linux: create a hidden window inside the platform

It allows us to receive messages from the dispatcher,
which breaks us out of waiting and lets us execute
main thread runnables as a part of the main loop.

crates/gpui/src/platform/linux/dispatcher.rs

@@ -7,29 +7,50 @@ use async_task::Runnable;
 use parking::{Parker, Unparker};
 use parking_lot::Mutex;
 use std::{
-    panic, thread,
+    panic,
+    sync::Arc,
+    thread,
     time::{Duration, Instant},
 };
+use xcb::x;
 
 pub(crate) struct LinuxDispatcher {
+    xcb_connection: Arc<xcb::Connection>,
+    x_listener_window: x::Window,
     parker: Mutex<Parker>,
     timed_tasks: Mutex<Vec<(Instant, Runnable)>>,
     main_sender: flume::Sender<Runnable>,
-    main_receiver: flume::Receiver<Runnable>,
     background_sender: flume::Sender<Runnable>,
-    background_thread: thread::JoinHandle<()>,
+    _background_thread: thread::JoinHandle<()>,
     main_thread_id: thread::ThreadId,
 }
 
-impl Default for LinuxDispatcher {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
 impl LinuxDispatcher {
-    pub fn new() -> Self {
-        let (main_sender, main_receiver) = flume::unbounded::<Runnable>();
+    pub fn new(
+        main_sender: flume::Sender<Runnable>,
+        xcb_connection: &Arc<xcb::Connection>,
+        x_root_index: i32,
+    ) -> Self {
+        let x_listener_window = xcb_connection.generate_id();
+        let screen = xcb_connection
+            .get_setup()
+            .roots()
+            .nth(x_root_index as usize)
+            .unwrap();
+        xcb_connection.send_request(&x::CreateWindow {
+            depth: 0,
+            wid: x_listener_window,
+            parent: screen.root(),
+            x: 0,
+            y: 0,
+            width: 1,
+            height: 1,
+            border_width: 0,
+            class: x::WindowClass::InputOnly,
+            visual: screen.root_visual(),
+            value_list: &[],
+        });
+
         let (background_sender, background_receiver) = flume::unbounded::<Runnable>();
         let background_thread = thread::spawn(move || {
             for runnable in background_receiver {
@@ -37,21 +58,23 @@ impl LinuxDispatcher {
             }
         });
         LinuxDispatcher {
+            xcb_connection: Arc::clone(xcb_connection),
+            x_listener_window,
             parker: Mutex::new(Parker::new()),
             timed_tasks: Mutex::new(Vec::new()),
             main_sender,
-            main_receiver,
             background_sender,
-            background_thread,
+            _background_thread: background_thread,
             main_thread_id: thread::current().id(),
         }
     }
+}
 
-    pub fn tick_main(&self) {
-        assert!(self.is_main_thread());
-        if let Ok(runnable) = self.main_receiver.try_recv() {
-            runnable.run();
-        }
+impl Drop for LinuxDispatcher {
+    fn drop(&mut self) {
+        self.xcb_connection.send_request(&x::DestroyWindow {
+            window: self.x_listener_window,
+        });
     }
 }
 
@@ -66,6 +89,18 @@ impl PlatformDispatcher for LinuxDispatcher {
 
     fn dispatch_on_main_thread(&self, runnable: Runnable) {
         self.main_sender.send(runnable).unwrap();
+        // Send a message to the invisible window, forcing
+        // tha main loop to wake up and dispatch the runnable.
+        self.xcb_connection.send_request(&x::SendEvent {
+            propagate: false,
+            destination: x::SendEventDest::Window(self.x_listener_window),
+            event_mask: x::EventMask::NO_EVENT,
+            event: &x::VisibilityNotifyEvent::new(
+                self.x_listener_window,
+                x::Visibility::Unobscured,
+            ),
+        });
+        self.xcb_connection.flush().unwrap();
     }
 
     fn dispatch_after(&self, duration: Duration, runnable: Runnable) {
@@ -76,24 +111,17 @@ impl PlatformDispatcher for LinuxDispatcher {
     }
 
     fn tick(&self, background_only: bool) -> bool {
-        let mut ran = false;
-        if self.is_main_thread() && !background_only {
-            for runnable in self.main_receiver.try_iter() {
-                runnable.run();
-                ran = true;
-            }
-        }
         let mut timed_tasks = self.timed_tasks.lock();
+        let old_count = timed_tasks.len();
         while let Some(&(moment, _)) = timed_tasks.last() {
             if moment <= Instant::now() {
                 let (_, runnable) = timed_tasks.pop().unwrap();
                 runnable.run();
-                ran = true;
             } else {
                 break;
             }
         }
-        ran
+        timed_tasks.len() != old_count
     }
 
     fn park(&self) {

crates/gpui/src/platform/linux/platform.rs

@@ -7,6 +7,7 @@ use crate::{
     PlatformTextSystem, PlatformWindow, Point, Result, SemanticVersion, Size, Task, WindowOptions,
 };
 
