Thread-local query cache

4 files changed, 138 insertions, 87 deletions

diff --git a/src/export/render.rs b/src/export/render.rs
index 50257e1c..34fb4331 100644
--- a/src/export/render.rs
+++ b/src/export/render.rs
@@ -12,6 +12,7 @@ use crate::geom::{
     self, Geometry, Length, Paint, PathElement, Shape, Size, Stroke, Transform,
 };
 use crate::image::{Image, RasterImage, Svg};
+use crate::query::query_ref;
 use crate::Context;
 
 /// Export a frame into a rendered image.
@@ -240,17 +241,15 @@ fn render_outline_glyph(
         return Some(());
     }
 
-    // TODO(query)
+    // Rasterize the glyph with `pixglyph`.
     // Try to retrieve a prepared glyph or prepare it from scratch if it
     // doesn't exist, yet.
-    let glyph = ctx
-        .query((text.face_id, id), |ctx, (face_id, id)| {
-            pixglyph::Glyph::load(ctx.fonts.get(face_id).ttf(), id)
-        })
-        .as_ref()?;
+    let bitmap = query_ref(
+        (&ctx.fonts, text.face_id, id),
+        |(fonts, face_id, id)| pixglyph::Glyph::load(fonts.get(face_id).ttf(), id),
+        |glyph| glyph.as_ref().map(|g| g.rasterize(ts.tx, ts.ty, ppem)),
+    )?;
 
-    // Rasterize the glyph with `pixglyph`.
-    let bitmap = glyph.rasterize(ts.tx, ts.ty, ppem);
     let cw = canvas.width() as i32;
     let ch = canvas.height() as i32;
     let mw = bitmap.width as i32;
diff --git a/src/lib.rs b/src/lib.rs
index 06324c11..5173b022 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -47,13 +47,11 @@ pub mod library;
 pub mod loading;
 pub mod model;
 pub mod parse;
+pub mod query;
 pub mod source;
 pub mod syntax;
 
-use std::any::Any;
 use std::collections::HashMap;
-use std::fmt::{self, Display, Formatter};
-use std::hash::Hash;
 use std::mem;
 use std::path::PathBuf;
 use std::sync::Arc;
@@ -68,7 +66,7 @@ use crate::model::StyleMap;
 use crate::source::{SourceId, SourceStore};
 use crate::util::PathExt;
 
-/// The core context which holds the loader, configuration and cached artifacts.
+/// The core context which holds the loader, stores, and configuration.
 pub struct Context {
     /// The loader the context was created with.
     pub loader: Arc<dyn Loader>,
@@ -86,8 +84,6 @@ pub struct Context {
     styles: Arc<StyleMap>,
     /// Cached modules.
     modules: HashMap<SourceId, Module>,
-    /// Cached queries.
-    cache: HashMap<u64, CacheEntry>,
     /// The stack of imported files that led to evaluation of the current file.
     route: Vec<SourceId>,
     /// The dependencies of the current evaluation process.
@@ -236,77 +232,9 @@ impl ContextBuilder {
             std: self.std.clone().unwrap_or_else(|| Arc::new(library::new())),
             styles: self.styles.clone().unwrap_or_default(),
             modules: HashMap::new(),
-            cache: HashMap::new(),
             route: vec![],
             deps: vec![],
             flow: None,
         }
     }
 }
-
-/// An entry in the query cache.
-struct CacheEntry {
-    /// The query's results.
-    data: Box<dyn Any>,
-    /// How many evictions have passed since the entry has been last used.
-    age: usize,
-}
-
-impl Context {
-    /// Execute a query.
-    ///
-    /// This hashes all inputs to the query and then either returns a cached
-    /// version or executes the query, saves the results in the cache and
-    /// returns a reference to them.
-    pub fn query<I, O>(
-        &mut self,
-        input: I,
-        query: fn(ctx: &mut Self, input: I) -> O,
-    ) -> &O
-    where
-        I: Hash,
-        O: 'static,
-    {
-        let hash = fxhash::hash64(&input);
-        if !self.cache.contains_key(&hash) {
-            let output = query(self, input);
-            self.cache.insert(hash, CacheEntry { data: Box::new(output), age: 0 });
-        }
-
-        let entry = self.cache.get_mut(&hash).unwrap();
-        entry.age = 0;
-        entry.data.downcast_ref().expect("oh no, a hash collision")
-    }
-
-    /// Garbage-collect the query cache. This deletes elements which haven't
-    /// been used in a while.
-    ///
-    /// Returns details about the eviction.
-    pub fn evict(&mut self) -> Eviction {
-        const MAX_AGE: usize = 5;
-
-        let before = self.cache.len();
-        self.cache.retain(|_, entry| {
-            entry.age += 1;
-            entry.age <= MAX_AGE
-        });
-
-        Eviction { before, after: self.cache.len() }
-    }
-}
-
-/// Details about a cache eviction.
-pub struct Eviction {
-    /// The number of items in the cache before the eviction.
-    pub before: usize,
-    /// The number of items in the cache after the eviction.
-    pub after: usize,
-}
-
-impl Display for Eviction {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        writeln!(f, "Before: {}", self.before)?;
-        writeln!(f, "Evicted: {}", self.before - self.after)?;
-        writeln!(f, "After: {}", self.after)
-    }
-}
diff --git a/src/model/layout.rs b/src/model/layout.rs
index 3b82ddc2..1933fca1 100644
--- a/src/model/layout.rs
+++ b/src/model/layout.rs
@@ -14,6 +14,7 @@ use crate::geom::{
 };
 use crate::library::graphics::MoveNode;
 use crate::library::layout::{AlignNode, PadNode};
+use crate::query::query;
 use crate::util::Prehashed;
 use crate::Context;
 
