERM
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+command -v python3 >/dev/null || exit 101
+
+python3 -B - "$TEST_TMUX" <<'PY'
+import sys
+from image_test import image_test, sixel
+from image_terminal import Terminal
+
+
+def image(colour):
+    """Build one solid image cell which advances the cursor by one row."""
+    return sixel(8, 16, [colour], [0] * (8 * 16))
+
+
+def snapshot(test, client, rows):
+    """Check the image cells in the first column after a full redraw."""
+    test.redraw()
+    terminal = Terminal()
+    terminal.feed(client.data)
+    expected = {(x, y * 16 + py): colour for y, colour in rows.items()
+        for py in range(16) for x in range(8)}
+    terminal.check(expected)
+
+
+red, green, blue = (255, 0, 0), (0, 255, 0), (0, 0, 255)
+red_image = image((100, 0, 0))
+green_image = image((0, 100, 0))
+blue_image = image((0, 0, 100))
+
+with image_test(sys.argv[1]) as test:
+    client = test.attach()
+    test.emit(red_image + green_image * 999)
+    test.emit(blue_image)
+    snapshot(test, client, dict.fromkeys(range(14), green) | {14: blue})
+    # Images in scrollback count towards the quota; the oldest one is gone.
+    test.run('copy-mode')
+    test.run('send-keys', '-X', 'history-top')
+    snapshot(test, client, dict.fromkeys(range(1, 16), green))
+
+with image_test(sys.argv[1]) as test:
+    client = test.attach()
+    test.emit(red_image + green_image * 999)
+    test.run('copy-mode')
+    test.run('send-keys', '-X', 'history-top')
+    snapshot(test, client, {0: red} | dict.fromkeys(range(1, 16), green))
+    # The copied grid keeps these old images in use while a new window fills.
+    test.run('new-window', '-n', 'quota', '/bin/sh', '-c',
+        "stty raw -echo; printf '\033]2;QUOTA\007'; exec cat")
+    test.wait(lambda: test.run('display-message', '-p',
+        '#{pane_title}') == 'QUOTA')
+    test.emit(blue_image)
+    test.run('select-window', '-t', 'image:0')
+    snapshot(test, client, {0: red} | dict.fromkeys(range(1, 16), green))
+    # The first image below the redrawn rows was evicted from both grids.
+    test.run('send-keys', '-X', 'scroll-down')
+    snapshot(test, client, dict.fromkeys(range(15), green))
+    test.run('send-keys', '-X', 'cancel')
+    test.run('copy-mode')
+    test.run('send-keys', '-X', 'history-top')
+    test.run('send-keys', '-X', 'scroll-down')
+    snapshot(test, client, dict.fromkeys(range(15), green))
+
+with image_test(sys.argv[1]) as test:
+    client = test.attach()
+    # Replacing an image releases its slot rather than exhausting the quota.
+    test.emit((b'\033[H' + green_image) * 1001)
+    test.emit(b'\033[3;1H' + blue_image)
+    snapshot(test, client, {0: green, 2: blue})
+PY

tmux-image.h

@@ -102,6 +102,7 @@ struct image	*image_find(u_int);
 u_int		 image_get_id(struct image *);
 void		 image_ref(struct image *);
 void		 image_free(struct image *);
+void		 image_touch(struct image *);
 struct image_geom *image_get_geometry(struct image *);
 u_char		*image_get_pixels(struct image *, size_t *, size_t *);
 int		 image_get_bounds(struct image_geom *, u_int, u_int, u_int,
@@ -118,6 +119,7 @@ void		 image_grid_add(struct grid *, struct image *, u_int, u_int,
 void		 image_grid_remove(struct grid *, u_int, u_int, u_int, u_int);
 void		 image_grid_free_line(struct grid *, struct grid_line *);
 void		 image_grid_free(struct grid *);
+void		 image_grid_remove_all(struct image *);
 void		 image_grid_move_cells(struct grid *, u_int, u_int, u_int,
 		     u_int);
 void		 image_grid_duplicate_lines(struct grid *, u_int, struct grid *,