Modify architecture to run pipewire loop in second thread.

The pipewire loop now runs without interruption in a second thread and communicates with
the GTK thread via a channel in each direction, instead of checking for events once a second and using callbacks.

This allows changes to appear instantly in the view, instead of having to wait.

src/main.rs

@@ -4,7 +4,38 @@ mod view;
 
 use std::rc::Rc;
 
-use gtk::{glib, prelude::*};
+use controller::MediaType;
+use gtk::glib::{self, PRIORITY_DEFAULT};
+use pipewire::spa::Direction;
+
+/// Messages used GTK thread to command the pipewire thread.
+#[derive(Debug)]
+enum GtkMessage {
+    /// Quit the event loop and let the thread finish.
+    Terminate,
+}
+
+/// Messages used pipewire thread to notify the GTK thread.
+#[derive(Debug)]
+enum PipewireMessage {
+    /// A new node has appeared.
+    NodeAdded {
+        id: u32,
+        name: String,
+        media_type: Option<MediaType>,
+    },
+    /// A new port has appeared.
+    PortAdded {
+        id: u32,
+        node_id: u32,
+        name: String,
+        direction: Direction,
+    },
+    /// A new link has appeared.
+    LinkAdded { id: u32, link: PipewireLink },
+    /// An object was removed
+    ObjectRemoved { id: u32 },
+}
 
 #[derive(Debug)]
 pub struct PipewireLink {
@@ -18,20 +49,22 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     env_logger::init();
     gtk::init()?;
 
-    let view = Rc::new(view::View::new());
-    let pw_con = pipewire_connection::PipewireConnection::new()?;
-    let _controller = controller::Controller::new(view.clone(), pw_con.clone());
+    // Start the pipewire thread with channels in both directions.
+    let (gtk_sender, gtk_receiver) = glib::MainContext::channel(PRIORITY_DEFAULT);
+    let (pw_sender, pw_receiver) = pipewire::channel::channel();
+    let pw_thread =
+        std::thread::spawn(move || pipewire_connection::thread_main(gtk_sender, pw_receiver));
 
-    // Do an initial roundtrip before showing the view,
-    // so that the graph is already populated when the window opens.
-    pw_con.borrow().roundtrip();
-    // From now on, call roundtrip() every second.
-    glib::timeout_add_seconds_local(1, move || {
-        pw_con.borrow().roundtrip();
-        Continue(true)
-    });
+    let view = Rc::new(view::View::new());
+    let _controller = controller::Controller::new(view.clone(), gtk_receiver);
 
     view.run();
 
+    pw_sender
+        .send(GtkMessage::Terminate)
+        .expect("Failed to send message");
+
+    pw_thread.join().expect("Pipewire thread panicked");
+
     Ok(())
 }