Remove the single_threaded/multi_threaded feature flags

Always use parking_lot for mutexes, i.e. always be multi-threaded. Closes #1379 An alternative to #1389
emilk · Mar 20, 2022 · c7d6775 · c7d6775
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diff --git a/ARCHITECTURE.md b/ARCHITECTURE.md
@@ -19,7 +19,7 @@ Examples: `Vec2, Pos2, Rect, lerp, remap`
 
 Example: `Shape::Circle { center, radius, fill, stroke }`
 
-Depends on `emath`, [`ab_glyph`](https://crates.io/crates/ab_glyph), [`atomic_refcell`](https://crates.io/crates/atomic_refcell), [`ahash`](https://crates.io/crates/ahash).
+Depends on `emath`.
 
 ### `egui_extras`
 This adds additional features on top of `egui`.

diff --git a/Cargo.lock b/Cargo.lock
diff --git a/README.md b/README.md
@@ -85,7 +85,7 @@ On Fedora Rawhide you need to run:
 * Extensible: [easy to write your own widgets for egui](https://github.com/emilk/egui/blob/master/egui_demo_lib/src/apps/demo/toggle_switch.rs)
 * Modular: You should be able to use small parts of egui and combine them in new ways
 * Safe: there is no `unsafe` code in egui
-* Minimal dependencies: [`ab_glyph`](https://crates.io/crates/ab_glyph) [`ahash`](https://crates.io/crates/ahash) [`atomic_refcell`](https://crates.io/crates/atomic_refcell), [`nohash-hasher`](https://crates.io/crates/nohash-hasher)
+* Minimal dependencies: [`ab_glyph`](https://crates.io/crates/ab_glyph) [`ahash`](https://crates.io/crates/ahash) [`nohash-hasher`](https://crates.io/crates/nohash-hasher) [`parking_lot`](https://crates.io/crates/parking_lot)
 
 egui is *not* a framework. egui is a library you call into, not an environment you program for.
 

diff --git a/egui-winit/Cargo.toml b/egui-winit/Cargo.toml
@@ -45,7 +45,6 @@ serialize = ["egui/serialize", "serde"]
 
 [dependencies]
 egui = { version = "0.17.0", path = "../egui", default-features = false, features = [
-  "single_threaded",
   "tracing",
 ] }
 instant = { version = "0.1", features = ["wasm-bindgen"] }

diff --git a/egui/Cargo.toml b/egui/Cargo.toml
@@ -20,7 +20,7 @@ all-features = true
 
 
 [features]
-default = ["default_fonts", "single_threaded"]
+default = ["default_fonts"]
 
 # add compatibility with https://crates.io/crates/cint
 cint = ["epaint/cint"]
@@ -46,11 +46,6 @@ persistence = ["serde", "epaint/serialize", "ron"]
 # implement serde on most types.
 serialize = ["serde", "epaint/serialize"]
 
-# multi_threaded is only needed if you plan to use the same egui::Context
-# from multiple threads. It comes with a minor performance impact.
-single_threaded = ["epaint/single_threaded"]
-multi_threaded = ["epaint/multi_threaded"]
-
 
 [dependencies]
 epaint = { version = "0.17.0", path = "../epaint", default-features = false }

diff --git a/egui_extras/Cargo.toml b/egui_extras/Cargo.toml
@@ -27,17 +27,15 @@ svg = ["resvg", "tiny-skia", "usvg"]
 
 
 [dependencies]
-egui = { version = "0.17.0", path = "../egui", default-features = false, features = [
-  "single_threaded",
-] }
+egui = { version = "0.17.0", path = "../egui", default-features = false }
 parking_lot = "0.12"
 
 # Optional dependencies:
 
 # Add support for loading images with the `image` crate.
 # You also need to ALSO opt-in to the image formats you want to support, like so:
 #     image = { version = "0.24", features = ["jpeg", "png"] }
-image = { version = "0.24", optional = true, default-features = false, features = [] }
+image = { version = "0.24", optional = true, default-features = false }
 
