Avoid deadlocks by using lambdas for context lock (#2625)

ctx.input().key_pressed(Key::A) -> ctx.input(|i| i.key_pressed(Key::A))

examples/file_dialog/src/main.rs

@@ -65,9 +65,11 @@ impl eframe::App for MyApp {
         preview_files_being_dropped(ctx);
 
         // Collect dropped files:
-        if !ctx.input().raw.dropped_files.is_empty() {
-            self.dropped_files = ctx.input().raw.dropped_files.clone();
-        }
+        ctx.input(|i| {
+            if !i.raw.dropped_files.is_empty() {
+                self.dropped_files = i.raw.dropped_files.clone();
+            }
+        });
     }
 }
 
@@ -76,22 +78,25 @@ fn preview_files_being_dropped(ctx: &egui::Context) {
     use egui::*;
     use std::fmt::Write as _;
 
-    if !ctx.input().raw.hovered_files.is_empty() {
-        let mut text = "Dropping files:\n".to_owned();
-        for file in &ctx.input().raw.hovered_files {
-            if let Some(path) = &file.path {
-                write!(text, "\n{}", path.display()).ok();
-            } else if !file.mime.is_empty() {
-                write!(text, "\n{}", file.mime).ok();
-            } else {
-                text += "\n???";
+    if !ctx.input(|i| i.raw.hovered_files.is_empty()) {
+        let text = ctx.input(|i| {
+            let mut text = "Dropping files:\n".to_owned();
+            for file in &i.raw.hovered_files {
+                if let Some(path) = &file.path {
+                    write!(text, "\n{}", path.display()).ok();
+                } else if !file.mime.is_empty() {
+                    write!(text, "\n{}", file.mime).ok();
+                } else {
+                    text += "\n???";
+                }
             }
-        }
+            text
+        });
 
         let painter =
             ctx.layer_painter(LayerId::new(Order::Foreground, Id::new("file_drop_target")));
 
-        let screen_rect = ctx.input().screen_rect();
+        let screen_rect = ctx.screen_rect();
         painter.rect_filled(screen_rect, 0.0, Color32::from_black_alpha(192));
         painter.text(
             screen_rect.center(),

examples/hello_world_par/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "hello_world_par"
+version = "0.1.0"
+authors = ["Maxim Osipenko <maxim1999max@gmail.com>"]
+license = "MIT OR Apache-2.0"
+edition = "2021"
+rust-version = "1.65"
+publish = false
+
+
+[dependencies]
+eframe = { path = "../../crates/eframe", default-features = false, features = [
+    # accesskit struggles with threading
+    "default_fonts",
+    "wgpu",
+] }

examples/hello_world_par/README.md

@@ -0,0 +1,5 @@
+This example shows that you can use egui in parallel from multiple threads.
+
+```sh
+cargo run -p hello_world_par
+```

