Introduce simple cache memory management

libass' cache was basically unmanaged; it would grow without any limits,
depending on how complex the subtitles are.  Introduce a simple limiting
that resets the cache if certain limits are exceeded.  The bitmap cache
is limited to approx. 50 MB size by default, while the glyph cache
allows storing up to 1000 glyphs by default.  A few tests with rather
heavily softsubbed fansubs show that these limits are fine.
The API was extended with the function ass_set_cache_limits which allows
modification of these limits.

5 files changed, 58 insertions, 5 deletions

diff --git a/libass/ass.h b/libass/ass.h
index 6efcc0f..b92960a 100644
--- a/libass/ass.h
+++ b/libass/ass.h
@@ -202,6 +202,17 @@ void ass_set_fonts(ass_renderer_t *priv, const char *default_font,
 int ass_fonts_update(ass_renderer_t *priv);
 
 /**
+ * \brief Set hard cache limits.  Do not set, or set to zero, for reasonable
+ * defaults.
+ *
+ * \param priv renderer handle
+ * \param glyph_max maximum number of cached glyphs
+ * \param bitmap_max_size maximum bitmap cache size (in MB)
+ */
+void ass_set_cache_limits(ass_renderer_t *priv, int glyph_max,
+                          int bitmap_max_size);
+
+/**
  * \brief Render a frame, producing a list of ass_image_t.
  * \param priv renderer handle
  * \param track subtitle track
diff --git a/libass/ass_cache.c b/libass/ass_cache.c
index 4c7a3fa..524a1c8 100644
--- a/libass/ass_cache.c
+++ b/libass/ass_cache.c
@@ -223,6 +223,12 @@ static void bitmap_hash_dtor(void *key, size_t key_size, void *value,
 void *cache_add_bitmap(hashmap_t *bitmap_cache, bitmap_hash_key_t *key,
                        bitmap_hash_val_t *val)
 {
+    // Note: this is only an approximation
+    if (val->bm_o)
+        bitmap_cache->cache_size += val->bm_o->w * val->bm_o->h * 3;
+    else
+        bitmap_cache->cache_size += val->bm->w * val->bm->h * 3;
+
     return hashmap_insert(bitmap_cache, key, val);
 }
 
diff --git a/libass/ass_cache.h b/libass/ass_cache.h
index 83c9943..e31d8cf 100644
--- a/libass/ass_cache.h
+++ b/libass/ass_cache.h
@@ -45,6 +45,7 @@ typedef struct hashmap_s {
     hashmap_item_dtor_t item_dtor;      // a destructor for hashmap key/value pairs
     hashmap_key_compare_t key_compare;
     hashmap_hash_t hash;
+    size_t cache_size;
     // stats
     int hit_count;
     int miss_count;
diff --git a/libass/ass_render.c b/libass/ass_render.c
index 5caf8eb..aeeb0ac 100644
--- a/libass/ass_render.c
+++ b/libass/ass_render.c
@@ -44,6 +44,8 @@
 #define MAX_BE 127
 #define SUBPIXEL_MASK 63
 #define SUBPIXEL_ACCURACY 7    // d6 mask for subpixel accuracy adjustment
+#define GLYPH_CACHE_MAX 1000
+#define BITMAP_CACHE_MAX_SIZE 50 * 1048576;
 
 static int last_render_id = 0;
 
@@ -206,6 +208,8 @@ typedef struct cache_store_s {
     hashmap_t *glyph_cache;
     hashmap_t *bitmap_cache;
     hashmap_t *composite_cache;
+    size_t glyph_max;
+    size_t bitmap_max_size;
 } cache_store_t;
 
 struct ass_renderer_s {
@@ -319,6 +323,8 @@ ass_renderer_t *ass_renderer_init(ass_library_t *library)
     priv->cache.bitmap_cache = ass_bitmap_cache_init(library);
     priv->cache.composite_cache = ass_composite_cache_init(library);
     priv->cache.glyph_cache = ass_glyph_cache_init(library);
+    priv->cache.glyph_max = GLYPH_CACHE_MAX;
+    priv->cache.bitmap_max_size = BITMAP_CACHE_MAX_SIZE;
 
     priv->text_info.max_glyphs = MAX_GLYPHS_INITIAL;
     priv->text_info.max_lines = MAX_LINES_INITIAL;
@@ -335,6 +341,14 @@ ass_renderer_t *ass_renderer_init(ass_library_t *library)
     return priv;
 }
 
+void ass_set_cache_limits(ass_renderer_t *render_priv, int glyph_max,
+                          int bitmap_max)
+{
+    render_priv->cache.glyph_max = glyph_max ? glyph_max : GLYPH_CACHE_MAX;
+    render_priv->cache.bitmap_max_size = bitmap_max ? 1048576 * bitmap_max :
+                                         BITMAP_CACHE_MAX_SIZE;
+}
+
 static void free_list_clear(ass_renderer_t *render_priv)
 {
     if (render_priv->free_head) {
@@ -2873,6 +2887,7 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
         }
     }
 
+
     if (text_info->length == 0) {
         // no valid symbols in the event; this can be smth like {comment}
         free_render_context(render_priv);
@@ -3223,17 +3238,18 @@ static int
 ass_start_frame(ass_renderer_t *render_priv, ass_track_t *track,
                 long long now)
 {
-    if (render_priv->library != track->library)
-        return 1;
-
-    free_list_clear(render_priv);
-
     ass_settings_t *settings_priv = &render_priv->settings;
+    cache_store_t *cache = &render_priv->cache;
 
     if (!render_priv->settings.frame_width
         && !render_priv->settings.frame_height)
         return 1;               // library not initialized
 
+    if (render_priv->library != track->library)
+        return 1;
+
+    free_list_clear(render_priv);
+
     if (track->n_events == 0)
         return 1;               // nothing to do
 
@@ -3274,6 +3290,24 @@ ass_start_frame(ass_renderer_t *render_priv, ass_track_t *track,
     render_priv->prev_images_root = render_priv->images_root;
     render_priv->images_root = 0;
 
+    if (cache->bitmap_cache->cache_size > cache->bitmap_max_size) {
+        ass_msg(render_priv->library, MSGL_V,
+                "Hitting hard bitmap cache limit (was: %ld bytes), "
+                "resetting.", (long) cache->bitmap_cache->cache_size);
+        cache->bitmap_cache = ass_bitmap_cache_reset(cache->bitmap_cache);
+        cache->composite_cache = ass_composite_cache_reset(
+            cache->composite_cache);
+        ass_free_images(render_priv->prev_images_root);
+        render_priv->prev_images_root = 0;
+    }
+
+    if (cache->glyph_cache->count > cache->glyph_max) {
+        ass_msg(render_priv->library, MSGL_V,
+            "Hitting hard glyph cache limit (was: %ld glyphs), resetting.",
+            (long) cache->glyph_cache->count);
+        cache->glyph_cache = ass_glyph_cache_reset(cache->glyph_cache);
+    }
+
     return 0;
 }
 
diff --git a/libass/libass.sym b/libass/libass.sym
index c702842..e813a18 100644
--- a/libass/libass.sym
+++ b/libass/libass.sym
@@ -32,3 +32,4 @@ ass_step_sub
 ass_process_force_style
 ass_set_message_cb
 ass_fonts_update
+ass_set_cache_limits