 # svg feature
 resvg = { version = "0.22", optional = true }

diff --git a/egui_glium/Cargo.toml b/egui_glium/Cargo.toml
@@ -47,7 +47,6 @@ screen_reader = ["egui-winit/screen_reader"]
 [dependencies]
 egui = { version = "0.17.0", path = "../egui", default-features = false, features = [
   "convert_bytemuck",
-  "single_threaded",
 ] }
 egui-winit = { version = "0.17.0", path = "../egui-winit", default-features = false }
 

diff --git a/egui_glow/Cargo.toml b/egui_glow/Cargo.toml
@@ -57,7 +57,6 @@ winit = ["egui-winit", "glutin"]
 [dependencies]
 egui = { version = "0.17.0", path = "../egui", default-features = false, features = [
   "convert_bytemuck",
-  "single_threaded",
 ] }
 epi = { version = "0.17.0", path = "../epi", optional = true }
 

diff --git a/egui_web/Cargo.toml b/egui_web/Cargo.toml
@@ -43,7 +43,6 @@ screen_reader = ["tts"]
 [dependencies]
 egui = { version = "0.17.0", path = "../egui", default-features = false, features = [
   "convert_bytemuck",
-  "single_threaded",
   "tracing",
 ] }
 egui_glow = { version = "0.17.0", path = "../egui_glow", default-features = false }

diff --git a/epaint/Cargo.toml b/epaint/Cargo.toml
@@ -27,7 +27,7 @@ all-features = true
 
 
 [features]
-default = ["default_fonts", "multi_threaded"]
+default = ["default_fonts"]
 
 # implement bytemuck on most types.
 convert_bytemuck = ["bytemuck", "emath/bytemuck"]
@@ -47,23 +47,16 @@ mint = ["emath/mint"]
 # implement serde on most types.
 serialize = ["serde", "ahash/serde", "emath/serde"]
 
-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"]
-
 
 [dependencies]
 emath = { version = "0.17.0", path = "../emath" }
 
 ab_glyph = "0.2.11"
 ahash = { version = "0.7", default-features = false, features = ["std"] }
-atomic_refcell = { version = "0.1", optional = true }                     # Used instead of parking_lot when you are always using epaint in a single thread. About as fast as parking_lot. Panics on multi-threaded use.
 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"                                                      # Using parking_lot over std::sync::Mutex gives 50% speedups in some real-world scenarios.
 serde = { version = "1", optional = true, features = ["derive", "rc"] }
 
 [dev-dependencies]

diff --git a/epaint/src/mutex.rs b/epaint/src/mutex.rs
@@ -1,16 +1,10 @@
 //! Helper module that wraps some Mutex types with different implementations.
-//!
-//! When the `single_threaded` feature is on the mutexes will panic when locked from different threads.
-
-#[cfg(not(any(feature = "single_threaded", feature = "multi_threaded")))]
-compile_error!("Either feature \"single_threaded\" or \"multi_threaded\" must be enabled.");
 
 // ----------------------------------------------------------------------------
 
-#[cfg(feature = "multi_threaded")]
 #[cfg(not(debug_assertions))]
 mod mutex_impl {
-    /// Provides interior mutability. Only thread-safe if the `multi_threaded` feature is enabled.
+    /// Provides interior mutability.
     #[derive(Default)]
     pub struct Mutex<T>(parking_lot::Mutex<T>);
 
@@ -30,10 +24,9 @@ mod mutex_impl {
     }
 }
 
-#[cfg(feature = "multi_threaded")]
 #[cfg(debug_assertions)]
 mod mutex_impl {
-    /// Provides interior mutability. Only thread-safe if the `multi_threaded` feature is enabled.
+    /// Provides interior mutability.
     #[derive(Default)]
     pub struct Mutex<T>(parking_lot::Mutex<T>);
 
@@ -111,15 +104,14 @@ mod mutex_impl {
     }
 }
 
-#[cfg(feature = "multi_threaded")]
 mod rw_lock_impl {
     /// The lock you get from [`RwLock::read`].
     pub use parking_lot::MappedRwLockReadGuard as RwLockReadGuard;
 
     /// The lock you get from [`RwLock::write`].
     pub use parking_lot::MappedRwLockWriteGuard as RwLockWriteGuard;
 
-    /// Provides interior mutability. Only thread-safe if the `multi_threaded` feature is enabled.
+    /// Provides interior mutability.
     #[derive(Default)]
     pub struct RwLock<T>(parking_lot::RwLock<T>);
 
