Bug 1759891 - Ensure shared font keys have a unique namespace per WebRender instance. r=gw,gfx-reviewers

The blob font tables in Moz2DImageRenderer are currently shared across all WebRender instances.
So if different blob fonts from different WebRender instances happen to share the same font keys,
in particular the same namespace, the font keys can thus accidentally collide and blob fonts can
end up getting shared across WebRender instances unintentionally.

To guard against this, we need to ensure that SharedFontResources is provided with a unique
namespace for the WebRender instance in which to allocate shared font keys so that collisions
can no longer occur.

Differential Revision: https://phabricator.services.mozilla.com/D141929

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/26768254de772eb7d2ff50bccafa80e9f4a69f63

Author: lsalzman

webrender/src/glyph_rasterizer/mod.rs

@@ -549,6 +549,7 @@ struct MappedFontKey {
 }
 
 struct FontKeyMapLocked {
+    namespace: IdNamespace,
     next_id: u32,
     template_map: FastHashMap<FontTemplate, Arc<MappedFontKey>>,
     key_map: FastHashMap<FontKey, Arc<MappedFontKey>>,
@@ -561,15 +562,15 @@ struct FontKeyMapLocked {
 /// final shared key. The shared key will stay alive so long as there are
 /// any strong references to the mapping entry. Care must be taken when
 /// clearing namespaces of shared keys as this may trigger shared font keys
-/// to expire which require individual processing.
+/// to expire which require individual processing. Shared font keys will be
+/// created within the provided unique namespace.
 #[derive(Clone)]
 pub struct FontKeyMap(Arc<RwLock<FontKeyMapLocked>>);
 
 impl FontKeyMap {
-    const SHARED_NAMESPACE: IdNamespace = IdNamespace(0);
-
-    pub fn new() -> Self {
+    pub fn new(namespace: IdNamespace) -> Self {
         FontKeyMap(Arc::new(RwLock::new(FontKeyMapLocked {
+            namespace,
             next_id: 1,
             template_map: FastHashMap::default(),
             key_map: FastHashMap::default(),
@@ -600,7 +601,7 @@ impl FontKeyMap {
             locked.key_map.insert(*font_key, mapped);
             return None;
         }
-        let shared_key = FontKey::new(Self::SHARED_NAMESPACE, locked.next_id);
+        let shared_key = FontKey::new(locked.namespace, locked.next_id);
         locked.next_id += 1;
         let mapped = Arc::new(MappedFontKey {
             font_key: shared_key,
@@ -717,6 +718,7 @@ impl FontTemplateMap {
 }
 
 struct FontInstanceKeyMapLocked {
+    namespace: IdNamespace,
     next_id: u32,
     instances: FastHashSet<Arc<BaseFontInstance>>,
     key_map: FastHashMap<FontInstanceKey, Weak<BaseFontInstance>>,
@@ -729,15 +731,15 @@ struct FontInstanceKeyMapLocked {
 /// key to assign to that instance. When the weak count of the mapping is zero,
 /// the entry is allowed to expire. Again, care must be taken when clearing
 /// a namespace within the key map as it may cause shared key expirations that
-/// require individual processing.
+/// require individual processing. Shared instance keys will be created within
+/// the provided unique namespace.
 #[derive(Clone)]
 pub struct FontInstanceKeyMap(Arc<RwLock<FontInstanceKeyMapLocked>>);
 
 impl FontInstanceKeyMap {
-    const SHARED_NAMESPACE: IdNamespace = IdNamespace(0);
-
-    pub fn new() -> Self {
+    pub fn new(namespace: IdNamespace) -> Self {
         FontInstanceKeyMap(Arc::new(RwLock::new(FontInstanceKeyMapLocked {
+            namespace,
             next_id: 1,
             instances: FastHashSet::default(),
             key_map: FastHashMap::default(),
@@ -769,7 +771,7 @@ impl FontInstanceKeyMap {
             return None;
         }
         let unmapped_key = instance.instance_key;
-        instance.instance_key = FontInstanceKey::new(Self::SHARED_NAMESPACE, locked.next_id);
+        instance.instance_key = FontInstanceKey::new(locked.namespace, locked.next_id);
         locked.next_id += 1;
         let shared_instance = Arc::new(instance);
         locked.instances.insert(shared_instance.clone());
@@ -911,12 +913,12 @@ pub struct SharedFontResources {
 }
 
 impl SharedFontResources {
-    pub fn new() -> Self {
+    pub fn new(namespace: IdNamespace) -> Self {
         SharedFontResources {
             templates: FontTemplateMap::new(),
             instances: FontInstanceMap::new(),
-            font_keys: FontKeyMap::new(),
-            instance_keys: FontInstanceKeyMap::new(),
+            font_keys: FontKeyMap::new(namespace),
+            instance_keys: FontInstanceKeyMap::new(namespace),
         }
     }
 }

webrender/src/render_backend.rs

@@ -733,7 +733,7 @@ impl RenderBackend {
         }
     }
 
-    fn next_namespace_id(&self) -> IdNamespace {
+    pub fn next_namespace_id() -> IdNamespace {
         IdNamespace(NEXT_NAMESPACE_ID.fetch_add(1, Ordering::Relaxed) as u32)
     }
 
@@ -908,7 +908,7 @@ impl RenderBackend {
         match msg {
             ApiMsg::CloneApi(sender) => {
                 assert!(!self.namespace_alloc_by_client);
-                sender.send(self.next_namespace_id()).unwrap();
+                sender.send(Self::next_namespace_id()).unwrap();
             }
             ApiMsg::CloneApiByClient(namespace_id) => {
                 assert!(self.namespace_alloc_by_client);

webrender/src/renderer/mod.rs

@@ -1212,7 +1212,9 @@ impl Renderer {
         let sampler = options.sampler;
         let namespace_alloc_by_client = options.namespace_alloc_by_client;
 
-        let fonts = SharedFontResources::new();
+        // Ensure shared font keys exist within their own unique namespace so
+        // that they don't accidentally collide across Renderer instances.
+        let fonts = SharedFontResources::new(RenderBackend::next_namespace_id());
 
         let blob_image_handler = options.blob_image_handler.take();
         let scene_builder_hooks = options.scene_builder_hooks;

webrender/src/resource_cache.rs

@@ -540,7 +540,7 @@ impl ResourceCache {
         let workers = Arc::new(ThreadPoolBuilder::new().build().unwrap());
         let glyph_rasterizer = GlyphRasterizer::new(workers, true).unwrap();
         let cached_glyphs = GlyphCache::new();
-        let fonts = SharedFontResources::new();
+        let fonts = SharedFontResources::new(IdNamespace(0));
         let picture_textures = PictureTextures::new(
             crate::picture::TILE_SIZE_DEFAULT,
             TextureFilter::Nearest,