Display "Livebook is shutting down" flash on desktop app shutdown (#1645)

elixirkit/lib/elixirkit/server.ex

@@ -24,7 +24,6 @@ defmodule ElixirKit.Server do
 
   @impl true
   def handle_info({:tcp_closed, socket}, state) when socket == state.socket do
-    System.stop()
     {:stop, :shutdown, state}
   end
 end

lib/livebook/config.ex

@@ -115,6 +115,20 @@ defmodule Livebook.Config do
     Application.get_env(:livebook, :iframe_url)
   end
 
+  @doc """
+  Shuts down the system, if possible.
+  """
+  def shutdown do
+    case Livebook.Config.shutdown_callback() do
+      {m, f, a} ->
+        Phoenix.PubSub.broadcast(Livebook.PubSub, "sidebar", :shutdown)
+        apply(m, f, a)
+
+      nil ->
+        :ok
+    end
+  end
+
   @doc """
   Returns an mfa if there's a way to shut down the system.
   """

lib/livebook_app.ex

@@ -8,8 +8,9 @@ if Mix.target() == :app do
 
     @impl true
     def init(_) do
-      {:ok, _} = ElixirKit.start()
-      {:ok, nil}
+      {:ok, pid} = ElixirKit.start()
+      ref = Process.monitor(pid)
+      {:ok, %{ref: ref}}
     end
 
     @impl true
@@ -18,6 +19,12 @@ if Mix.target() == :app do
       {:noreply, state}
     end
 
+    @impl true
+    def handle_info({:DOWN, ref, :process, _, :shutdown}, state) when ref == state.ref do
+      Livebook.Config.shutdown()
+      {:noreply, state}
+    end
+
     defp open("") do
       open(LivebookWeb.Endpoint.access_url())
     end

lib/livebook_web/live/hooks/sidebar_hook.ex

@@ -7,17 +7,23 @@ defmodule LivebookWeb.SidebarHook do
   def on_mount(:default, _params, _session, socket) do
     if connected?(socket) do
       Livebook.Hubs.subscribe([:crud, :connection])
+      Phoenix.PubSub.subscribe(Livebook.PubSub, "sidebar")
     end
 
     socket =
       socket
       |> assign(saved_hubs: Livebook.Hubs.get_metadatas())
       |> attach_hook(:hubs, :handle_info, &handle_info/2)
+      |> attach_hook(:shutdown, :handle_info, &handle_info/2)
       |> attach_hook(:shutdown, :handle_event, &handle_event/3)
 
     {:cont, socket}
   end
 
+  defp handle_info(:shutdown, socket) do
+    {:halt, put_flash(socket, :info, "Livebook is shutting down. You can close this page.")}
+  end
+
   @connection_events ~w(hub_connected hub_disconnected hubs_metadata_changed)a
 
   defp handle_info(event, socket) when event in @connection_events do
@@ -33,15 +39,8 @@ defmodule LivebookWeb.SidebarHook do
   defp handle_info(_event, socket), do: {:cont, socket}
 
   defp handle_event("shutdown", _params, socket) do
-    case Livebook.Config.shutdown_callback() do
-      {m, f, a} ->
-        apply(m, f, a)
-
-        {:halt, put_flash(socket, :info, "Livebook is shutting down. You can close this page.")}
-
-      _ ->
-        socket
-    end
+    Livebook.Config.shutdown()
+    {:halt, socket}
   end
 
   defp handle_event(_event, _params, socket), do: {:cont, socket}