[egui_web] Prevent event handlers from running if code has panicked (#…

…1306)

Closes: #1290

Fix panic reported by @Titaniumtown
See #1306 (comment)

egui/src/widgets/plot/mod.rs

@@ -1,6 +1,6 @@
 //! Simple plotting library.
 
-use std::{cell::RefCell, ops::RangeInclusive, rc::Rc};
+use std::{cell::Cell, ops::RangeInclusive, rc::Rc};
 
 use crate::*;
 use epaint::ahash::AHashSet;
@@ -92,15 +92,15 @@ impl PlotMemory {
 pub struct LinkedAxisGroup {
     pub(crate) link_x: bool,
     pub(crate) link_y: bool,
-    pub(crate) bounds: Rc<RefCell<Option<PlotBounds>>>,
+    pub(crate) bounds: Rc<Cell<Option<PlotBounds>>>,
 }
 
 impl LinkedAxisGroup {
     pub fn new(link_x: bool, link_y: bool) -> Self {
         Self {
             link_x,
             link_y,
-            bounds: Rc::new(RefCell::new(None)),
+            bounds: Rc::new(Cell::new(None)),
         }
     }
 
@@ -132,11 +132,11 @@ impl LinkedAxisGroup {
     }
 
     fn get(&self) -> Option<PlotBounds> {
-        *self.bounds.borrow()
+        self.bounds.get()
     }
 
     fn set(&self, bounds: PlotBounds) {
-        *self.bounds.borrow_mut() = Some(bounds);
+        self.bounds.set(Some(bounds));
     }
 }
 

egui_web/CHANGELOG.md

@@ -3,6 +3,7 @@ All notable changes to the `egui_web` integration will be noted in this file.
 
 
 ## Unreleased
+* egui code will no longer be called after panic ([#1306](https://github.com/emilk/egui/pull/1306))
 
 
 ## 0.17.0 - 2022-02-22

egui_web/src/backend.rs

@@ -359,11 +359,37 @@ pub fn start(canvas_id: &str, app: Box<dyn epi::App>) -> Result<AppRunnerRef, Js
 /// Install event listeners to register different input events
 /// and starts running the given `AppRunner`.
 fn start_runner(app_runner: AppRunner) -> Result<AppRunnerRef, JsValue> {
-    let runner_ref = AppRunnerRef(Arc::new(Mutex::new(app_runner)));
-    install_canvas_events(&runner_ref)?;
-    install_document_events(&runner_ref)?;
-    text_agent::install_text_agent(&runner_ref)?;
-    repaint_every_ms(&runner_ref, 1000)?; // just in case. TODO: make it a parameter
-    paint_and_schedule(runner_ref.clone())?;
-    Ok(runner_ref)
+    let runner_container = AppRunnerContainer {
+        runner: Arc::new(Mutex::new(app_runner)),
+        panicked: Arc::new(AtomicBool::new(false)),
+    };
+
+    install_canvas_events(&runner_container)?;
+    install_document_events(&runner_container)?;
+    text_agent::install_text_agent(&runner_container)?;
+    repaint_every_ms(&runner_container, 1000)?; // just in case. TODO: make it a parameter
+
+    paint_and_schedule(&runner_container.runner, runner_container.panicked.clone())?;
+
+    // Disable all event handlers on panic
+    std::panic::set_hook(Box::new({
+        let previous_hook = std::panic::take_hook();
+
+        let panicked = runner_container.panicked;
+
+        move |panic_info| {
+            tracing::info_span!("egui_panic_handler").in_scope(|| {
+                tracing::trace!("setting panicked flag");
+
+                panicked.store(true, SeqCst);
+
+                tracing::info!("egui disabled all event handlers due to panic");
+            });
+
+            // Propagate panic info to the previously registered panic hook
+            previous_hook(panic_info);
+        }
+    }));
+
+    Ok(runner_container.runner)
 }