eframe native: persist app state in background thread

Gives smoother frame rate

CHANGELOG.md

@@ -18,6 +18,7 @@ NOTE: [`epaint`](epaint/CHANGELOG.md), [`eframe`](eframe/CHANGELOG.md), [`egui_w
 * Added `Link` and `ui.link`  ([#1506](https://github.com/emilk/egui/pull/1506)).
 * Added triple-click support; triple-clicking a TextEdit field will select the whole paragraph ([#1512](https://github.com/emilk/egui/pull/1512)).
 * Added `Plot::x_grid_spacer` and `Plot::y_grid_spacer` for custom grid spacing ([#1180](https://github.com/emilk/egui/pull/1180)).
+* Added `Ui::spinner()` shortcut method ([#1494](https://github.com/emilk/egui/pull/1494)).
 * Added `CursorIcon`s for resizing columns, rows, and the eight cardinal directions.
 
 ### Changed 🔧

eframe/CHANGELOG.md

@@ -23,7 +23,7 @@ NOTE: [`egui_web`](../egui_web/CHANGELOG.md), [`egui-winit`](../egui-winit/CHANG
 * Fixed potential scale bug when DPI scaling changes (e.g. when dragging a  window between different displays) ([#1441](https://github.com/emilk/egui/pull/1441)).
 * MSRV (Minimum Supported Rust Version) is now `1.60.0` ([#1467](https://github.com/emilk/egui/pull/1467)).
 * Added new feature `puffin` to add [`puffin profiler`](https://github.com/EmbarkStudios/puffin) scopes ([#1483](https://github.com/emilk/egui/pull/1483)).
-* Added `Ui::spinner()` shortcut method ([#1494](https://github.com/emilk/egui/pull/1494)).
+* Moved app persistence to a background thread, allowing for smoother frame rates (on native).
 
 
 ## 0.17.0 - 2022-02-22

epi/src/file_storage.rs

@@ -59,11 +59,17 @@ impl crate::Storage for FileStorage {
 
     fn flush(&mut self) {
         if self.dirty {
-            // eprintln!("Persisted to {}", self.path.display());
-            let file = std::fs::File::create(&self.ron_filepath).unwrap();
-            let config = Default::default();
-            ron::ser::to_writer_pretty(file, &self.kv, config).unwrap();
             self.dirty = false;
+
+            let file_path = self.ron_filepath.clone();
+            let kv = self.kv.clone();
+
+            std::thread::spawn(move || {
+                let file = std::fs::File::create(&file_path).unwrap();
+                let config = Default::default();
+                ron::ser::to_writer_pretty(file, &kv, config).unwrap();
+                tracing::trace!("Persisted to {:?}", file_path);
+            });
         }
     }
 }