+use async_task::Runnable;
 use collections::{HashMap, HashSet};
 use futures::channel::oneshot;
 use parking_lot::Mutex;
@@ -37,12 +38,13 @@ pub(crate) struct LinuxPlatform {
     atoms: XcbAtoms,
     background_executor: BackgroundExecutor,
     foreground_executor: ForegroundExecutor,
-    dispatcher: Arc<LinuxDispatcher>,
+    main_receiver: flume::Receiver<Runnable>,
     text_system: Arc<LinuxTextSystem>,
     state: Mutex<LinuxPlatformState>,
 }
 
 pub(crate) struct LinuxPlatformState {
+    quit_requested: bool,
     windows: HashMap<x::Window, Arc<LinuxWindowState>>,
 }
 
@@ -57,17 +59,24 @@ impl LinuxPlatform {
         let (xcb_connection, x_root_index) = xcb::Connection::connect(None).unwrap();
         let atoms = XcbAtoms::intern_all(&xcb_connection).unwrap();
 
-        let dispatcher = Arc::new(LinuxDispatcher::new());
+        let xcb_connection = Arc::new(xcb_connection);
+        let (main_sender, main_receiver) = flume::unbounded::<Runnable>();
+        let dispatcher = Arc::new(LinuxDispatcher::new(
+            main_sender,
+            &xcb_connection,
+            x_root_index,
+        ));
 
         Self {
-            xcb_connection: Arc::new(xcb_connection),
+            xcb_connection,
             x_root_index,
             atoms,
             background_executor: BackgroundExecutor::new(dispatcher.clone()),
             foreground_executor: ForegroundExecutor::new(dispatcher.clone()),
-            dispatcher,
+            main_receiver,
             text_system: Arc::new(LinuxTextSystem::new()),
             state: Mutex::new(LinuxPlatformState {
+                quit_requested: false,
                 windows: HashMap::default(),
             }),
         }
@@ -92,8 +101,7 @@ impl Platform for LinuxPlatform {
         //Note: here and below, don't keep the lock() open when calling
         // into window functions as they may invoke callbacks that need
         // to immediately access the platform (self).
-
-        while !self.state.lock().windows.is_empty() {
+        while !self.state.lock().quit_requested {
             let event = self.xcb_connection.wait_for_event().unwrap();
             match event {
                 xcb::Event::X(x::Event::ClientMessage(ev)) => {
@@ -129,15 +137,18 @@ impl Platform for LinuxPlatform {
                     };
                     window.configure(bounds)
                 }
-                ref other => {
-                    println!("Other event {:?}", other);
-                }
+                _ => {}
+            }
+
+            if let Ok(runnable) = self.main_receiver.try_recv() {
+                runnable.run();
             }
-            self.dispatcher.tick_main();
         }
     }
 
-    fn quit(&self) {}
+    fn quit(&self) {
+        self.state.lock().quit_requested = true;
+    }
 
     fn restart(&self) {}
 
@@ -186,6 +197,7 @@ impl Platform for LinuxPlatform {
             x_window,
             &self.atoms,
         ));
+
         self.state
             .lock()
             .windows

crates/gpui/src/platform/linux/text_system.rs

@@ -76,7 +76,7 @@ impl PlatformTextSystem for LinuxTextSystem {
         unimplemented!()
     }
     fn glyph_for_char(&self, font_id: FontId, ch: char) -> Option<GlyphId> {
-        unimplemented!()
+        None
     }
     fn glyph_raster_bounds(&self, params: &RenderGlyphParams) -> Result<Bounds<DevicePixels>> {
         unimplemented!()

crates/gpui/src/platform/linux/window.rs

@@ -237,6 +237,7 @@ impl LinuxWindowState {
         if let Some(fun) = self.callbacks.lock().close.take() {
             fun();
         }
+        self.xcb_connection.flush().unwrap();
     }
 
     pub fn expose(&self) {