Fail when another window manager is already running

lib/uh/wm.rb

@@ -11,8 +11,9 @@ require 'uh/wm/runner'
 
 module Uh
   module WM
-    Error         = Class.new(StandardError)
-    RuntimeError  = Class.new(RuntimeError)
-    ArgumentError = Class.new(Error)
+    Error               = Class.new(StandardError)
+    RuntimeError        = Class.new(RuntimeError)
+    ArgumentError       = Class.new(Error)
+    OtherWMRunningError = Class.new(RuntimeError)
   end
 end

lib/uh/wm/manager.rb

@@ -1,6 +1,8 @@
 module Uh
   module WM
     class Manager
+      INPUT_MASK = Events::SUBSTRUCTURE_REDIRECT_MASK
+
       attr_reader :display
 
       def initialize events, display = Display.new
@@ -11,6 +13,13 @@ module Uh
       def connect
         @events.emit :connecting, args: @display
         @display.open
+        Display.on_error do
+          fail OtherWMRunningError, 'another window manager is already running'
+        end
+        @display.listen_events INPUT_MASK
+        @display.sync false
+        Display.on_error { |*args| handle_error *args }
+        @display.sync false
         @events.emit :connected, args: @display
       end
 
@@ -27,6 +36,13 @@ module Uh
         when :key_press then @events.emit :key, event.key.to_sym
         end
       end
+
+
+      private
+
+      def handle_error *args
+        @dispatcher.emit :error, args: args
+      end
     end
   end
 end