Terminate app run loop on Windows when all windows have closed.

druid-shell/examples/perftest.rs

@@ -19,7 +19,7 @@ use time::Instant;
 use piet_common::kurbo::{Line, Rect};
 use piet_common::{Color, FontBuilder, Piet, RenderContext, Text, TextLayoutBuilder};
 
-use druid_shell::{Application, KeyEvent, WinHandler, WindowBuilder, WindowHandle};
+use druid_shell::{AppState, Application, KeyEvent, WinHandler, WindowBuilder, WindowHandle};
 
 const BG_COLOR: Color = Color::rgb8(0x27, 0x28, 0x22);
 const FG_COLOR: Color = Color::rgb8(0xf0, 0xf0, 0xea);
@@ -116,8 +116,9 @@ impl WinHandler for PerfTest {
 }
 
 fn main() {
-    let mut app = Application::new(None);
-    let mut builder = WindowBuilder::new();
+    let state = AppState::new();
+    let mut app = Application::new(state.clone(), None);
+    let mut builder = WindowBuilder::new(state);
     let perf_test = PerfTest {
         size: Default::default(),
         handle: Default::default(),

druid-shell/examples/shello.rs

@@ -18,8 +18,8 @@ use druid_shell::kurbo::{Line, Rect, Vec2};
 use druid_shell::piet::{Color, RenderContext};
 
 use druid_shell::{
-    Application, Cursor, FileDialogOptions, FileSpec, HotKey, KeyEvent, KeyModifiers, Menu,
-    MouseEvent, SysMods, TimerToken, WinHandler, WindowBuilder, WindowHandle,
+    AppState, Application, Cursor, FileDialogOptions, FileSpec, HotKey, KeyEvent, KeyModifiers,
+    Menu, MouseEvent, SysMods, TimerToken, WinHandler, WindowBuilder, WindowHandle,
 };
 
 const BG_COLOR: Color = Color::rgb8(0x27, 0x28, 0x22);
@@ -129,8 +129,9 @@ fn main() {
     menubar.add_dropdown(Menu::new(), "Application", true);
     menubar.add_dropdown(file_menu, "&File", true);
 
-    let mut app = Application::new(None);
-    let mut builder = WindowBuilder::new();
+    let state = AppState::new();
+    let mut app = Application::new(state.clone(), None);
+    let mut builder = WindowBuilder::new(state);
     builder.set_handler(Box::new(HelloState::default()));
     builder.set_title("Hello example");
     builder.set_menu(menubar);

druid-shell/src/application.rs

@@ -14,6 +14,8 @@
 
 //! The top-level application type.
 
+use std::sync::atomic::{AtomicBool, Ordering};
+
 use crate::clipboard::Clipboard;
 use crate::platform::application as platform;
 
@@ -36,14 +38,43 @@ pub trait AppHandler {
     fn command(&mut self, id: u32) {}
 }
 
+/// The top level application state.
+///
+/// This helps the application track all the state that it has created,
+/// which it later needs to clean up.
+#[derive(Clone)]
+pub struct AppState(pub(crate) platform::AppState);
+
+impl AppState {
+    /// Create a new `AppState` instance.
+    pub fn new() -> AppState {
+        AppState(platform::AppState::new())
+    }
+}
+
 //TODO: we may want to make the user create an instance of this (Application::global()?)
 //but for now I'd like to keep changes minimal.
 /// The top level application object.
 pub struct Application(platform::Application);
 
+// Used to ensure only one Application instance is ever created.
+// This may change in the future.
+// For more information see https://github.com/xi-editor/druid/issues/771
+static APPLICATION_CREATED: AtomicBool = AtomicBool::new(false);
+
 impl Application {
-    pub fn new(handler: Option<Box<dyn AppHandler>>) -> Application {
-        Application(platform::Application::new(handler))
+    /// Create a new `Application`.
+    ///
+    /// It takes the application `state` and a `handler` which will be used to inform of events.
+    ///
+    /// Right now only one application can be created. See [druid#771] for discussion.
+    ///
+    /// [druid#771]: https://github.com/xi-editor/druid/issues/771
+    pub fn new(state: AppState, handler: Option<Box<dyn AppHandler>>) -> Application {
+        if APPLICATION_CREATED.compare_and_swap(false, true, Ordering::AcqRel) {
+            panic!("The Application instance has already been created.");
+        }
+        Application(platform::Application::new(state.0, handler))
     }
 
     /// Start the runloop.