@@ -221,11 +222,13 @@ impl Layout for LayoutNode {
         regions: &Regions,
         styles: StyleChain,
     ) -> TypResult<Vec<Arc<Frame>>> {
-        ctx.query((self, regions, styles), |ctx, (node, regions, styles)| {
-            let entry = StyleEntry::Barrier(Barrier::new(node.id()));
-            node.0.layout(ctx, regions, entry.chain(&styles))
-        })
-        .clone()
+        query(
+            (self, ctx, regions, styles),
+            |(node, ctx, regions, styles)| {
+                let entry = StyleEntry::Barrier(Barrier::new(node.id()));
+                node.0.layout(ctx, regions, entry.chain(&styles))
+            },
+        )
     }
 
     fn pack(self) -> LayoutNode {
diff --git a/src/query.rs b/src/query.rs
new file mode 100644
index 00000000..97af0139
--- /dev/null
+++ b/src/query.rs
@@ -0,0 +1,121 @@
+//! Query caching.
+
+use std::any::Any;
+use std::cell::RefCell;
+use std::collections::HashMap;
+use std::fmt::{self, Display, Formatter};
+use std::hash::Hash;
+
+thread_local! {
+    /// The thread-local query cache.
+    static CACHE: RefCell<Cache> = RefCell::default();
+}
+
+/// A map from hashes to cache entries.
+type Cache = HashMap<u64, CacheEntry>;
+
+/// Access the cache.
+fn with<F, R>(f: F) -> R
+where
+    F: FnOnce(&mut Cache) -> R,
+{
+    CACHE.with(|cell| f(&mut cell.borrow_mut()))
+}
+
+/// An entry in the query cache.
+struct CacheEntry {
+    /// The query's results.
+    data: Box<dyn Any>,
+    /// How many evictions have passed since the entry has been last used.
+    age: usize,
+}
+
+/// Execute a query.
+///
+/// This hashes all inputs to the query and then either returns a cached version
+/// from the thread-local query cache or executes the query and saves a copy of
+/// the results in the cache.
+///
+/// Note that `f` must be a pure function.
+pub fn query<I, O>(input: I, f: fn(input: I) -> O) -> O
+where
+    I: Hash,
+    O: Clone + 'static,
+{
+    query_ref(input, f, Clone::clone)
+}
+
+/// Execute a query and then call a function with a reference to the result.
+///
+/// This hashes all inputs to the query and then either call `g` with a cached
+/// version from the thread-local query cache or executes the query, calls `g`
+/// with the fresh version and saves  the result in the cache.
+///
+/// Note that `f` must be a pure function, while `g` does not need to be pure.
+pub fn query_ref<I, O, G, R>(input: I, f: fn(input: I) -> O, g: G) -> R
+where
+    I: Hash,
+    O: 'static,
+    G: Fn(&O) -> R,
+{
+    let hash = fxhash::hash64(&input);
+    let result = with(|cache| {
+        let entry = cache.get_mut(&hash)?;
+        entry.age = 0;
+        entry.data.downcast_ref().map(|output| g(output))
+    });
+
+    result.unwrap_or_else(|| {
+        let output = f(input);
+        let result = g(&output);
+        let entry = CacheEntry { data: Box::new(output), age: 0 };
+        with(|cache| cache.insert(hash, entry));
+        result
+    })
+}
+
+/// Garbage-collect the thread-local query cache.
+///
+/// This deletes elements which haven't been used in a while and returns details
+/// about the eviction.
+pub fn evict() -> Eviction {
+    with(|cache| {
+        const MAX_AGE: usize = 5;
+
+        let before = cache.len();
+        cache.retain(|_, entry| {
+            entry.age += 1;
+            entry.age <= MAX_AGE
+        });
+
+        Eviction { before, after: cache.len() }
+    })
+}
+
+/// Details about a cache eviction.
+pub struct Eviction {
+    /// The number of items in the cache before the eviction.
+    pub before: usize,
+    /// The number of items in the cache after the eviction.
+    pub after: usize,
+}
+
+impl Display for Eviction {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        writeln!(f, "Before: {}", self.before)?;
+        writeln!(f, "Evicted: {}", self.before - self.after)?;
+        writeln!(f, "After: {}", self.after)
+    }
+}
+
+// These impls are temporary and incorrect.
+macro_rules! skip {
+    ($ty:ty) => {
+        impl Hash for $ty {
+            fn hash<H: std::hash::Hasher>(&self, _: &mut H) {}
+        }
+    };
+}
+
+skip!(crate::font::FontStore);
+skip!(crate::Context);