change mux empty poll to mux empty event

As part of reducing the amount of regularly scheduled stuff wezterm
does in the background, this commit restructures how an empty mux
is detected; now when the mux prunes dead windows it will emit
an Empty event.

The Activity type will now schedule a prune when it is dropped,
which will clean up and trigger the Empty event.

refs: https://github.com/wez/wezterm/issues/770

mux/src/activity.rs

@@ -1,4 +1,5 @@
 //! Keeps track of the number of user-initiated activities
+use crate::Mux;
 use std::sync::atomic::{AtomicUsize, Ordering};
 
 static COUNT: AtomicUsize = AtomicUsize::new(0);
@@ -25,5 +26,11 @@ impl Activity {
 impl Drop for Activity {
     fn drop(&mut self) {
         COUNT.fetch_sub(1, Ordering::SeqCst);
+
+        promise::spawn::spawn_into_main_thread(async move {
+            let mux = Mux::get().unwrap();
+            mux.prune_dead_windows();
+        })
+        .detach();
     }
 }

mux/src/lib.rs

@@ -41,6 +41,7 @@ pub enum MuxNotification {
         pane_id: PaneId,
         alert: wezterm_term::Alert,
     },
+    Empty,
 }
 
 static SUB_ID: AtomicUsize = AtomicUsize::new(0);
@@ -184,6 +185,11 @@ fn read_from_pane_pty(pane_id: PaneId, banner: Option<String>, mut reader: Box<d
             // We don't know if we can unilaterally close
             // this pane right now, so don't!
             state.write(b"\n[Process completed]");
+            promise::spawn::spawn_into_main_thread(async move {
+                let mux = Mux::get().unwrap();
+                mux.prune_dead_windows();
+            })
+            .detach();
         }
         ExitBehavior::Close => {
             promise::spawn::spawn_into_main_thread(async move {
@@ -454,6 +460,10 @@ impl Mux {
             log::trace!("window {} is dead", window_id);
             self.remove_window_internal(window_id);
         }
+
+        if self.is_empty() {
+            self.notify(MuxNotification::Empty);
+        }
     }
 
     pub fn kill_window(&self, window_id: WindowId) {

wezterm-gui/src/frontend.rs

@@ -66,6 +66,12 @@ impl GuiFrontEnd {
                         pane_id: _,
                         alert: Alert::TitleMaybeChanged,
                     } => {}
+                    MuxNotification::Empty => {
+                        if mux::activity::Activity::count() == 0 {
+                            log::trace!("Mux is now empty, terminate gui");
+                            Connection::get().unwrap().terminate_message_loop();
+                        }
+                    }
                 }
                 true
             } else {
@@ -76,17 +82,6 @@ impl GuiFrontEnd {
     }
 
     pub fn run_forever(&self) -> anyhow::Result<()> {
-        self.connection
-            .schedule_timer(std::time::Duration::from_millis(200), move || {
-                if mux::activity::Activity::count() == 0 {
-                    let mux = Mux::get().unwrap();
-                    mux.prune_dead_windows();
-                    if mux.is_empty() {
-                        Connection::get().unwrap().terminate_message_loop();
-                    }
-                }
-            });
-
         self.connection.run_message_loop()
     }
 }

wezterm-mux-server-impl/src/dispatch.rs

@@ -86,6 +86,7 @@ where
                 handler.schedule_pane_push(pane_id);
             }
             Ok(Item::Notif(MuxNotification::WindowCreated(_window_id))) => {}
+            Ok(Item::Notif(MuxNotification::Empty)) => {}
             Err(err) => {
                 log::error!("process_async Err {}", err);
                 return Ok(());