From fb80880ff89abf8674040229dab428b7b88b0b1a Mon Sep 17 00:00:00 2001
From: Konkitoman <konkitoman@users.noreply.github.com>
Date: Wed, 6 Sep 2023 16:30:20 +0300
Subject: [PATCH] * Fix posibile deadlock when sending a viewport command from
 a sync viewport

* Improve viewports example
---
 crates/eframe/src/native/run.rs | 19 --------------
 crates/egui/src/context.rs      | 17 +++++++++++--
 examples/viewports/src/main.rs  | 44 +++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 21 deletions(-)

diff --git a/crates/eframe/src/native/run.rs b/crates/eframe/src/native/run.rs
index e81066e0f..bfb5e46f1 100644
--- a/crates/eframe/src/native/run.rs
+++ b/crates/eframe/src/native/run.rs
@@ -1030,8 +1030,6 @@ mod glow_integration {
             let _painter = painter.clone();
             let time = integration.beginning;
 
-            let focused = self.is_focused.clone();
-
             // ## Sync Rendering
             integration.egui_ctx.set_render_sync_callback(
                 move |viewport_builder, viewport_id, parent_id, render| {
@@ -1129,17 +1127,6 @@ mod glow_integration {
                                     break 'try_render;
                                 }
                             }
-                            egui_winit::process_viewports_commands(
-                                output.viewport_commands,
-                                *focused.read(),
-                                |id| {
-                                    glutin
-                                        .read()
-                                        .windows
-                                        .get(&id)
-                                        .and_then(|w| w.read().window.clone())
-                                },
-                            );
                         }
                     }
                 },
@@ -2124,12 +2111,6 @@ mod wgpu_integration {
                                     break 'try_render;
                                 }
                             }
-
-                            egui_winit::process_viewports_commands(
-                                output.viewport_commands,
-                                *focused.read(),
-                                |id| _windows.read().get(&id).and_then(|w| w.window.clone()),
-                            );
                         }
                     }
                 },
diff --git a/crates/egui/src/context.rs b/crates/egui/src/context.rs
index 4ff4212f6..6857964ae 100644
--- a/crates/egui/src/context.rs
+++ b/crates/egui/src/context.rs
@@ -1570,9 +1570,13 @@ impl Context {
             avalibile_viewports
         });
 
+        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| {
-            let viewport_id = ctx.get_viewport_id();
             ctx.viewports
                 .retain(|_, (builder, id, parent, used, render)| {
                     let out = *used;
@@ -1581,6 +1585,10 @@ 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)
                 });
@@ -1601,13 +1609,18 @@ impl Context {
                 ctx.memory.resume_frame(viewport_id);
             });
         }
+
         FullOutput {
             platform_output,
             repaint_after,
             textures_delta,
             shapes,
             viewports,
-            viewport_commands: self.write(|ctx| std::mem::take(&mut ctx.viewport_commands)),
+            viewport_commands: if is_async {
+                self.write(|ctx| std::mem::take(&mut ctx.viewport_commands))
+            } else {
+                Vec::new()
+            },
         }
     }
 
diff --git a/examples/viewports/src/main.rs b/examples/viewports/src/main.rs
index e0babc547..b576990fa 100644
--- a/examples/viewports/src/main.rs
+++ b/examples/viewports/src/main.rs
@@ -86,6 +86,17 @@ impl eframe::App for App {
                                             if ui.button("Add").clicked() {
                                                 *state += 1;
                                             }
+
+                                            if ui.button("Set parent pos {0, 0}").clicked() {
+                                                let ctx = ui.ctx().clone();
+                                                let parent_id = ctx.get_parent_viewport_id();
+                                                ctx.viewport_command_for(
+                                                    parent_id,
+                                                    egui::ViewportCommand::OuterPosition(
+                                                        egui::pos2(0.0, 0.0),
+                                                    ),
+                                                );
+                                            }
                                         };
 
                                         show_as_popup(
@@ -111,6 +122,17 @@ impl eframe::App for App {
                                             if ui.button("Add").clicked() {
                                                 *state += 1;
                                             }
+
+                                            if ui.button("Set parent pos {0, 0}").clicked() {
+                                                let ctx = ui.ctx().clone();
+                                                let parent_id = ctx.get_parent_viewport_id();
+                                                ctx.viewport_command_for(
+                                                    parent_id,
+                                                    egui::ViewportCommand::OuterPosition(
+                                                        egui::pos2(0.0, 0.0),
+                                                    ),
+                                                );
+                                            }
                                         };
 
                                         show_as_popup(
@@ -160,6 +182,17 @@ impl eframe::App for App {
                                             if ui.button("Add").clicked() {
                                                 *state += 1;
                                             }
+
+                                            if ui.button("Set parent pos {0, 0}").clicked() {
+                                                let ctx = ui.ctx().clone();
+                                                let parent_id = ctx.get_parent_viewport_id();
+                                                ctx.viewport_command_for(
+                                                    parent_id,
+                                                    egui::ViewportCommand::OuterPosition(
+                                                        egui::pos2(0.0, 0.0),
+                                                    ),
+                                                );
+                                            }
                                         };
 
                                         show_as_popup(
@@ -185,6 +218,17 @@ impl eframe::App for App {
                                             if ui.button("Add").clicked() {
                                                 *state += 1;
                                             }
+
+                                            if ui.button("Set parent pos {0, 0}").clicked() {
+                                                let ctx = ui.ctx().clone();
+                                                let parent_id = ctx.get_parent_viewport_id();
+                                                ctx.viewport_command_for(
+                                                    parent_id,
+                                                    egui::ViewportCommand::OuterPosition(
+                                                        egui::pos2(0.0, 0.0),
+                                                    ),
+                                                );
+                                            }
                                         };
 
                                         show_as_popup(