fix: improve multi-monitor handling under wayland

When a monitor gets disconnected, the destroy event of all associated
windows gets called, and the window gets removed.

This patch changes that behavior: the window is still closed but the
configuration is kept using the existing reload mechanism.
In addition, a callback is added to listen for new monitors, triggering
a reload when a new monitor gets connected.

This logic also reloads already running windows, which has a positive and
negative effect:
- positive: if currently running e.g. on the second monitor specified in
  the list, the window can get moved to the first monitor
- negative: if reloading starts it on the same monitor, it gets reset
  (e.g. graphs)

I also had to work around an issue: the monitor model is not yet available
immediately when a new monitor callback triggers. Waiting in the callback
does not help (I tried 10 seconds). However, waiting outside, it always
became available after 10ms.

Tested with a dual monitor setup under KDE through a combinations of:
- enabling/disabling individual monitors
- switching between monitors
- specifying a specific monitor in the yuck config
- specifying a list of specific monitors in the yuck config

In all these cases the behavior is as expected, and the widget gets loaded
on the first available monitor (or stays unloaded until one becomes
available).
It also works when opening a window without any of the configured monitors
being available.

There is one remaining error from GTK when closing the window:
GLib-GObject-CRITICAL **: 20:06:05.912: ../gobject/gsignal.c:2684: instance '0x55a4ab4be2d0' has no handler with id '136'
This comes from the `self.gtk_window.disconnect(handler_id)` call. To
prevent that we'd have to reset `destroy_event_handler_id`.

CHANGELOG.md

@@ -17,6 +17,7 @@ All notable changes to eww will be listed here, starting at changes since versio
 - Fix the gtk `expander` widget (By: ovalkonia)
 - Fix wayland monitor names support (By: dragonnn)
 - `get_locale` now follows POSIX standard for locale selection (By: mirhahn, w-lfchen)
+- Improve multi-monitor handling under wayland (By: bkueng)
 
 ### Features
 - Add OnDemand support for focusable on wayland (By: GallowsDove)

crates/eww/src/app.rs

@@ -67,6 +67,7 @@ pub enum DaemonCommand {
     },
     CloseWindows {
         windows: Vec<String>,
+        auto_reopen: bool,
         sender: DaemonResponseSender,
     },
     KillServer,
@@ -146,16 +147,35 @@ impl<B: DisplayBackend> std::fmt::Debug for App<B> {
     }
 }
 
+/// Wait until the .model() is available for all monitors (or there is a timeout)
+async fn wait_for_monitor_model() {
+    let display = gdk::Display::default().expect("could not get default display");
+    let start = std::time::Instant::now();
+    loop {
+        while gtk::events_pending() && !gtk::main_iteration_do(false) {}
+        let all_monitors_set =
+            (0..display.n_monitors()).all(|i| display.monitor(i).and_then(|monitor| monitor.model()).is_some());
+        if all_monitors_set {
+            break;
+        }
+        tokio::time::sleep(Duration::from_millis(10)).await;
+        if std::time::Instant::now() - start > Duration::from_millis(500) {
+            log::warn!("Timed out waiting for monitor model to be set");
+            break;
+        }
+    }
+}
+
 impl<B: DisplayBackend> App<B> {
     /// Handle a [`DaemonCommand`] event, logging any errors that occur.
-    pub fn handle_command(&mut self, event: DaemonCommand) {
-        if let Err(err) = self.try_handle_command(event) {
+    pub async fn handle_command(&mut self, event: DaemonCommand) {
+        if let Err(err) = self.try_handle_command(event).await {
             error_handling_ctx::print_error(err);
         }
     }
 
     /// Try to handle a [`DaemonCommand`] event.
-    fn try_handle_command(&mut self, event: DaemonCommand) -> Result<()> {
+    async fn try_handle_command(&mut self, event: DaemonCommand) -> Result<()> {
         log::debug!("Handling event: {:?}", &event);
         match event {
             DaemonCommand::NoOp => {}
@@ -168,6 +188,10 @@ impl<B: DisplayBackend> App<B> {
                 }
             }
             DaemonCommand::ReloadConfigAndCss(sender) => {
+                // Wait for all monitor models to be set. When a new monitor gets added, this
+                // might not immediately be the case. And if we were to wait inside the
+                // connect_monitor_added callback, model() never gets set. So instead we wait here.
+                wait_for_monitor_model().await;
                 let mut errors = Vec::new();
 