examples/hello_world_par/src/main.rs

@@ -0,0 +1,132 @@
+//! This example shows that you can use egui in parallel from multiple threads.
+
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
+
+use std::sync::mpsc;
+use std::thread::JoinHandle;
+
+use eframe::egui;
+
+fn main() -> Result<(), eframe::Error> {
+    let options = eframe::NativeOptions {
+        initial_window_size: Some(egui::vec2(1024.0, 768.0)),
+        ..Default::default()
+    };
+    eframe::run_native(
+        "My parallel egui App",
+        options,
+        Box::new(|_cc| Box::new(MyApp::new())),
+    )
+}
+
+/// State per thread.
+struct ThreadState {
+    thread_nr: usize,
+    title: String,
+    name: String,
+    age: u32,
+}
+
+impl ThreadState {
+    fn new(thread_nr: usize) -> Self {
+        let title = format!("Background thread {thread_nr}");
+        Self {
+            thread_nr,
+            title,
+            name: "Arthur".into(),
+            age: 12 + thread_nr as u32 * 10,
+        }
+    }
+
+    fn show(&mut self, ctx: &egui::Context) {
+        let pos = egui::pos2(16.0, 128.0 * (self.thread_nr as f32 + 1.0));
+        egui::Window::new(&self.title)
+            .default_pos(pos)
+            .show(ctx, |ui| {
+                ui.horizontal(|ui| {
+                    ui.label("Your name: ");
+                    ui.text_edit_singleline(&mut self.name);
+                });
+                ui.add(egui::Slider::new(&mut self.age, 0..=120).text("age"));
+                if ui.button("Click each year").clicked() {
+                    self.age += 1;
+                }
+                ui.label(format!("Hello '{}', age {}", self.name, self.age));
+            });
+    }
+}
+
+fn new_worker(
+    thread_nr: usize,
+    on_done_tx: mpsc::SyncSender<()>,
+) -> (JoinHandle<()>, mpsc::SyncSender<egui::Context>) {
+    let (show_tx, show_rc) = mpsc::sync_channel(0);
+    let handle = std::thread::Builder::new()
+        .name(format!("EguiPanelWorker {}", thread_nr))
+        .spawn(move || {
+            let mut state = ThreadState::new(thread_nr);
+            while let Ok(ctx) = show_rc.recv() {
+                state.show(&ctx);
+                let _ = on_done_tx.send(());
+            }
+        })
+        .expect("failed to spawn thread");
+    (handle, show_tx)
+}
+
+struct MyApp {
+    threads: Vec<(JoinHandle<()>, mpsc::SyncSender<egui::Context>)>,
+    on_done_tx: mpsc::SyncSender<()>,
+    on_done_rc: mpsc::Receiver<()>,
+}
+
+impl MyApp {
+    fn new() -> Self {
+        let threads = Vec::with_capacity(3);
+        let (on_done_tx, on_done_rc) = mpsc::sync_channel(0);
+
+        let mut slf = Self {
+            threads,
+            on_done_tx,
+            on_done_rc,
+        };
+
+        slf.spawn_thread();
+        slf.spawn_thread();
+
+        slf
+    }
+
+    fn spawn_thread(&mut self) {
+        let thread_nr = self.threads.len();
+        self.threads
+            .push(new_worker(thread_nr, self.on_done_tx.clone()));
+    }
+}
+
+impl std::ops::Drop for MyApp {
+    fn drop(&mut self) {
+        for (handle, show_tx) in self.threads.drain(..) {
+            std::mem::drop(show_tx);
+            handle.join().unwrap();
+        }
+    }
+}
+
+impl eframe::App for MyApp {
+    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        egui::Window::new("Main thread").show(ctx, |ui| {
+            if ui.button("Spawn another thread").clicked() {
+                self.spawn_thread();
+            }
+        });
+
+        for (_handle, show_tx) in &self.threads {
+            let _ = show_tx.send(ctx.clone());
+        }
+
+        for _ in 0..self.threads.len() {
+            let _ = self.on_done_rc.recv();
+        }
+    }
+}

examples/keyboard_events/src/main.rs

@@ -33,14 +33,14 @@ impl eframe::App for Content {
                     ui.label(&self.text);
                 });
 
-            if ctx.input().key_pressed(Key::A) {
+            if ctx.input(|i| i.key_pressed(Key::A)) {
                 self.text.push_str("\nPressed");
             }
-            if ctx.input().key_down(Key::A) {
+            if ctx.input(|i| i.key_down(Key::A)) {
                 self.text.push_str("\nHeld");
                 ui.ctx().request_repaint(); // make sure we note the holding.
             }
-            if ctx.input().key_released(Key::A) {
+            if ctx.input(|i| i.key_released(Key::A)) {
                 self.text.push_str("\nReleased");
             }
         });

examples/puffin_profiler/src/main.rs

@@ -28,7 +28,7 @@ impl eframe::App for MyApp {
             ui.horizontal(|ui| {
                 ui.monospace(cmd);
                 if ui.small_button("📋").clicked() {
-                    ui.output().copied_text = cmd.into();
+                    ui.output_mut(|o| o.copied_text = cmd.into());
                 }
             });