Use parking_lot for wrapping TextureManager

Cargo.lock

@@ -1005,6 +1005,7 @@ dependencies = [
  "ahash 0.7.6",
  "epaint",
  "nohash-hasher",
+ "parking_lot 0.12.0",
  "ron",
  "serde",
  "tracing",

egui/Cargo.toml

@@ -57,6 +57,7 @@ epaint = { version = "0.17.0", path = "../epaint", default-features = false }
 
 ahash = "0.7"
 nohash-hasher = "0.2"
+parking_lot = "0.12"
 
 # Optional:
 ron = { version = "0.7", optional = true }

egui/src/context.rs

@@ -11,8 +11,10 @@ use epaint::{mutex::*, stats::*, text::Fonts, TessellationOptions, *};
 
 // ----------------------------------------------------------------------------
 
+// NOTE: we always use `parking_lot` here so we can
+// use `WrappedTextureManager` from any thread.
 #[derive(Clone)]
-struct WrappedTextureManager(Arc<RwLock<epaint::TextureManager>>);
+struct WrappedTextureManager(Arc<parking_lot::RwLock<epaint::TextureManager>>);
 
 impl Default for WrappedTextureManager {
     fn default() -> Self {
@@ -25,7 +27,7 @@ impl Default for WrappedTextureManager {
         );
         assert_eq!(font_id, TextureId::default());
 
-        Self(Arc::new(RwLock::new(tex_mngr)))
+        Self(Arc::new(parking_lot::RwLock::new(tex_mngr)))
     }
 }
 
@@ -163,6 +165,9 @@ impl ContextImpl {
 #[derive(Clone, Default)]
 pub struct Context {
     ctx: Arc<RwLock<ContextImpl>>,
+    // These are not inside of `ContextImpl` because we want to have thread-safe access to them
+    // even without running with the multi_threaded feature flag.
+    // See https://github.com/emilk/egui/issues/1379.
     repaint_info: Arc<RepaintInfo>,
     tex_manager: WrappedTextureManager,
 }
@@ -731,7 +736,7 @@ impl Context {
     /// You can show stats about the allocated textures using [`Self::texture_ui`].
     ///
     /// This is safe to call from any thread at any time.
-    pub fn tex_manager(&self) -> Arc<RwLock<epaint::textures::TextureManager>> {
+    pub fn tex_manager(&self) -> Arc<parking_lot::RwLock<epaint::textures::TextureManager>> {
         self.tex_manager.0.clone()
     }
 

epaint/Cargo.toml

@@ -51,7 +51,7 @@ single_threaded = ["atomic_refcell"]
 
 # Only needed if you plan to use the same fonts from multiple threads.
 # It comes with a minor performance impact.
-multi_threaded = ["parking_lot"]
+multi_threaded = []
 
 
 [dependencies]
@@ -63,7 +63,7 @@ atomic_refcell = { version = "0.1", optional = true }                     # Used
 bytemuck = { version = "1.7.2", optional = true, features = ["derive"] }
 cint = { version = "^0.2.2", optional = true }
 nohash-hasher = "0.2"
-parking_lot = { version = "0.12", optional = true }                       # Using parking_lot over std::sync::Mutex gives 50% speedups in some real-world scenarios.
+parking_lot = "0.12"
 serde = { version = "1", optional = true, features = ["derive", "rc"] }
 
 [dev-dependencies]

epaint/src/texture_handle.rs

@@ -1,8 +1,6 @@
-use crate::{
+use crate::{emath::NumExt, mutex::Arc, ImageData, ImageDelta, TextureId, TextureManager};
-    emath::NumExt,
+
-    mutex::{Arc, RwLock},
+use parking_lot::RwLock;
-    ImageData, ImageDelta, TextureId, TextureManager,
-};
 
 /// Used to paint images.
 ///