                 let config_result = config::read_from_eww_paths(&self.paths);
@@ -194,7 +218,7 @@ impl<B: DisplayBackend> App<B> {
             DaemonCommand::CloseAll => {
                 log::info!("Received close command, closing all windows");
                 for window_name in self.open_windows.keys().cloned().collect::<Vec<String>>() {
-                    self.close_window(&window_name)?;
+                    self.close_window(&window_name, false)?;
                 }
             }
             DaemonCommand::OpenMany { windows, args, should_toggle, sender } => {
@@ -203,7 +227,7 @@ impl<B: DisplayBackend> App<B> {
                     .map(|w| {
                         let (config_name, id) = w;
                         if should_toggle && self.open_windows.contains_key(id) {
-                            self.close_window(id)
+                            self.close_window(id, false)
                         } else {
                             log::debug!("Config: {}, id: {}", config_name, id);
                             let window_args = args
@@ -234,7 +258,7 @@ impl<B: DisplayBackend> App<B> {
                 let is_open = self.open_windows.contains_key(&instance_id);
 
                 let result = if should_toggle && is_open {
-                    self.close_window(&instance_id)
+                    self.close_window(&instance_id, false)
                 } else {
                     self.open_window(&WindowArguments {
                         instance_id,
@@ -250,9 +274,10 @@ impl<B: DisplayBackend> App<B> {
 
                 sender.respond_with_result(result)?;
             }
-            DaemonCommand::CloseWindows { windows, sender } => {
-                let errors = windows.iter().map(|window| self.close_window(window)).filter_map(Result::err);
-                sender.respond_with_error_list(errors)?;
+            DaemonCommand::CloseWindows { windows, auto_reopen, sender } => {
+                let errors = windows.iter().map(|window| self.close_window(window, auto_reopen)).filter_map(Result::err);
+                // Ignore sending errors, as the channel might already be closed
+                let _ = sender.respond_with_error_list(errors);
             }
             DaemonCommand::PrintState { all, sender } => {
                 let scope_graph = self.scope_graph.borrow();
@@ -337,7 +362,7 @@ impl<B: DisplayBackend> App<B> {
     }
 
     /// Close a window and do all the required cleanups in the scope_graph and script_var_handler
-    fn close_window(&mut self, instance_id: &str) -> Result<()> {
+    fn close_window(&mut self, instance_id: &str, auto_reopen: bool) -> Result<()> {
         if let Some(old_abort_send) = self.window_close_timer_abort_senders.remove(instance_id) {
             _ = old_abort_send.send(());
         }
@@ -357,7 +382,17 @@ impl<B: DisplayBackend> App<B> {
             self.script_var_handler.stop_for_variable(unused_var.clone());
         }
 
-        self.instance_id_to_args.remove(instance_id);
+        if auto_reopen {
+            self.failed_windows.insert(instance_id.to_string());
+            // There might be an alternative monitor available already, so try to re-open it immediately.
+            // This can happen for example when a monitor gets disconnected and another connected,
+            // and the connection event happens before the disconnect.
+            if let Some(window_arguments) = self.instance_id_to_args.get(instance_id) {
+                let _ = self.open_window(&window_arguments.clone());
+            }
+        } else {
+            self.instance_id_to_args.remove(instance_id);
+        }
 
         Ok(())
     }
@@ -369,7 +404,7 @@ impl<B: DisplayBackend> App<B> {
 
         // if an instance of this is already running, close it
         if self.open_windows.contains_key(instance_id) {
-            self.close_window(instance_id)?;
+            self.close_window(instance_id, false)?;
         }
 
         self.instance_id_to_args.insert(instance_id.to_string(), window_args.clone());
@@ -422,9 +457,17 @@ impl<B: DisplayBackend> App<B> {
                 move |_| {
                     // we don't care about the actual error response from the daemon as this is mostly just a fallback.
                     // Generally, this should get disconnected before the gtk window gets destroyed.
-                    // It serves as a fallback for when the window is closed manually.
+                    // This callback is triggered in 2 cases:
+                    // - When the monitor of this window gets disconnected
+                    // - When the window is closed manually.
+                    // We don't distinguish here and assume the window should be reopened once a monitor
+                    // becomes available again
                     let (response_sender, _) = daemon_response::create_pair();
-                    let command = DaemonCommand::CloseWindows { windows: vec![instance_id.clone()], sender: response_sender };
+                    let command = DaemonCommand::CloseWindows {
+                        windows: vec![instance_id.clone()],
+                        auto_reopen: true,
+                        sender: response_sender,
+                    };
                     if let Err(err) = app_evt_sender.send(command) {
                         log::error!("Error sending close window command to daemon after gtk window destroy event: {}", err);
                     }
@@ -443,7 +486,7 @@ impl<B: DisplayBackend> App<B> {
                         tokio::select! {
                             _ = glib::timeout_future(duration) => {
                                 let (response_sender, mut response_recv) = daemon_response::create_pair();
-                                let command = DaemonCommand::CloseWindows { windows: vec![instance_id.clone()], sender: response_sender };
+                                let command = DaemonCommand::CloseWindows { windows: vec![instance_id.clone()], auto_reopen: false, sender: response_sender };
                                 if let Err(err) = app_evt_sender.send(command) {
                                     log::error!("Error sending close window command to daemon after gtk window destroy event: {}", err);
                                 }