druid-shell/src/lib.rs

@@ -37,7 +37,7 @@ mod mouse;
 mod platform;
 mod window;
 
-pub use application::{AppHandler, Application};
+pub use application::{AppHandler, AppState, Application};
 pub use clipboard::{Clipboard, ClipboardFormat, FormatId};
 pub use common_util::Counter;
 pub use dialog::{FileDialogOptions, FileInfo, FileSpec};

druid-shell/src/platform/gtk/application.rs

@@ -31,10 +31,19 @@ thread_local!(
     static GTK_APPLICATION: RefCell<Option<GtkApplication>> = RefCell::new(None);
 );
 
+#[derive(Clone)]
+pub struct AppState;
+
 pub struct Application;
 
+impl AppState {
+    pub(crate) fn new() -> AppState {
+        AppState
+    }
+}
+
 impl Application {
-    pub fn new(_handler: Option<Box<dyn AppHandler>>) -> Application {
+    pub fn new(_state: AppState, _handler: Option<Box<dyn AppHandler>>) -> Application {
         // TODO: we should give control over the application ID to the user
         let application = GtkApplication::new(
             Some("com.github.xi-editor.druid"),

druid-shell/src/platform/gtk/window.rs

@@ -33,7 +33,7 @@ use gtk::{AccelGroup, ApplicationWindow};
 use crate::kurbo::{Point, Size, Vec2};
 use crate::piet::{Piet, RenderContext};
 
-use super::application::with_application;
+use super::application::{with_application, AppState};
 use super::dialog;
 use super::menu::Menu;
 use super::util::assert_main_thread;
@@ -111,7 +111,7 @@ pub(crate) struct WindowState {
 }
 
 impl WindowBuilder {
-    pub fn new() -> WindowBuilder {
+    pub fn new(_app_state: AppState) -> WindowBuilder {
         WindowBuilder {
             handler: None,
             title: String::new(),

druid-shell/src/platform/mac/application.rs

@@ -32,12 +32,21 @@ use crate::application::AppHandler;
 
 static APP_HANDLER_IVAR: &str = "druidAppHandler";
 
+#[derive(Clone)]
+pub struct AppState;
+
 pub struct Application {
     ns_app: id,
 }
 
+impl AppState {
+    pub(crate) fn new() -> AppState {
+        AppState
+    }
+}
+
 impl Application {
-    pub fn new(handler: Option<Box<dyn AppHandler>>) -> Application {
+    pub fn new(_state: AppState, handler: Option<Box<dyn AppHandler>>) -> Application {
         util::assert_main_thread();
         unsafe {
             let _pool = NSAutoreleasePool::new(nil);

druid-shell/src/platform/mac/window.rs

@@ -41,6 +41,7 @@ use log::{error, info};
 use crate::kurbo::{Point, Size, Vec2};
 use crate::piet::{Piet, RenderContext};
 
+use super::application::AppState;
 use super::dialog;
 use super::menu::Menu;
 use super::util::{assert_main_thread, make_nsstring};
@@ -104,7 +105,7 @@ struct ViewState {
 }
 
 impl WindowBuilder {
-    pub fn new() -> WindowBuilder {
+    pub fn new(_app_state: AppState) -> WindowBuilder {
         WindowBuilder {
             handler: None,
             title: String::new(),

druid-shell/src/platform/web/application.rs

@@ -17,10 +17,19 @@
 use super::clipboard::Clipboard;
 use crate::application::AppHandler;
 
+#[derive(Clone)]
+pub struct AppState;
+
 pub struct Application;
 
+impl AppState {
+    pub(crate) fn new() -> AppState {
+        AppState
+    }
+}
+
 impl Application {
-    pub fn new(_handler: Option<Box<dyn AppHandler>>) -> Application {
+    pub fn new(_state: AppState, _handler: Option<Box<dyn AppHandler>>) -> Application {
         Application
     }
 

druid-shell/src/platform/web/window.rs

@@ -29,6 +29,7 @@ use crate::kurbo::{Point, Size, Vec2};
 
 use crate::piet::RenderContext;
 
+use super::application::AppState;
 use super::error::Error;
 use super::keycodes::key_to_text;
 use super::menu::Menu;
@@ -296,7 +297,7 @@ fn setup_web_callbacks(window_state: &Rc<WindowState>) {
 }
 
 impl WindowBuilder {
-    pub fn new() -> WindowBuilder {
+    pub fn new(_app_state: AppState) -> WindowBuilder {
         WindowBuilder {
             handler: None,
             title: String::new(),