@@ -141,74 +133,7 @@ mod rw_lock_impl {
     }
 }
 
-#[cfg(feature = "multi_threaded")]
-mod arc_impl {
-    pub use std::sync::Arc;
-}
-
-// ----------------------------------------------------------------------------
-
-#[cfg(not(feature = "multi_threaded"))]
-mod mutex_impl {
-    // `atomic_refcell` will panic if multiple threads try to access the same value
-
-    /// Provides interior mutability. Only thread-safe if the `multi_threaded` feature is enabled.
-    #[derive(Default)]
-    pub struct Mutex<T>(atomic_refcell::AtomicRefCell<T>);
-
-    /// The lock you get from [`Mutex`].
-    pub use atomic_refcell::AtomicRefMut as MutexGuard;
-
-    impl<T> Mutex<T> {
-        #[inline(always)]
-        pub fn new(val: T) -> Self {
-            Self(atomic_refcell::AtomicRefCell::new(val))
-        }
-
-        /// Panics if already locked.
-        #[inline(always)]
-        pub fn lock(&self) -> MutexGuard<'_, T> {
-            self.0.borrow_mut()
-        }
-    }
-}
-
-#[cfg(not(feature = "multi_threaded"))]
-mod rw_lock_impl {
-    // `atomic_refcell` will panic if multiple threads try to access the same value
-
-    /// The lock you get from [`RwLock::read`].
-    pub use atomic_refcell::AtomicRef as RwLockReadGuard;
-
-    /// The lock you get from [`RwLock::write`].
-    pub use atomic_refcell::AtomicRefMut as RwLockWriteGuard;
-
-    /// Provides interior mutability. Only thread-safe if the `multi_threaded` feature is enabled.
-    #[derive(Default)]
-    pub struct RwLock<T>(atomic_refcell::AtomicRefCell<T>);
-
-    impl<T> RwLock<T> {
-        #[inline(always)]
-        pub fn new(val: T) -> Self {
-            Self(atomic_refcell::AtomicRefCell::new(val))
-        }
-
-        #[inline(always)]
-        pub fn read(&self) -> RwLockReadGuard<'_, T> {
-            self.0.borrow()
-        }
-
-        /// Panics if already locked.
-        #[inline(always)]
-        pub fn write(&self) -> RwLockWriteGuard<'_, T> {
-            self.0.borrow_mut()
-        }
-    }
-}
-
-#[cfg(not(feature = "multi_threaded"))]
 mod arc_impl {
-    // pub use std::rc::Rc as Arc; // TODO(emilk): optimize single threaded code by using `Rc` instead of `Arc`.
     pub use std::sync::Arc;
 }
 

diff --git a/epi/Cargo.toml b/epi/Cargo.toml
@@ -28,9 +28,7 @@ persistence = ["ron", "serde", "egui/persistence"]
 
 
 [dependencies]
-egui = { version = "0.17.0", path = "../egui", default-features = false, features = [
-  "single_threaded",
-] }
+egui = { version = "0.17.0", path = "../egui", default-features = false }
 glow = "0.11"
 tracing = "0.1"
 

diff --git a/sh/check.sh b/sh/check.sh
@@ -20,17 +20,15 @@ cargo doc -p egui_web --target wasm32-unknown-unknown --lib --no-deps --all-feat
 cargo doc --document-private-items --no-deps --all-features
 
 (cd emath && cargo check --no-default-features)
-(cd epaint && cargo check --no-default-features --features "single_threaded")
-(cd epaint && cargo check --no-default-features --features "multi_threaded")
-(cd epaint && cargo check --no-default-features --features "single_threaded" --release)
-(cd epaint && cargo check --no-default-features --features "multi_threaded" --release)
-(cd egui && cargo check --no-default-features --features "multi_threaded,serialize")
+(cd epaint && cargo check --no-default-features)
+(cd epaint && cargo check --no-default-features --release)
+(cd egui && cargo check --no-default-features --features "serialize")
 (cd eframe && cargo check --no-default-features)
 (cd epi && cargo check --no-default-features)
 (cd egui_demo_lib && cargo check --no-default-features)
 (cd egui_extras && cargo check --no-default-features)
 (cd egui_web && cargo check --no-default-features)
-# (cd egui-winit && cargo check --no-default-features) # we don't pick singlethreaded or multithreaded
+(cd egui-winit && cargo check --no-default-features)
 (cd egui_glium && cargo check --no-default-features)
 (cd egui_glow && cargo check --no-default-features)