* Fix crash when spamming a viewport with other viewports

The crash was causated because sync viewport, when was cleaning up inactive viewports, was cleaning his parent before he got cleaned, and his parent when tring to resume was causing the crash

* Better performance because now the cleanup will be only run by the async viewports

crates/egui/src/context.rs

@@ -1540,27 +1540,9 @@ impl Context {
             }
         }
 
-        // Context Cleanup
-        self.write(|ctx| {
-            ctx.input.retain(|id, _| viewports.contains(id));
-            ctx.layer_rects_prev_viewports
-                .retain(|id, _| viewports.contains(id));
-            ctx.layer_rects_this_viewports
-                .retain(|id, _| viewports.contains(id));
-            ctx.output.retain(|id, _| viewports.contains(id));
-            ctx.frame_state.retain(|id, _| viewports.contains(id));
-            ctx.graphics.retain(|id, _| viewports.contains(id));
-            ctx.memory
-                .new_pixels_per_viewport
-                .retain(|id, _| viewports.contains(id));
-        });
-
-        let repaint_after =
-            self.write(|ctx| ctx.repaint.end_frame(ctx.get_viewport_id(), &viewports));
         let shapes = self.drain_paint_lists();
 
-        // This is used for,
-        // If there are no viewport that contains the current viewpor that viewport needs to be destroyed!
+        // If there are no viewport that contains the current viewport that viewport needs to be destroyed!
         let avalibile_viewports = self.read(|ctx| {
             let mut avalibile_viewports = vec![ViewportId::MAIN];
             for (_, id, _, _, _) in ctx.viewports.values() {
@@ -1571,9 +1553,6 @@ impl Context {
 
         let viewport_id = self.get_viewport_id();
 
-        // We should not process viewport commands when we are a sync viewport, because that will cause a deadlock or a memory race
-        let mut is_async = viewport_id == ViewportId::MAIN;
-
         let mut viewports = Vec::new();
         self.write(|ctx| {
             ctx.viewports
@@ -1584,10 +1563,6 @@ impl Context {
                         *used = false;
                     }
 
-                    if !is_async && viewport_id == *id {
-                        is_async = render.is_some();
-                    }
-
                     viewports.push((*id, *parent, builder.clone(), render.clone()));
                     (out || viewport_id != *parent) && avalibile_viewports.contains(parent)
                 });
@@ -1598,6 +1573,7 @@ impl Context {
             ctx.frame_stack.pop();
             ctx.frame_stack.is_empty()
         });
+
         if !is_last {
             let viewport_id = self.get_viewport_id();
             self.write(|ctx| {
@@ -1607,15 +1583,38 @@ impl Context {
                     ctx.layer_rects_this_viewports.remove(&viewport_id).unwrap();
                 ctx.memory.resume_frame(viewport_id);
             });
+        } else {
+            // ## Context Cleanup
+            self.write(|ctx| {
+                ctx.input.retain(|id, _| avalibile_viewports.contains(id));
+                ctx.layer_rects_prev_viewports
+                    .retain(|id, _| avalibile_viewports.contains(id));
+                ctx.layer_rects_this_viewports
+                    .retain(|id, _| avalibile_viewports.contains(id));
+                ctx.output.retain(|id, _| avalibile_viewports.contains(id));
+                ctx.frame_state
+                    .retain(|id, _| avalibile_viewports.contains(id));
+                ctx.graphics
+                    .retain(|id, _| avalibile_viewports.contains(id));
+                ctx.memory
+                    .new_pixels_per_viewport
+                    .retain(|id, _| avalibile_viewports.contains(id));
+            });
         }
 
+        let repaint_after = self.write(|ctx| {
+            ctx.repaint
+                .end_frame(ctx.get_viewport_id(), &avalibile_viewports)
+        });
+
         FullOutput {
             platform_output,
             repaint_after,
             textures_delta,
             shapes,
             viewports,
-            viewport_commands: if is_async {
+            // We should not process viewport commands when we are a sync viewport, because that will cause a deadlock for egui backend
+            viewport_commands: if is_last {
                 self.write(|ctx| std::mem::take(&mut ctx.viewport_commands))
             } else {
                 Vec::new()

crates/egui/src/memory.rs

@@ -564,8 +564,11 @@ impl Memory {
     }
 
     pub(crate) fn resume_frame(&mut self, viewport_id: ViewportId) {
-        self.interaction = self.interactions.remove(&viewport_id).unwrap();
-        self.areas = self.viewports_areas.remove(&viewport_id).unwrap();
+        self.interaction = self.interactions.remove(&viewport_id).unwrap_or_default();
+        self.areas = self
+            .viewports_areas
+            .remove(&viewport_id)
+            .unwrap_or_default();
         self.viewport_id = viewport_id;
         self.window_interaction = self.window_interactions.remove(&viewport_id);
     }