Markdown pictures: an asset leaves the cache with its last holder

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/primitives/held.rs

@@ -1,26 +1,59 @@
-use std::sync::Arc;
+use std::{
+    any::TypeId,
+    collections::HashMap,
+    hash::{DefaultHasher, Hash, Hasher},
+    sync::Arc,
+};
 
-use gpui::{App, Asset, ElementId, RenderImage, Window};
+use gpui::{App, Asset, ElementId, Global, RenderImage, Window};
 
-/// An element's asset; freed on change or when it leaves.
+/// Holders of each asset, keyed as gpui's cache keys it.
+#[derive(Default)]
+struct Holders(HashMap<(TypeId, u64), usize>);
+
+impl Global for Holders {}
+
+fn key<A: Asset>(source: &A::Source) -> (TypeId, u64) {
+    let mut hasher = DefaultHasher::new();
+    source.hash(&mut hasher);
+    (TypeId::of::<A>(), hasher.finish())
+}
+
+/// An element's asset; the last holder to leave frees it.
 pub(crate) struct Held<A: Asset> {
     source: Option<A::Source>,
     image: Option<Arc<RenderImage>>,
 }
 
 impl<A: Asset> Held<A> {
+    fn take(&mut self, source: &A::Source, cx: &mut App) {
+        let holders = &mut cx.default_global::<Holders>().0;
+        *holders.entry(key::<A>(source)).or_default() += 1;
+        self.source = Some(source.clone());
+    }
+
     fn free(&mut self, cx: &mut App) {
-        if let Some(source) = self.source.take() {
-            cx.remove_asset::<A>(&source);
+        let Some(source) = self.source.take() else {
+            return;
+        };
+        let image = self.image.take();
+        let holders = &mut cx.default_global::<Holders>().0;
+        let key = key::<A>(&source);
+        let count = holders.get_mut(&key).expect("a held asset is counted");
+        *count -= 1;
+        if *count > 0 {
+            return;
         }
-        if let Some(image) = self.image.take() {
+        holders.remove(&key);
+        cx.remove_asset::<A>(&source);
+        if let Some(image) = image {
             // The window may be drawing; free after it.
             cx.defer(move |cx| cx.drop_image(image, None));
         }
     }
 }
 
-/// `source` as `A` for element `id`; the previous one freed.
+/// `source` as `A` for element `id`; the previous one let go.
 pub(crate) fn hold<A: Asset>(
     id: impl Into<ElementId>,
     source: &A::Source,
@@ -43,7 +76,7 @@ where
     held.update(cx, |held, cx| {
         if held.source.as_ref() != Some(source) {
             held.free(cx);
-            held.source = Some(source.clone());
+            held.take(source, cx);
         }
         if let Some(loaded) = &loaded {
             held.image = image(loaded);

src/typography/math/tests.rs

@@ -1,3 +1,5 @@
+use gpui::AppContext as _;
+
 use super::*;
 
 fn formula(source: &str, display: bool) -> Formula {
@@ -101,6 +103,12 @@ fn settle(cx: &mut gpui::VisualTestContext) {
     cx.run_until_parked();
 }
 
+/// Draws, then lets gpui release what the frame dropped.
+fn flush(cx: &mut gpui::VisualTestContext) {
+    cx.run_until_parked();
+    cx.update(|_, _| ());
+}
+
 /// Whether `source`'s picture sits in the asset cache.
 fn cached(source: &str, cx: &mut gpui::VisualTestContext) -> bool {
     cx.update(|window, cx| {
@@ -128,13 +136,44 @@ fn a_formula_frees_its_picture_when_it_changes_or_leaves(cx: &mut gpui::TestAppC
     assert!(!cached("b^2", cx), "gone with its element");
 }
 
+/// One formula in a view of its own.
+struct One;
+
+impl gpui::Render for One {
+    fn render(&mut self, _: &mut Window, _: &mut gpui::Context<Self>) -> impl IntoElement {
+        Latex::parse("one", "c^2").expect("parses")
+    }
+}
+
+/// Views of one formula, each drawn from gpui's view cache.
+struct Pair(Vec<gpui::Entity<One>>);
+
+impl gpui::Render for Pair {
+    fn render(&mut self, _: &mut Window, _: &mut gpui::Context<Self>) -> impl IntoElement {
+        div().children(
+            self.0.iter().map(|one| {
+                gpui::AnyView::from(one.clone()).cached(gpui::StyleRefinement::default())
+            }),
+        )
+    }
+}
+
 #[gpui::test]
-fn a_shared_formula_draws_on_after_one_user_leaves(cx: &mut gpui::TestAppContext) {
-    let (view, cx) = open(vec!["c^2", "c^2"], cx);
-    view.update(cx, |view, cx| {
-        view.0.pop();
+fn a_shared_formula_stays_until_its_last_holder_leaves(cx: &mut gpui::TestAppContext) {
+    cx.update(crate::theme::Theme::init);
+    let (pair, cx) = cx.add_window_view(|_, cx| Pair(vec![cx.new(|_| One), cx.new(|_| One)]));
+    settle(cx);
+    assert!(cached("c^2", cx), "drawn");
+    pair.update(cx, |pair, cx| {
+        pair.0.pop();
         cx.notify();
     });
-    settle(cx);
-    assert!(cached("c^2", cx), "the one left loads it again");
+    flush(cx);
+    assert!(cached("c^2", cx), "the cached survivor still holds it");
+    pair.update(cx, |pair, cx| {
+        pair.0.clear();
+        cx.notify();
+    });
+    flush(cx);
+    assert!(!cached("c^2", cx), "the last holder freed it");
 }