Implementing kernel status messages.

IPython/frontend/qt/console/frontend_widget.py

@@ -355,7 +355,12 b' class FrontendWidget(HistoryConsoleWidget, BaseFrontendMixin):'
             
             self._append_plain_text(text)
             self._control.moveCursor(QtGui.QTextCursor.End)
-    
+
+    def _handle_status(self, msg):
+        """ Handle kernel status messages.
+        """
+        pass
+
     def _started_channels(self):
         """ Called when the KernelManager channels have started listening or 
             when the frontend is assigned an already listening KernelManager.

IPython/zmq/ipkernel.py

@@ -172,6 +172,14 b' class Kernel(Configurable):'
         self.pub_socket.send_json(pyin_msg)
 
     def execute_request(self, ident, parent):
+        
+        status_msg = self.session.msg(
+            u'status',
+            {u'execution_state':u'busy'},
+            parent=parent
+        )
+        self.pub_socket.send_json(status_msg)
+        
         try:
             content = parent[u'content']
             code = content[u'code']
@@ -277,6 +285,13 b' class Kernel(Configurable):'
         if reply_msg['content']['status'] == u'error':
             self._abort_queue()
 
+        status_msg = self.session.msg(
+            u'status',
+            {u'execution_state':u'idle'},
+            parent=parent
+        )
+        self.pub_socket.send_json(status_msg)
+
     def complete_request(self, ident, parent):
         txt, matches = self._complete(parent)
         matches = {'matches' : matches,

docs/source/development/messaging.txt

@@ -671,6 +671,19 b' Message type: ``pyerr``::'
        # except the 'status' field is omitted.
     }
 
+Kernel status
+-------------
+
+This message type is used by frontends to monitor the status of the kernel.
+
+Message type: ``status``::
+
+    content = {
+        # When the kernel starts to execute code, it will enter the 'busy'
+        # state and when it finishes, it will enter the 'idle' state.
+        execution_state : ('busy', 'idle')
+    }
+
 Kernel crashes
 --------------