crates/eww/src/opts.rs

@@ -281,7 +281,7 @@ impl ActionWithServer {
                 })
             }
             ActionWithServer::CloseWindows { windows } => {
-                return with_response_channel(|sender| app::DaemonCommand::CloseWindows { windows, sender });
+                return with_response_channel(|sender| app::DaemonCommand::CloseWindows { windows, auto_reopen: false, sender });
             }
             ActionWithServer::Reload => return with_response_channel(app::DaemonCommand::ReloadConfigAndCss),
             ActionWithServer::ListWindows => return with_response_channel(app::DaemonCommand::ListWindows),

crates/eww/src/server.rs

@@ -105,13 +105,15 @@ pub fn initialize_server<B: DisplayBackend>(
         }
     }
 
+    connect_monitor_added(ui_send.clone());
+
     // initialize all the handlers and tasks running asyncronously
     let tokio_handle = init_async_part(app.paths.clone(), ui_send);
 
     gtk::glib::MainContext::default().spawn_local(async move {
         // if an action was given to the daemon initially, execute it first.
         if let Some(action) = action {
-            app.handle_command(action);
+            app.handle_command(action).await;
         }
 
         loop {
@@ -120,7 +122,7 @@ pub fn initialize_server<B: DisplayBackend>(
                     app.scope_graph.borrow_mut().handle_scope_graph_event(scope_graph_evt);
                 },
                 Some(ui_event) = ui_recv.recv() => {
-                    app.handle_command(ui_event);
+                    app.handle_command(ui_event).await;
                 }
                 else => break,
             }
@@ -136,6 +138,29 @@ pub fn initialize_server<B: DisplayBackend>(
     Ok(ForkResult::Child)
 }
 
+fn connect_monitor_added(ui_send: UnboundedSender<DaemonCommand>) {
+    let display = gtk::gdk::Display::default().expect("could not get default display");
+    display.connect_monitor_added({
+        move |_display: &gtk::gdk::Display, _monitor: &gtk::gdk::Monitor| {
+            log::info!("New monitor connected, reloading configuration");
+            let _ = reload_config_and_css(&ui_send);
+        }
+    });
+}
+
+fn reload_config_and_css(ui_send: &UnboundedSender<DaemonCommand>) -> Result<()> {
+    let (daemon_resp_sender, mut daemon_resp_response) = daemon_response::create_pair();
+    ui_send.send(DaemonCommand::ReloadConfigAndCss(daemon_resp_sender))?;
+    tokio::spawn(async move {
+        match daemon_resp_response.recv().await {
+            Some(daemon_response::DaemonResponse::Success(_)) => log::info!("Reloaded config successfully"),
+            Some(daemon_response::DaemonResponse::Failure(e)) => eprintln!("{}", e),
+            None => log::error!("No response to reload configuration-reload request"),
+        }
+    });
+    Ok(())
+}
+
 fn init_async_part(paths: EwwPaths, ui_send: UnboundedSender<app::DaemonCommand>) -> tokio::runtime::Handle {
     let rt = tokio::runtime::Builder::new_multi_thread()
         .thread_name("main-async-runtime")
@@ -216,20 +241,12 @@ async fn run_filewatch<P: AsRef<Path>>(config_dir: P, evt_send: UnboundedSender<
                     debounce_done.store(true, Ordering::SeqCst);
                 });
 
-                let (daemon_resp_sender, mut daemon_resp_response) = daemon_response::create_pair();
                 // without this sleep, reading the config file sometimes gives an empty file.
                 // This is probably a result of editors not locking the file correctly,
                 // and eww being too fast, thus reading the file while it's empty.
                 // There should be some cleaner solution for this, but this will do for now.
                 tokio::time::sleep(std::time::Duration::from_millis(50)).await;
-                evt_send.send(app::DaemonCommand::ReloadConfigAndCss(daemon_resp_sender))?;
-                tokio::spawn(async move {
-                    match daemon_resp_response.recv().await {
-                        Some(daemon_response::DaemonResponse::Success(_)) => log::info!("Reloaded config successfully"),
-                        Some(daemon_response::DaemonResponse::Failure(e)) => eprintln!("{}", e),
-                        None => log::error!("No response to reload configuration-reload request"),
-                    }
-                });
+                reload_config_and_css(&evt_send)?;
             }
         },
         else => break